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Gallery, Projects and General => How to's => Topic started by: Darren on May 08, 2009, 02:18:56 PM

Title: How to Make a Power Supply
Post by: Darren on May 08, 2009, 02:18:56 PM
As promised I am putting together a post on how to make a variable power supply suitable for many Madmodder projects.

In particular this one is being built as half a unit for my Valve amplifier which requires 10V at 10A. But along this journey I shall be showing how to make a supply for many projects including machine power using low voltage motors.

Such motors include 12V car windscreen units, stepper motors, 24v Garage door openers which is the type shown in this tutorial.

One of the hardest specifications to find in off the shelf power supplies is higher current outputs as most commercial supplies are very limited in this regard. That is what we shall be dealing with here. Commercially you would need to have very deep pockets for a 10A supply in the order of 100's.

The 24V garage motor chosen for the powering of the mill bed is quite efficient at less than one amp current draw, my car windscreen motor is at least double this if not more.

But, if you are going to the trouble to build from scratch then you might as well build a good-un. This supply will eventually be able to handle 25A but for now we'll concentrate on around 4A output (the limit of this transformer) with a voltage range of 1.5-30V.

So lets get on with it and see the basic components required

In this first picture we have the transformer at the top, this is a 12/24V type at 50VA. ( that's volts x amps =50, so at 12V it has roughly 4amps and at 24V it has 2 amps)
Middle row from the left:
a 5KOhm pot or potentiometer (same as a volume control on your stereo) This one is a fancy 10 turn type (ten turns from zero to full instead of the normal one turn)
Just use a cheap one turn type. less than a quid.
Next is the voltage regulator chip No' LM338T, this is a 1.2V-37V variable type
3rd is a standard resistor, in this case 100 Ohm, 120 would be better but I don't have one. The value is not that critical for a variable voltage supply, something close will suffice. If you were making a fixed voltage output then this would need to be exact.
Next we have the rectifier, this one is four diodes in one package, we could use four individual diodes to do the same job. I find this tidier and easier. less to think about...

Finally at the bottom is something to build it all on. You could use almost anything but beware of strip boards, their thin conduction strips will not be able to carry the currents in this application.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2000.jpg)

Believe it or not this is all you need to build this supply as I am about to demonstrate....

More coming, the supply is built and tested  :thumbup:

Some links

LM388T Voltage regulator, I bought mine for about a quid each off ebay
http://www.national.com/mpf/LM/LM338.html

Rectifier, you can find these on Ebay easily enough, mine is 25A but 6A would suffice for the mill drive.
http://www.datasheetarchive.com/D25XB60-datasheet.html


Title: Re: How to Make a Power Supply
Post by: Darren on May 08, 2009, 02:50:02 PM
Lets start putting this together,

Place the voltage regulator and rectifier as shown

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2002.jpg)

Then with a pair of long nose pliers bend the leads of the resistor similar to this. Beware, do not bend the leads close to the body as they usually fall off if you do !!

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2003.jpg)

It goes here between the left adjust and middle output leg of the regulator. The resistor itself has no orientation.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2005.jpg)

Then add a link from the positive leg of the rectifier to the input of the regulator. I used a wire from some household twin and earth cable.
Note: the middle two legs of the rectifier are for the AC input from the transformer. The outer two legs are + and -, but yours may be swapped around in relation to mine. Just be aware and connect accordingly.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2006.jpg)

Things will be getting a bit wobbly by now, so time to solder some parts in place. Although the regulator is a fairly tough device, try not to heat it up too much with the soldering iron. In other words get in, melt the solder and get out.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2010.jpg)

Prepare a pair of wires to connect to the transformer. I find with multi-strand wires it's often easier to tin them first. (pre-solder)

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2016.jpg)

Solder these wires to the board to the AC connections on the rectifier. Again there is no orientation.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2018.jpg)

Add a wire link on the left as shown. This is the DC negative rail.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2041.jpg)

The grey wires shown here are connected to the pot and the black and red go to the motor.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2042.jpg)

I'mm missing a picture, I'll be back....hold on..... :doh:

Title: Re: How to Make a Power Supply
Post by: Brass_Machine on May 08, 2009, 02:51:15 PM
Awesome Darren! I was going to PM you this week because I have to build a power supply. I have to build one for THIS (http://www.hobbycnc.com/products/hobbycnc-pro-chopper-driver-board-kits/). Can you assist with the design? Or will this work (your thread).

Eric


 :nrocks:
Title: Re: How to Make a Power Supply
Post by: Darren on May 08, 2009, 03:10:34 PM
Eric, This supply is perfect for your needs. As I said this is a very handy supply to have around as it has so many uses :thumbup:
Title: Re: How to Make a Power Supply
Post by: Darren on May 08, 2009, 03:44:45 PM
The grey wires connected to the pot, only two wires used. On a normal pot (unlike this one shown as it's the only 5K I had to hand) use the center and one outer connection. If the pot works the wrong way around use the other outer connection.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2048.jpg)

One grey wire goes here, the other to the negative rail.
The red wire goes to the motor, the other motor wire also goes to the negative rail

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2050.jpg)

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2042.jpg)

All you need to add now is a heat sink, I used some alluminuim strip, black as it's anodized but there is no requirement for this. You could use steel, brass etc, just don't make it too small. A propper finned heat sink would be better. Computer heat sinks or one from a salvage hifi amp would work well.

Be aware that the casing of the regulator is at full positive output voltage. Do not short this to earth. I have used an insulation kit to isolate the regulator it from the heatsink. The rectifier is already insulated so no need to worry about that. Some heat transfer paste would also be a good idea, it's the white stuff between the components that you can see oozing out.

I have attached a voltmeter and a temperature probe to keep an eye on things whilst testing.
The highest heat generated is at the lowest voltage output as the regulator gets rid of the unwanted voltage in the form of heat. As you turn the voltage up to increase the motor speed for example, more voltage/energy goes to the motor and everything runs cooler.
If you find you use the lower voltages all the time and have no need for the upper end then use a 12V transformer. Gives the regulator less work to do.

However, I found that even a stalling speed of the motor for over an hour the regulators temperature never rose above 90 deg C. it's rated at 125C.
The reg has a safety feature in that it will shut down to protect itself if it's pushed too hard or gets too hot (same thing as far as the reg is concerned) It will operate again when cooled a little.

So there we are, that is all that is required to make a variable voltage power supply of 1.2-30V, or up to 37V if the transformer had a higher output.
If you want just 12 or 18V then just use a lower voltage transformer, no circuit changes are required.


Here it is at 1.3V during the punishment test
(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2044-1.jpg)

At 4.3V

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2045.jpg)

30V

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2051.jpg)



You can by all means use this circuit as is, but we can make it better. In the next installment I'll be showing how to make the output smoother and how to protect the chip from short circuit accidents. You might not think you need this cos you are going to be careful right  :thumbup:

Why do you think I had to order some new regulators to make this post  :doh: Yep I popped a chip.

So if you bear with me I'll be showing you how to add two small and cheap components to prevent this  :thumbup:

Title: Re: How to Make a Power Supply
Post by: sbwhart on May 08, 2009, 04:23:54 PM
Wow Darren that's great work.

 :clap: :clap: :clap: :clap: :clap: :clap: :clap:

Even I could follow that

 :thumbup:

 :ddb:  :nrocks:  :ddb:  :nrocks:


Stew

Title: Re: How to Make a Power Supply
Post by: Divided he ad on May 08, 2009, 04:29:23 PM
Now what more can I add.... Stew's just told you all you need to know!!


An "electrophobe" who is happy to make a circuit  :zap: cause of the well detailed post  :thumbup:





Awesome  :nrocks:  Indeed  :thumbup:




Ralph.

Title: Re: How to Make a Power Supply
Post by: SPiN Racing on May 08, 2009, 07:08:49 PM
Very Nice :)

Im taking notes for another project I did in the past....
Title: Re: How to Make a Power Supply
Post by: Baldrocker on May 08, 2009, 09:18:06 PM
Nice.
Down to DSE to get a couple of parts tomorrow.
BR   :zap:
Title: Re: How to Make a Power Supply
Post by: Darren on May 10, 2009, 02:40:34 PM
I have not forgotten about this, I wanted to make a video to explain a couple of points before continuing, but my phone has died.

Please bear with me till I can get this sorted and don't make a power supply just yet as there will be some changes to the circuit.
There is only a little more to do but I need to explain why before continuing.... :ddb:
Title: Re: How to Make a Power Supply
Post by: CrewCab on May 10, 2009, 05:18:25 PM
Brilliant stuff Darren, thanks  :thumbup: ................ looking forward to more  :coffee:

CC
Title: Re: How to Make a Power Supply
Post by: Darren on May 10, 2009, 07:01:47 PM
I've been asked by PM what exactly is an insulating kit used for the regulator chip.

It consists of a silicon sheet as the insulator and a "top hat" nylon washer all held together with a 3mm nut and bolt.

Often heat sinks are fixed to the units chassis for stability and further heat sinking. This chassis is of course grounded, or at least should be, so we don't want the chip shorting out if this is done.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2053-1.jpg)
Title: Re: How to Make a Power Supply
Post by: Bernd on May 10, 2009, 08:17:01 PM
Darren,

Don't forget to add the silicone grease under the chip so it can transfer the heat better to the aluminum plate.  :)

Bernd
Title: Re: How to Make a Power Supply
Post by: SPiN Racing on May 12, 2009, 10:00:59 PM
I have a simple (I think) question for you about the power supply...

I have a power supply similar to what you are doing. It runs a headlight motor from a Mazda. I also wanted to be able to control the speed of it, and have it go faster, and slower.

In order to do this simply I got a transformer and a bridge rectivier (square block with two diodes to make AC into DC) and then ran the output to the motor.
To vary the voltage I used a Light dimmer switch, which allowed me to vary the incoming voltage to the transformer, and dropping the voltage out the other side.

The issue is.. I dont think its very smooth as it does generate a decent amount of heat. The regulated Video Game power supply I had previously, worked very very well, but wouldnt go over about 15 volts. (Was a Peter Chou regulated style)

I gather putting a big capacitor in the circuit will smooth things out.. but honestly I dont know where.. or if you put it across the circuit.. or inline... or use two etc..

Suggestions?

Line-O-Cad
(http://img141.imageshack.us/img141/5711/acdc.png)
Title: Re: How to Make a Power Supply
Post by: Darren on May 13, 2009, 03:43:40 AM
Hi Spin,

I'm about to cover this issue, hopefully later today. But yes capacitors are used. What you have there is not true DC and that is why things are running hot.
That power supply as it is will stress the motor.

Title: Re: How to Make a Power Supply
Post by: Darren on May 13, 2009, 09:29:12 AM
At last I've managed to put a vid together,

My mobile died, I've tried four others that failed for one reason or another, mostly poor sound or simply won't talk to the computer.... :bang:

So I ended up using a web cam connected to my laptop, mostly held by hand so the vid is a bit jumpy. Then there were software issues  :bang: :bang: :bang:

But it's done now  :D, I'm no movie maker or commentator so please excuse the amateurishness of this vid.

Hopefully it will answer a lot of questions and throw some light on the matter.
I doubt I've covered everything so any questions please speak up.  :ddb:

Enjoy....




Agg...the vid is too long for Photobucket.....oh the joy of computing !!!

Hang on......
Title: Re: How to Make a Power Supply
Post by: Darren on May 13, 2009, 10:41:16 AM
OK, vid now split into two, hope they don't bore you...... :ddb:

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/th_PowerSupplySmoothingPart1.jpg) (http://s401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/?action=view&current=PowerSupplySmoothingPart1.flv)

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/th_PowerSupplySmoothingPart2.jpg) (http://s401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/?action=view&current=PowerSupplySmoothingPart2.flv)

Title: Re: How to Make a Power Supply
Post by: Darren on May 13, 2009, 05:16:20 PM
A little more playing with this tonight, but first let me show you a better picture of where the two diodes go and their orientation.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2139.jpg)

We use these to protect the discharging energy from the smoothing caps when the circuit is switched off. Caps are in some ways like little batteries, except they can store quite a lot of energy. Even worse they can discharge all of it in an instant which is what they want to do when the power is switched off. The energy released from the caps will try to find the path of least resistance to dump to. This unfortunately is through the regulator chip. The diodes offer a new path of no resistance thereby diverting any possible catastrophe away from the regulator.

Most manufacturers will declare that this type of regulator has built in protection within, in the form of a diode. Maybe it has, but don't believe it with do as it says on the tin for a moment.
Maybe with lower voltages and currents it would be fine. But not here.


Now that the protection has been added it's time to think about some smoothing capacitors. But first I have added an extension to the neutral/earth rail to assist connection and mounting.
Bottom right of the board.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2136.jpg)

Now the caps, both negatives connected to the new earth rail.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2159.jpg)

And from one cap positive to the live bar/regulators input pin (3rd pin)

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2165.jpg)

Positive from the other cap to the regulators output, (middle pin)

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2166.jpg)

Now we have compleated the power supply smoothing and protection circuits.... :ddb:





Title: Re: How to Make a Power Supply
Post by: Darren on May 13, 2009, 05:37:04 PM
Some of you may have noticed that I have changed the resistor and indeed added another....

The original was 100 Ohms, and the two new ones are both 220 Ohms 1/4watt. When the circuit was first put together I used the manufactures recommended values.

However, as is usual, some testing and fiddling showed that the above sizes give us a closer result to our needs.... :smart:
There are online calculators to work this out for you, but I find a bit of fiddling works best.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2158.jpg)

Regarding the second resistor on the far left is inline with the adjusting pot, (in series) basically this adjust the lowest voltage output from 1.2V to a more usable 2.5V.
If we leave the lowest voltage at 1.2V what happens when we turn the pot down to slow the motor is that it will stop. This is highly undesirable if you are in the middle of machining and merely wish to slow the transverse speed. Adjusting the values in this way will always insure that when you turn the pot fully down you are at a nice comfortable slow speed setting.
(it also puts far less stress on the circuitry if you turn it down low enough to stop the motor and forget to switch the power off. Left in this state the circuit will become very hot and may possibly damage itself. This way you have to turn the power off to stop the motor)

Finally in this picture you can see that I have added a push to break switch inline with the adjusting pot. It's the one with the red button.

When the adjusting pot is turned to a higher resistance setting this will increase the speed of the motor. Lower resistance lowers the motor speed.
The "push" switch breaks the circuit offering an infinity resistance, ie very high. When the button is pushed the motor will spin at full speed. Useful for rapid transverse.
Let go of the button and the motor will resume to the pot setting speed as set previously.
This is useful not only for momentary rapid transverse of the mill bed, but it also allows you to leave the pot alone when you have found a comfortable cutting speed.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2161.jpg)


Well that's it, the power supply is done. This will provide 2.5V-34V at 5 Amps. 7-8A if you add a bigger heat sink, but I wouldn't recommend it as there are better ways to achieve this which I shall go into if anyone requests.

All you need now is a reversing switch and a box to put it in........ :nrocks: :nrocks: :nrocks:
Title: Re: How to Make a Power Supply
Post by: Divided he ad on May 13, 2009, 07:20:26 PM
Fair do's chief   :bugeye:  You've been working hard on this one today  :thumbup:


Very good videos, I think you sound like the guys on the videos they used to play for us to watch in science and engineering in school.... That's not a bad thing, you sound like the guys who used to narate.... Made me want to make paper airplanes and throw them at someone :lol:

 I like the use of the oh so silly scope, it allows you to not only show/prove the workings but just looks too damn cool  :headbang: 


I'm going to need a parts list if you would be so kind, I've got my motor all mounted and ready, Been fitting my new verticle DRO on my Z axis tonight... Slight dramas!! But this isn't the place for that disclosure!  :offtopic: 

I'm getting my mill up to a good working order DRO's getting there and then just waiting for this circuit to be made and I'll be machining hopefully much more accurate parts?!  :)



It is true that  :mmr: and that  :nrocks:    Top job, thank you  :thumbup:






Ralph.
Title: Re: How to Make a Power Supply
Post by: SPiN Racing on May 13, 2009, 11:54:29 PM
VERY NICE!!!!

Thanks A Ton!

I will put that in the brain box and let it rattle around and see what comes out  :D







 :proj:
Title: Re: How to Make a Power Supply
Post by: Darren on May 14, 2009, 07:05:41 AM


I think you sound like the guys on the videos they used to play for us to watch in science and engineering in school....

Does that mean you fell asleep  :ddb:

I realise it must be droll viewing, but necessary to explain why certain components are used and indeed required.

I'll sort out a parts list later  :thumbup:
Title: Re: How to Make a Power Supply
Post by: Darren on May 14, 2009, 07:23:03 AM
VERY NICE!!!!

Thanks A Ton!


Thanks for the feedback, I just hope it was clear enough and not an overload of info to put anyone off.

I realise it looks complicated, but in reality it's a very simple and well respected circuit.

Years ago you would have had many more components to put together to do the same job. Nowdays they pack much more of the circuit into chips, thankfully...!!

This is what is inside the regulator, imagine having to get your head around this, let alone build it...

First image

image 17 is basically what has been built here

http://www.datasheetcatalog.org/datasheet2/8/0ujhh2scud4dfop1xfyut2u2qopy.pdf
Title: Re: How to Make a Power Supply
Post by: Darren on May 14, 2009, 07:25:37 AM
(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/00906001.jpg)
Title: Re: How to Make a Power Supply
Post by: Divided he ad on May 14, 2009, 01:27:56 PM
Quote
Does that mean you fell asleep   :ddb:


I plead the fifth!   :D  ( my usual daily routine involves falling asleep in front of my computer, usually just after I get in from work and helped along by my literature induced narcolepsy!   ::) )



The first image can take a running jump.... I ain't soldering that lot up!!


Without the key that circuit you posted is a little like Welsh to me... I can read it and basically pronounce it.... But I sure can't understand it and use it!   :lol:

Well, I can identify the resistors (variable with the arrow) the chip (cause it's labled) and the capacitors 1 and 2..... Now what I don't know of, is that there reason why C2 is sad!?

The symbols used there are the old ones right?  I never used the zigzag resistors I had to draw little rectangles!.... Schools, full of jobsworths who do just as the curriculum states.... Something to do with losing their job? (I have 4 mates who are teachers.... I do like to tease them about their lack of teaching freedom! )


Anywho... Still much appreciate all your works on this  :thumbup:




Ralph.

Title: Re: How to Make a Power Supply
Post by: Darren on May 14, 2009, 01:56:44 PM
Rectangle resistors I believe is the old symbol, Er then again  :scratch: Never really thought about it..

Try here, I used a polarized cap btw...http://library.thinkquest.org/10784/circuit_symbols.html
Title: Re: How to Make a Power Supply
Post by: Brass_Machine on May 14, 2009, 02:24:58 PM
Ok... so Darren... I need a PS that can do up to 42v and 3.0 Amps Maximum per Phase. What do I have to do different to pull this off? Looking at the pictures of other PS for this they have a BIG cap.

(http://www.hobbycnc.com/wp-content/uploads/2008/02/hcncpropkg_1.jpg)

What do you think?

Eric
Title: Re: How to Make a Power Supply
Post by: Bernd on May 14, 2009, 02:37:14 PM
Eric,

The important thing is what the transformer puts out and what the rectifier is rated at. A big cap like that is for smoothing out the AC ripple on the DC voltage.

A transformer of 50volts and maybe 5 amps would be needed. The rectifier could be a 100volt and a higher rating than 5 amps.

I'll check out what size those rectifiers come at. Probably can get one at the Rat Schack (Radio Shack)

gotta go be back later with an answer I hope.

Bernd
Title: Re: How to Make a Power Supply
Post by: CrewCab on May 14, 2009, 05:48:20 PM

I'm just not sure if anyone here is really that interested?
I might have overloaded this topic already !!!

 :ddb: :ddb: :ddb:



Darren ................... I think half the civilised world is interested, I for sure am anyway ........... "Overload" .......... got to be honest and say ........ yes I'm struggling a bit, I've never really done much witrh electronics though I'd like to.......... I regognise a lot of what you describe and am conversant with a soldering Iron, my LandRover sports more lights relays and switches than you can usefully shake a stick at  :poke: .............  together with an odd Zenner or two so I can flash 8 lights at once but switch them in pairs ........... but ............... could I ask for a simple wiring diagram to help me along a little ......... old fashioned I know ......... but wth  :med:

take care, great thread  :bow:

CC
Title: Re: How to Make a Power Supply
Post by: Darren on May 14, 2009, 06:26:10 PM
CC Steve?,

No need for the  :bow:, my knowledge of electronics is very limited, I only know how to build these things cos I have needed them in the past for my valve amplifiers.

Get much further out of this narrow field and I'm truly sunk  :thumbup:


In fact I have no doubt someone here could make suggestions for improvements. If that is you then please speak up !!
Title: Re: How to Make a Power Supply
Post by: bogstandard on May 14, 2009, 06:46:38 PM
Darren,

Not one single person in the world knows everything about their specialist subject (contrary to what some people believe).

So your sharing what you do know is great, and no apologies are required.

In fact I have been lying all along, after working in the electronics and computer peripheral industry for a fair while, and against what I have always said before, I do actually understand all about wigglies and string, but don't want to be involved because my knowledge is a long time old, and how things are done is slightly different nowadays.

You just keep sharing what you know for definite, and I don't think anyone on here can have any complaints.


John
Title: Re: How to Make a Power Supply
Post by: CrewCab on May 14, 2009, 06:48:40 PM
CC = Dave  ::) ................ Steve = Cedge  :wack:    ::)

Darren, it's a brilliant thread, please keep going ......... your "limited" knowledge is just fine mate ........ and I'm sure quite a few others will agree .......... so    :bow: ........... av it .......    :smart: :beer: :coffee:


The real challenge is when I get a pcb and a few bits then start wielding a soldering iron  :zap: ...... at that time just duck  :borg:


Dave ........... aka ............ CC 
Title: Re: How to Make a Power Supply
Post by: Darren on May 14, 2009, 06:59:26 PM
CC = Dave  ::) ................ Steve = Cedge  :wack:    ::)

I never was very good with names Pete... :(
Title: Re: How to Make a Power Supply
Post by: Brass_Machine on May 14, 2009, 09:42:45 PM
unlocked & pruned the thread a little. Keep it light!  :med:

Sorry guys.

Eric
Title: Re: How to Make a Power Supply
Post by: CrewCab on May 15, 2009, 05:26:30 AM
I never was very good with names Pete...

 :thumbup:

CC
Title: Re: How to Make a Power Supply
Post by: Darren on May 15, 2009, 12:11:50 PM
Eric,

For your supply I would build this

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/lowpass.jpg)


It's simple, it's safe and it will be very reliable.

If you need more help just shout up 
Title: Re: How to Make a Power Supply
Post by: spuddevans on May 15, 2009, 03:31:13 PM
Eric,

For your supply I would build this

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/lowpass.jpg)


It's simple, it's safe and it will be very reliable.

If you need more help just shout up 

Just a little point that occured to me when looking at your circuit diagram above, I cant see how that will deliver 3amps if those 2 resistors are (as I read it) 1K each, surely you will only get a few 10's of milli-amps if that? Even if you had just 2x 1ohm resistors in series, at 3amp the voltage drop would be 6v giving an output well below 24V.

I assume ( very dangerous thing to do, it tends to make an ass out of me  :lol: ) that this circuit is in responce to Erics post
Ok... so Darren... I need a PS that can do up to 42v and 3.0 Amps Maximum per Phase. What do I have to do different to pull this off? Looking at the pictures of other PS for this they have a BIG cap.

If I'm completely wrong, and lets face it, most of the time I am, please disregard my ramblings.

If you are wanting a PSU circuit for 24V @3amps, That circuit diagram is great, I would maybe just change the value's of the 2 1k resistors to 0.5 Ohm each and change the 1st capacitor to 6800uF and the 2nd to 10,000uF, that should give you a nicely smoothed DC output.


Just my thoughts,


Tim
Title: Re: How to Make a Power Supply
Post by: Darren on May 15, 2009, 06:20:19 PM
Tim you could be perfectly right, I copied this circuit off the net as I have never used resistors in a smoothing circuit.

I always use chokes in my supplies.

I guess what I should really do is make that supply above and see what really happens, I took it from a respected sited and just took it that is was a working schematic as portrayed.

I've been very busy today but when I get change I'll power up PSUD and pop those values in and see what it comes up with.

Tim, those caps seem rather large capacitance to me? I'm not doubting you, they just seem large. I remember once I built a PS with only 10uf and it was prob the smoothest I've ever seen. Your talking about a combined 16,800uf  :bugeye:
Title: Re: How to Make a Power Supply
Post by: Darren on May 15, 2009, 07:10:05 PM
Silly me, I was looking at a low pass filter circuit not a smoothing circuit, modified it and never even noticed  :doh:

Yep 1R resistors at 24V would indeed drop 3V each so a 6V drop.

You're spot on Tim... :thumbup:

18VAC rectified would be 18V x 1.41 = 25.38VDC - then 1.4V dropped by the rectifier = 23.98VDC

Then minus the volt drop over one 0.5 Ohm resistor at 3A = 1.5V, times that by two = 3V

so the result would be 23.98VDC at no load and 20.98V at a 3A load.

I doubt the circuit pulls 3A so the real voltage would be somewhere in between. Call it 50% so the result would be around 23V

Perfect.


Thanks for pointing out that huge error on my part Tim  Total brain fade on my part there..... :doh:


Now then, those huge caps, could you explain this to me Tim cos I'm lost there? I would prob in reality have tried two 330uf caps cos I have hundreds of them.
( my power supplies are usually in the order of 300 - 1,500VDC at around 60 -200 ma for valve HT supplies with about 20uf max and two chokes around 10-20H each)

Title: Re: How to Make a Power Supply
Post by: spuddevans on May 16, 2009, 04:18:27 AM
Now then, those huge caps, could you explain this to me Tim cos I'm lost there? I would prob in reality have tried two 330uf caps cos I have hundreds of them.
( my power supplies are usually in the order of 300 - 1,500VDC at around 60 -200 ma for valve HT supplies with about 20uf max and two chokes around 10-20H each)


The reason for the bigger caps is because of the greater current draw, from what I read, Eric was wanting a PSU for a stepper motor driver, perhaps CNC. If his steppers are rated for 3amp and he has at least 2 of the ( x & y axis) there will be times when both are operating at the same time. Now even if you have a (say for arguments sake) 10A transformer, with a instant current demand there could be a slight delay (1/100th sec if using a bridge rectifier, 1/50th sec if just normal rectifier) in the supply of said current demand, this could lead to lost steps and innaccuracies in the CNC. Hence the need for such big caps, they just hold more current that is instantly available for use. In fact I would be tempted to put 2 10,000uF caps instead of the 2nd single cap in case of greater current demand in the future (ie a z axis and even a 4th stepper for a rotab), and I would get 63volt rated caps in case he wanted to up the transformer voltage to gain a higher top end speed. ( I know steppers rotate in fixed steps, but the speed that they can "Step" from one position to the next is limited by the voltage they are driven at)

The reason you will have used lower values of Cap on your valve amps is that they draw much less current, although at heart-stoppingly high voltages. While the wattage may work out similar for Eric's psu needs, when dealing with lower voltage and higher amperage the uf of the caps need to be much higher for them to work  effectively as buffers/smoothers of the DC.

In low voltage, high amperage you can not have too much uF, the only thing you have to be careful of is to limit the inrush of current to charge the caps at switch-on, and that is achieved by the 2 0.5ohm resistors, if you dont have those you will find yourself going through a lot of fuses and in extreme cases possibly damaging the transformer. (but that would be in a very extreme case)


But take all that with a healthy dose of salt,(or beer  :beer:) I am not qualified by any secular organisation, all this comes from just reading a lot, experimenting a lot, and also a miss-spent youth  :zap: messing around building various electronic projects like power mosfet amps, psu's, my dad's LGB railway layout controllers and other stuff.

Hope this explains my thinking,

Tim
Title: Re: How to Make a Power Supply
Post by: Darren on May 16, 2009, 04:49:31 AM
Thank you Tim,

Understood that perfectly and it even made sense to me  :clap:

Now I know why they use huge 1 farad caps in car stereo setups  :thumbup:
It's funny how people go down different paths for similar uses. That is, I use voltage regulators with much less uf for valve filaments which are low voltage and high current.

Maybe I should try what is being suggested for Erics situation and see how it sounds, it might be simpler but it does really depend on the resulting sound.

I don't know how much you know about valves?
With indirectly heated types we can use AC voltage to heat them and get away with it. With directly heated valves (which I prefer) this only seems to work with lower voltages of up to around 4V helped with the use of hum buckers. Above that they hum too much so we then switch to DC heaters.

My largest transformer has taps at 3,3K and 4.2K and I must try these higher supplies with my larger valves one day.

But as you can guess, that presents a whole new set of issues.

 :thumbup:
Title: Re: How to Make a Power Supply
Post by: Darren on May 16, 2009, 11:30:59 AM
Back to the power supply that is the subject of this thread.

I have spent some time testing and measuring the circuit under load with one 24V motor as shown in the pictures.
The unit has been left on overnight at the max stressful 2.5V low speed setting with a 24V input from the transformer. The temperatures of the regulator have been monitored and I'm happy to say it's still running  :D

Max temp recorded of the regulator has been 88deg C, but it typically sits at 74 deg.

I have come to the conclusion that given a larger heat sink this supply could run 3 motors at the same time.

Below you will find the data as recorded, I hope this information will help those that wish to see a more in depth technical side of the goings on.

I will continue this thread to show how to increase the current output capabilities by adding one, two, three or even four power transistors.
Done properly this will provide a very powerful and possibly dangerous outputs depending on how you handle it.
I accept no liability if you follow my examples, I'm merely providing a demonstration. Not forcing you to copy, that would be your choice and yours alone.

The data recorded as follow, sorry the formatting has become a little lost transferring it onto here, but it should still be clear enough.

Motor    V   I   W                  
H Speed    31.6   0.4   12.64                  
1/2 Speed   15   0.26   3.9                  
Low Speed   2.5   0.15   0.375                  
                           
                           
Regulator V      I      W                           
H   4.8   0.4   1.92                  
M   21.6   0.26   5.616                  
L   33.9   0.15   5.085                  
                           
                           
                           
Pot   V   R   I   W               
H   28.9   5000   0.00578   0.167042               
M   12.6   2500   0.00504   0.063504               
L   0   0   0   0               
                           
                           
V=Volts   I=Current in Amps   W=Watts   R=Resistance in Ohms         
                           
Ohms Law      V=IxR      
               
                           
Watts      W=VxA                     
                           
                           
LM338 Voltage Regulator Max Values                  
                           
Current   5A Continous   With extra cooling 7-8A   12A Peak Start up such as motors
Wattage   24V = 120W   24V = 192W      24V =288W      
Temperature 125Deg C                        


Ref: http://www.datasheetcatalog.org/datasheet2/8/0ujhh2scud4dfop1xfyut2u2qopy.pdf
Title: Re: How to Make a Power Supply
Post by: spuddevans on May 16, 2009, 02:33:30 PM
It's funny how people go down different paths for similar uses. That is, I use voltage regulators with much less uf for valve filaments which are low voltage and high current.

True, there are many ways to get the same results.  Would I be correct in remembering that valve heaters have a constant current draw? If so that would be why you can use smaller uf caps, and especially if you use a choke as well. Constant current draw requires less uF than intermittent current draw.
Quote
I don't know how much you know about valves?
With indirectly heated types we can use AC voltage to heat them and get away with it. With directly heated valves (which I prefer) this only seems to work with lower voltages of up to around 4V helped with the use of hum buckers. Above that they hum too much so we then switch to DC heaters.

Not a huge amount, I always wanted to build a nice high-end type valve amp for the hi-fi, but got scared off by the price of decent quality output transformers and the scarily high voltages involved. (I dont mind working up to 200-240v, but most of the designs I looked at were 600-800v  :bugeye:)

Do you use Valve rectifiers for the HT supply?



Tim
Title: Re: How to Make a Power Supply
Post by: Darren on May 16, 2009, 04:10:21 PM


Would I be correct in remembering that valve heaters have a constant current draw?


Not a huge amount, I always wanted to build a nice high-end type valve amp for the hi-fi, but got scared off by the price of decent quality output transformers and the scarily high voltages involved. (I dont mind working up to 200-240v, but most of the designs I looked at were 600-800v  :bugeye:)

Do you use Valve rectifiers for the HT supply?



Tim

Yes the heater current is constant, can be anything from 0.3 - 10Afor the sort of valves I use.
Typical power valves are around 3-5A  3.15-10V

Output transformers new are a price, 200 a pair is about average, I think my dearest for the 833's cost me around 450 the pair and that is middle of the road.

But, you can get pretty good results with old radio ones and the mains transformers are handy too.
Then again 9V toroidal used in parafeed also works well for outputs and these are cheap.

I have about 3-4000 valves to play with, some are valued at 1,500 a pair (no I didn't). My main little amp uses PX4's (a vintage triode from the 1920's about 100 each) That is valve rectified but I also use silicon sometimes.
My 833 amp uses silicon rectifiers. But I do have a few mercury rectifiers that I could use instead. It's the 1,500VDC that limits what you can use here because of voltage breakdown issues.

If you still want to build a valve amp let me know, I have about half a ton of mains transformers and could do with slimming them down a bit. A real understatement !!!

For caps, I have many, no idea how many but the PIO's alone fill about 3 large stacker boxes. If you want to use electrolytics those disposable cameras with flash are hiding one of the best quality ever made, little Rubycons that can take some hammering 100uf 300V.

I'll takes some pictures for you. Valve amps are easy to make  :thumbup:

Regards Darren

Title: Re: How to Make a Power Supply
Post by: spuddevans on May 17, 2009, 04:01:24 PM
If you still want to build a valve amp let me know, I have about half a ton of mains transformers and could do with slimming them down a bit. A real understatement !!!

I would love to build one but if I take up another hobby(or resurrect an old one) I think my better half will explode. I already have a long list of jobs to do around the house that keep getting put off, I dont think I should push it.

Back when I was big into electronics I did consider building one of the Hi-Fi World valve amp kits, I built a pair of floorstanding speakers from one of their kits and loved them, still use them as part of the home cinema system.

Quote
I'll takes some pictures for you. Valve amps are easy to make  :thumbup:

I'd like to see some of your electrical handywork, that'd be great  :thumbup: :thumbup:


Tim
Title: Re: How to Make a Power Supply
Post by: Divided he ad on May 17, 2009, 04:50:37 PM
Well you've lost me on most of this guys! :scratch:


I'd appreciate it if you could point me in the right direction with components Darren.... For the PSU you've been making for the mill's  :thumbup: 

I really want to get one built.... Did we (you) settle on a fully usable circuit?  I got lost in all the heavy talk about the ins and outs!  :smart:




Thank you,



Ralph.
Title: Re: How to Make a Power Supply
Post by: Darren on May 17, 2009, 07:02:23 PM
Sorry Ralph, I've been a little sidetracked more than once.

The one I've been building in this thread will be fine..


One rectifier (you have one)
two 1n4007 rectifiers (you might have those too)
one LM338T voltage regulator
Two 220 ohm 1/4W resistors
Two 1000uf 50V Electrolytic Caps  (don't need to be too rigid with these values, just make sure the voltage is over 35V)
One board to mount it all on.
5K linear Potentiometer

One transformer, 9 or 12V for 12V motors, 18 or 24V for 24V motors.

You might want to get a 2n3055 transistor while you are at it. I'll explain another time but it would be handy to have it ready.


Try Maplins first for the parts, most other places require you have an account and even I don't have one these days.

So Ebay for the parts Maplin don't have is a good option.

If you get stuck or are unsure, just shout  :thumbup:
Title: Re: How to Make a Power Supply
Post by: Darren on May 18, 2009, 05:35:20 AM
I found this in the US for those who don't have the confidence to build their own, just swap the LM317 for a LM338 and use a bigger heat sink.

http://www.electronickits.com/kit/complete/powe/ck402.htm

Title: Re: How to Make a Power Supply
Post by: Darren on May 18, 2009, 12:17:23 PM
The diagram....

Now before anyone pipes up, this is what I built and tested, it works and it works well.

I have no doubt others may do things differently, maybe add some small value caps, bigger caps, different resistor values, pot etc, ect.
There are many ways to build these types of circuits, and each to their own.
Mine works as is and I couldn't see the point in going further to make the ultimate. If you feel the need then by all means go ahead and do it.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/LM338copy.jpg)
Title: Re: How to Make a Power Supply
Post by: spuddevans on May 18, 2009, 01:19:48 PM
Now before anyone pipes up

I just thought I'd pipe up here to say...   :poke:








That looks great  :thumbup:


Tim
Title: Re: How to Make a Power Supply
Post by: Bernd on May 18, 2009, 01:37:12 PM
Darren,

You might want to add a fuse on the mains side of the tranny for saftey sake. Other than that it looks OK. :thumbup:

Bernd
Title: Re: How to Make a Power Supply
Post by: Darren on May 18, 2009, 01:43:54 PM
Good point Bernd,

It easy to forget what comes without question for some of us could be missed by others  :thumbup:

You could also add a fuse after the transformer, say 5A or if you know you current demand is low like these motors then a 3A would be better.

But, DO fit a mains fuse as Bernd suggested.
Title: Re: How to Make a Power Supply
Post by: Bernd on May 18, 2009, 02:04:33 PM
As far as I know and have seen in electrical magazines in the US all such projects have a fuse in line on the incoming voltage to the transformer.

Seems each country has different electrical codes for such devises.

Looking good Darren. Carry on and sorry for the interruption.  :thumbup:

Bernd

Title: Re: How to Make a Power Supply
Post by: Darren on May 18, 2009, 02:08:14 PM
In the UK many electrical goods do not have an internal fuse.

This is because our wall socket plugs have internal fuses. This makes it quite hard to connect anything to the mains supply without a fuse.


Do I understand from your post that US plugs don't have internal fuses?  :scratch:
Title: Re: How to Make a Power Supply
Post by: Divided he ad on May 18, 2009, 02:29:50 PM
Thank you for the parts list Darren :thumbup:


I'll get figuring out the stuff and where to buy it ASAP  :)




Got to get my mill powered  :dremel:


The plug thing.... Odly the other side of the pond do not have fuses in the plugs.... like the French (And I suppose other European countries?)
It seems a little under protected to me..... But hey, someone must know what they're doing? right?  :zap:







Ralph.
Title: Re: How to Make a Power Supply
Post by: Bernd on May 18, 2009, 03:22:16 PM
Darren,

Here's a quick run down of how the power gets into the house. 220v to outside meter. From meter to panel box. Panel box has the circuits for all the rooms. Power is run through a circuit breaker, usally 15 to 20 amps. Then the wire is run to the room plugs. No fuses in the plugs themselves, except for any outlet near water supply, usally kitchen and bathroom. These plugs have ground fault interupt circuits in them and will shut power off to the wall outlet.

Usally when somebody shows a diagram of a circuit they include a fuse and power light on the mains side of the transformer for saftey reasons. A majority of the applances do have an interanl fuse. Just today the microwave oven blew the internal fuse. It is a 15amp fuse. The power line it's connected to has a 20 amp circuit breaker. A dead short would probably open both fuse and breaker.

I don't know if all electrical appliances have internal fuses or not. Rather confusing, I know. :zap:

You won't want to look through the electrical code book, it's quite thick.  :)

Probably hasn't helped any but you get the idea.

Bernd
Title: Re: How to Make a Power Supply
Post by: Bernd on May 18, 2009, 07:03:29 PM
Darren,

I've done a bit more research on published power supplies, but couldn't find some of my electronic books. I did a google search and came up with this PDF file. It's call Power Supply Design Basics (http://us.st.com/stonline/books/pdf/docs/1707.pdf).

I don't see any fuse, on/off switch or power on indicator on the mains line in their example. I still think it's good practice though.

Hope you don't mind me adding this to your thread.

Bernd
Title: Re: How to Make a Power Supply
Post by: Darren on May 18, 2009, 07:16:28 PM
Bernd I can't see that page for some reason, must be the US anti terrorist action coming into play, must think I need it to do some bad things  :lol:


Generally if you need telling that you need a fuse in a mains circuit then you shouldn't be playing with this stuff anyway.

As a rule, people showing other people electronic circuits do not include the peripherals.


It would be a bit like me giving you a slap on the wrist for showing someone how to mill a chunk of metal and not mentioning that they need to wear safety glasses.  :thumbup:
Title: Re: How to Make a Power Supply
Post by: Bernd on May 18, 2009, 07:49:54 PM
Bernd I can't see that page for some reason, must be the US anti terrorist action coming into play, must think I need it to do some bad things  :lol:


Interesting. It's an app note on basic power supplys from the SGS-Thomson Microelectronics.

All right I'm giving up on this while I'm still somewhat sane.  ::) Must have been to many of these  :zap: when I was younger.

Bernd
Title: Re: How to Make a Power Supply
Post by: Alan Haisley on May 21, 2009, 10:11:14 PM
In the UK many electrical goods do not have an internal fuse.

This is because our wall socket plugs have internal fuses. This makes it quite hard to connect anything to the mains supply without a fuse.

Darren,

Does UK house wiring include fuses or circuit breakers at the service point in addition to the plug fuses? If not I'd worry about a broken wire short in the wall.

Alan
Title: Re: How to Make a Power Supply
Post by: Darren on May 22, 2009, 05:29:32 AM
Yes we have one of the highest safety standards in the world I believe.

Don't worry about us Brits  :thumbup:
Title: Re: How to Make a Power Supply
Post by: raynerd on May 30, 2009, 02:28:35 AM
If I want to run a driver at 2.5A and 3.75V but ulimately I have three boards to drive 2.5 x 3 = 7.5A - will my PS have to be rated 7.5A or above? It is this link between voltage and current that confused me and the requirements to power components I don`t get. When selecting a power supply to drive the above, am I just interested in the ampage that it can draw and the fact that it needs to draw 7.5A maximum. The voltage will just be adjusted to achieve this current right?

The power supply that they actually sell for this setup is rated:

Quote
Small Power Supply for our 2.5A 3 Axis Driver Kit.
Input voltage of 100-240V; AC 50-60Hz; 1.5A
24V DC Output
Short circuit, over voltage and over current protection.
 24 Volt Power Supply 33 Each + 6.50 P&P
 

One last thing, to throw a spanner in the works, if I only wanted to run one 2.5A driver would this need to be a variable supply or would it be suitable to plug into one driver as it is?

Any help appreciated.
Chris
Title: Re: How to Make a Power Supply
Post by: John Hill on May 30, 2009, 03:56:40 AM
Chris, when that power supply is outputting 7.5 amps at 24 volts  thats 180 watts but you say your load voltage is only 3.75 volts?   3.75*7.5 =28.125 watts, more than 150 watts going 'somewhere'.  I dont think we have the fully story here but at least we can be confident the 24volt power supply can supply the 10 amps just by doing a check that the power supply input watts is comfortably more than the required power supply output watts.

I assume this is a controller board to drive three stepper motors? Can you provide a link to a description of these controller boards?


No, you would not have to change the supply if you reduce the number of drivers.  Assuming the voltage stays the same the amount of current that will flow will increase as the load units are increased up to the maximum current available from the supply.
Title: Re: How to Make a Power Supply
Post by: Bluechip on May 30, 2009, 05:12:18 AM
Chris

I would suggest that a 24V PSU for a 3.75V motor is not suitable. You can put dropper resistors in series, but is is a very inelegant way to go about it.

There is not enough info. on the stepper motor, but here's a quick ball park guess .. lot of assumptions tho'

24 - 3.75 = 20.25 V to be lost.

Assume motor load = 2.5A (  & constant, which it won't be)

Series resistor = ( R = ( E / I ) 8.1 R

Power to dissipate = I^2 x R  = 50W
Thats a lot, it will get hot.
If I were doing this, I would not go with that PSU. It doesn't really come close to what is reqd.


John. If the PSU has effective current limiting, you wont get 7.5A out of it. I presume if it's designed for 2.5A, the internals would be stressed at 7.5A.


I would make my own PSU, (do a Darren  :D, )with my favourite Reg. ic, the L200, with a series pass transistor.

This chip is a variable output from 2.7V to 37V at 2A, more with a pass transistor.

Try looking for L200.pdf

Lots of circuits thereon..

Dave











Title: Re: How to Make a Power Supply
Post by: raynerd on May 30, 2009, 05:30:47 AM
Ok - I`m sorry but still some of this is going over my head:

The driver:
http://www.routoutcnc.com/singlesmall.html

The motor:
http://web.archive.org/web/20050318040147/http://www.homeshopcnc.com/page3.html   first one on that page but now wired 4 wire bipolar.

The ""available" power supply -
http://www.routoutcnc.com/hardware.html - down at the bottom - the 2.5A kit PS, not the others.

I don`t want to go with their power supply because I have a feeling that this driver, and I only have one at present just to try it, won`t be good enough to drive my motors or it will be good enough but the motor won`t be! Basically, I think I`ll end up upgrading! I want to make a PS so that I know how to go about upgrading in future, to save money (hopefully) and also so that I have a better understanding...



So i I had a go at making Darrens power supply - would it work as it and what "settings" would I need it on to power first of all just one motor and driver and then eventually 3 motors?

Chris
Title: Re: How to Make a Power Supply
Post by: Darren on May 30, 2009, 06:41:22 AM
Chris, I think you mean you want 2.5A @ 37.5V?

But really if you read the instructions 24V output is ideal.

Yes this power supply would do that, but it's not the type I would use as you don't need the variable voltage facilities.

In all honesty at 33 quid each I would use theirs.

Any computor/laptop telephone, printer etc supply should do somewhere near 24V, some are 19V, they would do.

Just check the Amp outputs are high enough.

Title: Re: How to Make a Power Supply
Post by: Bluechip on May 30, 2009, 06:44:18 AM
Chris

Sent you a PM

dave
Title: Re: How to Make a Power Supply
Post by: raynerd on May 30, 2009, 06:58:13 AM
I see Darren! I`ve just looked at the pdf spec sheet and I took this from it:

Quote
Setting the current for your stepper motors.
The formula VREF = Motor Current X 1.4 can be used to determine the Value for VREF
The most common current ratings are shown in a table below.
Motor Current
(A)
VREF Voltage
(V)
2.5 A - 3.5V
2.0 A - 2.8V
1.75 A - 2.5 V
1.5 A - 2.1 V
1.25 A - 1.8 V
1.0 A - 1.4 V
0.75 A - 1.05 V
0.5 A - 0.7 V
Note: It is normal to exceed the motors rated voltage by up to 20 times, for instance a
5V stepper motor run at 24 V would be perfectly expectable.

D Never exceed a motors rated current or the drive cards 30V DC Max. Doing so could
damage the motor and the stepper drive card.

How can a PS running 24V not blow a motor only requiring 3.75V ?

I think I understand the current a little more - is it saying that if the driver is rated 2.5A then that driver will draw 2.5A from the power supply, if your PS isn`t able to provide that current then your PS will blow as the components are drawing too much current from it - is that right? So in actual fact, to run one motor - it doesn`t matter as long as the PS is rated above 2.5A.

I still don`t get the voltage though, if the motor only runs at 3.75V how can I plug into the driver a 24v supply - surely it will blow the motor?

Chris

EDIT: the PS I have spare is a laptop 75W AC adaptor - DC output is 18-20V - 3.79A, would this be any use?
Title: Re: How to Make a Power Supply
Post by: Darren on May 30, 2009, 07:12:39 AM
What does it mean by vref?

That to me is in respect to the power supply setup and not the voltage output to the motor?

I could be wrong as I do not know the full facts,

In all honesty their power supply is a good price, you'd have a job to better it if you needed to buy all the components to make one yourself.
Title: Re: How to Make a Power Supply
Post by: raynerd on May 30, 2009, 07:15:48 AM
VREF = voltage reference.

I understand that their PS may be a good deal but I am interested to learn more about it myself and see if I could save money by using my own spare PS.

I appreciate your time and help.

Chris
Title: Re: How to Make a Power Supply
Post by: Darren on May 30, 2009, 07:20:21 AM
Sorry Chris, yes I know what vref is, but to what is it referincing?

I guess it's to the voltage regulator chip to set the output voltage to the motor. Which is very different to vref value.

That is, do not confuse vref with the motor requirement voltage.
Title: Re: How to Make a Power Supply
Post by: raynerd on May 30, 2009, 04:37:55 PM
Oh I see!! So the driver has a voltage regulator on it anyway so even though your running into it a 24V PS the regulator chip will reduce it to the required voltage to run your motor at 2.5A?? 

A couple of thoughts - why would it "need" to take in a 24V to throw out only 3-4V for the actual motor?  Also, any 24V PS will be ok - but what current should it be rated - anything over 2.5A or should it ideally be a little higher?

All the best, I am understanding this a little more now.

Chris
Title: Re: How to Make a Power Supply
Post by: John Hill on May 30, 2009, 05:04:04 PM
I do not believe this is a simple thing that can be understood by refering to Ohm's Law.

The  motors are not being fed simple DC,  they are being pulsed at some high audio frequence (the description refers to being able to hear the motor making a noise in the windings).

Motors winding are highly inductive and it is a common practice to feed an inductive load via a resistance where a quick reaction is required.  Ancient telegraph practice in fact.  The principal is that there is a high voltage across the coil when there is a low current but when the current begins to flow so the voltage drop across the resistor rises and stops the coil overheating.   I am not suprised that they are proposing such relatively high voltages for nominally low voltage windings.

Any power supply Chris that can provide at least the amps at the voltage you require. 
Title: Re: How to Make a Power Supply
Post by: raynerd on May 30, 2009, 05:11:22 PM
Cheers for the info John - I`m going to give this spare laptop charger a go as it is rated 18-20v @3.79A. Please do tell me if this is well too low powered.
Chris
Title: Re: How to Make a Power Supply
Post by: John Hill on May 30, 2009, 08:52:56 PM
Chris, I think that is a little light on capacity but it might work.
Title: Re: How to Make a Power Supply
Post by: jatt on July 26, 2009, 04:38:04 AM
Hi all,

This is my first post here.  Have done a bit of experimenting in the past with basic power supplies.

This is aimed more for those who dont know much about capacitors.

When I was building things I would use 105 degree rated units at the very least.  Personaly I dont feel the 85 deg are suitable for the task, especially when there is a fair amount of heat involved.

From personal experience I recon the grey insulating material that is shown to back the regulator case to the heatsink is a better way to go than the clear mica washers.  Found the mica splits easily.


Happy power supply building

Title: Re: How to Make a Power Supply
Post by: websterz on October 02, 2009, 08:05:52 PM

Finally in this picture you can see that I have added a push to break switch inline with the adjusting pot. It's the one with the red button.

When the adjusting pot is turned to a higher resistance setting this will increase the speed of the motor. Lower resistance lowers the motor speed.
The "push" switch breaks the circuit offering an infinity resistance, ie very high. When the button is pushed the motor will spin at full speed. Useful for rapid transverse.
Let go of the button and the motor will resume to the pot setting speed as set previously.
This is useful not only for momentary rapid transverse of the mill bed, but it also allows you to leave the pot alone when you have found a comfortable cutting speed.

(http://i401.photobucket.com/albums/pp92/thebodger/Sealey%20Milller/Power%20Drive%202/IMG_2161.jpg)



Quick question Darren. My homebrew power feed utilizes a 14.4 volt cordless drill motor and an ATX computer power supply. I control the speed with this controller:
(http://www.kevlau.com/auctions/hydro/PWM/photo-1.jpg)

I added a DPDT switch between the controller and the motor for reversing the table feed. It all works very well...I am shocked I was able to get it to do what I wanted actually. You should see my collection of burned out controllers and power supplies!  :bugeye: Anyway, the only feature my set-up lacks is the rapid traverse you talked about. With my controller and power supply arrangement can I add a "go really fast" button like your's?  :dremel:  :proj:
Title: Re: How to Make a Power Supply
Post by: Darren on October 02, 2009, 08:12:21 PM
The short answer is I'm not sure, only because I don't know the circuit.

But that pot is the voltage/speed control so I guess then yes you can. All my go faster button did was create a high resistance as in an open circuit. Push to break switch in series with the pot connection.

So I guess you will be able to do the same.
Title: Re: How to Make a Power Supply
Post by: websterz on October 02, 2009, 08:34:07 PM
With the pot on mine being mounted to the pcb it would involve a certain level of disassembly I am sure. I think I'll just be content that it works as-is and not start pulling stuff apart.  :zap: