Author Topic: How to Make a Power Supply  (Read 55871 times)

Offline Darren

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Re: How to Make a Power Supply
« Reply #25 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
« Last Edit: May 14, 2009, 01:59:32 PM by Darren »
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Offline Brass_Machine

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Re: How to Make a Power Supply
« Reply #26 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.



What do you think?

Eric
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Offline Bernd

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Re: How to Make a Power Supply
« Reply #27 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
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Offline CrewCab

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Re: How to Make a Power Supply
« Reply #28 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

Offline Darren

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Re: How to Make a Power Supply
« Reply #29 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 !!
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Re: How to Make a Power Supply
« Reply #30 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

Offline CrewCab

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Re: How to Make a Power Supply
« Reply #31 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 

Offline Darren

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Re: How to Make a Power Supply
« Reply #32 on: May 14, 2009, 06:59:26 PM »
CC = Dave  ::) ................ Steve = Cedge  :wack:    ::)

I never was very good with names Pete... :(
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Offline Brass_Machine

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Re: How to Make a Power Supply
« Reply #33 on: May 14, 2009, 09:42:45 PM »
unlocked & pruned the thread a little. Keep it light!  :med:

Sorry guys.

Eric
« Last Edit: May 14, 2009, 10:51:24 PM by Brass_Machine »
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Offline CrewCab

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Re: How to Make a Power Supply
« Reply #34 on: May 15, 2009, 05:26:30 AM »
I never was very good with names Pete...

 :thumbup:

CC

Offline Darren

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Re: How to Make a Power Supply
« Reply #35 on: May 15, 2009, 12:11:50 PM »
Eric,

For your supply I would build this




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

If you need more help just shout up 
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Offline spuddevans

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Re: How to Make a Power Supply
« Reply #36 on: May 15, 2009, 03:31:13 PM »
Eric,

For your supply I would build this




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
« Last Edit: May 15, 2009, 04:02:03 PM by spuddevans »
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Offline Darren

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Re: How to Make a Power Supply
« Reply #37 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:
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Offline Darren

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Re: How to Make a Power Supply
« Reply #38 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)

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Offline spuddevans

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Re: How to Make a Power Supply
« Reply #39 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
« Last Edit: May 16, 2009, 04:37:01 AM by spuddevans »
Measure with a micrometer, mark with chalk, cut with an axe  -  MI0TME

Offline Darren

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Re: How to Make a Power Supply
« Reply #40 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:
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Offline Darren

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Re: How to Make a Power Supply
« Reply #41 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
« Last Edit: May 17, 2009, 02:08:49 PM by Darren »
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Offline spuddevans

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Re: How to Make a Power Supply
« Reply #42 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
Measure with a micrometer, mark with chalk, cut with an axe  -  MI0TME

Offline Darren

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Re: How to Make a Power Supply
« Reply #43 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

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Offline spuddevans

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Re: How to Make a Power Supply
« Reply #44 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
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Offline Divided he ad

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Re: How to Make a Power Supply
« Reply #45 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.
I know what I know and need to know more!!!

Offline Darren

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Re: How to Make a Power Supply
« Reply #46 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:
« Last Edit: May 17, 2009, 07:23:10 PM by Darren »
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Offline Darren

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Re: How to Make a Power Supply
« Reply #47 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

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Offline Darren

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Re: How to Make a Power Supply
« Reply #48 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.

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Offline spuddevans

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Re: How to Make a Power Supply
« Reply #49 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
Measure with a micrometer, mark with chalk, cut with an axe  -  MI0TME