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Author Topic: Mill Power feed  (Read 64331 times)

Offline Darren

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Re: Mill Power feed
« Reply #25 on: April 19, 2009, 05:20:11 AM »
Quote from: John Hill on April 18, 2009, 10:47:06 PM
Darren, if the 'top' to the zenor goes to the base of a small transistor you may find the collector of that transistor is connected to the base of the big transistor,  this is a Darlington pair configuration and the small transistor is amplifying the base current for the big transistor and allows the use of a smaller wattage zenor.


I'd have to draw the circuit out, but the emitter of the 1st transistor should go to the base of the 2nd transistor as shown in this diagram for a Darlington pair.



The two collectors should be common? That's how they increase the current capabilities in the order of 10,000.

Unless I'm missing something?

This is the schematic you are proposing....I think? Would that be correct?



And this is what I have done, replaced the zenner with a variable resistor.




Sorry but I still can't see how the zener helps? You have it in series with the pot with both ends tied to ground. At one end the voltage/current will flow through the zener (high speed) and at the other it will flow through the pot (low speed).

But the high speed will be limited to 12V by the zener, whereas they way I have it I can go to the full 20V of the transformer.
Unless I'm misunderstanding the schematic you are proposing, entirely possible...!
« Last Edit: April 19, 2009, 06:36:34 AM by Darren »
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Offline John Hill

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Re: Mill Power feed
« Reply #26 on: April 19, 2009, 03:45:30 PM »
Darren, your schematics are exactly as I was thinking.  One advantage of leaving the zener in the circuit is that you wind up with a regulated output.

More significantly however consider what happens in your circuit if you set the pot to near the top of its travel, set up there you have the full supply voltage over a small segment of the pot, high voltage over low resistance means hight current and quite possibly a little puff of smoke escaping from the pot as it suddenly burns out!

Of course you dont have to keep the zener but I suggest you have the pot in the configuration as per my schematic that way you wont be stressing the pot.


I think the pot should be a few Kohms and be aware that pots come in different 'tapers', linear and log(aka audio), I think a linear would be best for this job but might be harder to find.

Sorry for my mistake regarding the configuration of a Darlington, your diagram is correct and shows how the gain of the first transistor multiplies the gain of the second.
[Well, those are my thoughts anyway! :coffee:]
« Last Edit: April 19, 2009, 05:27:00 PM by John Hill »
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Offline Paul Barker

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Re: Mill Power feed
« Reply #27 on: April 19, 2009, 04:17:21 PM »
Quote from: John Hill on April 18, 2009, 05:25:48 PM
how about this variation?



Zenner is upside down
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Offline John Hill

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Re: Mill Power feed
« Reply #28 on: April 19, 2009, 04:54:12 PM »
Quote from: Paul Barker on April 19, 2009, 04:17:21 PM
Quote from: John Hill on April 18, 2009, 05:25:48 PM
how about this variation?



Zenner is upside down

Antipodean Zener?

[Indeed that Zener is shown upside down assuming it is a positive supply circuit.]

 :bow: :bow:
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Offline Paul Barker

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Re: Mill Power feed
« Reply #29 on: April 19, 2009, 05:01:53 PM »
« Last Edit: April 19, 2009, 05:03:42 PM by Paul Barker »
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Offline Darren

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Re: Mill Power feed
« Reply #30 on: April 19, 2009, 08:46:09 PM »
Who wants to see a video of my mill with power feed operating the table.... :ddb: :ddb: :ddb:
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Offline Bernd

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Re: Mill Power feed
« Reply #31 on: April 19, 2009, 10:19:44 PM »
Oh Oh Oh Oh, I do I do.  :ddb: :ddb:
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Offline Darren

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Re: Mill Power feed
« Reply #32 on: April 19, 2009, 11:00:44 PM »
OK John, I see where you are coming from now,

Re the connection of the pot, yes I accept what you are saying, although I have several similar power supplies used for my Hifi to power large valve filaments.

In twenty years I have yet to see one let the magic out (smoke) The theory is sound though.
We have no need for a regulated supply here, after all we are only powering a motor, nothing critical. So the zenner is really overkill in this application whilst at the same time it becomes a limiting component. I'm more concerned with back EMF when switching the motor off. Normally one would use a reverse diode, but difficult here because we have a reverse polarity switch. I need to think some more on this. However, it may not really be a problem. More "correct" theory.

Simple is always best  :thumbup:

If I were to really want a proper regulated supply I would probably use a 317 as a variable voltage device to reference a 2n3055. Or as I have done in the past a pair of 2n's if the current demand warrants it. Sometimes it does. Valves with heaters at 10V/10A can be pretty demanding to build a supply for, esp when you have four of them to supply.
Remember, we don't want to feed them AC and this is where the problem starts.

However,
This thread was not intended to be an in depth electronic topic. It was about making a simple variable power supply for those with no real electronic experience.
I believe I have shown what can amount to not only the simplest method to achieve this, but the cheapest as well. These are important factors as this is not an electronics forum. Guys here mostly chop metal, not solder.

This thread was deliberately never intended to become technical, that really scares peeps from trying altogether. Quite honestly we have discussed things that didn't belong in this topic.

If anyone other than John and I are still reading this, what I have proposed is really quite simple and cheap. Ignore all the other stuff, none of it applies to what we need here.
I have now powered the mill with this power supply and motor. I was going to show you but my phone battery went flat. I'll take a video tomorrow.
BTW, nothing too exciting as I'm holding the motor by hand, but I have made a nice linkage in delrin.... :thumbup:

You should be able to make this supply for about a fiver, tenner at the most if you are unlucky.
If anyone decides to go down this path, there is always help available. Even if I have to do it for you !!  :dremel:

 

 
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Offline John Hill

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Re: Mill Power feed
« Reply #33 on: April 19, 2009, 11:16:24 PM »
Darren  :beer:

Just to summarise my position, a tranny, rectifier, pot, transistor is about as simple as you could get, if you need more current add a big transistor in a Darlington configuration, if you need lots more current add a bunch as 'pass transistors' (I have four 2N3055s in my old power supply).  If thats all too daunting the aforementioned lamp dimmer before the tranny and rectifier must be the easiest of all.

Good work, lets see that video!!! :ddb:

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Offline Divided he ad

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Re: Mill Power feed
« Reply #34 on: April 20, 2009, 02:47:16 AM »
Hi  :wave:

I seem to be a few days late to this party  :(

I couldn't have helped with the electrictrickery but I sure would have had the pom poms out cheering you on darren  :ddb: ...... Ok, that's just wrong! (Pom poms.... I would never.... Honest! :lol:)


I've got some reading to do to catch up with all this .... I'll have some stuff to figure out too as all my stuff is rated 24V!



Very good post Darren, and all other technical contributers  :thumbup:



Bring on the vid'!!!  :D




Ralph.
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Offline sbwhart

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Re: Mill Power feed
« Reply #35 on: April 20, 2009, 03:20:04 AM »
Way to go Darren  :thumbup:  :thumbup:

I'm having problem following what you're doing, but thats my fault not having any background at all in electronics.

Can't wait to see your mill working under power

Stew
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Offline Darren

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Re: Mill Power feed
« Reply #36 on: April 20, 2009, 08:02:30 AM »
Some photo's for now.... :wave:























I'll take the video later and post.... :thumbup:
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Offline Darren

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Re: Mill Power feed
« Reply #37 on: April 20, 2009, 06:36:52 PM »
Sorry to take so long to get this up...life got in the way today..... :ddb:

Bear in mind it has no frame yet to hold it in place, and I was balancing the camera with one hand, holding the motor with the other whilst wondering where my third hand was to control the speed and switches....fun, fun, fun...

But hey, it works and more will come of it  :ddb: :ddb: :ddb:

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ja2on

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Re: Mill Power feed
« Reply #38 on: April 20, 2009, 06:44:04 PM »
Nice job  :thumbup:
I would have never thought of coming out of the rear of the gearbox  :bow:
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Offline John Hill

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Re: Mill Power feed
« Reply #39 on: April 20, 2009, 06:54:48 PM »
That looks good so far! :thumbup:

Will you be able to turn the feed by hand with the motor attached when setting up etc?
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Offline Darren

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Re: Mill Power feed
« Reply #40 on: April 20, 2009, 07:11:59 PM »
Thanks Jason,

I'm afraid I can't take the credit for that idea, as much as I'd like to.... :clap:

Nope, the credit goes to Marc "The Tinkerer" From Australia  http://home.swiftdsl.com.au/~thetinkerer/projects/projects.html  :thumbup:
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Offline Darren

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Re: Mill Power feed
« Reply #41 on: April 20, 2009, 07:14:35 PM »
Quote from: John Hill on April 20, 2009, 06:54:48 PM
That looks good so far! :thumbup:

Will you be able to turn the feed by hand with the motor attached when setting up etc?

Thanks John, yes no problem there, I can think of three ways to achieve this quite easily. I'll have to decide which one I'm going to go with...

Ralph, one hand wheel can be got around, 24V motor would still work with this supply. In fact it might work better than the one I have.
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bogstandard

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Re: Mill Power feed
« Reply #42 on: April 20, 2009, 11:28:48 PM »
Prototype proven Darren, super job.

On the home run now. :ddb: :ddb: :ddb:

John
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Offline sbwhart

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Re: Mill Power feed
« Reply #43 on: April 21, 2009, 03:12:08 AM »
Well done that Man  :clap: :clap: :clap:

Stew
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Offline Darren

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Re: Mill Power feed
« Reply #44 on: April 21, 2009, 06:27:59 AM »
Quote from: sbwhart on April 20, 2009, 03:20:04 AM


I'm having problem following what you're doing, but thats my fault not having any background at all in electronics.

Can't wait to see your mill working under power
Stew

Stew/Ralph

If you want to take the easy way out have a look at this, if you want it then snap it up I have not seen many on Ebay.
It's suitable for 12/24V.

You will only need a 12V or 18V transformer to go with it, they are easy to find, Ralph has some....I might be able to sort one out as well. I'd have to go hunting....

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=260392906819

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Offline Darren

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Re: Mill Power feed
« Reply #45 on: April 21, 2009, 06:31:31 AM »
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Offline sbwhart

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Re: Mill Power feed
« Reply #46 on: April 21, 2009, 06:37:08 AM »
Darren

Thanks for the ebay links I've put a watch on the first one we've got to be carful, don't want to be bidding against Ralph  :doh:

I may go for the Euro one from Irland its got a buy it now, about 20 squid with postage.

Stew
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Offline Darren

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Re: Mill Power feed
« Reply #47 on: April 21, 2009, 06:43:15 AM »
Which one is that Stew, I can't see one from Ireland?
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Offline sbwhart

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Re: Mill Power feed
« Reply #48 on: April 21, 2009, 06:54:27 AM »
 :doh:  I got that wrong its Shangie

Unless ther's a Shangie in County Clare  :lol:

Stew
« Last Edit: April 21, 2009, 06:56:56 AM by sbwhart »
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Offline Darren

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Re: Mill Power feed
« Reply #49 on: April 21, 2009, 07:03:17 AM »
Oh I see, it's in China  :thumbup:

You will need a transformer as I said before and a rectifier to go with it.

Rectifier turns AC voltage from the transformer to DC which the module needs.

Now that is going to set you back  :lol: :lol: :lol:

http://cgi.ebay.co.uk/8A-Bridge-rectifier-100v-x-1-ROHS_W0QQitemZ270314229523QQcmdZViewItemQQptZUK_BOI_Electrical_Components_Supplies_ET?hash=item270314229523&_trksid=p3286.c0.m14&_trkparms=66%3A2|65%3A15|39%3A1|240%3A1318

Don't buy any old rectifier, let me see what you are looking at before you buy... :thumbup:

You want probably 6A minimum, bigger is better but no need to go silly. The one I linked is fine and easy to mount.
I'll show you how to connect it later. Easy I promise... :thumbup:
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