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#129351 - 01/29/05 06:23 PM High Current DC supply
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
This may sound like a silly question and possibly I should already know how to solve it.
I'm looking to get a DC supply together for some radio gear and I'm looking to do it as in-expensively as possible, but with any equipment necessary.
I need a continuous current capacity of 30-35A DC @ 13.8V +/- a certain amount of voltage.
I need the supply so that it is as ripple-free and as regulated possible and not an SMPS that could interfere with the radio gear.
I was thinking a car battery, but would a standard charger be able to keep up with the current draw?.
And the amount of current flowing in and out of the battery cells damage it?.
Anyone have any better ideas, I've built DC power supplies before, but never with this size of output.
Helllppp!!.
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#129352 - 01/29/05 08:46 PM Re: High Current DC supply
Bjarney Offline
Moderator
Registered: 04/10/02
Posts: 2527
Loc: West-Southern Inner-Northeast ...
Battery chargers have no filtering, but given ready avaiability I'd try an experiment with an auto battery and {larger} charger. You could ride herd on battery state with a DMM, and even measure output ripple on the DMM mVAC range.
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#129353 - 01/29/05 10:41 PM Re: High Current DC supply
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
Hi Bjarney,
Look I've been through the mountain of Electrical and Electronics "Cook-books" I've got here and I think the largest current capacity I can find is about 12A.
And that is with a Shunt-fed Transistor arrangement across an LM317T Regulator.
Other side of the coin too guys, I may be allowed a little ripple in there, but how much is too much with today's almost computerised radio gear?.
I will always have a 230V 50Hz supply with me, but to wind a Tranny with that sort of load on the secondary and find a Bridge rectifier and other down-stream equipment that will carry the currents in the circuit, am I just wasting my time and talking myself around in circles.
And should I just go out and buy a standard PSU at exorbitant (no real market for Ham gear here anymore) new prices, as second-hand ones are either being used or they have been repaired beyond recognition, before finally blowing once and for all.
Mind you at the same time, I can satisfy any requests for HV power supplies, Tesla coils and various other stuff.
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#129354 - 01/30/05 05:29 AM Re: High Current DC supply
Dnkldorf Offline
Member
Registered: 12/12/04
Posts: 1064
Loc: nowhere usa
This thought came to mind.
If the car battery charger can't keep up, I'm sure you can "doctor" a forklift charger to work. They are available in used conditions everywhere.
They should keep up with your draw..

Dnk....
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#129355 - 01/30/05 06:01 AM Re: High Current DC supply
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
Isn't a Forklift charger 24V?.
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#129356 - 01/30/05 07:20 AM Re: High Current DC supply
circuit man Offline
Member
Registered: 11/05/01
Posts: 273
Loc: saluda,s.c.
trumpy, yall don't have the big roll around chargers that you quick charge batteries in a garage with? they can supply 40 amps continously.you would need a couple of electrolic capacitors for filters to clean up the ripple , but should work fine.i opened up a regulated power supply & thats what i found.regulation would be done a lot by the capacitors , but i'm not sure how much. as for some big diodes i have some & would be glad to send ya a couple. these come out of a plating rectifier at work. belive they are 200amp ea.hope this helps!
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#129357 - 01/30/05 08:24 AM Re: High Current DC supply
Dnkldorf Offline
Member
Registered: 12/12/04
Posts: 1064
Loc: nowhere usa
Trumpy,
Some are 12v, 36v, 48v.

Look here:

http://search.ebay.com/forklift-ch arger

{ Link edited to keep width down -- Paul }


[This message has been edited by pauluk (edited 01-31-2005).]
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#129358 - 01/31/05 06:31 AM Re: High Current DC supply
pauluk Offline
Member
Registered: 08/11/01
Posts: 7520
Loc: Norfolk, England
Easy enough to build something like this, but if you had to go out and order all the parts these days it will be quite expensive for such a huge transformer. The reservoir and smoothing capacitors for such an application are getting quite pricey these days as well.

The most cost-effective is probably to pick up a suitable old surplus power unit. The U.K. branch of eBay has all sorts of stuff like this in the Ham radio area.

You might have a more limited choice for Australia/New Zealand though, and on something this heavy I hate to think how much it would cost to get shipped from England.
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#129359 - 02/01/05 10:06 AM Re: High Current DC supply
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
Thanks for the comments guys!.
I did also have an idea in bed last night of building a rotary converter from a fractional horsepower motor and a car alternator/regulator/battery set-up
I've decided to bite the bullet and go for a Switch-Mode type power supply.
After all, how bad can the EMI be from one of these things?, if they are used widely in industry.
And I found one that is rated at 600W and gives an output of 53A @ 13.8VDC @ 0.2% ripple @ maximum output.
I'll see how this goes.
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Let's face it, these days if you're not young, you're old - Red Green grin
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#129360 - 02/16/05 06:41 AM Re: High Current DC supply
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
Well, I really got what I wanted.
A guy just a couple of streets over from me (ZL3AAN) saw the earlier post and offered me an elderly Regulated Valve (tube) Power supply.
But it gives 60A @ 13.8V.
All I had to do was replace some old paper capacitors and it's going like a new one!.
It's from 1949, the front panel is so rusty, I have no idea what brand it is, but who cares?!.
And it has the knot in the cord, on the inside of the Chassis.
It reads "Earthed For Your Safety" on the back.
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Let's face it, these days if you're not young, you're old - Red Green grin
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