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Old 26th October 2005, 06:35 AM   #1
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Default 12V Regulator problem

Heres my problem. I want to take 160VDC and bring it down to 12V to run a TL494 PWM, It's part of a high current(50A) 12V power supply I'm building for testing car amps on before putting them in the car. My problem is that no matter what I get for my theory it just doesn't work. I will show you my schematic at the bottom. I'm useing a basic series pass regulator with a zener holding it at 12V. when I have no load on the supply it will output 12V(not including losses) but the moment I put any load on it, the supply drops to .33 or so.

Could you please tell me what I'm doing wrong.

P.S I know I'm working with mains at the moment so that is why I'm asking.

please see post #18 for additional information which assures me this isn't a suicide about to happen
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Old 26th October 2005, 06:52 AM   #2
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First: Get yourself a safe power source like a transformer, then we will be able to help you. We have a rule here which is that we don't discuss circuits powered directly from the mains.
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Old 26th October 2005, 10:49 AM   #3
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Default Re: 12V Regulator problem

Quote:
Originally posted by ifrythings
[snip]P.S I know I'm working with mains at the moment so that is why I'm asking.

ifrythings,

Man, you sure like to live dangerously. You realise this is a live mains circuit? And that you ground the mains through a diode?? As P-A said, get yourself a transformer. Otherwise you may need to change your name to ifrymyself .

Jan Didden
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Old 26th October 2005, 01:22 PM   #4
paulb is offline paulb  Canada
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Not only dangerous but impossible. You want 12V at 50 amps? You'll never get that out of a mains supply anyway. Besides saving you from killing yourself, a transformer lowers the voltage and allows for increased current while maintaining efficiency.
Here is a correct approach.
http://sound.westhost.com/project77.htm
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Old 26th October 2005, 01:33 PM   #5
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This is NOT the correct approach. Using two separate windings, rectifying them separately and then paralleling them is very sub-optimal. There will always be a difference between the two winding voltages and diode thresholds. The shown diagram will result in one winding being more loaded than the other. (It is also unnessesarily expensive as it uses two bridges).

If you have two windings, put them in series, ground the midpoint and use two diodes from each end to get the pos (or neg) voltage. That divides the load over the windings close to 50-50. It also gives you a bit more voltage because there is only one series diode in the supply line instead of two. And it saves you 6 diodes or at least one bridge.

Jan Didden
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Old 26th October 2005, 02:06 PM   #6
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Dude, you're INSANE!

My suggestion:

Get a battery charger from Canadian Tire with a starting circuit. My ages-old Motomaster charger has a 70A starting circuit. When it's in "start" mode, it puts out a regulated 12V, and really is good for up to 70A or so.

This will probably be cheaper than buying a transformer and associated bits to build a 600W 12VDC power supply, and it gets you something you can use for other things.

If the power coming out of the charger isn't clean enough, strap on a car battery in parallel. A motorcycle battery would do in a pinch, but DON'T charge it at more than 2A.

If that's not clean enough for a car amp, well, I'm not sure the alternator would be any cleaner.

Wes
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Old 26th October 2005, 02:18 PM   #7
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Hi Wes,

I am intrigued by your sig. The one I know says "Do robots dream of electric sheep?" - from a story by the late Isaac Asimov.

Jan Didden
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Old 26th October 2005, 03:05 PM   #8
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That's the origin, I coined my current .signature one night after a marathon of UNIX systems programming. I've been using it since the late 90s.

Hiliariously enough, if you google for it, you will find that I have made a few people's quote files. I never thought I was quotable!!

Wes
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Old 26th October 2005, 03:19 PM   #9
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Default Re: 12V Regulator problem

Quote:
Originally posted by ifrythings
Heres my problem. I want to take 160VDC and bring it down to 12V to run a TL494 PWM, It's part of a high current(50A) 12V power supply I'm building for testing car amps on before putting them in the car. My problem is that no matter what I get for my theory it just doesn't work. I will show you my schematic at the bottom. I'm useing a basic series pass regulator with a zener holding it at 12V. when I have no load on the supply it will output 12V(not including losses) but the moment I put any load on it, the supply drops to .33 or so.

Could you please tell me what I'm doing wrong.

P.S I know I'm working with mains at the moment so that is why I'm asking.
Hey...

I like that circuit... hmm, lemmesee... (160-12)x50=7400 Watts of waist, hmmm.... very "frytening" I have to say... this must be a joke, very fun indeed and entertaining circuit idea though!

Cheers Michael
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Old 26th October 2005, 03:29 PM   #10
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I wonder which will kill him first, the circuit itself or the electricity bills?


Don't even think about building that circuit, and if you already have, don't even think about using it.
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