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Old 9th October 2007, 04:47 AM   #1
MadMutt is offline MadMutt  Australia
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Default Simple BIG 12VDC supply ideas wanted

Freind has a car audio 'demo board'.
Has been running it off car batteries (with charger) for a while.
I don't believe this is the best idea as he goes through two batteries a year.

He needs a supply (12-14VDC) capable of around 30-50 amps.

I'm thinking a simple unregulated (transformer, bridge rectifier, filter cap) would be fine.

Yes a regulated supply would be better, but at those currents suitable transistor arrays would be expensive.

Is a regulated supply feasible for this current demand ?

No I don't want a switched supply (output noise).

Your thoughts are welcome.
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Old 9th October 2007, 06:03 AM   #2
star882 is offline star882  United States
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Output noise shouldn't be a problem. An automotive electrical system is very noisy.

I suppose if all else fails, you could have an AC motor spinning an alternator.
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Old 9th October 2007, 07:13 AM   #3
MadMutt is offline MadMutt  Australia
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I agree, cars are extremely noisy (electrically).
Hadn't thought of the motor driven alt.
Power wastage doesn't appeal to me though.

He does have one high current (15 A cont.) supply.
It was 'built' by someone with not many brain cells though.
It runs ultra hot and is not really protected at all.
17VAC trans --> bridge --> 10,000uf --> LM317 with two pass transistors.
The design is lifted straight from an application sheet.
So the reg/pass section is dissipating 12 volts to start with.
At a draw of 10A (normal drain) the poor thing is frying in it's tiny case.
The heatsink is barely big enough to mount the three TO3 trannies.

Hence why I'm trying to get him to let me build a proper supply.

I can design/build a regulated supply if he springs the $$$.
Just wondering if anyone has a better sugestion.

Must be as close to short term abuse proof as possible.
He aint always considerate of equipment
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Old 11th October 2007, 06:59 AM   #4
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This is taken directly from National's LM338 data sheet.
This might be worth consideration. It's modular design
lends itself well to scaling.

Anything worth doing, is worth overdoing.

Click the image to open in full size.

Cut to shape, file to size, pound to fit.
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Old 13th October 2007, 02:36 AM   #5
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i have a shortwave radio supply which is 20 amps continuous, 24 peak. you could clone one of those.

i've tested a car amp with a battery charger. there was a slight hum vs the clean sound of the regulated one. btw, deep cycle batteries would have worked better.
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Old 13th October 2007, 10:51 AM   #6
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Default Re: Simple BIG 12VDC supply ideas wanted

[QUOTE]Originally posted by MadMutt
[B]
No I don't want a switched supply (output noise).

hi,
a filter is not a problem.
car audio amps already have suppressors.


[QUOTE]Originally posted by star882
[B]Output noise shouldn't be a problem. An automotive electrical system is very noisy.

indeed!..the alternator itself is noisy..


check this out: http://www.meanwellusa.com/search/usp-500/default.htm

i have a mean well rated @ 25A running my car amp for almost 2yrs now w/o any probs..
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Old 13th October 2007, 01:22 PM   #7
Eva is offline Eva  Spain
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Default Re: Simple BIG 12VDC supply ideas wanted

Quote:
Originally posted by MadMutt

No I don't want a switched supply (output noise).

You already have one or two switching mode power supplies inside every car audio amplifier so who cares...
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Old 13th October 2007, 03:01 PM   #8
dukep is offline dukep  United States
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Default perhaps 2 supplies

Is this supply used for both head units and amplifiers?

Perhaps using the regulated unit for the cd decks. Likely more sensitive to 12v noise.

use the dirty unregulated for the big amps. My supply is unregulated but has 30,000uf in caps to supply power to an amp. For really big amps, a battery is a must to handle the peak amps.

I like the alternator idea. You can get alot of amps cheaper.
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Old 13th October 2007, 03:31 PM   #9
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Default cheapest...

...probably a 50amp car charger/starter with a battery in parallel, huge peak current capacity, but will supply 10-15 amps all day, total cost < $100.

If more average current is needed, parallel another charger. The only obvious drawback is the physical space required to hold the equipment.

HTH

Stuart
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Old 13th October 2007, 03:35 PM   #10
djQUAN is offline djQUAN  Philippines
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http://sound.westhost.com/project77.htm
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