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Pwr suppley Problem
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scott93727g  
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  More options Nov 20 2008, 8:54 am
Newsgroups: sci.electronics.design
From: scott93727g <eb3...@aol.com>
Date: Wed, 19 Nov 2008 19:54:21 -0800 (PST)
Local: Thurs, Nov 20 2008 8:54 am
Subject: Pwr suppley Problem
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Pwr suppley Problem
I made a power supply with 3 paralelled LM338 Regulators in paralell
(24V 12A trans), with 2 paralelled 20A rectifirs, worked great for 1
week, then all of a sudden, output dropped to 2 amps max (from 15A), ,
all componed seem to check out ok, getting full current out of filter
caaps past rectifiers, any ideas, tried substituting a good regulater,
and same thing, any ideas.

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D from BC  
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  More options Nov 20 2008, 9:17 am
Newsgroups: sci.electronics.design
From: D from BC <myrealaddr...@comic.com>
Date: Wed, 19 Nov 2008 20:17:44 -0800
Local: Thurs, Nov 20 2008 9:17 am
Subject: Re: Pwr suppley Problem
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On Wed, 19 Nov 2008 19:54:21 -0800 (PST), scott93727g <eb3...@aol.com>
wrote:

>Pwr suppley Problem
>I made a power supply with 3 paralelled LM338 Regulators in paralell
>(24V 12A trans), with 2 paralelled 20A rectifirs, worked great for 1
>week, then all of a sudden, output dropped to 2 amps max (from 15A), ,
>all componed seem to check out ok, getting full current out of filter
>caaps past rectifiers, any ideas, tried substituting a good regulater,
>and same thing, any ideas.

Sorry.. I'm a very visual person.. Schematic please..

Perhaps see:
http://cache.national.com/ds/LM/LM138.pdf
Page 14 has an example of paralleling regulators.

But what bugs me, why parallel regulators???
I'm inclined to get the same function by paralleling transistors, use
feedback and a Vref.

D from BC
myrealaddress(at)comic(dot)com
British Columbia
Canada


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legg  
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  More options Nov 20 2008, 7:31 pm
Newsgroups: sci.electronics.design
From: legg <l...@nospam.magma.ca>
Date: Thu, 20 Nov 2008 09:31:53 -0500
Local: Thurs, Nov 20 2008 7:31 pm
Subject: Re: Pwr suppley Problem
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On Wed, 19 Nov 2008 19:54:21 -0800 (PST), scott93727g <eb3...@aol.com>
wrote:

>Pwr suppley Problem
>I made a power supply with 3 paralelled LM338 Regulators in paralell
>(24V 12A trans), with 2 paralelled 20A rectifirs, worked great for 1
>week, then all of a sudden, output dropped to 2 amps max (from 15A), ,
>all componed seem to check out ok, getting full current out of filter
>caaps past rectifiers, any ideas, tried substituting a good regulater,
>and same thing, any ideas.

Simplify first. Get one regulator working by removing other parts -
then reintroduce the second, etc.

Most obvious failure is in low value sharing resistors. Perhaps these
were not good for 5A and they are now open/higherZ.

A schematic would be nice.

RL


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winhi...@gmail.com  
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  More options Nov 21 2008, 12:58 am
Newsgroups: sci.electronics.design
From: winhi...@gmail.com
Date: Thu, 20 Nov 2008 11:58:28 -0800 (PST)
Local: Fri, Nov 21 2008 12:58 am
Subject: Re: Pwr suppley Problem
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 I wonder if Scott used current equalizing resistors, as
 NSC recommended in the examples in the datasheet?

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