Pwr Supply Problem

[scott93727g]

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.

 

[ehsjr]

scott93727g wrote:

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.

I have mostly questions, but first a couple of points:
First, your transformer current rating needs to be about
1.5 - 1.8 times greater than the maximum current you will
draw. You didn't say what that is.
Why did you put rectifiers in parallel? That doesn't
give you the equivalent of a 40A rectifier - I assume
you thought it might.

Ok, now to the problem. How do you balance the current
drawn from each LM338? Schematic please.
How did you test that you are getting full current
out of the filter caps past rectifiers, and what is
"full current" - how many amps?
Are your LM338's installed on heat sinks?
How much current do you want to be able to draw?

Ed