Re: OT: Bridge Rectifiers

[Jim <alarminex@xxxxxxx>]

On Jan 10, 11:22=A0am, "Bob La Londe" <onebike...@xxxxxxxxx> wrote:
> "Jim Rojas" <jro...@xxxxxxxxxxxx> wrote in message
>
> news:PkFWo.34367$sx4.18943@xxxxxxxxxxxxxxx
>
> > Bob La Londe wrote:
> >> I am working retrofitting a control system (hobby stuff - (industrial
> >> hobby)) and I was considering reusing some of the components. One of t=
he
> >> things is a 230-60V transformer that feeds into a modularized bridge
> >> rectifier to produce 84VDC under load. The transformer is fine, the ca=
ps
> >> (BIG caps) need to be tested, but I was wondering if the diodes in the
> >> rectifier have a predictable service life? I can make my own easily
> >> enough with a handful of heavy diodes, but I really like the neat
> >> packaging of this modular one. One less thing to have to bread board.
> >> This is NOT a low current application.
>
> > Predictable? No. As long as the rectifier is rated 25+ percent higher t=
han
> > the actual load, you should expect a long life.
>
> 20 years? =A050 years? =A0This system is 26 years old. =A0I do not know h=
ow much
> use it actually saw, but it was not a cheap system in its day. =A0I imagi=
ne it
> saw some. =A0It was well beyond the price range of even the most dedicate=
d
> hobbiests in 1984. =A0Are you saying basically that if it works fine now =
under
> the load I plan to use, has a suitable safety margin, and doesn't get hot=
 it
> should be fine for an indefinite period?
>
> > High heat is what kills them. So if your rectifier is rated at 100A, Tr=
y
> > not to push anymore than 75A through it. You can also put rectifiers in
> > parallel. Since they are sharing the same AC input, they are automatica=
lly
> > in phase. This will greatly reduce the heat generated.
>
> Not a bad idea. =A0There are a couple salvageable modular rectifiers that=
 look
> the same as this one in the control cabinet, and one that is bread boarde=
d
> for the lower voltage stuff.
>
> Thanks Jim.

Jim is right Bob.
Component mfg's will give you life expectancy values on a general
basis, for production type components. For special components they can
give you a more specific life expectancy but it's always got an escape
clause. Solid state components can be used in too many different
applications for a specifice life expectancy to be guaranteed. A
resistor for instance could last a lifetime.and longer. But .... on
the other hand it could blow .... tomorrow ... just like that light
bulb  you bought yesterday. However, I've got some of those Ademco
keypads used with the 5600 wireless panels still in service. The
keypads have an incandescent lamp. That's gotta be about 30 years and
still working. I think they were 14 volt bulbs powered by 6 VDC.  Go
figure.............