On 2014-02-26, Ignoramus9393 wrote:
On 2014-02-26, DoN. Nichols wrote:
On 2014-02-25, Ignoramus9393 wrote:
I have a few welding rectifiers for sale, that I sold from some big
old welders. They look like this:

http://goo.gl/327zJ4

They have everything all together, heatsinking, mounting, isolation
etc. I already sold a bunch of them. I think that most buyers use them
to convert AC welders to DC welders.

O.K. That is for three phase in (via the aluminum straps which
appear to have been bent), and it is three each of forward polarity
diodes (on one plate) and of reverse polarity diodes (on the other
plate).

You can only put one phase in. No problem.

Of course.

Actually, for one phase, you can hook it up as follows:

Your in-terminals X, Y, Z, connected to single phase A and B like this:

A, B, A

In other words, one side of single phase is in the middle, and
another side of single phase is on both ends). That allows for
somewhat better cooling.

Reasonable. But given that the battery charger in question used
only two (selenium) rectifiers (and a center-tapped transformer
secondary), there is no need for the other half of the rectifier
assembly -- and it takes up space, so pull out one plate and only mount
the one which has the flavor of diodes (normal or reverse) needed by the
design of that battery charger. And with that, you probably don't even
need the insulating strips to insulate it from the chassis. Since he
said that there was only one wire going to each selenium rectifier, I
suspect that the chassis is serving as the common point of the two
rectifiers.

And -- a use for the extra rectifier place could be to swap in
one from the other plate (reverse or standard -- the opposite of what is
on the plate with the needed rectifiers) to block against reverse
connection to the battery frying the transformer or the diodes -- or
both.

Have you looked up the current rating for those diodes? Given
the cable leads instead of terminals, I suspect that it is rather
impressive. :-)

For the battery charger, you would only need one plate (which is
a function of the polarity of the original selenium rectifiers) and only
two of the three rectifiers on it. So -- just grab one of those, select
which plate has the right set of rectifiers for your needs, and either
pull out the third diode -- or leave it in there for a quick swap-in if
one fails (and trips the breaker before it cooks the other diode. :-)

Enjoy,
DoN.

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