[ARC5] Selenium rectifiers

[Tim]

Hi Ken - I agree.  The selenium FWB in my PU-181 AC generator grew some
white powder, genny ran full speed as a result (no voltage feedback to the
throttle solenoid).  https://www.n6cc.com/wp-content/uploads/IMG_4507.jpg
I use that generator to run my ARC-5 ACPS in the field - it's very quiet
electrically. After 71 years of faithful, though intermittent service the
diode bridge failed...Fortunately it didn't damage anything so I can't
complain.
I replaced the diode stack with 4 MR820's and a 3.5 ohm WW resistor, back
in business.  I also replaced the seleniums in my GRC-109 power supplies
with silicon long ago. A good preventive maintenance fix.

Tim
N6CC

On Sat, Mar 12, 2022 at 3:18 PM Kenneth G. Gordon <kgordon2006 at frontier.com>
wrote:

> On 12 Mar 2022 at 15:38, Jack Antonio wrote:
>
> > But yeah, I do treat seleniums with suspicion.
>
> Well, everyone here can, of course, do what they wish with regard to
> selenium rectifiers, but I
> won't have them in the shack if I can avoid it.
>
> Most will deteriorate over a long period of time, some even while being
> stored. They become,
> essentially, resistors, not rectifiers.
>
> Then, if they short out under load, they spit out a gas that is poisonous,
> besides stinking to
> high heaven.
>
> IMHO, it is far less hassle to simply replace them with silicon. than to
> continue to worry about
> them...and I am NOT in favor of shot-gun replacing any other component
> without testing it
> first.
>
> I can't and won't trust the darned things.
>
> In the unit in question, we were told that the selenium rectifiers in this
> rotary converter are in
> the voltage-regulation part of that unit. By the very fact that those are
> in that part of the circuit,
> I would be replacing them even if they "test" good....for now.
>
> Although I am not "intimately" knowledgeable of that particular circuit,
> it seems to me that if
> they control the voltage regulation of the unit, it would be far better to
> replace them, now, with
> silicon rather than depend on such an iffy component.
>
> It also seems to me that if that voltage-regulator was not completely up
> to specifications, that
> COULD be the reason for the unusually high current the unit exhibits at no
> load. If there was
> more AC on the output of the selenium rectifiers than there should be, for
> instance.
>
> Of course, you MAY have to consider and account for the differing
> voltage-drops of selenium
> vs silicon, but in most cases that won't matter.
>
> But since it is your equipment, you can do as you want.
>
> Ken W7EKB
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