Jim Lesurf wrote:
In article , Ian Bell
wrote:
David Looser wrote:
"Ian Bell" wrote
Yes, but unless it consumes a significant fraction of the load then
its decay time will be rather long.

True, but it's normal. How many bits of valve kit have relay connected
discharge resistors? - almost none. Is there any particular reason
why you need a very short discharge time?


The PSU is remote and the relay has an interlock to turn off the HT if
the PSU HT output lead is disconnected. I need to either disconnect the
HT or bleed it very quickly to avoid a possible shock hazard.

For the HT source side I assume you use female connectors, so physically
preventing accidental contact with fingers, etc.

Of courcse.

For the HT sink side you can use a silicon diode following a shunt resistor
to ground. Once the plug is pulled this isolates the HT from the prongs of
the male plug.


I don't quite follow that. Could you explain a little further.

Note this means the cable is *not* reversable as it has a male at one end
and a female at the other to ensure that whichever end is opened you can
apply the above correctly. The shunt resistor before the diode will also
help remove the charge from any cable capacitance if the disconnection is
at the source end.


Yes, that is the plan - female connector on PSU, male connector to
female connector in the cable and male at the equipment end. Still not
clear how the diode and shunt R work.

Afraid I don't recall you saying where the smoothing/reservoir caps are
located. So I'm assuming both/either ends of the link.


Mostly at the PSU end but there will be some in the equipment too (
order of magnitude less capacitance).

Also use a bleed resistor on the caps.

You could use something like a crowbar which trips if a loop via two
conductors of the cable is broken. However though neat in some ways it can
fall into the trap of being over-complex so designing in extra failure
modes. Hence if you are very safety conscious I'd still do the above.


That's effectively what the relay is supposed to do:

1. A NO contact disconnects the HT when the relay drops out
2. A NC contact rapidly discharges the resevoir caps..
My experience is that almost any type of conventional relay will end up
causing problems if the unit is used for many years. Avoid if at all
possible. Solid state relays would be much better if you can find one that
suits your purpose.

I think I just grokked the series diode shunt R at the equipment end.

Thanks

Ian

Slainte,

Jim