HT Relay

I am trying to select a relay for a delayed HT switch (which will also discharge the HT when off). Most relays I can find have contacts rated at 250VAC which translates into a peak of about 350V. However, data is scarce on what dc voltage these relays can switch. So far I have found only one that gives a dc current versus voltage curve and that stops at

210V dc (and 200mA) and I really want to be able to switch up to 350V at up to 200mA. The rest just give a dc voltage at max current value.

So, I am guessing that this problem has been faced before and there are relays that are known to work fine in this application. Any recommendations?

By the way I prefer a 5V coil.

Cheers

Ian

Reply to
Ian Bell
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On a sunny day (Thu, 24 Dec 2009 14:44:00 +0000) it happened Ian Bell wrote in :

You canot use an AC relay rated at 250V for DC at 350V (the sqrt(2) value). This because, as recently discussed here, in a DC circuit you get arc forming, and the arc will not extinguish. Most of those relays have a much lower DC rating.

A simple HV MOSFET perhaps? or transistor? Else a tube... Or a real HV relay.

Reply to
Jan Panteltje

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The problem with using relays on DC is that when the contacts open an
arc is established which is hard to put out.
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Reply to
John Fields

I can understand that with high currents which is why many of the 250VAC

10 or 20 amp relays I have seen are only rated at about 30Vdc for the same amps but here I am only switching a small fraction of an amp.

Understood.

I would rather not.

Cheers

ian

Reply to
Ian Bell

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12V coil, and a little pricey, but perhaps something like this, then:

http://www.jenningstech.com/pdf/rel/RF_1D_1E_1G.pdf
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Reply to
John Fields

LOL

Cheers

Ian

Reply to
Ian Bell

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And another:

http://relays.tycoelectronics.com/datasheets/k45c.pdf
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Reply to
John Fields

+r...

Also I would think there is benefit to adding an RC snubber network across the contacts.

You can even get fancy and add diodes to provide independent "attack" and "deacy" time constants...

Mark

Reply to
Mark

Kilovac?

Cheers

Reply to
Martin Riddle

"Jan Panteltje" Ian Bell

** Course you can, if you de-rate the breaking current figure sufficiently.

The OP has, like YOU, made a blunder in his interpretation of the specs.

.... Phil

Reply to
Phil Allison

On a sunny day (Fri, 25 Dec 2009 11:27:57 +1100) it happened "Phil Allison" wrote in :

Sigh, hey, zero current may work! How clever of you:-) But wanna bet he wants to switch some more current then zero?

Got nothing for Christmas Phil?

Reply to
Jan Panteltje

recommendations?

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I just found this, which might help:

http://schrackrelays.com/appnotes/app_pdfs/13c3236.pdf
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Reply to
John Fields

Just buy a contactor for goodness sake.

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Reply to
Sean_VN

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