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HT Relay

I

Ian Bell

Jan 1, 1970
0
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
 
I

Ian Bell

Jan 1, 1970
0
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.
With AC contacts the problem is minimized because as the AC waveform
goes through zero volts the arc is automatically extinguished.

Understood.

A trick I've seen before, but never used, is to wire two sets of
contacts in series, which will give you twice the effective gap, helping
to quench the arc.

Another trick is to use magnets to "blow out" the arc when the contacts
open, and some larger relays/contactors are designed that way.

Can you use high voltage transistors or solid-state relays instead of
mechanical relays?

I would rather not.


Cheers

ian
 
M

Martin Riddle

Jan 1, 1970
0
John Fields said:
---
The problem with using relays on DC is that when the contacts open an
arc is established which is hard to put out.

With AC contacts the problem is minimized because as the AC waveform
goes through zero volts the arc is automatically extinguished.

A trick I've seen before, but never used, is to wire two sets of
contacts in series, which will give you twice the effective gap,
helping
to quench the arc.

Another trick is to use magnets to "blow out" the arc when the
contacts
open, and some larger relays/contactors are designed that way.

Can you use high voltage transistors or solid-state relays instead of
mechanical relays?

Kilovac?
<http://relays.tycoelectronics.com/kilovac/>

Cheers
 
P

Phil Allison

Jan 1, 1970
0
"Jan Panteltje"
Ian Bell
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.


** 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
 
P

Phil Allison

Jan 1, 1970
0
"Jan Panteltje"
"Phil Allison"
"Jan Panteltje"

Sigh, hey, zero current may work!


** Only a bullet in the head would work on you

- you fucking illiterate wog idiot.




...... Phil
 
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