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Gunders 15th February 2003 08:20 PM

Using relays in high voltage circuits
 
Anyone who have any experience about using relays designed for 230Vac use in high voltage circuits.
How large voltages can these relays can tolerate, are there any risks about using relays in high voltage circuits?

I would like to hear any experience about using relays in high voltage circuits.

peranders 15th February 2003 09:58 PM

My answer is no but you have a spark at 3 kV per mm (when the air is dry!). You could increase the reliability by connecting the contacts in series if you have 2 poles or more. Real HV relays are big and expensive.

May I ask your application? Maybe it's better to switch somewhere else where the voltage is lower?

This is dangerous stuff :att'n: I hope I will not turn up in the Sin Bin for this? :cannotbe:

7N7 15th February 2003 10:21 PM

Re: Using relays in high voltage circuits
 
Quote:

Originally posted by Gunderz
Anyone who have any experience about using relays designed for 230Vac use in high voltage circuits.
How large voltages can these relays can tolerate, are there any risks about using relays in high voltage circuits?

I would like to hear any experience about using relays in high voltage circuits.

I'm with Peranders on this.

Switching AC is one thing; DC quite another - and quite often I am frustrated by having to face up to the fact that there is no simple way to switch high voltages.

In one of my amplifiers, I am using two pairs of taps to derive a +ve HT and a -ve HT; I have used a 6v AC-actuated relay that is rated at 250v (AC) so I am getting away with it, becasue I am switching AC.

The only cheap possibilty is perhaps a vacuum switch - as used with mercury rectifiers; I have some - DLS 10s - but you would have to investigate the data to see if DC is "on the menu"

7N7

Gunders 15th February 2003 10:48 PM

So.. it's no good idea for me to use a relay designed for 230V in my power supply where the voltage is about 470V?

Which other methods do I have to obtain a switch??
Could I use MOS-FET??
One problem with MOS-FET is their relative high ON-resistance compared to the resistance through a relay. And maybe they need some protection too.

fdegrove 15th February 2003 10:52 PM

???
 
Hi,

Why would you want to do that in the first place?

Cheers,;)

\Frank,caring about your health.:nod:

Sch3mat1c 15th February 2003 10:53 PM

What resistance? Even 10 ohms isn't going to be felt in a tube amp.

Tim

Gunders 15th February 2003 11:06 PM

Well... forget the thing about the MOS-FETs... just a side leap.

SY 15th February 2003 11:09 PM

If what you're trying to do is delay the B+ turn-on (a laudable goal), there are better and safer ways to do that.

Gunders 15th February 2003 11:15 PM

Yes, one reason why I planning to use relays is because I want to have a delayed start up for the main supply.

One way to solve the problem will be to use separate transformers for the mainsupply and the heater supply, but the transformer I use now have both main and heater windings.

And I do currently have about 10 2-pole relays who I would like to use.

SY 15th February 2003 11:37 PM

My first choice would be to bite the bullet and power the filaments separately, switching the B+ transformer at its primary. Second choice would be, assuming you're using a CT secondary with the CT grounded, to insert a HV bipolar or FET in the CT-to-ground lead and switch it on with a time delay. The "on" resistance will be pretty negligable.

For cost-no-object, you can build a slow turn-on HV regulator. But if cost were no object, you'd be using separate filament transformers!

The hard way is to use a tube rectifier, but you'll have objectively poorer regulation, more heat, and lower reliability. But there's a certain coolness factor that I understand.


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