Solid state relays???

Magura · 26th November 2004, 02:55 AM

Anyone knows how AC solid state relays get along with dc??

The load that is.

Cheers

Magura

TwoSpoons · 26th November 2004, 04:11 AM

Most of the AC solid state relays use a triac as a switch. Triacs only turn off when the current through them goes to zero, which generally happens twice in every AC cycle. So if you put DC through it you can turn it on, but not off!

Magura · 26th November 2004, 04:25 AM

So basicly a solid state relay is a thyristor with an optocoupler??

Cheers

Magura

cpemma · 26th November 2004, 11:45 PM

Quote:

Originally posted by TwoSpoons
...So if you put DC through it you can turn it on, but not off!

Interesting point, if it switches on zero-crossing, would it turn on with DC?

TwoSpoons · 28th November 2004, 08:41 PM

That depends on how fancy the relay is. Not all have zero-crossing turn-on circuits.

peranders · 28th November 2004, 08:46 PM

Quote:

Originally posted by Magura
So basicly a solid state relay is a thyristor with an optocoupler??

Cheers

Magura

There are also other types with mosfet's and photocells but normally those relays are rather small. Mosfet's creates a almost pure resistive switch. May I ask your application?

Magura · 29th November 2004, 01:50 PM

I am thinking about using SS relays for switching between one secondary and both secondaries in series in a 20A 25/50V power amp.

Maybe the simple solution would be to do this before the rectifiers to avoid DC?? I just have doubt that the boards from the previous groupbut can take such current.

Magura

LBHajdu · 29th November 2004, 02:02 PM

How are they for reliability? I’m thinking of using something like the pass labs A75 schematic to turn on and off an amp. It uses a triac. An other option is to use a real relay, they cost about the same. However I do done always trust semiconductors. Anybody got any opinions?

peranders · 29th November 2004, 02:13 PM

Quote:

Originally posted by Magura
I just have doubt that the boards from the previous groupbut can take such current.

Magura

I'd say skip your relay thought unless you really have a problem. If it ain't broken, don't fix.

What diodes are you using and how much capacitance do you have and also what is your supply voltage?

Notice also that if you really have such problems a soft starter at the primary is better, smaller currents.

Magura · 29th November 2004, 02:29 PM

Hmm, better explanation of the application required.

The point is to be able to switch between 25 and 50V for a Zen V7.

RURG3020 diodes, 200.000uF, 1KVA trafo 2*18V.

The alternative is a hefty contactor, but those tend to wear out and they are huge compared to a SS relay.

Magura

26th November 2004, 02:55 AM	#1
Magura diyAudio Member Join Date: Oct 2003 Location: Denmark, Viborg	Solid state relays??? Anyone knows how AC solid state relays get along with dc?? The load that is. Cheers Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com

26th November 2004, 04:25 AM	#3
Magura diyAudio Member Join Date: Oct 2003 Location: Denmark, Viborg	So basicly a solid state relay is a thyristor with an optocoupler?? Cheers Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com

29th November 2004, 01:50 PM	#7
Magura diyAudio Member Join Date: Oct 2003 Location: Denmark, Viborg	I am thinking about using SS relays for switching between one secondary and both secondaries in series in a 20A 25/50V power amp. Maybe the simple solution would be to do this before the rectifiers to avoid DC?? I just have doubt that the boards from the previous groupbut can take such current. Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com

29th November 2004, 02:29 PM	#10
Magura diyAudio Member Join Date: Oct 2003 Location: Denmark, Viborg	Hmm, better explanation of the application required. The point is to be able to switch between 25 and 50V for a Zen V7. RURG3020 diodes, 200.000uF, 1KVA trafo 2*18V. The alternative is a hefty contactor, but those tend to wear out and they are huge compared to a SS relay. Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com

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26th November 2004, 04:11 AM	#2
TwoSpoons diyAudio Member Join Date: Oct 2004	Most of the AC solid state relays use a triac as a switch. Triacs only turn off when the current through them goes to zero, which generally happens twice in every AC cycle. So if you put DC through it you can turn it on, but not off!

28th November 2004, 08:41 PM	#5
TwoSpoons diyAudio Member Join Date: Oct 2004	That depends on how fancy the relay is. Not all have zero-crossing turn-on circuits.

29th November 2004, 02:02 PM	#8
LBHajdu diyAudio Member Join Date: Feb 2002 Location: NY, USA	How are they for reliability? I’m thinking of using something like the pass labs A75 schematic to turn on and off an amp. It uses a triac. An other option is to use a real relay, they cost about the same. However I do done always trust semiconductors. Anybody got any opinions?

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