Relay spark problem

[marce]

http://relays.tycoelectronics.com/ap...fs/13c3236.pdf

this article has some interesting points regarding contact sparking, transformers and residual magnetic energy in transformer core.

[Dxvideo]

Originally posted by geminni



That is a must!
My regular 650VA transformer made some very unusual noise without soft start! It was scary! I thought that it will jump!

Exaclty agree. I was almost p i s s i n g when I heard it. Shock! I thought that it will blow as a renegade! (When I was in military service I heard a renegades explosion very near to me)

So the result;
I have to use a soft start: The RC solution wont work! Is it?

[AndrewT]

Hi,
go back to post4. It tells you there why it sparks at switch off.

The spark at switch on is extremely unusual. I wonder if the contact is bouncing? The breaking on the bounce will cause a spark.
What voltage are you using to close the relay?

RC snubber across switches is to quench the spark at switch off. They do work but you keep telling us that this is not your problem.

[Dxvideo]

"I wonder if the contact is bouncing?"
I am suspicied from that also! Because I was feeding the relay with DC 24v... And the coil was very hot!

[AndrewT]

Now you tell us you are driving the relay with the wrong voltage!

[Dxvideo]

Now I understand, 24VDC is bigger than 24VAC for the relays... But why is it bounced?

[KISS]

If you have the room, use one of these SSR's:

http://www.omega.com/pptst/SSRL240_660.html

What's the VA ratiing of the relay?
What's the model of the relay?
Is the relay rated for inductive loads?
Are the contacts rated for AC loads?

http://www.calcentron.com/Pages/AEGH...contactors.htm

If you look at the T30A-1* series

It's rated for 30 amps and 1 HP. 1 HP is 760 VA. Your contact rating has to be a lot higher than 8 amps because of the inductive component.

Your contactor (i.e. relay needs to be rated for (650/760) HP minimum. HP is horsepower.


A soft-start circuit would also eliminate that requirement. At that point the resistive rating could be used. I = P/V or I = (650/120) with a safety margin would be OK. 120 is the mains voltage in this case.

Aside:
If relays are used for AC/DC logic switching then the appropriate transient protections should be employed. It could be a RC combination (snubber), Quencharc (R), Transorbs (R) (fast zener), or ZNR's. The (R)'s are brand names.

Furthermore, a minimum wetting current is required to clean mechanical contacts.