why do relays get hot

javeria · #1 Sat 07 February 2009, 21:31

folks while re-building the controller on my other machine - I am facing a problem of relays getting hot - without any particular reason - I mean I am not able to find the exact cause - can any one help me here -

a schematic is here

http://www.cnczone.com/forums/showth...=60710&page=15
(end of the above page)

Thanks in Advance.

RGDS
IRfan

Gerald D · #2 Sat 07 February 2009, 21:44

In the other link you say "one of the 220V relays", but that schematic only shows one 220V relay, two 24V relays, one SSR, and one contactor. . . . .which seems to be far too many components . . .

A relay gets hot if:
1. You supply too high a voltage to its coil
2. the coil is rated for AC and you supply it DC
3. a contact pole is damaged and it adds resistance to the load current.
4. the manufacturer has a design or quality problem

javeria · #3 Sat 07 February 2009, 22:23

yes G' the 220v relay shown is getting hot - like hell - I tried replacing the relay but even then it has the heating issue -

1. The supply voltage to the 220v relay is 203V
2. the coil is supplied with AC 203V (measured)
3. I replaced the relay - so a damaged relay is out of Question
4. The supplier told me that he has been selling these relays without any complains

I am sort-a lost.

RGDS
Irfan

Richards · #4 Sat 07 February 2009, 22:47

I'm having a little trouble following your schematic. If possible, could you describe exactly what is supposed to happen? I'm not sure which points are connected to the coils on the various devices and which points are connected to the contacts on the relays and contactor.

As far as the 220V relay is concerned, is the 220V rating for the contacts, the coil, or both the contacts and the coil? Is is possible that you've mixed up the voltage rating for the contacts with the voltage rating of the coil? Powering the coil of a 24V relay with 203V would cause a lot of heat, and probably some foul smelling smoke.

javeria · #5 Sun 08 February 2009, 02:28

Seems that the relay was faulty - the coil and contacts of the relay are rated at 220V AC.

I took out the relay from the panel board and powered it direct from the wall socket - after a while it started getting very hot - no smoke or smell though - I think the supplier has given me a sub-standard relay - all the time the voltage was 204v AC

I will substitute it and get back to you folks.

RGDS
Irfan