Contactors welding together
Contactors welding together
(OP)
I have a problem with contactors welding together on an air compressor starter. It always happens on hot days so I suspect low voltage is the problem. Any ideas on an improvement that could be made to avoid this type of failure? Or am I venturing down the wrong path?





RE: Contactors welding together
Would be nice if you could use a fast data logger to look at the coil voltage on a startup.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Contactors welding together
Thanks for the tip.
RE: Contactors welding together
If it is a supply line low voltage problem, the answer would be to install a line voltage monitor and wire it so that the compressor cannot run at all if the voltage is that low, rather than chatter the contactor. Contactor coils usually have a 70% drop out voltage, meaning they should stay in at 71% of line voltage. If it is chattering, you are probably hovering around that that low level and that is NOT good for the motor either.
http:/www.jraef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Contactors welding together
In support of jraef's comments, I would expect to see motors failing if the voltage was low enough to cause starter chatter.
When I see welding, it is almost always a short circuit.
Is this a single phase or three phase motor?
Is this a magnetic contactor or a direct acting pressure controlled contactor?
Either way, it is probably undersized.
Either type may be remote mounted, but if unloading is combimed in a direct acting starter, it may be best to leave it in place. A direct acting starter (multi pole pressure switch) may be left in place to provide unloading if required and used to control a remote mounted magnetic contactor of higher capacity.
respectfully
RE: Contactors welding together
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Contactors welding together
There are also the new "electronic coil" contactors that are very voltage tolerant and never fail welding. They have the same foot-print as standard contactors. But not sure if they are available in small sizes.
Gunnar Englund
www.gke.org
RE: Contactors welding together
Contactors typically use special alloys for the pole faces which are resistant to welding and to erosion from arcing. Cheap contactors use copper rivets or something not much better, so a cheap contactor used at the limit of its rating is asking for problems. Either fit an oversize contactor, or find one from one of the reputable manufacturers.
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I don't suffer from insanity. I enjoy it...
RE: Contactors welding together
I once had a compressor with a soft starter where the unloader valve failed to open and the compressor needed almost locked rotor current for 20 seconds to start, which meant we were right up against the thermal overload curve. That would have been really hard on a contactor as well (had there been one in mine). I whacked the unloader valve with the back of my screwdriver and the starting current requirement dropped to 350% for 5 seconds.
http:/www.jraef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Contactors welding together
Glad yours hung on jraef.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Contactors welding together
Thanks again!
RE: Contactors welding together
http:/www.jraef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Contactors welding together
If the new compressor was the base machine, the old compressor would start if needed, but would then continue running until it was stopped manualy. The person who stopped it would also hit the unloader with a wrench so that it would be ready to start again when needed.
respectfully
RE: Contactors welding together
RE: Contactors welding together
RE: Contactors welding together
RE: Contactors welding together
Your contactor is somewhat under-rated and it's never fit to its duty. In IEC, contactors were classified as " AC " that would never found in NEMA size contactor.
If it happens that it is IEC, perhaps you'll check its AC class and application.