Inductive Ratings
Inductive Ratings
(OP)
Gentlemen,
Can somebody explain regarding Control relays why some manufacturers state the inductive ratings for their contacts but some do not, I have problems with a circuit that requires a max of 6 amp @ 125VDC to operate a solenoid, will a standard icecube relay rated 10A @150VDC will suffice, this manufacturer does not provide inductive ratings.
Thanks
Can somebody explain regarding Control relays why some manufacturers state the inductive ratings for their contacts but some do not, I have problems with a circuit that requires a max of 6 amp @ 125VDC to operate a solenoid, will a standard icecube relay rated 10A @150VDC will suffice, this manufacturer does not provide inductive ratings.
Thanks





RE: Inductive Ratings
I suspect the holding current is less than 6 amps, but even so, 125 V dc solenoid switching is tough duty. You'll probably want to use a good machine tool relay and some type of snubber. If it is really breaking 6 amps, you'll want to put multiple contacts in series.
RE: Inductive Ratings
Thanks
RE: Inductive Ratings
RE: Inductive Ratings
One thing is to use a free-wheeling diode parallel to the coil. Then, the relay doesn't have to take care of the inductive part of the load, that current just circulates in the diode until the energy is dissipated and the coil releases. One problem with this is that your breaker will be correspondingly delayed. If you can tolerate the delay, fine. If not, you can use a resistor in series with the diode, a zener or an RC combination. Lots of possibilities. But letting the contact operate the coil all by itself will kill it quickly.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Inductive Ratings
David and Gunnar have given excellent advice - I can't add anything to that.
As to why manufacturers publish different types of ratings, I can't say. There are NEMA standards for machine tool relay contact ratings that will cover ac, dc and inductive switching. Those are more useful than a vendor's arbitrary ratings.
As a general rule of thumb, if a relay contact can break 10 A at 120 V ac, it will have a rating of about 1 amp at 125 V dc, if you're lucky.