relay contacts sticking

[ELA]

Try adding some load in parallel with the relay coil. Take a look at this document

Great reference Don,

Figures 1 & 2 are a great starting place for diagnosing whether or not capacitance is the issue. I believe they are talking about the wire capacitance as being a "reactive impedance" in series with the power supply feeding the relay load (when the control sw. is open) , as opposed to "capacitive coupling" from other wire sets in this ref.

makes for an interesting read Thanks.

 

[readydave8]

I probably won't be back to job until next week at the soonest, posted my question without having all the data, but here's what more I know.

The transformer is a 600 watt that feeds landscape lighting. I don't know what's inside it, but has c1 and c2 terminals, then t12, t13, t14, t15. I thought it was just a winding with t in the center and c1 and c2 being the ends but don't know enough to say so, usually I just hook things up and don't worry a whole lot about how its engineered.

This was a lighting setup to a boathouse, wire man asked me to help. When I first saw it there was a pvc conduit with #12's, 3way and 4way still connected at house. Figured out which was the hot, which two were travellers, and which was a return to work two lights in soffit at house. Extended wiring with romex (12/3 wg).

The two soffit lights at house are in parrellel to the coil, "return" hot runs in same conduit as traveller, there's a neutral in that conduit but the lights are getting their neutral from up at the house.

Total one way distance from first 3/way to second 3/way could be as much as 250 feet.

Thanks for all the good advice so far, when I get it solved maybe I won't mention MH forum to customer & he'll think I'm brilliant

 

[LarryFine]

Next time can you remove the coil wires and see if it drops out prior to tapping on the relay case?

Great idea! I might even install a switch temporarily to make that easier.

 

[don_resqcapt19]

100929-0836 EST

An AC relay will work on DC with a sufficiently lower voltage that does not burn out the coil. A DC relay will not work on AC, it will just buzz. ...

Gar,
Is the construction of a relay that much differnet from that of a solenoid? We had an equipment supplier that used a 24 vdc relay where he should of used a 120 vac one. It worked fine for over a year. It seamed hot to me, but the solenoid manufacturer's tech information says, "if it is not smoking, it is not too hot".

 

[gar]

100929-1942 EST

don:

AC relays and solenoids are made with a shading coil in part of the magnetic circuit. This is usually a slug of copper or aluminum jammed around a portion of the end of a pole in the magnetic circuit. This causes a phase shift in part of the magnetic circuit so the magnetic force never drops to zero during the cycle. Besides this flat pole pieces are required to prevent AC noise in the relay or solenoid.

I opened up an AB #2 starter and its solenoid has the the shading coils. Some small single phase AC motors are made on this same principle, and called shaded pole AC motors.

Also these AC devices will have laminated cores to reduce core losses.

A DC solenoid will possible work on AC if the mass is great enough relative to the spring force to average the magnetic force, and/or AC noise may be ignored. A solid core will run hotter than a laminated one.

Relative to applied voltage. In a DC device only the resistance limits the coil current. In an AC unit the inductance contributes to current limiting. Before an AC solenoid or relay is energized its inductance is lower than after full seating from energization. Thus, on an AC unit there is higher pull-in force than a DC unit. The number of turns on a DC relay coil will be much greater than for the same relay on AC. Different resistances. A rough figure for an AC relay with DC excitation will be about 1/3 the DC voltage compared to the AC RMS voltage for pull-in.

.

 

[SG-1]

100929-0836 EST

An AC relay will work on DC with a sufficiently lower voltage that does not burn out the coil. A DC relay will not work on AC, it will just buzz.

The AC 120 V relay I tested above has a coil resistance of about 2.2 K. A 1.0 mfd shunt capacitor with this coil resistance has a time constant of 2200*10^-6 = 0.0022 seconds. 1 mfd has a capacitive reactance of about 2700 ohms at 60 Hz.

DC pull-in of said relay is about 35 V and drop-out about 4 V.

.

I saw this very situation a few weeks ago with 2 ice cube relays in a PLC circuit. 6 relays were ordered correctly as 24VDC. 2 were ordered as 120VAC. The 120AC relays picked up just like their 24VDC counterparts. What gave them away was their built in green led indicator light did not come on.

 

[readydave8]

2 3/way and 3 4/way switches to the coil on icecube relay, long runs of wire. Relay works a receptacle with lighting transformer plugged in. Often when switch is turned off transformer receptacle stays energized, they can tap relay to make contacts open.

Relay rated for 10 amps. Transformer is 2 circuit, 600 watt, reduces 120v to 12 v ( also has taps for 13, 14, and 15 volts). Loaded approx 135 watts on one circuit, somewhat less on the other (I can get more accurate figures if needed).

Tried changing the ice cube relay and the replacement did the same thing.

Any advice?

I don't like when I never find out the conclusion to a problem so posting an update:

I finally was able to go back to the job today. Couldn't reproduce the problem, everything worked fine. I changed the ice cube relay to a contactor. Everything still worked fine. So I left.

 

[ptonsparky]

Go home collect your pay, and wonder for the rest your days "What the heck?"

 

[readydave8]

Go home collect your pay, and wonder for the rest your days "What the heck?"

didn't charge for this trip

and hopefully my memory is getting worse so I'll only wonder for part of the rest of my days