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Testing DPDT relay switch

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JonP

New Member
Hoping to repair my sump pump, power transfer switch. Switch detects power from battery backup but not from wall outlet . Relay switch is an 8 screw, DPDT open connector type. This is no longer in production and manufacturer offers no support.

It appears there is one of two possible sources for the problem. Either the relay is bad or the timer delay circuit board is bad, see photo.



With both power plugs connected, The switch only picks up power from the battery side. If I push the switch down with a stick to the opposite poles, the test light goes out. I release the stick and the light comes back on. I would expect the light to go on from either side of the relay switch.

I removed the timer delay and found no change to the problem so I believe it is a bad relay switch.

Is that a valid test or is there another way to check the relay ?

Not sure how to check the circuit board.
 

Reloadron

Well-Known Member
Most Helpful Member
See if the relay coil has the coil voltage marked on it. For example 12 VDC, 24 VDC, 120 VAC or 220 VAC. With an open contact relay as you have if it is driven by your mains voltage it is a simple matter of applying the rated coil voltage and seeing if the relay pulls in with a click. A relay will either pull in or it won't. If you have a meter measure across the coil when the relay should be energized and see if coil voltage is present. Once the relay is isolated as faulty or not then a replacement can be found. There really isn't much to a relay like this. When the coil is energized the relay should pull in with a click transferring from the NC Normally Closed to the NO Normally open contacts. Since this is a sump pump with battery backup there should be a switch, likely a float switch, in the sump which calls for the pump to run at a set level. Not sure what the timer is all about? Normally the pump turns on and when the sump level drops the pump turns off based on a float switch.

Also since the relay looks like it drives the pump with either mains or backup power the relay coil is likely low voltage DC. Any part number and manufacturer information on the relay?

Ron
 
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JonP

New Member
See if the relay coil has the coil voltage marked on it.
I couldn't find any markings on the relay, but it is for a 120v 15 amp household circuit.

There really isn't much to a relay like this. When the coil is energized the relay should pull in with a click transferring from the NC Normally Closed to the NO Normally open contacts. Since this is a sump pump with battery backup there should be a switch, likely a float switch, in the sump which calls for the pump to run at a set level. Not sure what the timer is all about?
Yes, that describes exactly how it works, but the pump and float are a separate set of components.

This transfer box simply supplies power to the pump/float. The primary power source is the wall outlet. If not available, the relay switches to the battery/inverter as the backup source.

The timer circuit delays the switch back to primary for 30 seconds to prevent problems if the main power supply should flicker.

Since the transfer box is plugged into the wall outlet and the timer circuit was removed, I expected the relay to open but it doesn't so I am thinking that the relay is bad. I just wanted to learn if my thinking is correct.
 

Reloadron

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Less a schematic I will venture a guess, Your relay has, as you mentioned, eight terminals. Since that is a DPDT relay that makes sense. Looking at your image the relay has what look like two levers which are the Common contacts. When the relay is active those levers are pulled down so the Common to Normally Open on each side closes. Using 120 VAC mains the simple way to transfer is allow the mains to hold in the relay (active) by applying 120 VAC to the relay coil. When mains power is lost the relay will open, the coil is DeEnergized. My guess here is that when mains power is available the relay should be energized, when mains power is lost the relay drops out and the Normally Closed contacts close. Those would be the upper contacts on the top of your image, So the lever looking pieces travel between a NO and NC on each side of the relay. Relays used like this are continuous duty meaning they are designed to be on all the time. If you measure across the coil my guess is that you should see mains voltage and if you have coil voltage and those contacts are not pulled down there is a good possibility the relay coil has failed. There really isn't much to a relay like this.

The only trick is to be sure the relay coil has failed and knowing what the coil voltage actually is. That makes for easy replacement along with knowing what the relay contacts are rated for as to switching current. The older open contact relays have slowly gone away but there are replacements which are simple to replace. Just a matter of determining that the relay is in fact bad. Do you have a meter and know how to use it?
With both power plugs connected, The switch only picks up power from the battery side. If I push the switch down with a stick to the opposite poles, the test light goes out.
That would make sense but I have no idea what the test light is all about at this point. Does the pump motor have a data plate listing pump voltage and current?

Ron
 

JonP

New Member
Just a follow up.

It was suggested I might just need to clean all the contacts. I didn't before because everything looked so clean.

But I cleaned the relay and circuit board contacts and added a thin film of bulb grease and SUCCESS ! All is working again.

Thanks for hearing me out. I'm glad this turned out to be a simple thing.
 

Reloadron

Well-Known Member
Most Helpful Member
Glad it's working. Yay! As we are heading into a thaw I have been watching my pump and fortunately we have whole house emergency generator power backup. I also have a spare pump in case I lose one. I was going to mention contacts and cleaning but skipped it so again glad you found it and things are working. :)

Ron
 

dr pepper

Well-Known Member
Most Helpful Member
Diamond spatula's are good for contact cleaning.
Only thing now is you will have lost the flashing or plating on the contacts so they'll need cleaning a lot sooner than this first time, maybe start looking for a new one.
 

JonP

New Member
I also keep a spare pump. I'll look around for a spare power transfer switch since this one is over 10 years old.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Check the coil voltage, so you know the next time.

This series was common in my day and http://www.galco.com/scripts/cgiip.exe/wa/wcat/catalog.htm?searchbox=R04-11A30-24 might even work for you.

Another thing you can do, is change the state and the relay should pull in.

Now, here's the tricky part. With the pump running or supposedly running, the voltage ACROSS the closed contact should be small, like in the mV range.
If the pump isn't supposed to run, you would have the motor voltage across these contacts.
 

kinarfi

Well-Known Member
where do you live, I'm about to throw some stuff away that may work for you.

HYJACK --- I'm chucking some SSRs, any one want to pay shipping for them? 3-32 20 amp crydon style
 
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