Overheating Relay

[hpinson]

I wonder if anyone might help me troubleshoot a DC electric problem with a relay.

I have a relay that is controlled by a DC Flexcharge timer. The relay is 12V 30 amp, an automotive relay from NAPA, and controls the on/off circuit of a pump. Max amperage through the relay is about 23 amps. I know this because the charge controller continually monitors amperage out to the load.

This a is a new behavior - the relay had been working as expected for about a month after installation.

As of about a week, after about half an hour of operation the relay starts to get really hot. At some point after that, the pump switches off and the relay starts making a loud and rapid ticking noise, and will not restart the pump.  Turning off and on the power lead to the relay seems to reset it, but after another five minutes of operation, the same happens.

Can anyone explain what is happening and how to remedy?

Thanks!

[MountainDon]

Maybe it is not a continuous duty rated relay and it has been damaged over time by heat build up?    Or if it is a cont. duty relay it is defective?

[hpinson]

Continuous duty would be a specification to look for in the replacement?

[hpinson]

Looked into that, and my guess is that you are right, the cheap relay was not continuous duty. It looks like Bosch has one to try as a replacement:

http://www.texasindustrialelectric.com/relays_0332019150.asp

P.S. to MountainDon -- Nice rain over the last few days... feel much relieved, though it looks like parts of Albuquerque took it on the chin.

[MountainDon]

H.   We had lots of rain in our area of the Jemez last week. Nearly 3 inches in a day!!  And then a week before 2.5 in a day.  Was good to see even if some dirt washed downhill. Hail too, but the usual peas sized stuff, some a little larger but nothing big enough to cause damage. Ground is nicely soaked. Fire danger down to Low.      Not as much wind as ABQ.

Note for the rest of the world... ABQ had gusts to 89 mph   

[Rob_O]

Looked into that, and my guess is that you are right, the cheap relay was not continuous duty. It looks like Bosch has one to try as a replacement:

You will blow up that Bosch relay just like the other one. You just cannot run that much power through one of those little relays and expect it to live very long.

[MountainDon]

Glenn uses a starter relay to turn his well pump on and off. Two in series actually as he uses 24 VDC.

[hpinson]

Hi Gary. Do you have any specific suggestions for an alternative? I'm not sure I understand why it would burn up. If the relay is rated at 30 AMP continuous duty, why would it burn up at 20 -23 amps?

I see similar 12V relays available that are rated to 40 amps and even 80 amps. Would those be a better choice?

Also there is this industrial control:

http://www.radioshack.com/product/index.jsp?productId=12491821&utm_source=Google&utm_medium=PPC&utm_term=55048250&utm_content=Exact&utm_campaign=PLA&%7bifmobile:ds_dest_url=http%3A%2F%2Fm.radioshack.com%2Fradioshack%2Fproduct%2Fdetail.do%3FitemId%3d12491821%26utm_source%3dGoogle%26utm_medium%3dPPC%26utm_term%3d55048250%26utm_content%3dExact%26utm_campaign%3dPLA%7d&cagpspn=pla&gclid=COiAvdSo17gCFcnlKgodhTUAAA&gclsrc=ds.ds

There must be a reliable known solution-- pumps driven by timers are common.

I'm looking at the starter relays Don.

[UK4X4]

23 amps steady

thats fine

but what you won't see is the surge current and the arcing when the relay is moved from on to off

something like this would work better for a high powered electrical pump


http://www.amazon.com/CONTINUOUS-SOLENOID-RELAY-CARTS-1114208/dp/B008R1T5IM/ref=cm_cr_pr_sims_t

[MountainDon]

That's like Glenn uses. Like an old Ford starter relay
Used to be cheap

[hpinson]

Thanks UK4X4. I'll give that a try.

I think 20 amps is the highest surge I've actually seen.  The relay is connected to a Morningstar Prostar 30M Charge Controller with real-time amperage monitoring.   When pumping the low flow well, you can actually see the amp surge on the LCD monitor, at the upstroke of the pump, and then drop way down on the downstroke.  Daily, with a recharged well, when pumping the surge starts at about 12 amps, and as the well draws down, it approaches 20, after about an hour of pumping. At least that is what I am seeing. At that point I always stop pumping, so as not to pump the well dry. That was the idea behind the timer.

What accounts for the relay stopping working and making the clicking noise and needing to be reset. Is that some sort of heat related automatic safety shutdown of the relay?

[lobster]

normal starter solenoid as from a car is made for intermittent duty and should not be activated continuously. when you are cranking the engine to start it, the solenoid is normally activated for just a few seconds. the magnetic coil generating the magnetic field to pull in the contacts will get warm and may overheat if you activate it for too long.

"continuous duty" solenoids can take a continuous voltage on the coil. see for example
http://www.gpartsinc.com/p-1450-continuous-duty-solenoid-80amp-12v.aspx?catargetid=1816008475&cadevice=c&cagpspn=pla&gclid=CJ6zlNXy17gCFQai4Aod7G4AHQ

i had a motor home and used such a relay to connect in parallel the factory-installed engine battery and the "house battery" but only when the ignition switch was on. this allowed the two batteries to be charged in parallel by the engine when it is running, but isolates (separates) them when not running. so the engine battery is never drained (and the engine cannot be started) by operating too many appliances etc when parked at the campground.

[Rob_O]

Also there is this industrial control...

Yeah, something like that. Power consumption is low and it's physically large... large contacts and thicker wiring for the switched load. The solenoids the other guys posted would probably work just as well if they have a reasonable power consumption

[hpinson]

Thank you everyone. Great explanations as always. 

[hpinson]

New continuous duty solenoid relay, like what UK4x4 suggested, is installed and seems to be working well.