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12V relay surging

One problem here hopefully I can get this to work.. I wired a an automotive relay to drive a 12VDC RV water pump.

from a power supply,

12V+ going to 30 and 87 output to pump. split same 12V going to coil +

ground going to the pump directly split same ground going to the pump and also the coil -, I put a switch inline with this wire to turn the relay on and off.

I am not sure which one 85 or 86 for the coil, it should not matter?

When the switch is on, coil is energized and supposed to connect 30 and 87.. but the problem is that the relay clicks on and off repeatedly.

The relay does say negative spike suppression, is this the problem or do I need some kind of isolation, I have not wired up a relay sharing the same 12V before... Another thing may be the pump has a strong startup surge and dropping the power supply voltage, but I am not sure.

Reply to
jeremy_ho
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Hi, Jeremy. Using automotive relays can be chancy. They're made to be produced by the tens or hundreds of thousands, and are made specifically to the manufacturers' requirements. That can mean internal connections between the coil and contact, chassis connection to coil and/or contact, or whatever.

Since you didn't mention specifically which relay you're using, it's not possible for even a seasoned automotive pro to tell you if you've got a wiring problem. And this is the wrong group for seasoned automotive technicians, anyway.

Coil dropout from voltage sag is possible, but not likely. Once a typical 12V relay coil pulls the armature in, the voltage across the coil will have to drop below 4V for it to open. It's your call. If you don't have a meter, put a small 12V bulb across the power supply, and watch the light intensity when the motor turns on. At 4V, the lamp should really dim big time.

One thing you might want to do is pop off the relay cover, and take a look at the wiring.

I'd recommend springing for a new relay, though.

Good luck Chris

Reply to
Chris

Sorry, I am not familiar with this designation.

I think this last sentence is the answer. The same thing happens with the starter relay when a car battery gets really low. The moment the load sucks amps, the voltage sags and the relay drops out. But then, there is not so much load and the voltage springs back up, and the relay pulls in again, etc.

Try the circuit powered from a 12 volt battery, instead of the supply, or add a large capacitor across the supply, to help with the pump start surge. Have you tried running the pump directly from the supply, to make sure the supply is capable of driving that load?

Reply to
John Popelish

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85, 86 are the coil. 30 is common.

If you apply 12 V to the relay and it clicks the voltage is too low or you have miswired.

Reply to
Homer J Simpson

Well, you just answered your own question. your 12 V is getting sucked down. this is what you do that may correct it. Feed the Relay coil with a diode, a simple 1N4001 and equal will do. the line side goes to coil side for the + side of the voltage. put a capacitor (larger one) like 1000 uf across the coil.. what this will do, is hold a charge to keep the relay closed long enough to allow the motor to recover from the inrush of current. The Diode is to prevent the draining of current to not pull it from the cap. P.S. May I suggest that you use a much higher amp supply and larger wire.

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Reply to
Jamie

Circa 18 May 2007 23:24:40 -0700 recorded as looks like jeremy snipped-for-privacy@my-deja.com sounds like:

I get the impression that the "automotive relay" in question just might be a turn signal flasher. In which case, it is working just fine.

Reply to
Charlie Siegrist

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