12V DC Relay Issues (Diesel Engine)

[Holden Customs]

Hello all. I am having an issue with a 12V DC Relay I am trying to install to run a kill switch on a John Deere Diesel engine that runs a high pressure water pump. I have the relay wired in such that it will send power to the ignition when an electrical signal comes from a water sensor in the pump (dry running protection). The issue I have is that whenever it is hooked up all I get is chatter from the relay. I have tested my wiring by connecting the "switch" wire to battery and everything works as it should. I read somewhere that if the switch voltage is less than the feed that it can cause chatter. The fees voltage is 12.56 and the switch voltage is 12.22. Could this be the reason and how should I go about fixing it? Thanks

 

[telectrix]

12.22V should be enough to energise the relay. is it dropping under load?

 

[Spoon]

So the signal from the water sensor is ok then and this is not causing the relay to chatter?

 

[telectrix]

relay needs cheesecake.

 

[Holden Customs]

The sensor is sending a constant 12.22 volts. And the chatter happens whenever the sensor wire is sending power, engine running or not. When it's chattering there is no power to the box with the ignition so it can't be running anyway.

 

[Holden Customs]

relay needs cheesecake.

If only cheesecake could fix everything

 

[Spoon]

I presume you don't have a variable power supply. To feed 12.22v from this to the relay and still see if you get chatter...

 

[Holden Customs]

I presume you don't have a variable power supply. To feed 12.22v from this to the relay and still see if you get chatter...

I do not unfortunately

 

[Lucien Nunes]

A 12V relay will usually pull in around 8-9V on the coil, and will hold in down to about 6V. Anywhere between 9 and 18V should be OK, it is not critical. There is no relationship between the coil voltage and the contact switching voltage. Probably, the sensor output is not giving a steady voltage, or there is a bad connection somewhere, or the relay is not actually a 12V relay.

 

[Holden Customs]

A 12V relay will usually pull in around 8-9V on the coil, and will hold in down to about 6V. Anywhere between 9 and 18V should be OK, it is not critical. There is no relationship between the coil voltage and the contact switching voltage. Probably, the sensor output is not giving a steady voltage, or there is a bad connection somewhere, or the relay is not actually a 12V relay.

Okay thanks. I will check with the sensor manufacturers and see if it is constant or not to double check. If it isn't, is there anything that can be done or a different style relay to use?

 

[ruston]

Is it grounded properly?

 

[Lucien Nunes]

What type of output does it have - contact closure, open collector? Is it designed to operate a relay or just trigger an electronic input of a system controller?

 

[Holden Customs]

It is grounded to a point on the frame of the unit. When it senses the water it closes a circuit with the power feed to send power down the switch wire. I think it is designed to be used in a system controller but the dealer said people have used it to operate a relay.

 

[ruston]

Is the battery ground and the frame ground connected to give the relay a good connection?

 

[Holden Customs]

Is the battery ground and the frame ground connected to give the relay a good connection?

Yes, the battery ground is run to the alternator and both are connected to the frame. All grounds are from that point.

 

[ruston]

Are they long cable runs of adequate size?

 

[ruston]

Are they long cable runs of adequate size?

 

[Holden Customs]

The battery and alternator grounds are the typical battery connection sizes, 4awg or 6awg, the relay and sensor grounds are 12awg, and 20awg respectively as those are the wire sizes of the connectors

 

[Holden Customs]

The battery and alternator grounds are the typical battery connection sizes, 4awg or 6awg, the relay and sensor grounds are 12awg, and 20awg respectively as those are the wire sizes of the connectors

Lengths range from 6 to 8 ft

 

[ruston]

What is the kill switch connected to out of interest. Is it to disable the ignition or the fuel pump .