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 .

 

[Holden Customs]

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

Sorry I may have worded it wrong before, there is no actual kill switch. The relay acts as the kill switch. The ignitions power flows through it so if it ever switches off then the whole engine control unit goes dead and it shuts down fuel as well. I have tested the function of the relay and just used an alternate power source as the switch instead of the sensor and everything works as it should.

 

[ruston]

We

Sorry I may have worded it wrong before, there is no actual kill switch. The relay acts as the kill switch. The ignitions power flows through it so if it ever switches off then the whole engine control unit goes dead and it shuts down fuel as well. I have tested the function of the relay and just used an alternate power source as the switch instead of the sensor and everything works as it should.

Well done .

 

[Jim_e_Jib]

Sorry I may have worded it wrong before, there is no actual kill switch. The relay acts as the kill switch. The ignitions power flows through it so if it ever switches off then the whole engine control unit goes dead and it shuts down fuel as well. I have tested the function of the relay and just used an alternate power source as the switch instead of the sensor and everything works as it should.

It sounds like, as I think Lucien was suggesting in post #12, the sensor cannot supply enough current to operate the relay, causing the voltage to drop and make it chatter.

 

[Holden Customs]

It sounds like, as I think Lucien was suggesting in post #12, the sensor cannot supply enough current to operate the relay, causing the voltage to drop and make it chatter.

If that is the case, then is there a different relay I can use?

 

[Jim_e_Jib]

If that is the case, then is there a different relay I can use?

You'd need to look at the specs for the sensor but I imagine some extra bit of circuitry involving a transistor or perhaps an optoisolator would be needed to use the voltage from the sensor to switch a higher current supply to latch the relay.

 

[Shoei]

Maybe the sensor produces pulses instead of continuous DC, either because it works that way or because the water flows in pulses. If you can get hold of an oscilloscope or scope meter it would be worth checking that the sensor output voltage isn't jumping around.
If it is DC but doesn't have enough current drive for the relay then a solid state relay may work, they work on small drive current over a wide voltage range but would need to be one made for DC loads, many are for AC only.
Out of interest, did you measure the sensor voltage with the relay coil connected?

 

[DPG]

I would look at using a ready built relay module which has a transistor driving the coil of the relay. This is more likely to work with the possibly weak output of the sensor. They would usually take the form of a circuit board with a handful of components pre-assembled and should be available from ebay or other web sources.

Obviously this would want mounting in a little ABS project box.

You could have got one from Maplins up until last year sadly.

 

[Marvo]

The pump may not be giving smooth pressure, it may be more like a series of rapid pressure pulses which is causing the sensor to give an output that isn't smooth which in turn is causing the relay to chatter.

The sensor might not be particularly well suited to this application but it might work if you can build in a delay somewhere in the system such as a relay with a magnetic 'slug' built into it which makes it slower to release.

 

[Holden Customs]

Hello Everyone. Thanks to all who replied with helpful comments and solutions. I just wanted to update that work has been busy and we had to move off of getting this problem fixed but in my spare time I managed to find out that the sensor does not send a constant feed and is causing the relay to chatter. I will be talking to the manufacturers to see if there is a way to re program it or a different option. Thanks again

 

[Spoon]

Depending on the sensor output, is it possible to add a capacitor to extend the signal length?