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
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.
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?
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?
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.
Yes, the battery ground is run to the alternator and both are connected to the frame. All grounds are from that point.
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
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.
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
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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?
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?
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.
Obviously this would want mounting in a little ABS project box.
You could have got one from Maplins up until last year sadly.
M
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.
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.
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
That could be possible. The output wire is about 20ga I think and is 0 volts until charged when it senses water. How would one go about that?
Please could you post a link to the specific sensor, so that we know exactly what kind of output it has and how it responds. I'll post a suggested circuit to convert its signal into a relay drive voltage.
Hey thanks for the offer. I have attached a data sheet of the sensor. It is a Baumer Clever Level LBFI.
Okay. I'm not too sure what that exactly means but I think I get it. Could the chattering in any way he caused by the different sizes of wire? It's all fed right into the relay, the ground, + , and switched + to the ignition are 12 Ga and the switch feed from the sensor is 22 ga
It is the opposite. As when the sensor is active it energizes the relay which in turn energizes the ignition.
Could you provide the full type number of the sensor (order number) which begins LBFI..
See page 4 of 4 of:
And, if you know it or can measure it, the resistance of the relay coil in Ohms.
What is the source of the 12V supply? A lead acid 12V battery? Is it the same one as starts the engine?
See page 4 of 4 of:
And, if you know it or can measure it, the resistance of the relay coil in Ohms.
What is the source of the 12V supply? A lead acid 12V battery? Is it the same one as starts the engine?
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Or just a link to the type of relay. The point here is that the different models of sensor have different output circuits; one requires the relay coil return to positive, one requires it to go to negative, one probably doesn't matter. The sensor's 100mA output current rating is sufficient to drive some relays but not all; yours may well be presenting it with a borderline overload and triggering its output protection if the coil resistance is too low.
Re wiring, no, the cable size is more or less immaterial at these low currents, any normal cable physically strong enough to use will be ample for the sensor circuit unless it's tens of metres long.
Re wiring, no, the cable size is more or less immaterial at these low currents, any normal cable physically strong enough to use will be ample for the sensor circuit unless it's tens of metres long.
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