12V DC Relay Issues (Diesel Engine)

[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?

 

[Holden Customs]

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

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?

 

[Lucien Nunes]

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.

 

[Spoon]

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.

Now that is an offer you can't refuse @Holden Customs

 

[Holden Customs]

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.

 

[DPG]

Looks like that sensor should give a definite logic output, and it has hysteresis which should prevent any 'chattering'. Unless the hysteresis gap is too small maybe.

 

[Holden Customs]

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

 

[James]

Is the circuit such as when the sensor is active, it energises the relay which in turn kills the ignition circuit that is feeding the sensor, creating a feedback loop resulting in a constant chatter?

 

[Holden Customs]

Is the circuit such as when the sensor is active, it energises the relay which in turn kills the ignition circuit that is feeding the sensor, creating a feedback loop resulting in a constant chatter?

It is the opposite. As when the sensor is active it energizes the relay which in turn energizes the ignition.

 

[marconi]

Could you provide the full type number of the sensor (order number) which begins LBFI..

See page 4 of 4 of:

https://www.baumer.com/ch/de/produktubersicht/prozesssensoren/fullstandsmessung-/fullstandsschalter-/industrieanwendungen/lbfi/p/medias/__secure__/Baumer_LBFI_EN_20190513_DS.pdf?mediaPK=8940481773598

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?

 

[Lucien Nunes]

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.