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

 

[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.

 

[Holden Customs]

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.

Hello. I wont be able to get the full type number of the sensor for about 3 weeks as it is on our machine at another spot in the country. As for the relay I am using it is this one attached. I think I am starting to see what you are saying. Thanks for the help.

 

[marconi]

I have tried a number of searches using the pico relay information but been unable to find out its coil resistance. Could you measure it or measure the current flowing through it at 12V? Then Lucien Nunes will have the information he needs on it.

 

[dmxtothemax]

QUOTE - is there a different relay I can use?
YES !
Use an electronic relay

3-32VDC Solid State Relay 240VAC at 3A | Jaycar Electronics

This is a PCB mounting, single in line package relay capable of switching up to 240V AC at 3 amps. Solid state relays are particularly useful when onl...

www.jaycar.com.au

 

[DPG]

The solid state relay option is a good idea.

 

[marconi]

Re #43; Good idea but I don't think the one you pointed to is suitable because it is designed for ac switching applications, the minimum mains voltage from spec is 24V and it is a zero-crossing device so will need a sinusiod main power input to trigger the conduction of the thyristors. It relies on the ac current regularly being zero to turn off when the dc control voltage is removed.

A transistor or another relay is probably a better bet. We will have to wait for Dr Nunes...