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

 

[DPG]

Good point Marconi.

 

[Lucien Nunes]

That is a general purpose automotive style relay, which are usually rather insensitive and require high coil current. I would be surprised if it did actually use more than the 100mA available. as it would get quite warm dissipating a nominal 1.2W, but we can't tell.

See this link for an example of an industrial product that would definitely work if the sensor model you are using has a 100mA output. This switches up to 25A using 500mW coil power. The 12V version has a resistance of 300Ω so will use 40mA at 12V or 50mA at the system's likely highest voltage of 15V. Socket bases with screw terminals are available to suit. You should add a protection diode (e.g. a 1N4007) or buy a base with one built in. There are bazillions of other options, just look for relays with coil resistance of no less than say 250 ohms.

46.61.9.012.0040 | Finder Plug In Power Relay, 12V dc Coil, 25A Switching Current, SPDT | RS

uk.rs-online.com

Of course, if the relay is not taking in excess of 100mA, it's not the problem, but as yet we can't tell.

 

[Holden Customs]

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.

Thanks. I will be able to measure it once I am back with the equipment. I am away until August 12th unfortunately. But when I am, I will update it on the thread. Thanks again to everyone for the continued help.

 

[Holden Customs]

That is a general purpose automotive style relay, which are usually rather insensitive and require high coil current. I would be surprised if it did actually use more than the 100mA available. as it would get quite warm dissipating a nominal 1.2W, but we can't tell.

See this link for an example of an industrial product that would definitely work if the sensor model you are using has a 100mA output. This switches up to 25A using 500mW coil power. The 12V version has a resistance of 300Ω so will use 40mA at 12V or 50mA at the system's likely highest voltage of 15V. Socket bases with screw terminals are available to suit. You should add a protection diode (e.g. a 1N4007) or buy a base with one built in. There are bazillions of other options, just look for relays with coil resistance of no less than say 250 ohms.

46.61.9.012.0040 | Finder Plug In Power Relay, 12V dc Coil, 25A Switching Current, SPDT | RS

uk.rs-online.com

Of course, if the relay is not taking in excess of 100mA, it's not the problem, but as yet we can't tell.

Thanks. I will update with the measured amount when I can. If it ia what you are saying then hopefully I can get a mew relay together like you suggested.