Solid State Relay/Driver Question

Question

I have a question about solid state relays.

I am into drag racing and we use a solid state relay/driver to control the transbrake solenoid(large solenoid in the transmission that allows the transmission to be held in place while loading the engine). We use the holley performance 554-111. We use solid state because we want to pulse the solenoid so the car creeps forward under large engine loads. This allows us to creep into the staging beams and then launch the car.

So I was playing with this driver/relay last night and this is how it's wire. Orange Wire: 16v in Small Yellow and Black Wire: Ground trigger from ECU Blue wire: Output to transbrake solenoid

When I check voltage at the transbrake solenoid without the relay being engaged it still shows voltage. When I engage the relay the same wire increases in voltage about .6v(from 16v to 16.6v).

Everything works as it should, but I dont understand how. If the output wire always has voltage why is it not engaging the solenoid even when its activated off?

Answer 1

You are probably seeing leakage current through the relays's internal protection circuitry

when testing without the solenoid, use a dummy load (eg: a brake lamp) in place of the solenoid to get a more realistic picture of the voltages involved.