4wd control module

[FDLecuyer]

Hi, I'm working on 24vdc system on a backhoe, I replace the module for the 4wd system. The module activate a solenoid on spool valve. Everything works fine but when I shift gear the output of my module turn off and back on in a second. The shifter is all electronic it activate solenoid on the transmission/transfer case assembly. The only link between the two circuits is the power supply, they share the same fuse, I try to supply a positive and negative from the batteries but no difference. When I disconnect the solenoid from the transmission the problem goes away in which gears it disconnected my 4wd solenoid and transmission solenoids are wired separately. I'm in a dead end and need new ideas. Thanks.

 

[alec_t]

I'm guessing a voltage spike generated when the solenoid turns off is interfering with the electronics. The solenoid should have a snubber or freewheel diode across it. If there's one already it may have failed.

 

[FDLecuyer]

I guess your right, I think the circuit design is wrong. I have 3 transmission solenoids, all of them without diode, but one goes thru a relay and it's the only one not affecting my module. If I remove the relay and jump it, it does interfere. So now with all my testing I burned my new module, I'm waiting for a new one and the customer to modify the circuit. My solenoid have 2 wires if I want to install a diode, we're I need to install it? Inline on the positive side or across the negative and positive.

 

[alec_t]

The diode would be reverse-biased, i.e. connected directly across the solenoid coil, with the cathode going to the + side of the coil and the anode going to the - side of the coil. The diode should have a current rating greater than (e.g. at least 1.5 times) the coil peak current and a voltage rating greater than (e.g. at least twice) the voltage applied to the coil.