MOSFETS and Solenoids

[Tobias]

I am attaching a color and B/W PCB view from my software. The wiring on race cars aren't ideal. Battery ground is connected to the chassis. Then there are three or four other points on the chassis components are grounded.

I have one other team with the same problem and they are using a transbrake aswell. They are also activating first stage right after transbrake release.

[Jerson]

I would prefer seeing just the copper layers without the overlaying idents. However, first impressions, GND signal traces are way too thin to be useful unless you have copper filled your board for the GND net. The way it is now, you will get huge surges on the GND line whenever a MOSFET switches. The GND trace, if not copper filled plane, should be at least as thick as the traces on Stages 5,6,7,8

[Tobias]

I do have a ground plane. I took it out so you could see the traces easier. I am attaching a PDF with the ground plane.

Thanks
Toby

[Jerson]

Toby

Couple of things I would check on.

1 - the trace going under the lower edge (going to R5) of the PCB. I do not know if it drives any heavy loads there.

2 - Vin to the MOSFETs - perhaps they are on the second layer and have thick tracks??

Jumper thick wires direct to the Vin lines till you find the cause. Jumper thick wires direct to the Ground points near the Mosfets till you find the cause. I suspect some heavy current switching on is ticking off your PIC to malfunction. I would typically see that the heavy currents flow first to the load switching devices(heavy loads) and then come back to the CPU(flea power)

Maybe someone else might see something I haven't caught

[falingtrea]

One other thing you might want to look into is the temperature of your board. The thermal enviroment under the hood of a car is quite different from the thermal enviroment of a lab bench. You might need more heat sink for your MOSFETS.

[mackrackit]

For what it is worth I agree with all the above comments, but I have a question or two that might help.

When the car is on the track are you using an alternator? In my day we did not. We put a couple deep cycle batteries in the back to help with traction and would run everything frm that. I am getting at two things. Maybe the battery is just low enough not to satuarate the FET or if you are using an alternator by the time the second stage kicks in it is giving "dirty" power.

If it works on the bench or sittng in the garage, like Tim was getting at, also look for heat or mechanical stresses.

[spcw1234]

One other thing I didn't see mentioned is the solenoids have to work harder when there is 900PSI of pressure behind it. This would require more current to open the solenoids. When you tested in the garage there was no pressure in the line. I don't know if you log battery voltage either, but with the load of fuel pumps and ignition amps under heavy load will drop the battery voltage regardless of using an alternator, since you said 16V I doubt you use an alternator.