MOSFETS and Solenoids

[Tobias]

I made the board that has eight MOSFETS. I take two MOSFETS and put them in parallel. So I have four outputs. An output is going to power four solenoids. The solenoids take 26 amps.

I am attaching the spec sheet for the MOSFETS and also a schematic. In the schematic, the MOSFETS are in the top right area.

The solenoids are for four nitrous stages in a race car. For this race car, only two stages of nitrous. Here is my problem, on the racetrack I can't get the second stage to activate. Friday I went to the shop, we started the engine and activated the my controller without the nitrous bottle open. On the data recorder both stages activated and the battery voltage looked clean with two steps for each stage activation.

On the track the first stage activates and the second doesn't. When my board activates, the battery voltage gets upward spikes. So the final test run, the team used a mechanical push button so the driver could activate the second stage, in which it worked fine.

The only difference between the shop test and the race track is that the transbrake was not activated on the shop test. The transbrake is a solenoid that literally puts the transmission in low and reverse gear. This is what holds the car at the starting line until the driver releases the transbrake button and the car leaves. This release also activates my box that controls the activation of the nitrous stages by time.

This afternoon I am going to have the team do a shop test with the transbrake. So here is my question, why would the nitrous stage activate using the mechanical pushbutton and not the MOSFET? The wiring is essentially the same between the two scenarios. Hypothetical situation, if a circuit barely has enough ampacity, would a mechanical switch work and a MOSFET would not? Meaning does a MOSFET not like it when a circuit is starved for current? This is a 16v system

Thanks ahead for your input. I also attached the transistors I am using to turn on the ground to the Source leg of each MOSFET and a pic of the board with the MOSFETS and busars.

[mackrackit]

Still looking at the schematic but looking at the pic I would reflow those solder connections. Might not be making good contact between the Drain and bus.

[Tobias]

Yea thats pretty ugly. What you see in the pix is actually excess solder from solder rod I melt onto the bus with hot air. I am using a hot plate and solder paste now to flow the solder. It works pretty nice and looks alot better.

Still looking at the schematic but looking at the pic I would reflow those solder connections. Might not be making good contact between the Drain and bus.

[Tobias]

One thing I should add..I sent a board to a nitrous manufacturer. They put the board on their flowbench and the board activated four stages at the same time for 15 seconds several times.

[Jerson]

I suspect the layout of components and traces. Can you post a pix of your board? A ground loop is possibly taking you down.

[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.