Having Trouble with Megasquirt WI
 

I implemented WI control through my MSPNP9093 as described in the MSNS-Extra Hardware Manual. See attachement. I only implemented the X2/JS0 circuit to turn the WI pump on and off with a relay ("relay 1" in the diagram). The circuit was implemented internally to the MSPNP with the "12V Ignition Feed" tied to internal, unregulated power and the "0V" tied to MSPNP ground. The only modification to the circuit is the use of a 1N4004 instead of the 1N4002 depicted.

Anyways, my issue is tied to flyback from the relay. Almost every time the WI shuts off, flyback from the relay causes noise that resets the MSPNP. The flyback diode protects the circuitry so nothing is damaged, but it is really annoying. Usually, it happens on throttle lifts for gear changes -- no big deal although I can see my tach go to 0 for a split second. However, every so often it happens on acceleration as the boost bounces around my turn-on set point (currently set a 120kPa). Since there is no deadband in the circuit, if the boost signal bounces from, say, 121kPa to 118kPa, I get a flyback event. The engine cut REALLY gets your attention.

I have some ideas to try (including the KISS method of decoupling from the MS and using a plain old boost switch). However, I wanted to see if anyone had some ideas on this. Surely, I'm not the first to try to control WI from the MS?

You could try running the flyback diode to an external 12 volt source instead of the MSPNP's 12 volt plane.

To clarify, you are only using the top p2n2222 circuit?

where exactly on the board is your diode attached to?

I'll give that a shot. Any thoughts on adding capacitance between the MSPNP's 12 volt plane and its ground?

That's correct. Only the top circuit.

I've attached a drawing of the internal mod. The diode goes from the 2N2222 collector to what I think is unregulated 12VDC of a v3.57 board.

It already has 3300uF.

I'd try adding a diode across the relay itself, from the coil to the high current 12V. Or replace the relay for one with built in protection.

This AM did a quickie and added an external flyback diode across the relay coil. However, wasn't able to remove the internal diode. "Seems" a bit better. When I get more time, I'll open the MSPNP and remove the internal diode from my grandaughter board. Hopefully, that will do it.

So, finally got a chance to get inside my MSPNP and clip out the flyback diode on my "granddaughter" board. That leaves the relay in question powered by an external switched 12VDC source with a local flyback diode.

Bottom line . . . problem solved. No more noise or resets of the MSPNP.

Thanks guys.

Glad to hear.

To avoid having to clip the internal diode, use a Schottky diode across the relay winding, such as an SB340 (3A, 40V Schottky).

The 100 ohm resistor in the gate of the IRLZ44 should be increased to 1k in order to slow down its switching speed and noise generation. And said resistor should be mounted physically close to the MOSFET, and the trace connecting it to the gate pin should be short, as in < 1 inch. If not it can oscillate in the MHz range and cause all kinds of weird EMI problems.