PDM absorbing back emf

[Martin]

Would the pdm be capable of absorbing the energy from a normal bosch coil if the coil negative is ON and the PDM turns the output of supplying the coil?

[figgie]

Hi Martin, I assume you mean coil not boil.

I am curious why you would want to power the coils from the PDM instead of like a CDI-8 or M&W. That is a lot of stored energy to try and absorb if running the coils in an inductance fashion.

[Martin]

Sorry, yes it mean a coil



The coil will be driven by an igniter.Im worried about the 12V side being turned off while the Coil is turned ON by the igniter. This will make the floating 12V side of the coil produce a back EMF. With the primary haveing a lower Inductance (less turns) the energy from it can not be that greats, but I would like to know if the PDM will absorb it if it does turn OFF with the negative still connected?

[figgie]

There is only one channel that can absorb back EMF on the PDM and that is Output 9 (Pin B_A).

[Martin]

Do you think it will handle a coil?


Arent all of them clamped but just different voltages? -0.7v and -42v?

[figgie]

Martin

not according to MoTeC as that is the only output that can handle parking duties of the windshield wiper motor.

[DarrenR]

figgie, that is correct about output 9 but it is not meant for inductive load clamping, the switch to ground happens 1mS after the output is shut off so most of the load dump will have happened.

The outputs can easily take the load dump from shutting off a coil, and yes Martin reverse voltage clamping starts at -42V.

If you're worried about it tho, just turn off the ECU 20mS before the coils!