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PDM absorbing back emf
Posted:
Thu Apr 22, 2010 3:34 amby 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?
Re: PDM absorbing back emf
Posted:
Fri Apr 23, 2010 7:01 amby 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.
Re: PDM absorbing back emf
Posted:
Fri Apr 23, 2010 3:29 pmby 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?
Re: PDM absorbing back emf
Posted:
Tue Apr 27, 2010 6:35 amby figgie
There is only one channel that can absorb back EMF on the PDM and that is Output 9 (Pin B_A).
Re: PDM absorbing back emf
Posted:
Tue Apr 27, 2010 10:50 pmby Martin
Do you think it will handle a coil?
Arent all of them clamped but just different voltages? -0.7v and -42v?
Re: PDM absorbing back emf
Posted:
Thu Apr 29, 2010 5:01 amby figgie
Martin
not according to MoTeC as that is the only output that can handle parking duties of the windshield wiper motor.
Re: PDM absorbing back emf
Posted:
Thu May 20, 2010 4:17 pmby 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!