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Power Ground Design Sanity Check

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hi All,

I have put together a diagram of my intended power ground design. Would appreciate your feedback on how it looks. Thank you very much. Trying to keep the engine as my Star Point. This is on a 13B rotary engine just in case.

Bonus questions for those of you running a PMU16. What size wire are you running for pin 25 (PMU ground). There is not much information on the ECU Masters documentation about this ground on the PMU. I suspect it is only use for the reference ground of the analog inputs so currently planning on running a 20AWG wire for it.

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As I understand it, the PMU has the otion of using sinks/grounds for switching some circuits - that would suggest the PMU ground will need to be able to handle the total sink current expected, as well as potentially being a reference ground.

However, I haven't had a good look at the device, so may be quite wrong there?

Hello Michael,

The grounding plan looks good. Just be sure your battery isolator will definitely be killing the engine before isolating, as your alternator will still be powering your PMU16 otherwise.

As for the PMU16 ground, they do put it on one of the 25A header pins suggesting it should be run with 12AWG, but the documentation shows it being used as a reference ground for the analogue inputs, as you said, in which case 20AWG would be plenty big enough. I would recommend asking ECUMaster to get clarification. The PMU16 Autosport has low side drivers and requires high current grounding, but I don't think that's the same with the standard PMU16.

Thank you Gord, yes that is the case for the Autosport version of the PMU16 which has low side drivers as well (as Callum also points out). I am running non autos port version but will definitely contact ECU masters to confirm whether or not 20AWG is enough on the non autosport PMU.

Callum, thank you for taking a look, glad to know I'm on the right path. You are absolutely correct about the alternator powering the PMU. I intend to wire the MSEL isolator as per their documentation. Meaning I will have a cabin switch as well as an exterior switch, when either one is triggered the isolator sends the "kill" message to the PMU/ECU before isolating the battery.

Excellent! You're all over it then Michael!

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