Main power wiring

PMU
1

I’m just planning out my main power runs for my car and the neatest option would have the main battery cable run straight to the PMU through a 150a fuse and then daisy chaining off the pmu stud to the starter motor.

Can anyone see any issues with this? Ideally I don’t want to go to the starter first and then back through the bulkhead grommet to the pmu. Likewise I don’t want to run an extra cable if I can help it.

2

Depending on the starter and engine size, a 150 A fuse might not be enough for cranking.
That’s something you have to check.

From the description, I assume the battery is in the back of the car and the engine is in the front.
Solutions from best to worst:

  1. Independent wire from the battery to the starter.
    Wire from battery to PMU and wire from alternator to PMU.
    With this solution, the wire size can be optimized differently for each path.
    The starter wire voltage drop does not impact the PMU and devices supplied by the PMU.

  2. Wire from battery to PMU, from PMU to starter, and from starter to alternator (or starter and alternator swapped, depending on the physical layout).
    This solution uses the least amount of wire, but bigger wires must be used to accommodate cranking and the PMU load through a single wire. The voltage drop of the wire during cranking affects the PMU.

  3. Wire from battery to the starter and back to PMU.
    This uses more wire than solution 2, and the PMU sees more voltage drop. That solution is the worst, and there is no point in doing it that way.

3

Thanks for you reply. I had it in my head that you shouldn’t “tee” off the alternator feed to power things as its can cause issues. I dont know why i had that idea but when ive looked its pretty much how all the manufacturers do it.

My new plan is to have a dedicated starter run. 35mm with a cicuit breaker (i just cant bring myself to run no circuit protection at all through the cabin)

Then a 100 to 125a fused leg to the alternater either teeing off to the pmu or if I’ve got enough space, running a second 125a run from the battery to the pmu

4

I often use a firewall bulkhead stud/radlok for the battery to starter run and jump the PMU feed from there. Battery in the trunk/interior and pmu usually near the firewall

5

Yeah so in essence thats what i was initially looking to do the difference being i was going to use the pmu as the junction instead of the bulkead stud