Tyco Relay as Kill Sw and PMU

PMU
1

Searched far and wide but did not find anything regarding correct or rather safe way to wire in a Tyco/TE high current relay as a battery isolator along with PMU.

Long story short, had a runaway engine, kill switch was used at around 4,5k rpm, ADU displayed “PMU overcurrent” error and PMU got fried. No fuses were tripped. As far as I can tell, power distribution is as in the image bellow, there is a 5A fuse between Relay Pin87 and PMU ignition sw input (image at bottom of the post, hand drawn).

This got me questioning what is the correct way to do it with a high current relay so alternator load dump does not fry anything.

I always followed the motec guide for wiring and simply setup a master switch as a condition for every output. Works and kills the engine but never tried activating the master switch under non-idle conditions. (Bellow the hand drawn diagram)

But then I realized that motec does not have a wake-up/ignition sw input and ECU Master Battery Isolator shows the kill signal going to PMU ignition sw input.

Any input is greatly appreciated.

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You need to drain current form alternator . For all relay isolateor we use spike protector with tvs diode. Have a look on wiring of manual battery isolators with 2 big and 4 small terminals when you turn it off current form alternaoer is drained to ground via big ceramic resistor. That typical installation error.

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I understand the need for load dump protection and ways to achieve that. I always use a TVS for installations with no PMU but it’s my understanding the PMU has an internal TVS, hence the operating voltage description: 6-22V, immunity to transients according to ISO 7637. I haven’t actually purchased the ISO but it does deal with load dump among other things. Tyco relay has load dump test data referencing the same ISO.

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