Temporary PMU switched inputs during retrofit

PMU
1

I’m in the process of a retrofit in my car, and there are some temporary connections that I would like to make to remove relays. Until I change the way the wiring and switches work, they carry automotive voltage, so around 13.8 V while the car is on.

Since the PMU accepts a switched input from 0-5 V (protected until 20 V), I was thinking of using a voltage divider R1 = 10k and R2 = 3.9K, which would bring input voltage during normal operation to 3.87 V. If the system voltage drops to 6 V during a transient, input would see 1.7 V, and rising until 20 V it would see 5.6 V (so barely activating the protection).

Then I would configure the input to read >3V as high, <1V as low, and hysterisis to take care of transient behaviour.

Does this looks like a sound plan? Anything I overlooked or improvement I could make? I would use this idea to actuate headlights, horns, windshield washer and so on connected to PMU outputs.

2

Just feed it 12v. It only reed 5V but will work fine.

2 Likes
3

I thought the car transient electrical peaks surged above 20 V and the input was protected until 20 V (or 30 V for the 7A IO channels of the 24DL), so should not receive potential above it.

What did I misunderstand about the input protection?

4

The input protection means that the specified voltage can be applied constantly.
Transients are not crucial in this case.
It’s not like the voltage exceeds 20 V, and the input is immediately fried.

You can safely connect battery voltage directly to the PMU input.

5

Thank you for clarifying my misunderstanding! You just my lifer super easy. Thanks everyone.