LDU Forward and Reverse LV power issue

[Boxster EV]

When selecting a direction, either FWD or REV, the LV current draw seems to be very high. Only occurs when pulling a direction high.

I wondered if I had a short to ground on the car but I’ve eliminated that by giving the FWD pin 12v directly from the battery and the issue still remains.

I can have all ancillaries on including power steering and the battery holds a steady 13.9v. As soon as a direction is pulled the voltage is pulled down to about 11v after just a few minutes. It’s bizarre.

LDU seems to be behaving normally (other than suffering with low voltage issues after a few minutes of driving).

Any wisdom gratefully received.

[Boxster EV]

Just to add, I have a 5 amp fuse on the 12v FWD signal which doesn’t blow. How can such a drain be evident without blowing the fuse?

I recall Johannes saying that once the gate drive boards are active they can be quite power hungry, but this fault / issue is new.

[johu]

The pwm indeed becomes active when pulling a direction pin high and commanding torque.
Then the power draw is around 1A. Many other devices consume much more than that.
Measure currents, as many as you can

[Aragorn]

some sort of noise/interference tripping out the DC-DC converter?

The controller or inverter cant be pulling sufficient current itself to pull the DC-DC output down by that much, its hundreds of amps. But if the DCDC shut down, all the loads on the 12v would see the lead acid droop pretty quickly.

[Boxster EV]

Yes, there’s a load somewhere that’s significantly pulling the DCDC power down, or its enable signal is being intermittently interrupted (probably the latter). What I don’t understand is why it only happens when selecting a direction.

Will start testing current draw as a first step.

I also have a cheap 12v distribution box that looks after the enable signals for most ancillaries. I need to eliminate that too.

[P.S.Mangelsdorf]

What DC-DC are you using?

[Boxster EV]

What DC-DC are you using?

This one. https://shop.fellten.com/shop/tdc-iy-32 ... cba1185463

Think I found the issue; my little Davis Craig water pump was dying and pulling like 50 amps (I won’t mention that I fitted 40amp fuse to it temporarily 4 years ago) - I noticed that it sounded unusual and then felt the relay which was hot. Therefore my theory is that the DCDC was on the limit and tripping an overcurrent protection due exceeding tolerances.

Just driven about 30 miles without an issue so hoping it’s resolved.

[Aragorn]

Surprisingly small DC-DC output. Many OEM units seem to be in the 150A+ range.

[Boxster EV]

Surprisingly small DC-DC output. Many OEM units seem to be in the 150A+ range.

Indeed. It was a bit of a rash purchase a few years back when my Chevy Volt one went bang.

[johu]

50A?? That must have generated a lot of heat. 600W actually

[Boxster EV]

50A?? That must have generated a lot of heat. 600W actually

I feel a bit stupid for relating issue this to the DU in the first place. Yes, the relay was too hot to touch even after a minute or two.