Splicing EV 12v into ICE 12v

[Scrappyjoe]

Hello,

I appreciate that most projects are full EV conversions, so this is moot for most. I'm working on a hybrid conversion, with one axle driven by an Outlander drive unit and the other driven by a petrol motor. The petrol motor has an alternator, and is started conventionally by a starter motor. The EV system may or may not use a DCDC convertor, I am not sure yet.

The outlander unit is mounted, and I'm going to do my first drive shortly.

For first drive, I'll simply use a spare 12v battery and leave the ICE system off. But, before this is 'done' I'll want to integrate the two 12v systems. I know that I can just ground both 12v systems to the chassis, and the positive 12v to a single rail and call it a day. But my vehicle is really old, and there is 30 year old wiring all over the place. Let's just say that the petrol, 30 year old part can happily tolerate spiky voltages and all manner of poor wiring, but I'm worried about exposing the more delicate EV components to that sort of wiring.

Is there a way I can use a common 12v rail, but 'isolate' my EV 12v components from the rest? For current spikes, I can use a fuse. What about voltage fluctuations? Some sort of voltage regulator?

Questions:

1. At the interface between the two circuits, do I fuse both positive and negative, or just positive?
2. At the interface between the two circuits, is there a way to regulate voltage? DO I do this on both positive and negative? Is this even a good idea?
3. Or is this just overkill, and I should trust the system and think of them as one circuit?

I appreciate that the deep fix is to sort out the 30 year old wiring. But that's a huge undertaking, and it'll slow me down significantly.

[J0hannes]

Just ground everything to same reference (preferrably body/chassis). A gross oversimplification, but if the housing is conductive, it is meant to be grounded and keeping it isolated if propably impossible.

Youll risk having weird ground loop issues and such phenomena, if you try to have different ground reference for the original 12v system and the ev stuff.

The EV stuff should not any more delicate than ICE related stuff. A properly designed automotive component can operate on a wide voltage range.

Signal grounds are a separate thing and those usually have a shared reference point with the ecu/vcu etc using the sensor

If you route a single main +12v from the battery to the EV parts and distribute from that to the equipment, you don't have to rely on the old ,possibly sketchy wiring. Just have a properly rated fusible on the battery end of the cable, to protect from a possible short along the way.

[Scrappyjoe]

Cool, thanks J0hannes, will do!