Progress has continued apace since my last update. Mostly on the wiring and plumbing, including for the vacuum pump and power steering.

12V Wiring

Somewhere in my workshop are two fuse boxes. Where they are, I have no idea. So I’ve ordered yet another one. The way I sell it to myself is that I’m just stocking up on parts for the next project…

I need two additional fuse boxes in my new setup because I’m basically using them as distribution panels. One provides power to everything that is engaged when the ignition key is turned to the ‘on’ position. The second when the ignition is fired and the inverter starts running (though not in all circumstances – see below).

I have been wrestling with how to latch the ‘run’ relay on but have it reset when the car is turned off. I wanted to keep it simple and avoid having this run on some logic on a microcontroller, with all the complexity of having that interface with 12V. With the old ECU removed, there was no latching circuit left in the car, so I had to add one.

I first went for a latching relay and ordered what I thought was a batch of cheap ones. They turned out to be standard changeover relays. This was annoying until Jamie (@bigpie on the openinverter forums) pointed out that I could just loop the output of one relay back to its input and it would latch stably until power was removed. If I take the power for the coil of this ‘run’ relay from the ‘on’ relay, then it will open when the power is turned off at the key.

I hooked up a relay with a 12V fan to my bench power supply (actually an old ATX PSU from a desktop PC) and sure enough, Jamie’s suggestion worked.

So, I designed and 3D printed a mount for two relays side by side (I didn’t like the springy metal clips they came with), and soldered up the connections to make it work as intended. This was then screwed into the car on the underside of the MDF mount I put in in the last update to carry the electronics. The new relays replaced the old BMW ones and look much neater.

When the new fuse box arrives I can get this all hooked up and give it a test. In the meantime, I have continued to tidy the wiring. I’m not going to wrap it all in Tesa tape until I know it works, but I am experimenting with routing so that I can cut everything to length, and I’m very happy with the layout now.

[Update: with the exception of the oil pump and vacuum pump, this is now finished since I started writing this post.]

Charging

The more awkward situation from a wiring perspective is charging. In order for charging to work, I need the ‘on’ fuse box to be live, and I also need the inverter to be in its ‘run’ state, so that it closes the contactors that connect the charger and inverter to the battery pack. But crucially, I want to ensure that the inverter is in neutral, and I don’t want to turn on the power steering pump, vacuum pump, or motor cooling pump that would be engaged by the ‘run’ fuse box going live. I also want to be able to leave the car securely locked and know that people can’t just drive it away without the key.

My plan for this is to have a toggle switch in the cabin that allows me to turn on the ‘on’ relay. This switch will also be connected to the ‘charge mode enable’ line on the battery management system. So that the charge mode isn’t enabled every time the ‘on’ relay goes live, I will need a diode in the line to the ‘on’ relay.

Alongside the toggle switch will be a push button. This will run to the start signal input of the inverter so that I can close the contactors for charging. Again I will need a diode so that pressing this button doesn’t also turn on the ‘run’ relay.

I’ve tried to sketch this all out below. My plan at some point is to start to turn all these notes into a manual for myself, including diagrams.

None of this is ideal or permanent. I want to be able to just get out of the car, plug in the charging cable, and have it begin charging safely. There are lots of ways to accomplish this by sensing the connection of the charging cable, commanding the inverter via CAN bus etc. But this should get me to the point where I can charge for now with the minimum of fuss.

Inverter/Signal Wiring

The EVBMW board in the inverter needs a bunch of signal wires:

• Temperature sensors and resolver signals from the motor
• Start/brake/forward/reverse signals from the cabin
• Outputs to control contactors in the battery box

I had all these wired up probably nine months ago but after the failed tests back then, it had all come apart again as I tried to make it all work, and so need reassembling.

I’ve wired it all up with choc blocks for testing and then will use plugs or solder it direct once I know it all works.

Power Steering

I’ve finally sorted out the plumbing for the power steering. I had a custom high pressure line made up by Hydraulic Megastore that runs from the Zafira power steering pump to the banjo bolt on the BMW steering rack.

For the return line I’m going to try a bodge at first. I’ve cut down the hard line that ran from the return banjo through the cooling loop back to the reservoir. This I will clamp to a rubber line that runs straight back to the pump, which just has a barbed plastic connector for the return. If this doesn’t work, I’ll get another line made up.

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This post has been hanging around as a draft for ages so I’m just going to get it out there now. Next one will have more images.