Tuesday, September 1, 2015

Building Better Boxes

A couple of nights ago I woke up at 2:30am with a brilliant idea that came to me in a dream. OK, maybe not so brilliant, but gives you some idea about what I've been dreaming about lately. It actually made sense the next morning, and had nothing to do with Dilithium Crystals, Gigawatt Transformers, or Ancient Aliens.

I have not been happy with the contactor box being in the rear of the car with the battery pack. I had already run high voltage wires through the passenger cabin along with the control wiring, which made me nervous. It just wasn't right.

I had wasted the better part of two days trying to find a space in the motor bay, but they were either too low and subject to water splash, or too precariously fragile. 

Here's the dream: (In the voice of Charlton Heston) Build ye a box around the inverter, and behold thy contactor module may be affixed thereto. Yea, verily I did proceed to do just that, using pressure treated exterior 5/8" plywood that was left over from the evTD project. Some scrap aluminum angle and a treaded rod to hold it all in place, and that's the box. With some T-nuts and three bolts, it's a comfortable fit in the space between the inverter and the coolant catch tanks with all the plumbing below.

The contactor module was included with the Better Place battery pack and contains the positive and negative contactors along with the precharge resistor and control relay, all nicely integrated. It has the connections for the high voltage wiring from the battery pack and output connections for the inverter.

The front of the box will mount the charger controller and the GEVCU system controller will mount on the back. The GEVCU manages a whole range of car functions in addition to the motor speed control, and needs a way to connect a bunch of wires in some orderly way.

I had spent hours laying on my back under the dashboard in a contortionist pose that would would make Cirque de Soleil proud. I found and removed what Porsche calls the "Digital Motor Electronic Control Unit". Just as I suspected, once it was disconnected, the basket of snakes under the hood slithered off. All that messy wiring was there to feed sensor information about the gas motor to the ECU so it could fiddle the timing and fuel injection. After hours of searching, I finally found the switched 12 volt wire, a single wire among the seven bundled into the cruise control harness. With all of that gone, the motor bay is a much neater place.

So now the electric motor needs the same sort of inputs and outputs, so a circuit box was built and mounted on the top rear of the inverter. Four relays and twenty six terminal connections will be centrally housed here with all wiring entering and exiting through the open back. I think I'll put a hinged lid on it for easy access later.

A coat of black paint will make the whole apparatus disappear, then I can mount the components and wire everything up. That should basically finish the under-hood activity and we'll move on to the back. Tomorrow is another day ...

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