Monday, February 15, 2016

Tidying Up a Bit

I like to keep things neat and organized, but to a certain extent, things got out of hand with this build. For one thing, it's rather more complex than the last two projects with Siemens AC power and the supporting DMOC inverter and GEVCU controller. The electric air conditioning compressor and its plumbing are a challenge yet to be addressed. The OEM charger and DC/DC converter also have their own controllers, leading to an upcoming consolidation project. Then there is the spaghetti monster in the wiring box.

To disguise that mess, a cover was constructed with 1/4" plywood skin over a 5/8" marine plywood core that was clearanced to allow for the height of the wiring bundles coming from the harness. A little black spray paint makes it disappear, and it's secured with a velcro strap. Not only does it clean up the appearance, it also protects the wiring and terminal blocks from accidental shorts. The GEVCU has been relocated  to the top of the DMOC, held in place by two inch wide industrial strength velcro. I had to unplug the connector to add a terminating resistor, and simply didn't have enough room or leverage to plug it back in where it was previously installed on the back of the DMOC. There's a surprising amount of hood clearance, so it works well and certainly is more accessible.

Here's the view from the other side:

I'm not entirely happy with the GEVCU cable, but it's a dark color and could be worse. 

On the other side, I plan to enclose the contactor and precharge circuits as well now that I think I have that sorted out. With Spring in the air here in Texas, I think it will be time soon to have the air conditioning system charged and get that working before the summer heat sets in.

Tuesday, February 9, 2016

More Precharge Challenges

The precharge circuitry on the Porsche has been a challenge since day one. I'm appreciating more and more the well integrated design of the Soliton1 controller in my evTD. I never had to even think about precharge on that because it was built in. Sorry they've left the EV scene.

You may recall that the first time I powered up the Porsche, I fried the contactors. Then I did it again. Third time is the charm, you say? Well, after 200+ miles I came close to another wholesale contactor replacement. This time, after a jaunt up the MOPAC (that's a highway here in Austin, so named because it parallels the Missouri Pacific railway line), I parked it and came back a few minutes later to run an errand, turned the key to see only 6 volts register for the pack! That just can't be, so I spot checked some battery cells - all fine - then  pulled the contactors yet again to find they worked ok after cycling them a time or two, but the precharge resistor was dead - no reading on the multimeter in the ohm setting. So once again, even though it was in the circuit, no precharge was taking place. The contactors likely would have welded closed if I had put them through one more startup sequence.

I had wired the precharge resistor using this diagram from the GEVCU manual:

So my guess is that I either had a defective resistor, or it didn't like being in the circuit full time. After receiving a replacement resistor, I reworked the arrangement adding the yellow high voltage precharge relay to energize the resistor only on precharge and keep it out of play at all other times.

After a quick spin around the block, things seem to be back to normal. We'll give it a more extended test run tomorrow.