15 May 2008

Fabricate - housing for contactor

The car had a contactor and two shunts mounted out in the open. The contactor (big object in the center of the photo) is a really heavy duty switch/relay that connects the motor controller to the battery pack. The shunts measure current flow to/from the battery pack. There are two shunts because the original conversion just had an analog current meter using the shunt along the top of the photo. Later a digital "e-meter" was added and that had it's own shunt (the little one on the right of the photo). The problem is its too easy to get dust and dirt inside the contacts of the contactor (the large opening on the left). Also all of the bolts in the photo are high voltage (~144VDC). Not something you want to accidentally touch or drop tools onto!

To solve these problems I want to put the contactor and one shunt (get rid of one) inside an plastic weatherproof enclosure. Again I brought home a scrap box from work that might just barely fit the parts.

I made some brackets and fit the e-meter shunt and the contactor in with some room for a control circuit. The big cable will come in from the battery negative and attach to the shunt on the left, then leave out the right to the controller negative. I'll also need to attach the charger between the shunt and contactor as well as add a precharge circuit across the contactor. A precharge circuit saves the contactor from switching the high voltage by slowly (a couple seconds) charging the controller before letting the contactor close.

I'm still working on the control circuits and trying to figure out where to put this box. Eventually I'd like to make a single box that takes both cables from the battery pack, contains the current sensor, two contactors, possibly the circuit breaker, and control circuitry and puts out two cables to the motor controller.

1 comment:

storm said...

It is amazing to me that a blog will have many visitors, but no one leaves comments to show they appreciate your work. I wish I had gotten such a good deal on a car!

My comment is that worry about "touching the high voltage connections" is misplaced and may cause the uneducated to think that electric cars pose a danger of electrocution. Since the HV is floating, touching anything with one hand poses no danger at all.

If you happen to touch a negative with one hand and a positive with the other, you could have a problem.

Dropping tools on batteries could also get exciting. I have a rolling table I force myself to pull over to the EV whenever I am working under the hood. All parts and tools on the table, never laid on the controller or batteries.

Nice blog. Thanks.
storm