28 June 2008

Fabricate - crimper

To attach the lugs to the ends of the 2/0 welding cable I need some kind of crimper. It is possible to solder them on, but solder is not really that good of high current joint. I asked the EVDL what crimp method is the best and eventually it came out that either a hex crimp or a stake crimp would suffice.
I found a pair of 36" bolt cutters on sale for $13 at Harbor Freight. I'm not sure I would use them for very long as bolt cutters, I think the "blade" would get dull quick. After thinking for a while, I thought it would be easier to make the stake style crimper than the hex type. I used an angle grinder and rotary tool to cut the half round (more of a hex really) into one jaw. Then I used the rotary tool to cut a tooth into the other jaw so that it lined up with the other jaw.
My test crimp looked pretty good. I still need to add a little more metal on the end of the stake so it is not so narrow. After making the test crimp I attached it to the ceiling and put all my weight on it. Then I had my wife put her weight on it with me (about 300lbs together). The insulation jacket started sliding so we stopped, but the crimp held! The next thing to do is cut it apart and look at the insides. I used a cutoff blade and cut the lug in two in the midle of the crimp. Then I filed and sanded down to 800 wet/dry until is was fairly clear what was going on. It looks like the crimp is sufficient, but I want it tighter. The dark spots in the photo are from the wet sandpaper. I left it in there to provide more contrast.
I call the crimper a success. With just a little larger stake it will be perfect. To make it easier to use, I have replaced one handle with a new link. Now I need to make a bench mount and possibly make the handle shorter, it doesnt take that much pressure to crimp. I may grind off the tips of the crimper that are not used, if I feel like it.

25 June 2008

Fabricate - electromechanical computer

I said in a previous post I was thinking about some kind of safety computer to manage the electrical system. I've finally come up with something after a few iterations. Don't be deceived by the complicated looking name! All it means is I used a few relays to make some simple logic.

The operation is such that there are two safety interlocks. The first is the charger interlock. In my case the charge door has to be closed. In a more generic case where there may not be a charge door a switch or 120VAC relay must close to enable the rest of the system.
The next interlock is an internal latch that will disable the system if both the go pedal and the brake pedal are pressed. This could be a problem when trying to start out on a hill. But the easy solution is to use the parking brake instead of the foot brake, which I do in an ICE anyway. I have two design versions: one for dual contactors and one for a single contactor.
With the dual contactor design, the low side contactor is enabled when the key is turned to run (I assume a precharge resistor is mounted across the high side contactor). On the single contactor design, the precharge relay is activated.
When the key is moved to start, the 'active' relay latches on (it turns off when the key is moved way from run or an error condition occurs). Once the controller sufficiently precharges a relay that detects the precharge voltage closes, enabling the high side contactor controls. When the user presses the go pedal it latches the go relay on, activating the high side contactor and controller. This stays latched until the user presses the brake (or an error condition occurs). Then the go relay drops out, dropping the high side contactor and disabling the controller.

I've put all the high voltage parts into a separate enclosure for some safety. All the connectors link up all the electric parts, so future upgrades already have connections to everything. Also built into this system is a reverse speed limiter. When the car is put into reverse, it limits the maximum speed of the controller to about half its maximum.

I have all this designed into one weatherproof enclosure with two connectors and a screw terminal block. It can feed two dashboard indicators for fault and ready. I'm also working on a design to signal a fault when the motor over revs.

16 June 2008

Fabricate - mounting brackets

I finally decided how to arrange the parts to put back in. I had to bend a 1"x3/16" steel bar into what I call the bridge. It goes from one frame rail to the other across the motor bay. It is bolted only to the two frame rails. On the bridge I'll mount one end of the controller, relay box, and contactor box (below the controller). It's finally starting to look almost done! Just one more bracket to hold the controller, one to hold the contactor box, and figure out where to put the DC-DC. Then the high voltage wiring and I'm ready for batteries :).

The relay box is a little circuit I designed to control the contactor mostly. I was never very happy with the contactor clunking on and off every time I touched the go pedal. This design incorporates the charge interlock switch, key switch, brakes, and go-pedal. When the charge door is closed and the key is pushed to start, a relay latches on, enabling the contactor system and the pre-charger (it is deactivated by moving the key away from run). When the go pedal is pressed, the contactor and controller are activated. It stays active until the brake pedal is pressed, then it deactivates. Basically I built a relay flip-flop! With the design I have, it also detects when you press the go pedal and the brake at the same time. I don't do anything with this signal, but it could shut down the main enable latch or something.
Another feature (yet to be added) is when the car is put in reverse, it will limit the maximum speed of the controller (the Curtis manual shows how to do this trick).
It would be possible to use this trick to automatically reduce speed if an over-rev, over-temp, or over-current condition arises, without complicating (making less reliable) the current simple pot-box. I may add this "feature" later.