Thursday, August 20, 2009

Back Component Box

Pictured above is the box in the trunk with three of the cars components in it. The charger on the right, and two DC to DC converters. None of it is wired up yet, or even bolted in for that matter. This is just a dry fit test. Though you can't see it, there's a cord that runs out of the back of the box on the charger's side. That runs to the fuel door on the passenger side of the car. One of those cables you see will be routed back to connect to that. The other cable will be connected to the batteries in the box that you can barely see at the very bottom of the picture.

Also on that side is a 2" tube ducted into the box to provide fresh air to the charger when it's operating. The charger has two fans in the back that vent air out the front into what will be the interior of the trunk. I need to make sure fresh air can get to those fans, and that stale air has a way out (that vent will be elsewhere). Once I've put some paint on the steel I cut to make room for that, I'll be ready to bolt it all into place.

The DC to DC converters will be wired in parallel and will put out the 12 volts needed for the car's normal electric systems, and about 80 amps continuous, 100 amps peak.

Wednesday, August 19, 2009

Battery Support Part V

This may be the last post were the focus is battery support. Today my friend Tim and I welded up what should be the last of the bracing to support the battery trays. With the choice of the newer lighter batteries, I'm confident that the bracing is more than up to the task.

Here you see the cross bracing we put together on the passenger side of the car. The other side is similar.

This is a shot of the new trays I built out of 14 gauge steel. All in all, it saved 15 lbs of weight swapping the heavier ones out. With the batteries being lighter than the lead acid I'd planned, I no longer need the trays themselves to be a structural support, they just need to hold the boxes in position. You'll notice that the box in the back is smaller than the tray. Well that's the one I mentioned I was going to have to have redone. You can see the size of the footprint the box will take up has grown a bit.

I'm leaving the heavier tray at the very front because the power steering pump will be suspended from that one. It's going to need the strength.

Last is a shot of all the boxes in place. I haven't secured the trays down to their moorings just yet; I'll be doing that tomorrow. There's only a few more mechanical items to sort out now; mounting the blower fan for the motor, the vacuum pump for the brakes and the compressor for the A/C system. The compressor is going to be a challenge. It may not be running when the car hits the road, but it will need to be working before next summer.

Friday, August 14, 2009

Odds & Ends Part V

Well, it's been a very busy week and today was the first chance I've had to work on the Z3. Let's tally up what I did, shall we?

1. Finished the mount for the box that's going in the trunk. It will fit through the hole I've cut and into the cavity that was occupied by the fuel tank. Luckily, there was a mounting bracket welded to the chassis in very nearly the perfect spot for use to support the box. I cut a piece of light steel to bolt to it, and the box will simply rest on it, kind of wedged into place. I'll clamp it down on the front edge, and that will prevent it from moving at all.

2. I also cut a 2 inch hole in the back of the box. I will connect some ducting to it and it will do one, possibly two things. It will provide fresh air to the fans of the charger while it is running, and it may also be the conduit for the AC power line to the charger. I might just drill a separate hole for that so there is nothing in the tube obstructing air flow.

3. I figured out how I'm going to mount the power steering pump. I had decided that I would simply suspend it from the front battery box making use of the room there. Today I cut and fitted all the steel needed to support it. Next up for that is simply weld the steel up and then drill out a few holes so that I can mount it in place, easily removing it if necessary.

4. One of the biggest pieces of news this week is I've opted to scrap the idea of lead acid batteries in favor of Sky Energy LiFePo4 batteries. I'd come across a fabulous series of videos put together by a gentleman by the name of Jack Rickard, in which he talks about how best to treat LiFePo4 batteries. All fascinating stuff, but what really caught my attention was the price he mentioned that he paid for the batteries. When I started looking into the project a year and a half ago, a similar pack of Thunder Sky's would have run me over $20,000. Well they've come down substantially, making them much more economically viable. Jack was kind enough to answer some of my questions, and encourage me along. If you care to check out his project, you can see it here. First rate stuff!

The Sky Energy's will weigh in at 475 lbs, versus the 737 lbs that the lead acid I had intended to use would have weighed. In addition, if handled properly, they are rated to handle 3000 charge/discharge cycles. That amounts to approximately 150,000 miles, or for all practical purposes, the life of the car.

5. To that end, I need to redesign one of the battery boxes and the tray that holds it to accommodate the different shape of the batteries. Fortunately, there is no need to adjust any of the bracing that we'd welded up over the past few weeks. However, I will be able to reduce the weight of two of the trays used to hold the battery boxes. The two trays weigh in at about 32 lbs, and I should be able to drop that to about 10. Today I took all the necessary measurements and began cutting up the new lighter steel to hold it all.

That's all for now. Hopefully next week, I'll have more time for the project.

Wednesday, August 5, 2009

Battery Support Part IV

I know what you're saying, "Enough with the steel, and the welding and support and what not!" Well, I feel your pain. Trust me when I say that I'd much rather move on to sexier things, but I have a few remaining things to do to try and make the supports as road ready as I can.

Today I spent several hours cutting, fitting and shaping some steel tubing for cross bracing on the existing mounts we've already welded into place. Once they are welded to the existing supports, they should offer the extra bracing needed to support the batteries in the event of hard stops or accelerations.

I also spent some time cleaning up the hole I cut in the trunk's bulkhead yesterday. Took a lot of careful measurements and then went down and ordered the plastic box that's going to fit in the cavity. That should take a week to build. In the mean time I need to cut some more steel to support and hold that box in place. Ideally, I'd like to build yet another frame to mount in the area the fuel tank was in, to hold the accessory battery. I'm thinking I'm going to use an Optima battery for that because I can mount it anyway I want, even upside down!

Tuesday, August 4, 2009

More Cutting in the Trunk

Today was spent cutting out the bulk head in back of the trunk, that separated the trunk from the fuel tank area. Here's what it looked like before:

And after:

I have a bit grinding to do to get the opening nice and even, but that won't take too long. I'm going to have a plastic box built, just like the battery boxes, to fit in that space. I built another mock up out of cardboard to make sure it all fits.

This new box won't hold batteries (not enough room). Instead I'll be mounting the charger and the DC to DC converters. After giving it lots of thought, I decided to go with two DC to DC converters. Each one can put out about 40 amps at 12 Volts DC. The power steering pump alone can pull up to 75, so clearly one just wouldn't be enough.

I had thought that I'd put in an auxiliary 12 battery to handle the extra load, but realized the battery alone wouldn't be a good plan. Instead I'm going with two converters AND the battery. It just keeps getting more complicated. But that's ok, I'm trying to build this so that I have as few compromises as possible.

By the way, thanks to my good friend Len in Malta for the great suggestion of using the back of the trunk and fuel tank cavity in such a productive way. Hope you're well Len!