Archive for January, 2011

Here’s a video of a walk around I did describing some of the car’s elements. I fumbled on “contactor” :)

Download – Plug Bug – Walk around.m4v 65 MB or you tube.

http://www.youtube.com/watch?v=-kpw42cXKEk

Here’s an old video tour of my paint booth when I painted the bug earlier last year:

http://www.youtube.com/watch?v=Ko3zn4Lw44E

I have a lot more details later, but here it is!

Download the .m4v: Plug Bug First Drive.m4v

You tube direct link: http://www.youtube.com/watch?v=lBJYqB81qx4

You tube embedded:

There needs to be a way to connect one 3.2v Thundersky battery to another to form the battery pack. I’ll have a total of 48 cells in two separate packs. Apparently some batteries come with interconnects, and others don’t. Evolve Electrics sells them separate for $4.50 each. Multiply it by 42 (the last two don’t need a connection as it will be connected via 2/0 wire) and you get $189. In addition, they may not be quite the right size that I needed, as I was planning on a crazy configuration. So, I was going to have to make some of them anyways, and decided to just make them all and save some bucks.

I found the volt 914 project that did a cool job on making them here. Thanks Ross for posting that information! Ross used 7 layers of 0.020” copper to make his interconnects. I also talked to Travis (who also made an EV bug) and he also went with the layered approach and used 5 layers of 24 gauge sheet (~.026 thickness). People use layers with a slight kink in the middle to allow them to stretch out when the batteries (possibly) swell up.

So, how thick do I need?

The cross sectional diameter of 2/0 wire is 0.03648”. Times pi that is ~0.115 in^2 (I’m not sure how Ross got 0.105 in^2 — maybe it was a typo). I like the idea of using 24 gauge copper to make the bars — but I might use 6 layers since: 0.026” (thickness) * 6 (layers) * 0.j75” (width) = 0.117 in^2 — definitely bigger than 2/0 wire. Or, I could use 1” wide and 5 layers, which might be easier (I think it would have been).

Or, I could just use solid copper bar stock and avoid cutting out a bunch of small pieces. I liked that idea the best, even though it might be “extra rigid”. The fear of using solid bar stock is that the cells will swell a bit and might tear apart if the bus bars don’t have some give in them. However, people use solid aluminum bus bars and don’t seem to have a problem with tearing the cells apart (as far as I can tell), and swelling is only a problem if you don’t compress your cells good enough, or abuse them by running them past their constraints. I hope to not do that, so I’m using solid stock. I also think my cells are quite well contained. If they do end up moving then I’ll have to readdress this.

I bought some 1/8″ by 1″ metal copper bar stock from onlinemetals.com. Two 96″ pieces and one 48″ piece for $114 (including shipping).

I also had to buy hardware — I stupidly thought these came with the cells, but instead they come with the bus bars. I bought the following from Bolt Depot:

Product #4815
Metric lock washers, Stainless A-2 (18-8), 8mm
Quantity: 1 box of 100
Price: $5.81
Subtotal: $5.81

Product #4778
Metric hex nuts, Stainless A-2 (18-8), 8mm x 1.25
Quantity: 1 box of 100
Price: $9.85
Subtotal: $9.85

Product #5024
Socket head screws, Alloy steel, 1/4-20 x 1/2
Quantity: 1 box of 100
Price: $5.89
Subtotal: $5.89

Product #5027
Socket head screws, Alloy steel, 1/4-20 x 1
Quantity: 1 box of 100
Price: $8.00
Subtotal: $8.00

Product #8749
Metric socket set screw cup point, Stainless A-2 (18-8), 8mm x 1.25 x 30mm
Quantity: 1 box of 100
Price: $30.19
Subtotal: $30.19

Another $76. So, it would have been cheaper to just buy the bus bars in the first place. Live and learn! I think my solid copper bars will conduct better than what the Thundersky ones do.

corbin

I’ve been working hard on the car, but progress has been slow. I was missing some BMS boards — I should have counted them 6 months ago! So, I had Justin and Evolve overnight them to me so I could work on the car last weekend. I was hoping to get it running and charged, but it takes quite a while to do all the wiring. The Elithion Lithiumate BMS is quite complex, and it has been fun learning it. So far, the BMS has been the trickiest part of the car to put together, and I’m not quite done with it. While installing it, I discovered two cell boards aren’t working. I don’t want to have to pay another arm for shipping, so I’ll just have to wait for the replacement boards to arrive. Hopefully by this weekend!

The charger (Manzanita Micro PFC30) is mounted on two angle iron pieces that are mounted to the car chassis in the front trunk:

Notice the clear lexan cover on top of the batteries.

Rear pack with hold down strap. It’s breaking point would be past 7g’s (based on the weight of the batteries). Each group of cells is strapped together with the end plates:

BMS installation work in the front. I’m using solid bus bars, which might be controversial in the EV world. Ideally, bus bars that have some sort of play should be used in case the cells swell. I’m opting to not do that, as I have seen other installs that use solid aluminum bars and seem to be fine. I’m also not planning on abusing the cells, so they shouldn’t swell.

Tonight I spent about 3 hours running wires from the front to the back of the car.

I hope to get the BMS all interconnected by Friday night, and hopefully the replacement boards will arrive and I can charge it!

The lexan cover: I went with something a little too flimsy — I think it is 3/16″, but I need to double check. I wish I would have gone 1/4″, or larger, and I might replace it. Unfortunately, lexan (polycarbonate sheet) is hell of expensive. Here’s the rear sheet before I uncovered it:

It sits on little acrylic column posts with a hole drilled in the middle. A bolt is then put in, and the top of the battery box is tapped to hold it down:

The posts were cut with the horizontal metal band saw and then drilled on the lathe. A cleanup pass on the end was done to bring them all to the equal height. I did a few, but Aaron was over last weekend and made a bunch for me (thanks man!)

Other completed things: the pack is all wired, with High Voltage wires running from the front to the rear of the car. The reside inside the car, on the passenger side. To avoid signal noise and interferance, all low voltage wires are on the driver’s side.

Despite the batteries not being charged, I couldn’t resist putting the car up on blocks and hitting the throttle a little — it came alive! I discovered I had the DC-DC converter always wired “on”, and had to get another relay so it would only be on when the key was flipped on. Some people have it always on, but I prefer turning it off to avoid it draining the high voltage pack.

How about just some pictures?