Saturday, January 31, 2009

Front battery racks

I was going to post all of the battery rack and battery installation in one post but there is a lot involved and it's taking longer than I thought so figured I'd break it up some.

After reading through the Thundersky documentation I found on their website it said if you want to remove a cell from a group to discharge all the cells of the group first. Turns out these cells will expand and become ruined if they are used. It was hard to read the directly translated documents but it also sounded like you were fine if you recompressed the cells before use.

SinceI knew I needed groups of cells other than the five they came in I didn't hookup and start charging the cells immediately as I've noticed others doing because I didn't have a good way to discharge them again in a timely fashion.

I built a quick and simple cell compressor more for storing the od cells while I was waiting to build a new group. So for example I needed a group of seven which left three cells sitting around. I didn't know exactly how many cells I would need in each group and designed as I went (I'm bad at planning really far ahead).

Here is a new group of the seven cells. I got some huge zip ties and a tool to tension them. I noticed this actually is providing better tension than the stock setup. The stock setup is loose enough that the cells can still shift a little which allows them to get out of alignment. This method keeps the cells very snug. Below is also the first base frame for the group.

Another shot of the frame as I progressed. The batteries will sit on top of the motor mount and be allowed to move slightly with it.

The rack placed on top of the motor mount frame.

Here is a near completed battery rack holding three groups of seven cells above the motor. All three racks, especially the center are angled forward to account for the slope of the hood. There are very tight clearances all around between the sides and hood.

Just another shot from the front.

Here is the rack all painted. You'll notice I added some feet on the sides near the back. These, including the length of the rubber feet rivoted on, are 1/4" inches longer than the rest of the feet. This allows for all this weight to be evenly displaced downward on the engine mounts instead of only towards the center.

I can't remember the names of these things but they are basically a really long nut. They may be called couplers which is what they do. They are used throughout the racks with the threaded shafts to provide adjustable points for securing the cells as you'll see later.

Here is the rack bolted in place on the motor mount frame. Again notice those feet I mentioned earlier on the outsides of the motor mounts applying most of the weight to the outside and avoiding sag and strain.

Here are the 21 cells in place for a test fit. All looks good.
A final shot with the support bars securing the cells.

Now there is some room up front where the radiator use to be. Technically this isn't the best place for batteries. In case of an accident they are not as well protected and can be ruined during a front in collision. Of course so can the batteries over the motor if the crash is bad enough. Either way I don't have the room to pick and choose the locations so they are going in here.

After doing some measuring I determined I can squeeze nine cells in here. I changed my mind a couple times but then finally decided on the best way to secure the frame as well see in a second.

This rack needed to built in two pieces and bolted together to allow it to fit into the confined space and get to the mounted points.
Here is the front cross member which convienently had two bolt holes where the original engine stop was. This was the rubber bumper used to stop the engine from dropping too far down when you discount the tranny. I'll be using it as one of the main mounting points.

Here is a shot of the frame in place. I had to also drill holes in the side frame (unfortunately no other available holes).

Here are those side holes that were drilled. You can see these beems with the front bumper removed.

The finished assembly.

I installed the finished assembly. Things were so tight I couldn't help but scrapping a little of the paint. I hate that!

I wanted to add this picture since I forgot to mention it earlier. The white plastic sheet seen here was also used on the first three groups of cells to protect from anything that may come up from the road. The plastic is what is called wonder wall. It was thin, very hard and yet could bend without breaking. It was very lightweight and cheap so seemed worth trying out. When I get things rolling I plan to come back and build a lightweight shell around the batteries with this material. We'll see how that works out later.

One final shot with the 30 cells in the front of the car. This leaves another 15 to fit into the trunk.

Computer Revision 1

While I was waiting for my batteries I also finished up the first computer revision. I plan on making a more advanced version but figured I'd do a basic setup which will give just what I need to get things rolling and then later, with the car mobile, I can test and prototype to see exactly what I want.

I figured the basics I needed were to monitor the RPM signal from the motor and relay this to the tach gauge and EPS system. I also wanted to make sure I could watch the temperature of the motor and controller. I can also added an output port so I could optionally install a small LCD screen to show this information although I haven't used it yet (just using a connected laptop currently). This version uses a BASIC Stamp microprocessor. I'm using an ADC0831 to convert the signals from the LM34 temperature sensors to a digital output. This sensors will output 10 millivolt per 1 degree F. The only other IC on the board is a 5v voltage regulator.

Below is a picture of the basic circuit board after it was etched. I've done chemical etching myself but for something critical like this I wanted it done professionally. I used ExpressPCB for the job. They offer free software to download which is very easy to use. It's not very advanced compared to other PCB software but will do basic jobs like this. After you design your board you can click an option to compute the cost of the board. There are a few options. You can get everything from prototyping to full production work. Below is the prototyping board. I think it cost $50 or so and you get three boards in case you mess up something while soldering. The prototyping version requires the exact board size shown below. I think it was 2.5" x 3.2" or close to that. It goes up in price considerably for full silkscreening and solder masks for surface mounting. After I placed the order, completely through the software, I received the boards in the mail within 3 days.

I guess I didn't need the flash here. This is just a loose fitting of the components. Yep it all fits.

Here is a shot of the board with all the components and IC sockets soldered in.

Added the BASIC stamp chip and ADC IC.

Here is a project box I picked up at radio shack. Turns out it's just a little too deep to fit where my original ECM was and I need to replace it later. For now the access panel is still off and I'm going to live with that way under the car is rolling and I have time to go back and clean things up.

Here is the finished box. You can see the serial port I added so I can update the software and tweak anything later. There is an external LED to show power and an external fuse for protection.

The computer is in the car and working as expected. That's it for the computer until revision 2.

Tuesday, January 20, 2009

Who killed the electric car?

I've heard about a movie called, "Who killed the electric car?", but never watched it till recently. This is extremely eye opening. I had no idea we could have had MANY EV vehicles on the street already. I just figured there were always good technological reasons for the cars never making full production runs. This movie really gets into the details of how auto makers, oil companies and I'm sure some money under the table with political figures have been working towards killing the electric car. You'll be amazed at what GM has done!

It can be found here on YouTube. It's broken up into ten parts so make sure to watch them in the correct order it could be rather confusing. You can also purchase this video off the Internet.

Watch it, you'll be amazed.

Friday, January 16, 2009

Batteries arrive

After a very long wait (6-7 weeks) the order of lithium batteries, charger and BMS have finally arrived! I actually ended up picking up the shipment from the freight distribution point closest to me instead of waiting another couple days to schedule the delivery with them.

As I've mentioned before I ordered everything through Elite Power Solutions. You really don't know what to expect when dealing with people online and especially for this kind of money but everything went smoothly and they are legit.

Below is a picture of the crated delivery. Five boxes total. Three boxes contain 15 cells each, one for the charger and another for the BMS system.

Here you can the first box opened. I didn't know what I was going to get really other than lithium cells. They came pre-bound with nice aluminum end plates and handles to carry them. It's very important these cells stay bound while there is any charge on them. So for example if you need to exchange a single cell for some reason the entire block that is bound together must be drained completely first. I didn't know this until reading the instruction manual. I didn't get this with the order but found the info on the Thunder-Sky website.

Here is just a picture of everything received in the order. You can see charger isn't small.

I measured and added the post dimensions for these cells. Again these are the 160Ah cells so I doubt they are the same for other cell sizes but I'm not sure. This info will be helpful if you are making a per cell battery balancing system. The BMS only monitors the and reports information about the cells. The only active BMS piece to it is shutting down the charger when the highest cell reaches a set voltage. I will be charging to 3.8v max. This means the cells can become out of balance which will reduce the overall power you can get from the pack safely.

Here is the best shot I could get showing a side and front angle of the aluminum end caps that came with the cells. You may need to, as I do, use longer or shorter groups of cells than five. I need to find some similar straps that are longer but will reuse the end caps.

Here is a box of all the connector bars, bolts and locking washing to put your cells in series. These also came with the cells. The wires you see there are actually part of the charger. There are two connectors which you must wire into the outlet style you want (one for 120v and one for 240v). I was expecting only 240V so this is nice I will now add two separate plug types on the car so I can recharge anywhere (120V plugs are much more common here). Using 120V will double the time it takes to charge, but it's better than not charging.

Here is the charger. Elite has a variety of options here. I picked the 200V max, 24 amp max charger. You can dial in the voltage and amps you'd like to charge at. This makes this charger very versatile for different pack configurations and charge stations. So if perhaps you are sharing an outlet with some other amp sucking EV you can dial down the amp draw and avoid a tripped breaker. The back, which I forget to show, has a DB9 connector for the BMS interface and the two power connectors.

Here is the BMS. Damn there are a lot of wires and connectors in this box. I'll go into more detail on the pieces here and the others as I install them to show which connections go where. I'm also currently waiting on the English instruction version for the BMS. I don't read Chinese sadly.
That's it for now until I get time to start building the battery racks and get this all installed. Hopefully soon!