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Battery Box Work III
The fun continues with the battery boxes. I completed the rubber insulation and installing the custom silicon heating pads in all the boxes. I found because the size of the batteries were bigger than what I had planned for that the thickness of the rubber insulation had to be adjusted on all the boxes. Unfortunately I could not adjust the size of the front box so only 17 batteries will be going in that box. It was planned for 18. That is not a huge loss in overall battery capacity and actually could not have been avoided, even if I had planned on batteries that were thicker. That front battery box fits between the two front fenders so the width is fixed. Now that all the boxes are finished they can be installed in the car and as batteries are bottom balanced they can be installed in the boxes. I still don't have a solution for mounting the trunk box. I was thinking I would like it to have it on some type of roller so it could be rolled out for maintenance.
I also did some testing of the silicon heating pads to see how much heat they would produce, inside the battery box, with batteries sitting on the pad. I used a 120V 250W pad that I had purchased just for this testing. The result of the testing is that the pad will generate at least 30 degrees C heating. That should be enough to thaw out cold batteries, if that is ever needed. I don't plan on leaving the car out in the cold and then try to charge it. Usually what I do now with my Leaf is drive it into the garage and immediately attach the charging cable.
Still no spline adapter from EV West but I did get some other parts from them. I got another large contactor box, some fuses and fuse holders and a maintenance switch. I got the Gigavac switch that is hermetically sealed. That will be used in the engine compartment. I plan to have another disconnect switch inside the passenger compartment. That will go between the rear seat battery boxes.
A video of the battery box prepartion can be seen here. There is a short section in this video that was repeated from my last video, because that vidoe was not shown on EVTV.
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More Battery Box Work
I finished painting all the battery boxes with the bed liner material. I had to touch up some of the sides of the rear seat boxes. Once all the painting was done I could start on the next phase of battery box preparation - the lining of the insides of the box with rubber sheeting. This is done to provide both a thermal as well as a electrical insulator layer. The material I chose was a Buna-n rubber, medium strength, 1/4" thick. The rubber comes in different hardness, I chose the 60A which is medium hard. That seemed like the best compromise for stiffness and elasticity. It is available in 12" wide sheets in many lengths, which is perfect because all my battery boxes are 12" tall. The material can be found from many sources, I bought some from both McMaster Carr and Ebay. The price on Ebay was 20 to 30% less than McMaster Carr, but there is a limited selection that had an adhesive back. I am not sure how important that is, except for assembly purposes (it is possible to apply your own adhesive). The battery boxes were designed to use this 1/4" rubber sheeting. I first installed the rubber sheets in one of the rear seat boxes. The material can be cut with a box cutter, but it is not easy - pretty tough material. After I got the material on both of the long sides I decided to test the fit of the batteries. Until now I could not do that measurement. I could slide two batteries side-by-side very tightly in the middle of the box but, unfortunately, I found I could not slide two batteries at either end. It looked like there was only as small offset that was preventing them from being inserted (less than a 1/16"!). Probably the box has a very small dimension variation at the corners because of the fabrication technique. This is one of the problems with battery boxes. The batteries have a fixed size, so if the box is too small the batteries cannot be inserted. Also the thickness on the rubber sheet can vary +/- 0.031". Fortunately with the rubber sheeting there is an easy solution. The material is available in 3/16" thickness. I ordered one sheet to test it out and it worked! Batteries can be inserted at both ends of the box. The still are very tight, but that is what is desired. Another part of the battery box preparation is to install a silicon heating pad in the bottom of all the boxes. The heating pad is designed to heat the batteries when their temperature drops below 0C because they will not take a charge at that temperature. The pad does not get very hot and is just designed to warm the batteries. I found a Chinese Ebay vendor that offers custom size heating pads. They not only can customize the pad size, but also the wattage and voltage of the pad. I chose 400W and 400V because I plan to power the pads with the battery pack voltage. This seemed the most simple electrical solution, with the wattage of the pads they will only draw an amp of current. I plan to use 22AGW wire so the wire will act as a fuse if there is a short. I also plan to have a high voltage 5A fuse in circuit as a failsafe. Each of the pads will have a thermistor - I don't plan to control the temperature but rather just have a upper limit for control. All the pads will be wired in parallel so they see the same voltage. The pads will sit on some of the rubber sheet material on the bottom of the box. This is done to prevent the heat from the pad being conducted away by the battery box. With all the sides of my boxes being insulated there is no reason to heat the box. The heating will be directly into the battery cases.
Other work on the interior of the car has progressed. I was able to remove all the underlayment material and install new underlayment. The next step is to install the new carpeting. That should happen soon, but first I need to finish running all the wiring to the engine compartment. Now I have heaters in all the boxes there are another 4 cables to run. I also want to get the rear seat boxes fully installed before the carpeting goes in.
No news on the Siemens spline adapter from EV West. Should arrive any day.
video of all this fun can be found here.
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Interior Blues and Painting Fun
In the last video before EVCCON I showed a new carpet that I received for the interior of the 320i. I finally got around to ripping out the old carpeting. From the first day I got the car over a year ago it always had a musty smell to the interior. I assumed that was due to its age but when I was routing battery cables and had to pull up part of the carpeting and I found the padding underneath was wet. I assumed the carpet was moldy so I ordered the new carpeting. The old carpet was really in good shape, in fact I am sure it was replaced at least once and it had no worn spots on it. It took a lot of work to get the old carpet out, the e-brake handle had to be removed, the whole console removed and gas pedal. The carpet was also glued in some places so it hard to removed. Once I got the carpet out I found that the carpet was not really that moldy, but all the padding on both the driver and passenger sides was totally soaked. That really is amazing since the car has been in the garage since last January and at least in the winter the garage is very dry. What is interesting is the padding was not the typical jute padding usually used with carpeting but rather an urethane foam padding. From the shape of the it definitely was OEM, because it was cut to fit the floorboards and the holes for the gear shift and e-brake. The padding really was not that moldy either. Underneath the padding was what looked like a thermal insulation underlayment. That was also totally soaked and when I tried to remove it , the layer just fell apart. And what a terrible smell! I guess the fibers used for the insulation must have rotted and that is what was producing the smell in the car. The other fun part of this insulation is that it was really well glued to the floor board. I had to use a paint scraper to scrape it off and for parts that would not scrape I used paint thinner to dissolve the glue. The amazing part of all this is that the metal under all this wet crap was not even slightly rusted. A tribute to the BMW undercoating. I found on a website for company called TP Tools that they make a similar insulation underlayment so I ordered enough for the all the floorboards. I also had received insulation and padding with the new carpet. Comparing the old carpet to the new one shows there are a lot of holes to cut in the new carpet. I am sure that the old carpet was OEM because the holes were all die cut, at least for the gear shift and e-brake. It is going to be quite a task to get all those holes cut in the correct places.
Other work I have been doing is getting the battery boxes prepared to use. The fabrication was just the beginning. All the boxes need to be painted. I am also installing rubber sheeting on the inside of the boxes for thermal and electrical isolation. The best "paint" used by EVTV is this material used for lining pick-up truck beds. It is very durable and is black. To use the bed-liner material the boxes have to be primed with a special primer that etches the aluminum for a stronger bond. Fortunately I have a lot of experience painting and all the tools so it was not too difficult to get all the boxes primed with the special primer. The bed liner material is like undercoating material. The kit I bought came with a spray gun that screwed right to the bottle of material. The kit came with 4 quart bottles that have to be mixed individually with a catalyst material. That is good and bad. Good because the material does not have very long pot time once it is mixed. But if you have a big job you have to stop and mix another bottle. I only had to use two bottles to coat all three of the boxes. The fourth box, the one that goes in the engine compartment I decided to paint the color of the car. That way it will blend in. The car came with some touch-up paint when I bought it. The touch-up paint was premixed and in spray cans. Unfortunately the cans did not spray well. I got enough paint on the box so it look painted, but I ordered some more touch up paint that I could shoot with a real spray gun. I also might coat the lid with some clear coat to give it the same luster as the car paint.
And lastly I removed the Siemens motor once again. This time it was to remove the Rebirth spline adapter so I could send it to EV West. They have a solution for the Siemens spline and will be sending that to me shortly.
A video of all this fun can be found here.
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EVCCON 2014
I attended the fourth annual Electric Vehicle Conversion Conference that was held in Cape Girardeau MO. Earlier this year I had planned on taking my BMW 320i to the 2014 EVCCON. Unfortunately it just took too much time and it could not be completed in time. The conference was last week, from August 11 - 17th. This was the third year for me. It was great to see all my EV enthusiast friends that I have met in previous years. Part of the conference is a car show and many of the cars from last year were there along with a few new notable ones. I really look forward to getting my car there next year. Another part of the conference is that there are presentations by people on various subjects about EVs. I presented a talk on the Battery Monitoring System or BMS that I have developed with the Sendyne module. I have shown this design in earlier videos, but his is the first public presentation I have made on the subject.
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Battery Boxes Received
I received the aluminum battery boxes I had fabricated by New Hampshire Precision Metal Fabricators in Londonderry, NH, who are about 20 miles from my house. They did a fantastic job on the fit and finish of the boxes. There is one box for the front of the car, two for the rear seat area and one for the trunk. They had given me one of the rear seat boxes before it was welded to check the size of the holes I had cut in the rear seat deck. Those boxes were 1/4" wider than I had originally modeled. The reason for the discrepancy is that I plan to line the inside of the boxes with neoprene rubber sheeting for both electrical and thermal isolation. Here in the northland you need to worry more about keeping the batteries warm than cool. I did not catch outside dimension had grown because of the sheeting on the inside of the box. My friend that did the CAD drawings forgot to inform me of that change also. However, the increased size of the box was not a big deal. I just cut more metal out of the rear seat deck. The only tough spot was the back right corner. The box just fits before a support rail. On the one side the weld at the bottom of the rail was too big to get the box in so I had to use a cut-off saw to cut away part of the weld. That was almost the 1/8" that kills battery box designs. The second rear seat box only took about 30 min to get the hole cut to the correct size, because I had the first one to measure from. Another issue with a battery box was with the box for the front of the engine compartment. Brackets were designed to attach the box on the inside of the area where the radiator once resided. I has assumed the radiator was in the center of the engine compartment but after I got the box I found the area was not in the center. It is displaced by over two inches to the left, looking out from the engine compartment. So one bracket fit because it was 1 inch outside, but the other one did not because the 1 inch overlap interfered with the rest of the metal around the radiator area. I had to have the bracket removed and a new one welded in the correct place. Fortunately NHPMF did that rework for no charge.
I also did some more battery discharging using another grid tie power inverter. I got a second one on Ebay for very little money. It is 1200W which is half the wattage of the first one I got that had failed. It can only can be used up to 50V input, but that is good for smaller groups of batteries. The inverter work without any issue and I discharged the rest of the battery pack. Now I have to build the bottom balancing systems. I have a design that uses a MOSFET to vary the load on the battery, so that the battery voltage can be precisely tuned.
A video of the battery boxes can be found here.