Lexan BMI pack

[mcstar]

I've posted some pictures of my custom assembled BMI pack cased in lexan for those interested. It includes the BMI VMS and a Ping charger inside the lexan. I've got two main connections, 48V output and a 120V input for the charger. It mounts on my bike's rear rack.
It's on photosyth, so if you're not familiar with that, this will be doubly interesting. Just hit the play button or click around to see more camera angles...
http://photosynth.net/view.aspx?cid=F3E45F5F-5578-4A51-9217-A0C66831049E

 

[pwbset]

It's on photosyth

Only works on Windows... man I hate that. Maybe just post one photo here?

 

[mcstar]

Ouch! I wasn't aware of that either. Here are a few of the pictures.





This box is not water proof, but it does add considerable protection to the batteries. With it I expect to get maximum life from the pack even in the harsh e-bike environment.

BTW, can anyone explain how to show pitures in the post? I've tryed the attachment and the img tags without success. Thanks.

 

[Ypedal]

Before you "submit" a reply, look further down for a " Browse " button, find the file and then hit submit ! :wink:

Nice box, i'm a bit worried about the charger tho.. if it gets nearly as hot as some of the units i got from many places.. it really needs open air !!

 

[karma]

nice box i had the same charger working in a air Conditioned room and it still fried, i would leave the charger out.

its nice to see another lexan case only takes about a hour with a good table saw

 

[mcstar]

i had the same charger working in a air Conditioned room and it still fried, i would leave the charger out.

Thanks for the warning on the charger. The charger was not my first choice, but I was going for small and reasonaly low cost. It seems like noone really understands the e-bike market. I've found chargers that are much larger and more expensive, but who want's to cart that around with them on a bike? I do have vents on the exhaust side and so far it's been OK. The area around it gets warm to the touch, so I'll keep an eye on it. It's got about 20 recharge cycles in the box so far so. I built the box to make it easy to remove the pack and charge at work. It charges on my desk in front of me.

 

[tropmonky]

Nice, if heat gets to be a problem maybe a vent fan can be put in that only runs when charging or something like that.

Nice box!

Kyle

 

[powerdog69]

Hi guys
Can someone tell me where you get bmi batteries from?

cheers

 

[Ypedal]

BMI, Lifebatt, envirosafe, Yesa even uses them aparently, all come from PSI.

Mcstar, what is the thickness of the lexan you used ?

 

[mcstar]

I'm using 3/8" lexan. It's very strong. I'd recommend you use a drill press though to make the holes. I used a hand held drill and they didn't all come out very straight. I also lost a couple of drill bits too. The really small bits tend to stick and break off if you let them stop moving while in the lexan. I think that when it's moving the material stays hot and melted, but as soon as you stop to reverse the drill bit, it tends to freeze in place and break the drill bit off. I learned to keep the bit moving forward and just pull it back out without stopping.

I got the 48V pack from the BMI distributor in Australia. His name is Armin and he's just great to work with. He's very informative and always answers emails. I even got updates when he was travelling! Let me know if you want his contact info via PM. Just keep in mind, these are high current and very high quality cells. The terminals are metal bolts that you can actually work with and reconfigure to your heart's desire. I reconfigured my pack from a cube into the rectangle you saw in the pictures with ease. Each of the BMI cells can deliver bursts of 200amps of current I've seen the test results by Sandia Labs and they have been shown to give their full capacity through more than 30amps of continuous draw. My experience confirms this too. In the Sandia tests, they were cycled more than 5000 times and are still good with most of their capacity. Even with all these advantages, I calcuated the cost of these cells amoratized over the number of recharges to be about $.20/charge vs a cost of about $.38/charge for the foil pack LIFEPO4s. SLA's are even higher ($100 /200cycles = $.50/cycle) This is why I decided to go with these BMI LIFEPO4 cells. I figure my cost over time will be even less than either the foil type packs or the SLAs. Still, you'll pay quite a bit more up front, so you need to determine how serious you are about riding your bike for the next 5-10 years before jumping in. However, there are a ton of other applications that these batteries are great matches for. For instance; boat trolling motors, electric cars, hybrid pack conversions and car start batteries all need high current, lot's of recharges and long life.

 

[pwbset]

However, there are a ton of other applications that these batteries are great matches for.

That's why I like tool pack batts for ebikes because in the winter or bad weather at least I can still get some work done in the garage.

If you don't mind me asking could you tell us what you paid for your setup? Thanks.

 

[mcstar]

Oooo, good question. At this point I've got about $1000 in the pack. It does seem like a high price, but it was an upgrade for me from the foil pack type of LIFEPO4. I used the foil pack for about 1000miles before I started having problems with the foil tabs breaking off. I repaired my foil pack a few times but it was become a real PITA tearing the pack down every couple weeks to fix more torn foil tabs. Those tabs are just tiny, and very hard to work with. They don't take solder very well and leave you frustrated. Frankly, the roads I use the bike on are very rough and I hit some bumps that can be bone jarring. At the speeds I was travelling it just beat the ping pack I had to death. I know my situation was pretty extreme though. I'm sure many people are fine on the foil packs.

These BMI batteries are currently pretty pricey if you look at just the sticker price. However, if you consider they are tested to last over 5000 recharges and offer a very solid construction with bolt terminals and tremendous current capacity, then in the end they offer the best value for us e-bike hypermilers. I plan to run them at least 5-7years (maybe considerably more), so they will end up at much lower cost per use than the alternatives. I've already go about 500 miles on them. So, I figured the investmen was well worth it. I'll save around $40,000 over the expected life of these batteris compared to the gasoline I would use, so what's a $1000? That's really what I was looking for originally with LIFEPO4 was a way to save money over time. I built the case to really protect the batteries from any abuse and make them last as long as possible, but I'm sure I'll never have the foil tab issue with this pack. So far this pack is the best I ever had. I'm very satisfied with it and the price I paid for it.