mcstar
100 W
We've been getting a flood of questions and interest in the BMI battery packs lately. It's difficult to cover everything in individual emails, so I'm starting this thread as a repository of the tips tricks and answers to the many questions we see over and over again. To get things started, there are three distributors of the BMI batteries around the world. There's Armin in Australia who serves all the English speaking countries in that part of the world. Then there is the Taiwan manufacture which serves the Asian market. Finally, I'm in the US serving the Americas. Things have been getting pretty busy lately as everyone's gearing up for the summer riding season. There also seem to be a lot of independent people working on EV upgrades and conversion. We plan to keep the factory very busy this year! The following is from an email thread about some of the experiences I've personally had with the BMI HPS-4810 pack.
The weather is just starting to become ride able around here, so my head’s getting back into the EV game. There’s so much going on right now it’s a lot to keep up with. I agree with you about needing to send a cell to Dr. Bass to be tested. In fact, I had one sitting here on my desk for several weeks waiting for me to find the time to get the shipping setup and send it out. My wife finally helped me out on that one. The package went out today. I got home and found out Andy Hecker even offered to purchase one for just the same purpose! So, in a week or so, we can all stop waiting and start seeing the numbers. I haven’t located Dr.Bass’ email address yet, so if someone can forward this to him, please let him know it’s on the way. Expect it in a week or so. It’s a fresh original grey cell with a black label.
I can tell you from personal experience, the BMI cells just keep going and deliver their rated capacity recharge after recharge. I’ve got an HPS-4810 pack on my e-bike. The pack’s got more than 200 cycles now and has gone almost 3000 miles since I installed it last year. Today I rode it in to work from home (13.9miles) then I charged it at work for 3.5 hours with a 2amp Chinese charger. The red light had just turned to green (no time for the balancing cycle) when I unplugged it from the wall and started riding. I rode it over 20 miles mostly into to the wind. It delivered .45KW during that cycle according to my watts up meter, and the terminal voltage was about 50V with no load. Under a load of 20 Amps it was sagging to about 46V at that point. The motor still felt strong and could climb hills well. I stopped when the meter read 9.6AH because I was tired and at my destination, not because the battery was done. The HPS pack’s BMS alarm still wasn’t going off, so I obviously don’t have any weak cells. Owning this pack has been a joy. In fact, I think my motor is going to need service before the pack does (it starting whining under load up some long hills today).
I’ve included pictures of the pack to answer the question about whether the HPS packs use the terminals to support the cells. The answer is definitely not. There are plastic supports that the cell body fits into to that support the weight. This is just like the lego brick concept. I’ve also thought about writing a document to describe the proper way to support the cells in a custom enclosure. Here’s an abbreviated version…
Chapter one : Don’t use the terminals to support the weight of the cell. Only the cell body is designed for this.
Chapter two : Only use non-conductive materials to support the cell body since the body is made of aluminum and if shorted to either another cell or either terminal, will cause the cell to discharge.
Chapter three : the nut on the terminals of the cell should not be removed or used to hold the wires or bus on since this nut is there to hold the plastic seals in place. Remove it and the cells will leak.
Chapter three : The terminal nut (another nut added to hold the terminal on) should be put in place AFTER you put a split washer on, and the nut should be tightened to 6in-lbs (not foot-lbs) or until the split washer is squashed flat. That’s all the tightening need. More pressure cause undue stress and can break the terminal.
In case you’re wondering why my HPS pack doesn’t look like the other ones from the factory. I took the original pack and modified it to fit my e-bike layout better. Basically, I opened the pack and reorganized it so the two sections are laid out in a rectangular shape instead of a cube.
The original side panels didn’t fit this arrangement, so I built a custom enclosure out of lexan. I made the back part a little larger than the rest (not visible in the pictures) and was able to include the charger. The whole pack is removable from my bike allowing me to take it in to my office and leave the bike outside. The pack mounts on the back rack which is the only suboptimal part. I couldn’t think of a convenient way to split it into two parts to put in saddle bags that were also easily portable.
I do appreciate all the interest in the BMI products. I’d like to address more questions, and will add more information write more later.
