fossilfool
100 µW
- Joined
- May 15, 2020
- Messages
- 7
Hello,
Long time reader, first time poster. I come seeking a BMS recommendation for my Choprical Chopper and other projects. The chopper looked like this in its hay day. Now it's a charred but recoverable mess after a battery fire.
I have been using Hobby King LiPo "Multi Star 12000 mAH 8S 29.6V batteries with a 2C discharge rating. These were being sold cheaply by Hobby King a few years ago and I stocked up. I was aware that LiPo pouch batteries can catch fire while charging. I went through a process of trying 2 different safety methods: BMS and small voltage alarm.
The BMSs didn't work reliably!
I have 6 packs in my chopper in a series parallel arrangement: 3 series levels of 2 packs each. Within a pack of 2, what would happen is that one of the BMSs would shut off, causing the other pack in that pair to do twice the work. To my memory this happened repeatedly with packs that weren't out of balance. I would check with the voltmeter on the small connector periodically and after an incident like this. I stopped using BMSs.
The alarms went off way lower than what I deemed safe. Even though the alarm voltage was settable, I wasn't getting good results. I later found out that all the alarms (I bought one for each pack) were made wrong and cell 7 and 8 were measuring way wrong as confirmed by my voltmeter.
I stopped using the alarms.
I tried to ensure safety with frequent voltmeter checks. Then recently I made a mistake in following my own protocols and overcharged a weak pack and nearly caught fire to my shop! I was able to drag the bike outside but as as soon I did the fireball got too intense for me, so I yelled fire and got some backup from my employees. The powder fire extinguishers were not that effective. What really worked was a garden hose aiming steadily at the pack. Then when it was less energetic but still smoking I removed it from the bike with thick leather gloves and dunked it in a bucket. If this had happened on a weekend, I would have had to do it all by myself and I'm not sure I would have had the presence. So I'm very grateful that we put it out together, and that no one was hurt, that we didn't lose our building, and that the bike wasn't even all that damaged. What looked like a huge fireball was happening mostly above the bike, and there wasn't as much damage as I feared.
Now I plan to rebuild the Choprical Chopper and I plan to do other electric bike projects. The energy density of these LiPo packs, and the fact that I already have them, make me want to use them but certainly with a BMS, and hopefully with my custom fiberglass saddle designed differently so that I can remove the battery easily and charge it in the middle of an open space.
Experienced builders: I seek your advice. What BMS do you trust? This bike peaks out at 3000W so each pack is being asked to do 500W or 16A. As mentioned above they are rated at 2C which would mean up to 24A. So I am running the packs within their rating.
Thank you, Paul
Long time reader, first time poster. I come seeking a BMS recommendation for my Choprical Chopper and other projects. The chopper looked like this in its hay day. Now it's a charred but recoverable mess after a battery fire.
I have been using Hobby King LiPo "Multi Star 12000 mAH 8S 29.6V batteries with a 2C discharge rating. These were being sold cheaply by Hobby King a few years ago and I stocked up. I was aware that LiPo pouch batteries can catch fire while charging. I went through a process of trying 2 different safety methods: BMS and small voltage alarm.
The BMSs didn't work reliably!
I have 6 packs in my chopper in a series parallel arrangement: 3 series levels of 2 packs each. Within a pack of 2, what would happen is that one of the BMSs would shut off, causing the other pack in that pair to do twice the work. To my memory this happened repeatedly with packs that weren't out of balance. I would check with the voltmeter on the small connector periodically and after an incident like this. I stopped using BMSs.
The alarms went off way lower than what I deemed safe. Even though the alarm voltage was settable, I wasn't getting good results. I later found out that all the alarms (I bought one for each pack) were made wrong and cell 7 and 8 were measuring way wrong as confirmed by my voltmeter.
I stopped using the alarms.
I tried to ensure safety with frequent voltmeter checks. Then recently I made a mistake in following my own protocols and overcharged a weak pack and nearly caught fire to my shop! I was able to drag the bike outside but as as soon I did the fireball got too intense for me, so I yelled fire and got some backup from my employees. The powder fire extinguishers were not that effective. What really worked was a garden hose aiming steadily at the pack. Then when it was less energetic but still smoking I removed it from the bike with thick leather gloves and dunked it in a bucket. If this had happened on a weekend, I would have had to do it all by myself and I'm not sure I would have had the presence. So I'm very grateful that we put it out together, and that no one was hurt, that we didn't lose our building, and that the bike wasn't even all that damaged. What looked like a huge fireball was happening mostly above the bike, and there wasn't as much damage as I feared.
Now I plan to rebuild the Choprical Chopper and I plan to do other electric bike projects. The energy density of these LiPo packs, and the fact that I already have them, make me want to use them but certainly with a BMS, and hopefully with my custom fiberglass saddle designed differently so that I can remove the battery easily and charge it in the middle of an open space.
Experienced builders: I seek your advice. What BMS do you trust? This bike peaks out at 3000W so each pack is being asked to do 500W or 16A. As mentioned above they are rated at 2C which would mean up to 24A. So I am running the packs within their rating.
Thank you, Paul
