General Category > eBike Mods/Legalization
Is there a fix for the wimpy GM battery Battery Management System?
OCD:
Hi All:
After running the 48 volt 10 amp/hr GM battery pack through it's paces, I'm a bit disappointed to find that the BMS kicks out with the power of the 1000 watt MPIII. I was actually hoping to use these packs with controllers larger than 1000 watts. I have a V-power 20 amp pack that costs about $100 more than the 48v 10a GM one, but it obviously has a higher rated BMS as it doesn't cut out under the load of my 3000 watt controller. Has anyone found a 35-50amp BMS that would fit inside the GM case to replace the wimpy 25amp one? I can't see this battery being reliable at power levels over 500 watts. I'm not happy that I spent $1200 on two batteries that will not reliably supply the motors as sold by GM without running two in parallel which would effectively give me 20amp/hr with 50amp BMS (combined). There is no indication anywhere on any GM site that these batteries are not up to the task. I mean really, I'm sure it wouldn't kill the cells if there was a 35amp BMS in these from the factory. :o
(the other) Alan
Morgen 3Eman:
Hi, the other Alan
I'm kind of surprised at your experience, because when I had an analog ammeter on my trike I would routinely peg it hard and long at something over 60 Amps….(Lyen/MP3)
TTFN,
Dennis
Bikemad:
I discovered the same current limitation on my GM 48V10Ah LiFePo4 battery:
--- Quote from: Bikemad on October 21, 2014, 05:38:12 PM ---
The 10Ah LiFePO4 cells are rated for 30 Amps continuous and 50 Amps peak current, but I seem to recall that the BMS is limited to 30 Amps.
I have carried out a quick check using my modified MPII, and my new 48V 10Ah GM battery only delivers 31.21 Amps maximum @ 46V (1,433 Watts) yet my knackered 4.5 year old 14S 5Ah LiPo pack (without a BMS) is able to deliver 38.53 Amps maximum @ 42V (1,618 Watts). So I guess the BMS on the GM battery is holding back the current.
--- End quote ---
My MP4 usually draws a maximum of 30 Amps when using my LiPo pack with no BMS to restrict it.
If the GM battery can supply more than 30 Amps, it should not cut out unless the voltage of one of the cells falls below the lower voltage limit.
You could swap the existing BMS for a high current BMS like this:
BMS-LFP-PCM-SMT-System-16S-16x-3-2V-eBike-Battery-16x-3V/221172143478][/url][/acronym]
But if you are pulling more than 30 Amps continuous from the pack, I suspect the cells would start to suffer.
Alan
Morgen 3Eman:
So is my BMS faulty?
Dennis
OCD:
I know it's not just me, there is another GM 48 volt 10amp user not far from me complaining about the same thing. It's not hard to open the battery case and change a BMS (although a decent one likely won't fit the space inside) but that will of course void the warranty. The cells are rated at 50 amp max so you'd think a 30 amp BMS would have been fine to put in the first place. I don't have a cycle analyst to measure the actual current draw and realize this likely wouldn't happen with the MPIII if I were pedalling at the time, it mainly shows when I'm riding my drift trike or trying to use on a bike with a 1500 watt controller. I realize running two batteries in parallel would solve the problem but that adds more weight/cost than I wanted. Nice to know I'm not the only one experiencing this problem. I know I have a lead thumb...
(the other) Alan
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