Sorry this is so long. The TL;DR version is: I have two motors and a high-output battery pack that seems to be overwhelmed by what I'm doing with it, and I'm not sure the best way to fix it.
Long Version:
I have an Organic Transit Elf that I have modified. I swapped out the stock mid-drive motor with a XOFO DD45_STD motor (from Grin Tech.) and installed a Single Side All Axle motor on one of the front wheels. To support the extra load, I built a 14x4 battery pack of Molicell P42A cells and a Daly 120A BMS. The 21700 cells are rated for 45A continuous output, so I should have 180A of theoretical output, but I limit my output to 100A because that is plenty and I believe the batteries will have a longer service life if I don't drive them to their limits.
I use a Cycle Analyst connected to a Phaserunner to drive the front motor and a Baserunner to drive the rear motor.
(Why do I need so much juice? Well, it is a fairly heavy vehicle and I always travel with my 75 lb dog. And, my home and work are both on top of long hills without much of a bike lane.)
With 26" wheels, and both motors in the 9-10 rpm/V the 52-ish volts keeps me moving right along with traffic, most of the time. And, the output is high enough to handle the load of the hills I need to climb ... but ...
I have my BMS configured to fault-out if:
a) The sum voltage drops below 40V, or;
b) Any cell drops below 2.8V, or;
c) The difference between the lowest and highest cell is > 0.5V.
On a full charge, it performs great!
As soon as I get down to around 75% - 80% charge, it seems that pushing hard up a hill puts one of the cells below 2.8V and the voltage differential close to 1V. I believe this is because it is discharging too rapidly for the pack to balance, so the weakest cell takes a beating and the BMS shuts down before it can rebalance.
When I recharge, everything comes into balance, and ... here's the weird thing ... it isn't always the same cell that drops lowest. That would make sense - just a bad cell. But, it is a different cell everytime (or at least not always the same cell).
So, I have a few questions:
I'm betting that I can configure my Cycle Analyst and/or controllers to prevent this condition. Maybe I just need to limit the current to a lower number. My hill-climbing performance would suffer, but that may be the price I have to pay. Thoughts/advice?
Also, I'm not against replacing the battery entirely if I could find something that can handle that load. (Most use a 40A or 50A BMS, which wouldn't cut it.) Would probably need one custom-made. Like I said, I did this myself, but I suppose it is entirely possible that the quality control of the cells is inconsistent. If someone makes the pack for me, I am not responsible for rebuilding the pack if there is a bad cell - and that's appealing. Does anyone have a recommendation for a company that could sell me a suitable pack? (52V, 100+A output, around 16 Ah)
Is there something else I am not considering?
Any help/advice is greatly appreciated.
Long Version:
I have an Organic Transit Elf that I have modified. I swapped out the stock mid-drive motor with a XOFO DD45_STD motor (from Grin Tech.) and installed a Single Side All Axle motor on one of the front wheels. To support the extra load, I built a 14x4 battery pack of Molicell P42A cells and a Daly 120A BMS. The 21700 cells are rated for 45A continuous output, so I should have 180A of theoretical output, but I limit my output to 100A because that is plenty and I believe the batteries will have a longer service life if I don't drive them to their limits.
I use a Cycle Analyst connected to a Phaserunner to drive the front motor and a Baserunner to drive the rear motor.
(Why do I need so much juice? Well, it is a fairly heavy vehicle and I always travel with my 75 lb dog. And, my home and work are both on top of long hills without much of a bike lane.)
With 26" wheels, and both motors in the 9-10 rpm/V the 52-ish volts keeps me moving right along with traffic, most of the time. And, the output is high enough to handle the load of the hills I need to climb ... but ...
I have my BMS configured to fault-out if:
a) The sum voltage drops below 40V, or;
b) Any cell drops below 2.8V, or;
c) The difference between the lowest and highest cell is > 0.5V.
On a full charge, it performs great!
As soon as I get down to around 75% - 80% charge, it seems that pushing hard up a hill puts one of the cells below 2.8V and the voltage differential close to 1V. I believe this is because it is discharging too rapidly for the pack to balance, so the weakest cell takes a beating and the BMS shuts down before it can rebalance.
When I recharge, everything comes into balance, and ... here's the weird thing ... it isn't always the same cell that drops lowest. That would make sense - just a bad cell. But, it is a different cell everytime (or at least not always the same cell).
So, I have a few questions:
I'm betting that I can configure my Cycle Analyst and/or controllers to prevent this condition. Maybe I just need to limit the current to a lower number. My hill-climbing performance would suffer, but that may be the price I have to pay. Thoughts/advice?
Also, I'm not against replacing the battery entirely if I could find something that can handle that load. (Most use a 40A or 50A BMS, which wouldn't cut it.) Would probably need one custom-made. Like I said, I did this myself, but I suppose it is entirely possible that the quality control of the cells is inconsistent. If someone makes the pack for me, I am not responsible for rebuilding the pack if there is a bad cell - and that's appealing. Does anyone have a recommendation for a company that could sell me a suitable pack? (52V, 100+A output, around 16 Ah)
Is there something else I am not considering?
Any help/advice is greatly appreciated.