low batter voltage cutoff.
- Thread starter tony40150
- Start date
Note under high-current loads, voltage sags below the LVC setpoint, then starts to recover soon as that heavy load stops.
What communications options are available with that BMS?
If none, would it be difficult to swap it out for an adjustable BT one?
What communications options are available with that BMS?
If none, would it be difficult to swap it out for an adjustable BT one?
After I pedal home after the motor quits, (it is a Bafang BBS HD) it doesn't have a clutch so when one pedals the motor is rotating at a pretty high rate because the double reduction is now a double step up, it is painful pedalling uphill!
I digress, the voltage check is after I have returned home and checked with a voltmeter.
I digress, the voltage check is after I have returned home and checked with a voltmeter.
So it may very well have hit 39.2V on the road, then by the time you measure, recovers to 48.1V.
If that is the case, your pack may be composed of crap quality cells, or very worn, have you used it over 100 cycles?
An Ah totalizing meter is a very useful diagnostic tool, cheap one will do if you don't want to invest in a CA.
If that is the case, your pack may be composed of crap quality cells, or very worn, have you used it over 100 cycles?
An Ah totalizing meter is a very useful diagnostic tool, cheap one will do if you don't want to invest in a CA.
The BBSHD has a clutch so pedaling should not be turning the motor. You may have a bad clutch. But pedaling a heavy bike sucks anyway.
There could also be one cell that's lower than the others so the BMS trips at a higher pack voltage. Balancing the pack might help.
There could also be one cell that's lower than the others so the BMS trips at a higher pack voltage. Balancing the pack might help.
It's also possible the BBSHD's own LVC is set too high, and cutting off early?
dustNbone
10 kW
If it's the BBSHDs LVC it shouldn't turn the system off, it will just stop the motor. The display will stay on.
Oh I forgot to mention that the screen just goes blank. I have checked the programme in the BBS HD it is set to 41v low V. I have a 48V battery I use on my Tong Sheng powered bike, the screen shows when the battery gets close to the cutoff by showing 1 bar and flashing, I have used this battery on the BBS HD powered bike, it also shows when it gets into a low voltage situation. Oh also I have cycled this battery about 30 times at the most.
thundercamel
10 kW
Get a voltmeter so you can watch battery voltage in realtime as you bike, if you can. This will help to understand what's going on.
999zip999
100 TW
It may be a low parallel set of cells or more. Do you run battery to cut off lvc ? You can check the state of charge by finding out each group of parallel cells voltage and write down on paper like this.
1. 3.85v
2. 3.99v
3. 4.00v
14. Xxx volt
Plus check voltage of charger ???
Write it down
1. 3.85v
2. 3.99v
3. 4.00v
14. Xxx volt
Plus check voltage of charger ???
Write it down
I’d still say most likely there is one cell group that is weaker than the rest and causing it to cut off early. Unfortunately you have to take apart the pack to measure the individual cell groups.
Most BMS don't really balance until the voltage reaches 58.8v. Possibly your charger output is too low to make it balance. Try measuring the pack voltage just before the charger kicks off. You can measure on the controller wires.
Also, balancing the cells takes a long time, like days. You might try leaving the pack on the charger for a few days and see if there is any improvement. Most chargers will just shut off when the pack reaches the charger voltage, so no further balancing will happen. It may take repeated shallow discharge and full recharge cycles to get anywhere.
Also, balancing the cells takes a long time, like days. You might try leaving the pack on the charger for a few days and see if there is any improvement. Most chargers will just shut off when the pack reaches the charger voltage, so no further balancing will happen. It may take repeated shallow discharge and full recharge cycles to get anywhere.
999zip999
100 TW
The bms should drain the high cell(s) then charger turns back on and try to fill up the low cells. Then when high cells bleed down charger should return on. If not you can unhook charger and let bms drain cells after 3-4 hours plug back in. What battery do you have a link ? All batteries are made different.
hemo
100 W
Just my penneth worth, don't froget this is 14s not 13s.
39.2v is too low and is 2.8v per cell group, 48.1v is more sensible and 3.43v per cell group. The bms or controller cuts out when lvc is hit and at 48v or so is likely down to voltage sag.
39.2v is too low and is 2.8v per cell group, 48.1v is more sensible and 3.43v per cell group. The bms or controller cuts out when lvc is hit and at 48v or so is likely down to voltage sag.
999zip999
100 TW
As a rule do you run the battery down to a cuts out yes no
14S is nominally 51V, charge 57-58V, realistic cutoff should be 49V, maybe 45V at very high C-rates if you don't care about longevity.
13S is nominally 47V, charge 53-54V, realistic cutoff should be 45V, maybe 42V at very high C-rates if you don't care about longevity.
When crappy cells are used, and / or the pack starts to wear out, voltage sag means range is greatly reduced, compared to better / newer quality cells.
If your protective circuits let the voltage drop lower than the above, the pack will wear out **much** faster.
The way to get longer range **and** decent longevity is to pay extra for good quality cells known more for capacity and longevity rather than low cost, and/or go to larger Ah capacities.
13S is nominally 47V, charge 53-54V, realistic cutoff should be 45V, maybe 42V at very high C-rates if you don't care about longevity.
When crappy cells are used, and / or the pack starts to wear out, voltage sag means range is greatly reduced, compared to better / newer quality cells.
If your protective circuits let the voltage drop lower than the above, the pack will wear out **much** faster.
The way to get longer range **and** decent longevity is to pay extra for good quality cells known more for capacity and longevity rather than low cost, and/or go to larger Ah capacities.
That would be foolishly low for 14S, kill longevity without increasing range much at all.
Keep in mind the **battery** protection LVC should never kick in.
Your controller / CA or human judgment should be stopping long before it gets to that point.
Keep in mind the **battery** protection LVC should never kick in.
Your controller / CA or human judgment should be stopping long before it gets to that point.
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