I've been doing some experiments too. I found out that if you keep the cells at the 3.7v they arrive at, they last forever.
Charging pack to 41V experiment
- Thread starter WheezyRider
- Start date
All very interesting. So might there be a fairly safe regime using a programmable charger to limit the cut off to whatever voles, with an ordinary battery. There was a comment that BMS only needed after 100 charges. So play safe and do BMS one in 20 or something. It would extend the life by some amount.
It seems to be the case that if you have a good quality pack, you could get away with a balance charge once every 100 cycles. To be safe it's probably best to do a balance charge once a month.
Some BMS units have a Bluetooth connected app which allows you to look at all the individual bank voltages without opening up the pack. Definitely worth considering if you are building your own pack.
Depends whether you could get any useful output from your experiment.
The point is it's about the compromise between useful capacity and battery life. 40.5V max charging may be a bit low in terms of useful capacity. 41V seems to give both a decent capacity and a reasonable life. The amount of capacity between 42V and 41V is negligible, yet charging to 42V seems to have a significant effect in reducing the life of the battery.
The whole idea is fraught with risks and full of ifs and buts and probability, plus it's a load of hassle to organise and monitor.
As I said before, unless you're a very high mileage rider, just charging normally, your battery will last for years, by which time there will be better ones. Batteries have been improving by about 10% per year, so in 3 or 4 years time, you'll be at a 30% to 40% disadvantage compared with a new one. When I built my bike 6 years ago, I had 11.6Ah. Now I have 17.5Ah for more or less the same weight.
As I said before, unless you're a very high mileage rider, just charging normally, your battery will last for years, by which time there will be better ones. Batteries have been improving by about 10% per year, so in 3 or 4 years time, you'll be at a 30% to 40% disadvantage compared with a new one. When I built my bike 6 years ago, I had 11.6Ah. Now I have 17.5Ah for more or less the same weight.
Yes, I agree, at the moment, for most people, it's not worth the hassle.
However, if you are technically minded, have a pack which costs more than the motor and controller combined, if you can, doesn't it make sense to try and extend it's life where possible?
We live in a throwaway society and it can't carry on forever.
The world is full already of electronic waste. The extraction of the lithium is energy and water intensive and causes environmental and social issues in its extraction. There are also lots of unpleasant/strategic chemicals in lithium cells that have to be manufactured, creating further issues with waste products and then ultimate disposal. Most lithium cells are still not recycled.
Furthermore, from these kind of experiments, it becomes likely that more intelligent chargers will be manufactured to prolong the life of battery packs by charging to <42V most of the time and then occasionally doing a balance charge. For instance, if you had a Bluetooth BMS, it could transmit to the charger whether a balance charge was needed or not. Then it would all be automatic and hassle free.
The simple answer would be for all future generic BMS to be programmed so they balance at 4.1v per cell group to extend the life of the cells/battery. The throw away world can't go on for ever with resources being used up.
My 29E's batteries both 6 years old and only 3 or 4 digits difference between serial numbers behave the same at 41v max charge. No deterioration in mileage use or an shenanigan's in use, I simply adjust/set the San's voltage pot to the voltage required and they charge up nicely. All I do is check the battery charge voltage when the green light appears and monitor mileage usage, the longer I eke them out for my local usage then the more user friendly they are for the planet. In the bigger pics of things not going to make much difference but I'm doing my little bit for the world.
My 29E's batteries both 6 years old and only 3 or 4 digits difference between serial numbers behave the same at 41v max charge. No deterioration in mileage use or an shenanigan's in use, I simply adjust/set the San's voltage pot to the voltage required and they charge up nicely. All I do is check the battery charge voltage when the green light appears and monitor mileage usage, the longer I eke them out for my local usage then the more user friendly they are for the planet. In the bigger pics of things not going to make much difference but I'm doing my little bit for the world.
Up to 50 cycles now. Still nothing to report, other than all banks within 0.1V charged, 0.005V discharged to 3.68V.
Should hit 60 cycles tomorrow, at 59 at the moment.
After 56 cycles I measured the pack on a Fluke bench top multimeter, with 4 decimal places, as ordinary cheap multimeters are not that accurate and I wanted to be sure I was getting reliable data.
Discharged to 37.079V:
Bank no. ) Voltage
1) 3.7097
2) 3.7090
3) 3.7092
4) 3.7076
5) 3.7075
6) 3.7110
7) 3.7114
8) 3.7100
9) 3.7107
10) 3.7080
Biggest variation 3.9mV
Charged to 41.034V:
Bank no. ) Voltage
1) 4.1025
2) 4.1004
3) 4.0990
4) 4.0999
5) 4.1003
6) 4.1114
7) 4.1042
8) 4.1056
9) 4.1029
10) 4.1088
Biggest variation 12.4 mV
After 56 cycles I measured the pack on a Fluke bench top multimeter, with 4 decimal places, as ordinary cheap multimeters are not that accurate and I wanted to be sure I was getting reliable data.
Discharged to 37.079V:
Bank no. ) Voltage
1) 3.7097
2) 3.7090
3) 3.7092
4) 3.7076
5) 3.7075
6) 3.7110
7) 3.7114
8) 3.7100
9) 3.7107
10) 3.7080
Biggest variation 3.9mV
Charged to 41.034V:
Bank no. ) Voltage
1) 4.1025
2) 4.1004
3) 4.0990
4) 4.0999
5) 4.1003
6) 4.1114
7) 4.1042
8) 4.1056
9) 4.1029
10) 4.1088
Biggest variation 12.4 mV
As promised, went through 60 cycles today.
Put the pack on the Fluke bench top multimeter again and had another look:
Discharged to 37.363V:
Bank no. ) Voltage
1) 3.7356
2) 3.7356
3) 3.7351
4) 3.7345
5) 3.7341
6) 3.7398
7) 3.7380
8) 3.7389
9) 3.7383
10) 3.7375
Biggest variation 5.7mV
Charged to 40.913V:
Bank no. ) Voltage
1) 4.0901
2) 4.0883
3) 4.0870
4) 4.0880
5) 4.0882
6) 4.0992
7) 4.0919
8) 4.0936
9) 4.0909
10) 4.0966
Biggest variation 12.2 mV
So still no significant difference.
For comparison, I had a look back through my logbook and I found I did actually put the pack on the Fluke back in August, after only 9 cycles of 41V charging:
Charged to 40.984V:
Bank no. ) Voltage
1) 4.0981
2) 4.0949
3) 4.0940
4) 4.0937
5) 4.0955
6) 4.1067
7) 4.0989
8) 4.0996
9) 4.0997
10) 4.1031
Biggest variation 13 mV
So no significant difference from 9 to 60 cycles.
Put the pack on the Fluke bench top multimeter again and had another look:
Discharged to 37.363V:
Bank no. ) Voltage
1) 3.7356
2) 3.7356
3) 3.7351
4) 3.7345
5) 3.7341
6) 3.7398
7) 3.7380
8) 3.7389
9) 3.7383
10) 3.7375
Biggest variation 5.7mV
Charged to 40.913V:
Bank no. ) Voltage
1) 4.0901
2) 4.0883
3) 4.0870
4) 4.0880
5) 4.0882
6) 4.0992
7) 4.0919
8) 4.0936
9) 4.0909
10) 4.0966
Biggest variation 12.2 mV
So still no significant difference.
For comparison, I had a look back through my logbook and I found I did actually put the pack on the Fluke back in August, after only 9 cycles of 41V charging:
Charged to 40.984V:
Bank no. ) Voltage
1) 4.0981
2) 4.0949
3) 4.0940
4) 4.0937
5) 4.0955
6) 4.1067
7) 4.0989
8) 4.0996
9) 4.0997
10) 4.1031
Biggest variation 13 mV
So no significant difference from 9 to 60 cycles.
Good work WR, I don't bother recording with my 29e's as I have no extra sense wires on the exterior to measure off. Though am not seeing any major reduction in voltage sag or range so cell groups are appearing to to be maintaining good relative balance.
Passed 71 cycles today.
Put the pack on the Fluke bench top multimeter again and had another look:
Discharged to 36.963V:
Bank no. ) Voltage
1) 3.6963
2) 3.6956
3) 3.6957
4) 3.6945
5) 3.6946
6) 3.6983
7) 3.6981
8) 3.6980
9) 3.6978
10) 3.6959
Biggest variation 3.8 mV
Charged to 41.041V:
Bank no. ) Voltage
1) 4.1029
2) 4.1008
3) 4.0995
4) 4.1006
5) 4.1009
6) 4.1121
7) 4.1048
8) 4.1063
9) 4.1034
10) 4.1094
Biggest variation 12.6 mV
So still no significant difference.
Put the pack on the Fluke bench top multimeter again and had another look:
Discharged to 36.963V:
Bank no. ) Voltage
1) 3.6963
2) 3.6956
3) 3.6957
4) 3.6945
5) 3.6946
6) 3.6983
7) 3.6981
8) 3.6980
9) 3.6978
10) 3.6959
Biggest variation 3.8 mV
Charged to 41.041V:
Bank no. ) Voltage
1) 4.1029
2) 4.1008
3) 4.0995
4) 4.1006
5) 4.1009
6) 4.1121
7) 4.1048
8) 4.1063
9) 4.1034
10) 4.1094
Biggest variation 12.6 mV
So still no significant difference.
After a break following Christmas and then an accident on the ice in January, I've started riding again this week and collecting data.
82 cycles now. After charging:
Charged to 41.013V:
Bank no. ) Voltage
1) 4.1013
2) 4.0998
3) 4.0982
4) 4.0967
5) 4.0982
6) 4.1092
7) 4.1018
8) 4.1038
9) 4.1007
10) 4.1067
Biggest variation 12.5 mV
Still no significant change...
82 cycles now. After charging:
Charged to 41.013V:
Bank no. ) Voltage
1) 4.1013
2) 4.0998
3) 4.0982
4) 4.0967
5) 4.0982
6) 4.1092
7) 4.1018
8) 4.1038
9) 4.1007
10) 4.1067
Biggest variation 12.5 mV
Still no significant change...
Today the pack finally passed the 100 Cycle mark!
Charged to 41.001V:
Bank no. ) Voltage
1) 4.0986
2) 4.0972
3) 4.0955
4) 4.0972
5) 4.0966
6) 4.1079
7) 4.1006
8) 4.1027
9) 4.0995
10) 4.1055
Biggest variation 12.4 mV
So 100 cycles, charging to 41V and no significant change in balance.
Bank 3 seems to be consistently the lowest voltage after charging and bank 6 the highest. However, bank 3 seems to maintain voltage better than some other banks when discharged, although these changes are tiny really.
Either this is an example of a well behaved pack, or the BMS is still balancing, even though it is only being charged to 41V and the balance feature is not supposed to activate until 4.18V is reached.
Charged to 41.001V:
Bank no. ) Voltage
1) 4.0986
2) 4.0972
3) 4.0955
4) 4.0972
5) 4.0966
6) 4.1079
7) 4.1006
8) 4.1027
9) 4.0995
10) 4.1055
Biggest variation 12.4 mV
So 100 cycles, charging to 41V and no significant change in balance.
Bank 3 seems to be consistently the lowest voltage after charging and bank 6 the highest. However, bank 3 seems to maintain voltage better than some other banks when discharged, although these changes are tiny really.
Either this is an example of a well behaved pack, or the BMS is still balancing, even though it is only being charged to 41V and the balance feature is not supposed to activate until 4.18V is reached.
However, even if the BMS is balancing at 41V, it's still a win, as without this experiment, I wouldn't know that it was.
I have another identical BMS and at some point I'll rig it up with some cells that are out of balance, charge at 41V and see what happens.
So after a year I finally got the pack back after lending it to someone with a charger set to 41V. It looks a little worse for wear now as it was attached with cable ties and gaffer tape to their bike! But it is still functioning fine.
It's been 3 years now of charging to 41V and hundreds of cycles.
In terms of the state of balance:
Pack voltage 40.882 V
Bank no. ) Voltage
1) 4.0856
2) 4.0872
3) 4.0830
4) 4.0883
5) 4.0835
6) 4.0957
7) 4.0872
8) 4.0920
9) 4.0861
10) 4.0939
So even after 3 years, the biggest variation between cells is still only 12.7 mV.
It's been 3 years now of charging to 41V and hundreds of cycles.
In terms of the state of balance:
Pack voltage 40.882 V
Bank no. ) Voltage
1) 4.0856
2) 4.0872
3) 4.0830
4) 4.0883
5) 4.0835
6) 4.0957
7) 4.0872
8) 4.0920
9) 4.0861
10) 4.0939
So even after 3 years, the biggest variation between cells is still only 12.7 mV.