Cells out of balance

[BG bicycle]

I started with a 2amp charger and a budget priced 16 amp BMS. Then moved to that hereinafter pictured BMS, the seller claimed it to be water proof and capable of 60 amp input/output.

I know now what damage fast charging does when your BMS, cannot handle the requisite draw down of higher voltage cells. Overall the battery appears fines until each cell is checked.

Cell 1 cannot it’s appears charge beyond 3.8 volts, Cell 2 was worse at 3.5 volts although has improved to 3.54 amps this upon additional charge. All other cells exception cell 8 are above 4 volts.

The BMS, is warm to touch, therefore does continue to draw down higher voltage cells.

What have Pedelecs members done to bring their battery back into a balanced state.

Also, require a better higher quality BMS, one more suitable to a fast charge. Any suggestions?

The cells are LG MH1.

 

[Nealh]

For BMS I use AnnPower products from Aliexpress circa $20, no issues and batteries are kept balanced during charge and after discharge.
https://annpower.aliexpress.com/store/group/BMS/623665_250784538.html?spm=2114.10010108.100008.1.47fa3347mrdcdZ

Best to charge at low a rate for better cell longevity though most good bms should cope with 5a charge.
Your 4v+ cells may be preventing the bms switching on to allow charging.
Either charge low cells manually up to higher voltages or discharge high cells down to lowest.

 

[Nealh]

For charging individual cells I manually use a 5v phone charger with the jack plug cut off and monitor the cell voltage with meter via the bms pins every 15-20 mins until voltage level is reached, then evry few mins as voltage gets near target voltage.
On each wire end I solder on a short pin or tin the 10-15mm of the wire.
Disconnect the sensing multiplug and on the cell side carefully (no shorting) attach one pin to the low cell pin out and the other to the cell pin out before, also attach meter to keep an eye on the voltage or manually check voltage charge every now and then. Then switch on charger power.

Easier to charge a couple of low cells then discharge a lot of higher cells.

 

[Nealh]

For bms no need to go for continuous 50/60a ones, if you read the bms specs carefully they will often have a min/ normal/ max over discharge rating as well. In most cases for ebikes a 20 - 30a continuous bms will suffice unless you are going for hot rodding and high amp discharge batteries.

 

[BG bicycle]

At the moment the pack is one and would require a bit of work to dismantle.

I accept there could be a problem with an individual cell.

Also these LG MH 1 cells are probably not up to the level of amp output necessary. I was pushing the pack. 30-40kmh with several journies requirement of two fast charges the total distance rode on those days 100km+. And add to that the hot weather.

One reason to fast charge when are away from home the shortest time spent at a charging point is optimum. Find cafes majority are very welcome to Ebikes.

The problem appears to be the speed of discharge when a cell is voltage high. Hence, was wondering if a better BMS, could be found.

I was frequent charging at 8 amp that brought the battery to 97% capacity within less than one halve hour. Prefer a 10 or 12 amp charger if could find a cell that could withstand that charge current.

 

[Nealh]

Even the top cells won't like a 10/12a charge rate all you are doing is killing the cells. You need to more modest and limit charging to 4/5a max.

Your issue is both charging and discharging, to high charge rate and a totally mismatched bms discharge (60a) rating for the cells. You need a bms with a more realistic 20/25a continuous discharge.

 

[BG bicycle]

The controller on average draws 200-400watts this is read from the Sw900 LCD display.

Does top 900 watts however, that situation is either when I’m heavy on the throttle, or on a short hill climb.

The controller via the LCD Sw 900, set to draw a maximum of 11 amps.

Just checked the cells direct -bypassed the balance leads- with a volt meter and cell two is at 3.51 volts.

I’ve a 13p battery with a 16 c type breaker.

 

[BG bicycle]

Even the top cells won't like a 10/12a charge rate all you are doing is killing the cells. You need to more modest and limit charging to 4/5a max.

Maximum charge I never viewed to be that straightforward. Panasonic cells 3c at 3400ma, or any quality 3c cell are surely rated for a large current inflow. And how short be a short life?

I was expectation least a year of use given the 8 amp charger cuts off at 40.50 volts. Add to that I charge with the 8amp charger somedays more than once at 97% battery capacity.

I knew was pushing these LG MH 1s in terms of discharge and charge. However, on a 13p battery wasn’t that large enough to cope? Appears the answer is at this moment no.

 

[DouglasXK]

Waterproof? And single charge/discarge? The claim that it’s waterproof must surely have made you suspicious? The AnnPower are as good as any and are only charge, discarge and battery connection (3 wire, yours appears 2 wire). This type is far more reliable as I’m sure Nealh would agree.

 

[Nealh]

If you are using 13p then no problems if the main battery leads have 3 or 4 contact points along the Paralleled buss bar to spread the load.
13P is a big battery and more liable for a buss bar bad connection, low voltage could be down to a poor connection on any parallel group.

Just noticed you are only charging to 40.5v then that is your likely problem/ cause of unbalance. Some bms have single cell balance like the AnnPower, others just use top cell balance and once the first cell reaches max voltage charging shuts off leaving other parallel groups sitting at whatever charge they hold.
Top cell balance in reality works if all cells accept equal charge and voltage at the same time but in reality we know this doesn't happen esp with basic bms functions, the safe way with cheap bms is single cell balance that allow individual cell charge and pack cell balancing.
All cheap bms will only balance the whole pack above 41.5v - 41.8v if they incorporate single cell balance.
If you want to use a lower charge value then you will have to get a smart programmable bms like the Neptune or make sure you try and charge your battery every 3 or 4 times to 42v.

 

[Nealh]

To now balance your pack you have to get to the bms and manually charge the low cells as I have mentioned so that they are all fairly equal voltage wise, discharge the pack some and then charge fully to 42v to see if it balances out ok.
Under charging cause more issues then it solves without a smart bms that is Bluetooth programmable or uses a programming cable.

 

[BG bicycle]

Thanks Nealth, that is exactly the solution a programmable BMS. Yes, the lower voltage on the 8 amp charger will confuse a standard BMS.

I’ve also a battery bloc ordered. http://www.batteryblocs.com/
Awaits the VAT and customs documents and obligatory fees before collection. This should help in the future as it’s easy to then remove individual cells.

Just returned from a 40km+ ride of the battery carried for 35km. 20kmh most of the way except hills of was a few. Final got some serious exercise

The Sw900 did display a full battery although the BMS, was cutting the power until final shutdown to the pint the LCD, screen no longer were activated.

That’s the battery now knackered will have to dismantle the thing. Least I achieved 2400km+

Will check out that brand Neptune BMS. Thanks again.

 

[BG bicycle]

Waterproof? And single charge/discarge? The claim that it’s waterproof must surely have made you suspicious? The AnnPower are as good as any and are only charge, discarge and battery connection (3 wire, yours appears 2 wire). This type is far more reliable as I’m sure Nealh would agree.

The company that manufacturers those BMS have a video with their product underwater. Apparently it’s part of the QC and testing procedure.

Been out on a few rides during monsoon weather, buckets of water falling from the sky. Once the battery did get wet and the wind that day I were forced to take shelter under some trees. That is the closest to any replication said video.

 

[BG bicycle]

Question. Anyone bled a pack on a cell by cell basis using a power resistor or 10 watt led?

Bought a smart BMS, however, will need to wait least two weeks for its arrival.

I’ve a 0-60 volt 10 watt led lamp on the bicycle and seen some usb power resistors 1-2 amp. Either of these could drain down each high cell.

Just wondered if anyone had tried this method?

 

[peter.c]

I used 3x 12 volt car headlamp bulbs connected in series to drain a pack

 

[awol]

Bought a smart BMS, however, will need to wait least two weeks for its arrival.

Which did you go for? I use the Speedict Neptune15 with 10s and it's really good. I am considering a second one for 12s but fancy finding a BMS programmable by usb to try. Anyone know of any?

 

[Nealh]

BMSBattery have Smart bms from $20 - $60 on top of that for $99 is a usb programmer that connects to them.
No much info otherwise on if they can programme as well as the Speedict Neptune.

 

[BG bicycle]

I used 3x 12 volt car headlamp bulbs connected in series to drain a pack

I don’t want to drain the pack just specific cells. Rather pull down all the high cells and attempt a balance charge from there.

I’m concerned cell two maybe a problem within as it’s not improved it’s capacity, actual now down to 3.44 volts. While the other two low cells have at least increased in voltage.


I didn’t purchase that Neptune, BMS. This BMS, is more modular https://www.aliexpress.com/item/10S-36V-Lithium-Battery-Smart-Protection-Board-Balance-Lipo-Li-ion-BMS-20A-30A-40A-60A/32870597593.html?spm=2114.search0104.3.64.3d8a3052QjXD0v&ws_ab_test=searchweb0_0,searchweb201602_4_10152_10151_10065_10068_10344_10342_10343_10340_10341_5723217_10696_10084_10083_10618_10304_10307_10820_10821_10302_10059_100031_10103_10624_10623_10622_10621_10620,searchweb201603_13,ppcSwitch_5&algo_expid=7d7145d1-6c5e-48d4-88fb-a5f44e566f1f-10&algo_pvid=7d7145d1-6c5e-48d4-88fb-a5f44e566f1f&priceBeautifyAB=0

That BMS, is the junior of a larger unit. Possibly the most serious BMS, ever seen.

I also found lithium-ion equalisers those appear very useful although for when I build that 70Ah battery. That one I’ll split into two and therefore an ability to series wire to 72 volts nominal.

 

[BG bicycle]

I’ve the option of purchase cell equaliser system, wait until the smart BMS, arrived, or connect some 12 volt lamps in parallel and drain two cells at a time.

Latter idea cost about a couple of quid and the wholesaler was very welcome to sell old stock halogen lamps.

I would prefer one cell at a time however, this will work unless cell 2 & 1 suffer from another issue.

Works a treat, although a nigh-time check in-order want this pack up and running again asap.



And yes, the pack is soldered together and I could do better 1) Some of roads around here are 4x4 territory, although very few these days 2) Only interested in a year’s operational functionality.

 

[BG bicycle]

Well, two in parallel 12 volt lamps worked a treat pulled the pack down to within 5 volts of the lowest cell.

2 amp charger and pack brought every cell up to 4.19-4.2 volts except cell two of since dropped 15 volts overnight.

I disconnected the BMS, this morning and if cell two voltage does remain stable that then does suggest a BMS, issue. Will then change the BMS, got a spare and try again.

Disclaimer. Lithium-ion battery has the potential to start a serious fire, cause serious injury, Times that one battery by 130 or 10s 13p. Do not attempt to follow my practical without self responsibility of the hazards and risks associated with any lithium-ion cell or battery pack. When in doubt seek professional assistance at all times.