further investigation of battery cutting out before set LVC

[minexplorer]

Hi further to a previous post. Ive now opened the 14s5p 52v battery (11mths old)and checked the voltages of the groups of cells .battery was fully charged ,left on charger for 12hrs.
4.2
4.2
4.1
4.0
4.0
4.0
4.1
4.2
4.2
4.2
4.0
4.1
4.2
4.2
To recap the LVC was 41v ,it would run to that.used to charge to 58.8v .now cuts out at 45v ,max charge 58.2v and only goes to 20miles of moderate power (PAS1 &2 very little wot,Carls special sauce).previously could get 25-27miles of that.

Much thanks to previous replys but im still stuck for an answer and solution .Electron cycles wearnt much help.just saying one parallel may be out of balance and saying the charger isnt sensitive enough to correct that. Id said ,no matter how long the battery is left on the charger, it never turns on and off ever or puts any further charge in. no sign of balancing going on basically. And regardless of whether the battery is switched on or off during this either.

Do these readings give any indication of whats wrong?

i dont see how pulling only 6amps at the end can cause a 52v battery with 30Q cells to sag .Yet it will still cut out permanently at 45v even at this low load.

Appreciate if anyone can shed more light this is really doing my head in.once i could do a dozen miles easy at constant 30amps 30+mph (not all in one straight go) and still another 7-10 at low power. doubt it wld do half that full power now.regards Minexplorer

 

[vfr400]

There's always a possibility of non-genuine 30Q cells, otherwise, it's just worn out. You'd need to put it under a load test to confirm that, which means running it at about 10 amps while the case is open so that you can measure actual cell voltages, especially at the point of cut-off.

It's moderately out of balance, which can be an indication that the cells aren't genuine or are worn out.

 

[minexplorer]

There's always a possibility of non-genuine 30Q cells, otherwise, it's just worn out. You'd need to put it under a load test to confirm that, which means running it at about 10 amps while the case is open so that you can measure actual cell voltages, especially at the point of cut-off.

It's moderately out of balance, which can be an indication that the cells aren't genuine or are worn out.

thanks vfr ,that doesnt sound easy ,how on earth do i put it under load tho whilst performing fiddly testing with a meter,i can see a recipe for disaster in the making. It was from a reputable uk vendor..Electroncycles. They say enough on their site about genuine 30Q, GA cells only used in their batteries. I only bought it 11months ago.about 1700 miles of use.

Do i go to the seller and start throwing accusations at them? Surely it cant be worn out after 11 months use ? The warrenty was 6mths,is there anything i can do ,it cost me a small fortune £449?

 

[Sturmey]

Hi. I spent a good bit of time investigating a similar problem with a 36v battery. I used a parallel element (5.5 ohm) from a 9 kw electric shower as a dummy load. The cells were similarly out of balance. I observed the following.
1. On charge, the high cells go to 4.25 volts and this stops the BMS from charging of the whole battery at about 40.7 volts.
2. On discharge with dummy load, the BMS shuts off the battery at 32.7 volts, because one of the low cells has dropped below 2.7 volts.
3.The usable capacity of the battery was about 63% of its nominal capacity.
4. I balanced up the battery mainly by draining down the high cells using various appropriate dummy load. (takes time)
5. I retested the battery and it worked ok, returning almost all of its full capacity. The battery is now giving good service.
6. The BMS fitted in the battery has no balance facility.
7. When I repacked the battery, I left it in such a way as I can recheck and re balance without having to unwrap. I have rechecked once after 3 months and about 30 discharge cycles and battery was only slightly out. (I done a small re-balance)

PS. When reading and testing cell voltages, you need to go to a third decimal place e.g 4.17v

 

[vfr400]

thanks vfr ,that doesnt sound easy ,how on earth do i put it under load tho whilst performing fiddly testing with a meter,i can see a recipe for disaster in the making. It was from a reputable uk vendor..Electroncycles. They say enough on their site about genuine 30Q, GA cells only used in their batteries. I only bought it 11months ago.about 1700 miles of use.

Do i go to the seller and start throwing accusations at them? Surely it cant be worn out after 11 months use ? The warrenty was 6mths,is there anything i can do ,it cost me a small fortune £449?

I don’t think you can hold the supplier responsible after 1700 miles. There are too many factors that affect the battery life.

Use Ohm's law to calculate the load R =V/I =52/10 = about 5 ohms.
Power = V x I = 50W, so it needs a way to dissipate that much heat. A fan will help.

I'm lucky, I have a proper lithium battery tester, which does it all for me. You could easily make something similar for about £30. A 250w brushed motor controller with a potentiometer for power adjustment instead of a throttle would regulate the amount of current you want to drain and provide the safety cut off voltage, and instead of a motor, use a big resistive load, like a heater element, and a fan to cool it. A wattmeter inline would provide all the information on capacity, voltage and current. 52V is a bit higher than your average ebike battery voltage, so you'd probably have to hunt around for one that high. This one looks OK.

6-72V 450W DC Brushless Motor Controller BLDC PWM Hall Driver Board 12v 24v 48V | eBay

Find many great new & used options and get the best deals for 6-72V 450W DC Brushless Motor Controller BLDC PWM Hall Driver Board 12v 24v 48V at the best online prices at eBay! Free delivery for many products!

www.ebay.co.uk

 

[minexplorer]

I don’t think you can hold the supplier responsible after 1700 miles. There are too many factors that affect the battery life.

Use Ohm's law to calculate the load R =V/I =52/10 = about 5 ohms.
Power = V x I = 50W, so it needs a way to dissipate that much heat. A fan will help.

I'm lucky, I have a proper lithium battery tester, which does it all for me. You could easily make something similar for about £30. A 250w brushed motor controller with a potentiometer for power adjustment instead of a throttle would regulate the amount of current you want to drain and provide the safety cut off voltage, and instead of a motor, use a big resistive load, like a heater element, and a fan to cool it. A wattmeter inline would provide all the information on capacity, voltage and current. 52V is a bit higher than your average ebike battery voltage, so you'd probably have to hunt around for one that high. This one looks OK.

6-72V 450W DC Brushless Motor Controller BLDC PWM Hall Driver Board 12v 24v 48V | eBay

Find many great new & used options and get the best deals for 6-72V 450W DC Brushless Motor Controller BLDC PWM Hall Driver Board 12v 24v 48V at the best online prices at eBay! Free delivery for many products!

www.ebay.co.uk

Thanks vfr .This is probably childs play to a expert like yourself, but for me i wouldnt have a clue what im doing or looking for. Is this device to test the battery cells for whether they are worn out or simply out of balance?

I have 3 36v batteries ,they have had years of use and all the cell groups still read the same voltage. i was expecting years of use from this 52v. Why on earth would the use i have had from it have worn it out so early. When ive read other posts on some cell groups being lower than others it only seems to be a matter of balancing them up.

Should i not try that ? ive read before of using a mobile phone charger for this? am i right in thinking you connect the negative to the negative on the plug that goes into the BMS and the positive to the relative cell group wire in the plug? i guess if it refuses to come up to 4.2v its worn? Thanks

 

[minexplorer]

Hi. I spent a good bit of time investigating a similar problem with a 36v battery. I used a parallel element (5.5 ohm) from a 9 kw electric shower as a dummy load. The cells were similarly out of balance. I observed the following.
1. On charge, the high cells go to 4.25 volts and this stops the BMS from charging of the whole battery at about 40.7 volts.
2. On discharge with dummy load, the BMS shuts off the battery at 32.7 volts, because one of the low cells has dropped below 2.7 volts.
3.The usable capacity of the battery was about 63% of its nominal capacity.
4. I balanced up the battery mainly by draining down the high cells using various appropriate dummy load. (takes time)
5. I retested the battery and it worked ok, returning almost all of its full capacity. The battery is now giving good service.
6. The BMS fitted in the battery has no balance facility.
7. When I repacked the battery, I left it in such a way as I can recheck and re balance without having to unwrap. I have rechecked once after 3 months and about 30 discharge cycles and battery was only slightly out. (I done a small re-balance)

PS. When reading and testing cell voltages, you need to go to a third decimal place e.g 4.17v

thanks sturmy.So is this device u used the same as what vfr was explaining to make in his reply. So do you drain each of the higher cell groups down to the lowest ones voltage one group at a time. Is this better than trying to use the mobile phone charger method to bring the low ones up?

 

[minexplorer]

now ive ridden the bike til the LVC and rechecked the voltages it doesnt look so bad.12 cell groups between 3.35v & 3.45v. only 2 at 3.07v & 3.16v. cant find anywhere a full detail of how to do this mobile phone charger method to bring up individual cell groups. Anyone?

 

[Nealh]

With the phone jack cut off you have a pair of wires one is v+ and one v-, I solder a pin/leg from a pcb component to each wire. With a pin on the end you get a proper solid connection rather then a bendy tinned wire end.
V+ goes into the corresponding pin out for the low cell group on the BMS, the V- goes in to the pin out of the cell group preceding the low group.
Just don't let them short across each other.
Monitor the voltage every 10-20 mins if you are only raising voltage by about 0.5v as it will rise quickly.
Phone charger is only 5v so the pins need to be in adjacent cells where voltage is no more then 3 - 4.2v.

 

[minexplorer]

With the phone jack cut off you have a pair of wires one is v+ and one v-, I solder a pin/leg from a pcb component to each wire. With a pin on the end you get a proper solid connection rather then a bendy tinned wire end.
V+ goes into the corresponding pin out for the low cell group on the BMS, the V- goes in to the pin out of the cell group preceding the low group.
Just don't let them short across each other.
Monitor the voltage every 10-20 mins if you are only raising voltage by about 0.5v as it will rise quickly.
Phone charger is only 5v so the pins need to be in adjacent cells where voltage is no more then 3 - 4.2v.

nice one neal ill try this while the batterys 'flat' get them all up to 3.45v .then see if they all reach 4.2v together on the full charge.when you say pin outs on the bms you of course mean the 16 wire plug that goes INTO the socket on the bms. just double checking.thanks

 

[Sturmey]

thanks sturmy.So is this device u used the same as what vfr was explaining to make in his reply. So do you drain each of the higher cell groups down to the lowest ones voltage one group at a time. Is this better than trying to use the mobile phone charger method to bring the low ones up?

The mobile phone charger is useful to bring back up the cells with low voltage and can be quicker than draining down all the other cells. I used a 1 amp mobile charger on some of the lower cells but I had to put something in series (12 v 18w lamp) in series to limit the current as the charger kept cutting out. I was able to drain the cells quickly by using a half ohm load made from a long coil of wire. I stripped back the battery wrapping and connected directly to the battery nickle balance strips. (My eyesight and hands are not steady enough to go onto the BMS plug) Its a tricky job and you have to be careful, so its not for everyone. (I use to test and maintain telephone exchange batteries before I retired)
Your battery is very badly out of balance as the lowest cell is 3.07 and the highest is 3.45v.

I wonder does your BMS have a balancing facility? My BMS was small, about 65 X 36 (size of two cells ). It had no load resistors fitted and a big empty space where they were normally fitted, and also had two thin white wires going to an off/on switch. I see similar BMS on aliexpress and they have no balance function. I was disappointed by this shortcoming.

 

[Nealh]

nice one neal ill try this while the batterys 'flat' get them all up to 3.45v .then see if they all reach 4.2v together on the full charge.when you say pin outs on the bms you of course mean the 16 wire plug that goes INTO the socket on the bms. just double checking.thanks

Yes use the jst sense wire connector.
Use the lower rated 400ma charger will take longer but will raise voltage on low cells at a slower steady rate. I use 500ma charger.

 

[Nealh]

As Sturmey has mentioned nearly 0.4v out of balance is a big difference if you have BMS with balance. If drifting continues then it may be you have a bad cell/s in the low groups or the bms not doing it's job properly. BMS typically balance at about 100ma so won't eradicate a large unbalance of 0.4v.

Do you short charge at all to a lower voltage or always to 4.2v ?
Short charging over time will lead to an unbalance in voltage and causes more issues then it solves.

 

[minexplorer]

As Sturmey has mentioned nearly 0.4v out of balance is a big difference if you have BMS with balance. If drifting continues then it may be you have a bad cell/s in the low groups or the bms not doing it's job properly. BMS typically balance at about 100ma so won't eradicate a large unbalance of 0.4v.

Do you short charge at all to a lower voltage or always to 4.2v ?
Short charging over time will lead to an unbalance in voltage and causes more issues then it solves.

the charger info from electroncycles suggests its a balancing bms,as it says to balance the battery every once in a while by leaving it on for 12 hrs after charging complete. When i contacted them recently they said the charger may not go on and off during balancing as its not sensitive to go on at 0....volt drops,whatever that means.he also asked am i charging with the battery turned on.

i have to admit i always charged with the battery off and to 100%. im in the habit of going as far as i can til its totally drained. a few times ive charged to 100% then not used it for days due to rain etc,which i know is not good. maybe these practices have harmed it?

 

[minexplorer]

The mobile phone charger is useful to bring back up the cells with low voltage and can be quicker than draining down all the other cells. I used a 1 amp mobile charger on some of the lower cells but I had to put something in series (12 v 18w lamp) in series to limit the current as the charger kept cutting out. I was able to drain the cells quickly by using a half ohm load made from a long coil of wire. I stripped back the battery wrapping and connected directly to the battery nickle balance strips. (My eyesight and hands are not steady enough to go onto the BMS plug) Its a tricky job and you have to be careful, so its not for everyone. (I use to test and maintain telephone exchange batteries before I retired)
Your battery is very badly out of balance as the lowest cell is 3.07 and the highest is 3.45v.

I wonder does your BMS have a balancing facility? My BMS was small, about 65 X 36 (size of two cells ). It had no load resistors fitted and a big empty space where they were normally fitted, and also had two thin white wires going to an off/on switch. I see similar BMS on aliexpress and they have no balance function. I was disappointed by this shortcoming.

i believe it has load resistors..7 things that look like fets from the bottom is all i can see of them.this also has 2 thin white wires going to the on/off switch.the charging info sheet talked of giving the battery a balancing charge every now and again leaving for 12 hrs after charging finished.i didnt know you had to have it switched on when charging/balancing til now. ive also been in habit of going too far an running it empty most times.

 

[Nealh]

My regime for charging is I only charge to full 4.2v per cell about 6 -10 hrs prior to using otherwise SOC is left at a suitable level above 3.6v per cell. If battery voltage is lower then I raise it to storage of about 3.8v.
The switch if fitted is a BMS switch which will allow correct balancing to occur otherwise BMS will just measure top cell voltage and stop when one group or more have reached 4.2v and balance will not be equal.
As I mentioned earlier lower voltage charging will/can eventually lead to unbalance amongst cell groups, it is different to storage charging then carrying out a full balance charge. Full voltage charging in general only affects cells if they are left for prolonged spells at full voltage level, not hours but days and weeks on end. Some worry about max cycle life but who really counts cycle charges unless your OCD about it.
Charging to a lower voltage of 4 - 4.1v is futile with a standard BMS in place as it simply will not carry out balancing, BMS is programmed to only balance when voltage is above 4.15v or so. Those that use a lower voltage either use a smart/programmable BMS or don't use one altogether and users faff about monitoring individual voltages or use lipo balance chargers. BMS has one or two sets of fets depending on the BMS type, either common or separate port charging and use bleed resistors during the balance function. If you have a battery switch use it and switch it on as it wired via the BMS to allow correct balancing.

 

[minexplorer]

My regime for charging is I only charge to full 4.2v per cell about 6 -10 hrs prior to using otherwise SOC is left at a suitable level above 3.6v per cell. If battery voltage is lower then I raise it to storage of about 3.8v.
The switch if fitted is a BMS switch which will allow correct balancing to occur otherwise BMS will just measure top cell voltage and stop when one group or more have reached 4.2v and balance will not be equal.
As I mentioned earlier lower voltage charging will/can eventually lead to unbalance amongst cell groups, it is different to storage charging then carrying out a full balance charge. Full voltage charging in general only affects cells if they are left for prolonged spells at full voltage level, not hours but days and weeks on end. Some worry about max cycle life but who really counts cycle charges unless your OCD about it.
Charging to a lower voltage of 4 - 4.1v is futile with a standard BMS in place as it simply will not carry out balancing, BMS is programmed to only balance when voltage is above 4.15v or so. Those that use a lower voltage either use a smart/programmable BMS or don't use one altogether and users faff about monitoring individual voltages or use lipo balance chargers. BMS has one or two sets of fets depending on the BMS type, either common or separate port charging and use bleed resistors during the balance function. If you have a battery switch use it and switch it on as it wired via the BMS to allow correct balancing.

Thanks for all this info Neal. Not switching the battery on when charging has brought this about i guess.Its never been balancing.Then once i found out it should be on there was some too large imbalances in place for it to rectify itself. Its such an important point but neither any battery charging instruction or hrs of research said it has to be on.

hopefully the few times ive left it fully charged for cpl days hasnt done too much harm.Trickle charging is proceeding perfectly as per your instructions. The proof of the pudding will be if they all reach 4.2v and the batt reads 58.8v again on a full main charge

 

[vfr400]

You can use pin-strip to charge your cell. You break off two pins, solder the wires from the charger, make sure you know which way round the plus is, then insert the pins into the correct pair of holes in the multipin connector that goes to the cells.

Pardon our interruption...

The amount of imbalance at the bottom of the charge is always exaggerated because the lower cells fall off a cliff when they get to 3.3v, so it's not unusual to see one at 3.0v (cut-off voltage) and others at 3.4v. You have a little bit of imbalance that can be improved, but I don't believe that it will solve your problem. The reason you need to do a load test is to monitor the sag, which gives an indication of how worn out the cells are. Ideally, you need to check each cell while it's under load to spot any weak ones. Another thing you can do is watch the voltage on your LCD when you go from no load to full load to see how much it sags.

 

[minexplorer]

You can use pin-strip to charge your cell. You break off two pins, solder the wires from the charger, make sure you know which way round the plus is, then insert the pins into the correct pair of holes in the multipin connector that goes to the cells.

Pardon our interruption...

The amount of imbalance at the bottom of the charge is always exaggerated because the lower cells fall off a cliff when they get to 3.3v, so it's not unusual to see one at 3.0v (cut-off voltage) and others at 3.4v. You have a little bit of imbalance that can be improved, but I don't believe that it will solve your problem. The reason you need to do a load test is to monitor the sag, which gives an indication of how worn out the cells are. Ideally, you need to check each cell while it's under load to spot any weak ones. Another thing you can do is watch the voltage on your LCD when you go from no load to full load to see how much it sags.

thanks vfr.yes ive noticed the lcd voltage drops more than it did months ago when pulling high amps.will have to wait an see if they will all charge up to 4.2v and if this improves.Again tho how can less than a years use wear out a battery.im sure they are genuine 30Q cells as claimed by the company. Electroncycles only do bbshd & cyc x1 kits and high performance batteries of 52-72v

 

[Sturmey]

Hi. When a battery in normally been charged, it will be noted that there is a constant current stage (about 60% of charge) and then a constant voltage stage, which brings the battery up to full charge.
Now, from my observations, the problem with cell imbalance is that even if a cell is 0.1 volt higher, it can trigger a BMS shut off before the constant voltage stage and hence stop charging with less than 60% of the battery capacity.
This was very noticeable in my case, the 7ah battery that use to take over 3 hours to charge, time started to reduce until eventually it only took 2 hours before charger light turned to green.

By the way, if you are using the BMS sense wires to drain down any of the high cells, you need to limit the current to perhaps only an amp or two, as the wires are fairly light.