48v lifepo4 battery only charging upto 50v

[harper]

as iam here observing some posts,i also have an issue with my battery pack.
it is a 15s3p pack with 48v nominal voltage. but, here are some issues with the pack. the charger provided is 54.6v with 6amp output and auto cut feature. it took me 3hrs to charge it to 50.7v and the charger will cut off automatically.
i have tested 15 of the parallel cell packs and they are with (0.1v)difference i think they are pretty balanced.i am out of ideas to deal with this thing.
i also contacted the seller but got no solution other then saying 15 to 20 charge,discharge cycles will make the pack to charge upto 100%.
this is my 22nd time charging the battery pack, and it only charges upto 50.7v then settles at 50.2 after removing charger .
i think the problem is with charger, the other guy who bought the same charger and home made battery(cells and bms from same seller) is also facing the problem.
(ignore my english, am not that educated).

 

[SlowCo]

Normally a "48V" LiFePo4 battery pack is 16S instead of 15S. LiFePo4 cells usually need to be charged to >3.45V for the BMS to start balancing. If you have a 15S LiFePo4 pack your charger should have a charging voltage of around 54.8V when not connected to the battery pack. So maybe your charger isn't meant for a 15S LiFePo4 chemistry? Please check the open charging voltage of the charger. And what does the label on the charger say (Voltage/Amps/Chemistry etc)? And are you sure there is a BMS circuit included in the pack?

 

[AngryBob]

Exactly what voltage do the individual strings show, and have you tested the battery charger output to verify it is as labeled?

 

[harper]

its 54.6v+or-0.5v given on the charger.every cell is balanced and it is an home made pack with cells bought from seller.
it is with the bms and works pretty fair with all protection features(over discharge,over temp etc)

these are the cells i used

this is the charger i am using

and this is the data sheet of the bmsView attachment 15S60A LFP datasheet (1).pdf

i have opened my battery pack now and measured the cells. the 3 parallel cells at negative terminal are discharged to 2.9v and all other parallel cells are at 3.2v.

as i have tested the charger now, it is putting out the same as mentioned (54.6v@6amps)
i am in a confusion now .

 

[SlowCo]

Does the charger shut off at 50.7V? Or could it be you need to let it charge longer? Normally a CC/CV charger will charge with a constant current up to a certain voltage and then switch to constant voltage with low current. I suspect your charger is not dialed in correctly. Do you have a manual with the charger? You can try and let the battery pack charge for much more hours and test the voltage every hour to see if it creeps up slowly. But if your charger (or BMS) shuts off completely at 50.7V (=3.38V/cell group) then the cells will not be balanced by the BMS.

 

[harper]

Does the charger shut off at 50.7V? Or could it be you need to let it charge longer? Normally a CC/CV charger will charge with a constant current up to a certain voltage and then switch to constant voltage with low current. I suspect your charger is not dialed in correctly. Do you have a manual with the charger? You can try and let the battery pack charge for much more hours and test the voltage every hour to see if it creeps up slowly. But if your charger (or BMS) shuts off completely at 50.7V (=3.38V/cell group) then the cells will not be balanced by the BMS.

charger automatically drops the amps to 0 when it is at 50.6 or near. and if i unplug and re plug it after some time, then it will charge the pack again to 50.9 or something and turns off. after some time from removing the charger, the voltage drops to 50.3 and stands on it without getting low.

i have tested this pack with a 250w motor and 40kmph speed with 150kg of load. it drew a peak of 30amps and gave me 30km range at this parameters.

the charger had no manual with it.

i think the problem is with the charger as it has an auto cut feature and also no user manual included

 

[jonyjoe303]

One thing that might be happening is one of the cells is climbing higher in voltage near the end triggering the bms to shutdown. You would only notice this if you were watching the cell voltages in real time while charging.

I always had balancing problems with some lifepo4 packs I built, and I encounter the situation where I would never get a full charge.

After it shutdowns, the voltage of the cells will drop and you might not notice anything wrong. Thats why its best to see the voltage of the cells while charging.

 

[harper]

One thing that might be happening is one of the cells is climbing higher in voltage near the end triggering the bms to shutdown. You would only notice this if you were watching the cell voltages in real time while charging.

I always had balancing problems with some lifepo4 packs I built, and I encounter the situation where I would never get a full charge.

After it shutdowns, the voltage of the cells will drop and you might not notice anything wrong. Thats why its best to see the voltage of the cells while charging.

i thought of the same ,i will charge the battery while monitoring each cell and post the thing tomorrow.
but, is it normal to have the negative terminal cells at 2.9v where as other cells at 3.2?

my pack is of 15s 3p configuration is it normal to have the negative end 3 parallel cells to be at 2.9v but all other 14 parallel cells at 3.2v

 

[john61ct]

Did not read it all.

3.45Vpc is a good charging voltage, will settle to 3.33-3.35Vpc as 100% SoC Full, any higher is stressful and just "surface charge", not actual more energy stored.

So anything above 52V for 15S is pointless.

And settling to anywhere near 50V is perfectly fine and normal.

 

[john61ct]

Balancing goal should be within 30-80mV, 0.1V is a crazy unbalanced delta, even 200-300mV should trigger a balancing session.

The start-balance voltage should be well below 3.4Vpc, and if balancing is needed frequently, a higher balancing rate is better

you do not want to keep the pack sitting there for hours longer at Full just to get the balancing done, unless that's just twice a year or so.

 

[john61ct]

my pack is of 15s 3p configuration is it normal to have the negative end 3 parallel cells to be at 2.9v but all other 14 parallel cells at 3.2v

No grossly unbalanced.

Might be a bad BMS

Might be a bad cell in that group.

I would stop using that BMS for balancing, get a dedicated balancer that works at any voltage, ideally "active" so the balance rate is not affected by the imbalance delta.

Or balance manually with an adjustable PSU.

 

[harper]

Balancing goal should be within 30-80mV, 0.1V is a crazy unbalanced delta, even 200-300mV should trigger a balancing session.

The start-balance voltage should be well below 3.4Vpc, and if balancing is needed frequently, a higher balancing rate is better

you do not want to keep the pack sitting there for hours longer at Full just to get the balancing done, unless that's just twice a year or so.

from the data sheet of bms,it is mentioned that balancing starts at 3.60+or-0.025vpc.

as of bms, it should at least have to stay on 51v and 3.4vpc . but, it only getting upto 3.35vpc .

i think it is not even balancing any cell because none of them reached the trigger voltage.

i will test each of them now while charging and post the result soon.

thanks for helping.

 

[harper]

Did not read it all.

3.45Vpc is a good charging voltage, will settle to 3.33-3.35Vpc as 100% SoC Full, any higher is stressful and just "surface charge", not actual more energy stored.

So anything above 52V for 15S is pointless.

And settling to anywhere near 50V is perfectly fine and normal.

in my case, charging vpc is 3.64. and cells are settling at 3.33v.

with a voltage drop of 3 to 4v in total,when accelerating the ebike bms turns off the battery without fully discharging :|

i think if i get 52v instead of 50v,it can increase my range.

 

[Rassy]

I think the math is right for a 15s LiFeP04. Most of my experience is with Ping 48V batteries and the voltages you have stated per cell are the same:

"in my case, charging vpc is 3.64. and cells are settling at 3.33v."

If you multiply 3.64 by 15 you get 54.6, which is what you said the charger was set for.
And if you multiply 3.33 by 15 you get 49.95, which is what you think is wrong, but I think everything is correct.

Except, you may need to leave the charger on for a day or so to get that low cell fully charged.

You may also be cutting out too soon during discharge because your controller was set up expecting a standard 48v nominal LiFeP04 pack which is 16s, as mentioned earlier.

Curious why you purchased a custom pack that would be lower voltage than a standard 48 volt pack?

If I missed some details from the discussion that make my statements wrong, sorry, please let me know. Thanks

 

[harper]

I think the math is right for a 15s LiFeP04. Most of my experience is with Ping 48V batteries and the voltages you have stated per cell are the same:

"in my case, charging vpc is 3.64. and cells are settling at 3.33v."

If you multiply 3.64 by 15 you get 54.6, which is what you said the charger was set for.
And if you multiply 3.33 by 15 you get 49.95, which is what you think is wrong, but I think everything is correct.

Except, you may need to leave the charger on for a day or so to get that low cell fully charged.

You may also be cutting out too soon during discharge because your controller was set up expecting a standard 48v nominal LiFeP04 pack which is 16s, as mentioned earlier.

Curious why you purchased a custom pack that would be lower voltage than a standard 48 volt pack?

If I missed some details from the discussion that make my statements wrong, sorry, please let me know. Thanks

thanks for your replay.

does leaving the charger for a day cause any issues with the fully charged cells

my controller cutoff voltage is at 42v as labeled,

when i accelerate with battery at 48v it instantly drops to 46v (bms low voltage cuttoff)and bms shut down and makes overall voltage to 3 to 4 volts :| .

it will take like 2 to 3min to regain its voltage after disconnecting load and then it will be at 40 to 42v (from 48v directly to 42 )

and, i my self made this pack(bought all components from 1 seller).

here in india it costs about 250$US to get a battery pack of this specifications.i have made it under 150$

A NEW ISSUE::

i am charging the battery pack now and the cells at negative end got up from 2.9 v to 3.2v in just 5min

every other cell is at 3.3v .

i have also checked charging amps (6 amps mentioned) it is varying from 4.9a to 5.6a repeatedly

the charging voltage is around 53.5 for now. its been 30min i am charging it.

HELPPPP...

 

[Rassy]

If your charger and BMS are working correctly you will not damage any cells by leaving the charger on until all cells are balanced. You will get different opinions on this, but I always fully charge and balance my LiFeP04 batteries after every ride so they are ready for the next ride. I have helped a number of friends and relatives add electric assist to their bikes and trikes and counting my own two batteries there are 7 other Ping batteries, some as much as 8 years old, that I either helped purchase or even gave to them, and all still balance fully during every charge. The Ping BMS has 16 LEDs that light up when the cell groups each reach full charge so they are easy to check. A few of my friends/relatives did not understand the importance of this and eventually their batteries became way unbalanced. In the worst case it took me two weeks to get the battery fully balanced. That was several years ago and the battery is still performing properly.

Since you are able to check the voltage at the cell (or 3 paralleled cells) level, you can verify that the low cell voltage is slowly increasing, and that the other cell groups are also within proper parameters. Did you balance all cells before you assembled your pack? And if so did you verify that they held their charge? You may have a faulty cell in that one group and it may need to be replaced.

As far as what happens when the battery cuts out you may just be seeing how the discharge curve works with LiFeP04. My 16s batteries hold steady in the 52 to 53 volt range for most of the discharge and then drop off very fast near the end. So I would expect your battery to hold steady several volts lower during use. Those numbers are at rest, and during actual use there will be some voltage sag, which varies depending on how hard you are pushing the battery.

EDIT: I also looked over your post again, and your test at 40 KMH (25 MPH) gave you a range of 30 KM (18 1/2 M) with a max draw of 30 amps (almost 2C on an 18AH battery) doesn't sound too bad. I don't know about your battery specs, but 2C is usually considered a high discharge rate for LiFeP04. Of course how much effort you add makes a difference, but at half the speed you would probably triple your range.

 

[harper]

If your charger and BMS are working correctly you will not damage any cells by leaving the charger on until all cells are balanced. You will get different opinions on this, but I always fully charge and balance my LiFeP04 batteries after every ride so they are ready for the next ride. I have helped a number of friends and relatives add electric assist to their bikes and trikes and counting my own two batteries there are 7 other Ping batteries, some as much as 8 years old, that I either helped purchase or even gave to them, and all still balance fully during every charge. The Ping BMS has 16 LEDs that light up when the cell groups each reach full charge so they are easy to check. A few of my friends/relatives did not understand the importance of this and eventually their batteries became way unbalanced. In the worst case it took me two weeks to get the battery fully balanced. That was several years ago and the battery is still performing properly.

Since you are able to check the voltage at the cell (or 3 paralleled cells) level, you can verify that the low cell voltage is slowly increasing, and that the other cell groups are also within proper parameters. Did you balance all cells before you assembled your pack? And if so did you verify that they held their charge? You may have a faulty cell in that one group and it may need to be replaced.

As far as what happens when the battery cuts out you may just be seeing how the discharge curve works with LiFeP04. My 16s batteries hold steady in the 52 to 53 volt range for most of the discharge and then drop off very fast near the end. So I would expect your battery to hold steady several volts lower during use. Those numbers are at rest, and during actual use there will be some voltage sag, which varies depending on how hard you are pushing the battery.

EDIT: I also looked over your post again, and your test at 40 KMH (25 MPH) gave you a range of 30 KM (18 1/2 M) with a max draw of 30 amps (almost 2C on an 18AH battery) doesn't sound too bad. I don't know about your battery specs, but 2C is usually considered a high discharge rate for LiFeP04. Of course how much effort you add makes a difference, but at half the speed you would probably triple your range.

thats great my friend.. you are awsome

i have got all the cells balanced from the seller (3.2v with 0.01v difference)
update: after 3 hrs of charge, now charger got cut off it self by charging the battery to 50.3v (50v stable after removing the charger)
it will not decrease until load is connected.(stable 50v)

now,after checking all 15 cell packs after full charge the voltages are as given

1(-) 2 3 4 5 6 7 8 9 10 11 12 13 14 15(+)

3.35| 3.37| 3.35 |3.35|3.36|3.35|3.36|3.36|3.35|3.35 |3.35 |3.36 |3.35|3.36 |3.35

after disconnecting the charger from battery these voltages are tested and the bms start to get slightly warm after disconnecting the charger.
the voltages of the cells are not stable when charging connected.they are varying from 2.98 to 3.59v

now after checking the voltage of all cells, i am charging it again.

i will update you soon.

after checking the mileage yesterday.i have noticed that,the battery dropped only 2.3v for 22km of range(from 50.3v to 48v) and then it gave me only 8km of range (from 48v to 42v with cut off because of bms protection). is this normal

the charger is showing it fully charged and dropped the amps to 0 now. is it ok to leave this connected

no change in the cell voltages.

i have opened the charger case and found two smd potentiometers labeled as CH-C and CH-V shoud i adjust them

i will discharge the battery after 4 to 5 hrs. and will update you soon

and i have made this battery for my home made recumbent trike which is equipped with 550w gear reduced motor connected as shown in the pictures

40%of the work done
.

till now the motor is an issue and now issue with battery pack :|

i think it will give a lot more mileage on the trike because of its free wheel and the design.
i have not checked the battery on trike yet.(only checked with 250w hubmotor based escooter)

thanks for being an helping hand..

this is my first battery pack (here our parents wont encourage to do these kind of things. after we get out of school, we only has
3 to 4 choices either to become an engineer,doctor,businessman,etc. )

 

[Rassy]

Now that you know you can fully charge and balance your battery, I would not leave it hooked to the charger once it has completed the cycle.

You mentioned some heat from your BMS. Most BMS systems will use some current from the battery even when you are not using the battery. Where the BMS obtains this current differs with different BMS designs. Your BMS may be causing some of your problems by getting its current from certain cells in your battery, thus causing an out of balance condition over a period of time.

You may be able to eliminate this from being a problem if you can either unplug the BMS from the battery when you are not using it or installing a switch that will accomplish the same thing. I can not advise you how to do this, but since you built the battery and installed the BMS you can probably figure out how to do this.

Nice set up on the tadpole trike. I could not see how the steering was connected. Since you can not supply any pedal input and I think you like to ride fast I expect you will have less range on the trike. If you go easy on the throttle you may be able to have a good range. When your battery runs out do you just plan to walk the trike home?

I would not adjust the potentiometers, since they seem to be set right for your battery, and they can be very touchy.

 

[harper]

Now that you know you can fully charge and balance your battery, I would not leave it hooked to the charger once it has completed the cycle.

You mentioned some heat from your BMS. Most BMS systems will use some current from the battery even when you are not using the battery. Where the BMS obtains this current differs with different BMS designs. Your BMS may be causing some of your problems by getting its current from certain cells in your battery, thus causing an out of balance condition over a period of time.

You may be able to eliminate this from being a problem if you can either unplug the BMS from the battery when you are not using it or installing a switch that will accomplish the same thing. I can not advise you how to do this, but since you built the battery and installed the BMS you can probably figure out how to do this.

Nice set up on the tadpole trike. I could not see how the steering was connected. Since you can not supply any pedal input and I think you like to ride fast I expect you will have less range on the trike. If you go easy on the throttle you may be able to have a good range. When your battery runs out do you just plan to walk the trike home?

I would not adjust the potentiometers, since they seem to be set right for your battery, and they can be very touchy.

as you said earlier,i have left the charger connected to battery for almost 6.5 hrs. then i checked all the 15 cell strings
and got to know that all the cells are at 3.35 and only the second cell bank is at 3.43. is it normal

i will test the range with the trike at all type of conditions first and take the average range in total. i will not exceed the range and charge it again with leaving some range .

steering was removed to fix some issues, it was mounted under the seat with tie rods connected to it :wink: .

i will update it here as the work goes on..

update: i am discharging the 2nd cell bank with a small motor as load. is it good to do so
the bank is at 3.37 now (from 3.42 to 3.37) i will disconnect the load when it reaches 3.35v.

 

[Rassy]

No harm adjusting the voltage of an individual cell group like you are doing, but I have no idea why one group has a higher voltage. At one time you reported all cell groups were at 3.35v to 3.37v. I am still inclined to think that your BMS has some strange operating characteristics, but it seems to me that you are on top of it and should get as good of service as is possible from your battery. Good luck with it!

 

[harper]

No harm adjusting the voltage of an individual cell group like you are doing, but I have no idea why one group has a higher voltage. At one time you reported all cell groups were at 3.35v to 3.37v. I am still inclined to think that your BMS has some strange operating characteristics, but it seems to me that you are on top of it and should get as good of service as is possible from your battery. Good luck with it!

cells does not even getting closer to bms trigger voltage for balancing(3.65v).may be i should charge each individual cell upto 3.65v and connect them back

hope this will work! i will try it soon if this remains the same.

thanks for clearing my doubts my friend.

hoping the same :wink:

 

[john61ct]

Let's please just talk in per-cell voltages, not x15.

Sitting charging at over 3.5V for a long period may not immediately "damage" the cells, but if done regularly will shorten lifespan.

Same with not charging, just Full at rest.

Most cheap shitty BMS are designed so this is inevitable.

Replace at least the balancing function with something better.

 

[john61ct]

No harm adjusting the voltage of an individual cell group like you are doing, but I have no idea why one group has a higher voltage. At one time you reported all cell groups were at 3.35v to 3.37v. I am still inclined to think that your BMS has some strange operating characteristics, but it seems to me that you are on top of it and should get as good of service as is possible from your battery. Good luck with it!

cells does not even getting closer to bms trigger voltage for balancing(3.65v).may be i should charge each individual cell upto 3.65v and connect them back

hope this will work! i will try it soon if this remains the same.

thanks for clearing my doubts my friend.

hoping the same :wink:

Manual balancing is easy and with quality LFP may only need doing once a year, or every 50 cycles or. . .

Put them all in parallel no BMS, charge to 3.6 and hold until current drops to 0.01 or 0.02C

Then let them sit in parallel for at least 24hrs, 48 even better, will perfectly naturally self-balance.

Diagnostic - atomize isolated, see if any drop lower / faster than the others.

If so likely weak links, capacity testing only way to quantify for sure.

Replace if needed, reassemble pack, fresh BMS of better quality recommended.

 

[john61ct]

Most BMS systems will use some current from the battery even when you are not using the battery. Where the BMS obtains this current differs with different BMS designs. Your BMS may be causing some of your problems by getting its current from certain cells in your battery, thus causing an out of balance condition over a period of time.

You may be able to eliminate this from being a problem if you can either unplug the BMS from the battery when you are not using it or installing a switch that will accomplish the same thing.

Yes and yes

very common and fatal over time if uncorrected.

Pack design should allow the pack to be isolated from the BMS

BMS usually needs replacing before cells, so make that easy

And dedicated balancers do a better job than most all in one.

Also cheap hobby chargers with balancing built in, 3 sub-packs at 5S each for example.

 

[harper]

Let's please just talk in per-cell voltages, not x15.

Sitting charging at over 3.5V for a long period may not immediately "damage" the cells, but if done regularly will shorten lifespan.

Same with not charging, just Full at rest.

Most cheap shitty BMS are designed so this is inevitable.

Replace at least the balancing function with something better.

when the seller provided the cells, they are at 3.23v with 0.01v difference.I think they are balanced...

i have not checked the internal resistances of each cell before assembling. may this be a problem for fast discharge of some cells and not others

i have mentioned that the other guy who also built a battery pack from same seller also have the same problem.

he have used daly bms (not same as mine) but,he also facing the same problem.

i think the charger is culprit. as it cut off at 3.3vpc.

i have charged it for around 6.5 hrs and got different voltage in second cell bank(3.42v). (i have not seen this happen when i charge it for 3 hrs. every cell remains at 3.35v to 3.37v).

i dont think the bms is a problem,as cells wont even get closure to trigger voltage for balancing(3.65v)..

as you have mentioned, i will try to balance with external balancer..hope it works

thanks