48V Charging Issue

Hi All,

I am having some issues charging my Ebike Battery. I built my first 48V pack using Sanyo 18650s in a 13s4P configuration. Spot welded up everything myself and installed a BMS. Currently the charger I have is outputting 54.7V however it comes up with a green light to say its finished charging but the battery is only reading 52.6V from the output terminals. Its on a Hai-Long Case.

I should mentioned I tested all batteries before installation and they were all within 0.01V of one another.

My first question is: How much battery percentage am I losing by it only charging to 52.6?

What could be the cause of the charger stopping at that voltage? BMS cutout?

BMS: https://www.aliexpress.com/item/Daly-3-6V-3-7V-13S-48V-E-bike-Li-ion-battery-18650-BMS-16A-18A/32878960507.html?spm=a2g0s.9042311.0.0.25544c4ddiObl8

Charger: https://www.aliexpress.com/item/48V-4A-Lithium-ion-battery-Charger/874817149.html?spm=a2g0s.9042311.0.0.25544c4ddiObl8

Its not fully balanced, so stopping early. Plus, always possible a weak cell somewhere fills too fast, stopping the charge on the normal cells early.

Spoof your bms to balance it more fully by charging full, then unplug and let it sit a half hour for the discharger in the bms to drain the high cells that stopped the charge. Then start charging again. If the charger wont restart, ride around the block to drain all the cells just enough to get the thing to start back up.

You might need to repeat this several times to see much improvement. Might even take ten times, since you are ending up pretty low.

Once you do force it to a full charge, go for a ride that will discharge it about 50%, and recharge. If it will charge to near full, like 53.9v or so, consider that pretty good. If it returns to only charging to 52.6v, then you have a fairly permanent condition, caused by one or more cell groups having sucky cells.

To be clear, its the sucky cell groups that are getting full. The higher capacity cell groups are not getting as full because the bms stops the charger when the low capacity groups are full.

If this persists, don't panic yet. At 52.6v, you are getting 100%,,, of your battery capacity. Its what it is, and nobody really gets the rated capacity from a big pile of cells, unless you do some really serious testing and capacity matching before you spot weld. So now its done, you got what you got, unless you find that one cell group is the entire problem, and then you rebuild that group. So don't sweat how much capacity you might have had, you have what you got. Test with a watt meter if possible, so you will know what your capacity is, and then that is your 100%. Then plan rides based on reality, not some manufacturers possibly bogus promise. The reality is nobody gets 200 perfect cells in a batch. They may test fine new, but a few cycles can make one or two cells develop lower capacity. it just is what it is.


I predict that you will get some improvement out of forcing some more balancing, and you won't have to do that every ride. You will have to repeat it anytime you ride till the pack is so empty the bms stops it though. So aim to stop when its got a bit more voltage left, for most rides. If you can get to the high 53's or low 54 most cycles, you are doing fine and have a basically normal pack.

It does sound like your BMS is terminating the charge early because some cells are getting to max voltage before others. If you can monitor individual cells with a meter, do so and you will find out if some are way low.

The only way to know the state of charge is to start at the neg end and check cell voltage and write down on a piece of paper like.

!. 4.01v
2. 4.51v
3. 4.55v

13. Xxxx volt
charger voltage Xxx volt
Pack voltage Xxx voltage
Report back.
state of charge.
Plus what cells where you get them ?

Hey Guys,

Thanks for the responses.

Its my first pack. (well first pack that wasnt made from recycled cells)

I made significant savings by building it myself with quality cells. Moreso practice for future builds in my mind.
I will attempt to try and spoof the BMS as you suggested dogman dan.
Hopefully I dont have to open the pack up because the case I bought is very tight with the bms installed in the way it is.

Definitely happy with it as it is, just wanted to see if it was builder error or something wrong with my kit!

I bought my cells from NKON . Sanyo 18650. bought about 60 of them in case some were bad.

What watt meter would you suggest to use? The one on the bafang LCD display?

A failed or poor parallel connection on any cell string can lead to lower total pack value/unbalancing as that string will charge quicker turning off the charger once 4.16v + is reached, it then leaves all other string voltages trailing at a lower voltage = lower pack voltage. If this was the case remaining strings would be 0.15 -0.2v lower = the approx. 2v missing.

As mentioned by 999zip measuring the 13 cell strings via bms connector will tell you if anything may be up.

Ok guys I have decided I'm opening the pack up.

I'll do it when my new case gets here. I have the first generation hailong case but the frame mount has a lot of flex.

The new 5 pin ones have a metal support through the centre to strengthen it up and it has more mounting points.

Has anyone had experience with the new cases ? Does the battery holder fit from old to new?