Odd Battery behavior

[jasonahf]

Got an ebike battery that's not behaving. It's a 48V 10AH battery.

Setup is:
My sons bike - new setup only a few rides on it.
Fat tire bike with rear 1000w direct drive hub motor (chinese brand CSC)
twist throttle
LCV readout (sw900)

So the battery at full charge reads around 54V. but only getting about 7-8km on a full charge. He headed out but battery died on his return. Completely... would not turn on. Put it on the charger for a few seconds and battery works again.
I ran the bike around the block until the lcd said the max Watts were around 200-300 and very low power. during this the battery gauge on the lcd was showing no bars, but letting off the throttle the battery gauge would come back up to around 3/4 full.

once I got back to the house I disconnected the battery and checked the voltage at the main power leads and it was still reading about 48V.

This is where I got confused as per my understanding at 48V it should still have lots of power unless there is something wrong... which I'm guessing there is... just not sure what.

spent quite a lot on the battery but was purchased second hand (unused though) as he had received an incorrect battery and sold it rather than return it. So getting a refund is pretty much off the table.

Another thing... during the build something contacted inside the charging port (barrel type) and shorted it... very energetically. port was destroyed and I had to replace it.

Wondering if the BMS might have been damaged... or if I have a bad set of cells in the battery. Any help would be appreciated.

 

[eMark]

... letting off the throttle the battery gauge would come back up to around 3/4 full. (weak cells - floating voltage)

... once I got back to the house I disconnected the battery and checked the voltage at the main power leads and it was still reading about 48V. (no load - floating voltage)

... during the build something contacted inside the charging port (barrel type) and shorted it... very energetically. port was destroyed and I had to replace it. (replace damaged battery)

Charging could be dire.
Get rid of it before fire.
It's beyond repair in mire.

 

[E-HP]

Got an ebike battery that's not behaving. It's a 48V 10AH battery.

So the battery at full charge reads around 54V. but only getting about 7-8km on a full charge. He headed out but battery died on his return. Completely... would not turn on. Put it on the charger for a few seconds and battery works again.
I ran the bike around the block until the lcd said the max Watts were around 200-300 and very low power. during this the battery gauge on the lcd was showing no bars, but letting off the throttle the battery gauge would come back up to around 3/4 full.

spent quite a lot on the battery but was purchased second hand (unused though) as he had received an incorrect battery and sold it rather than return it. So getting a refund is pretty much off the table.

Did the battery work properly when you got it, and this is a recent behavior? The symptoms indicate that the battery can't supply sufficient current and voltage is sagging a lot. That could be bad cells in some of the groups, or just that the cells are not up to the task. Unused doesn't mean the battery is like new, since you don't know how the battery was stored while not being used. If the voltage dropped to low during storage, cells could have been damaged.

Do you have more info on the construction of the battery and the cells used. `10Ah could be as little as 13S3P, so the battery itself may not be up to the task of powering a 1000W motor. If the construction is with generic cells, this could easily be the case.

 

[jasonahf]

battery is a 13s3p.

Last time he took under my advisement he was very light on the throttle... trying to keep it at 500w or less... but still very little capacity.

and yes it's been like this from the start (only finished assembling the ebike last week)

It's a cheaper Chinese looking battery pack (wrapped in blue)... I agree that there must be some bad cells... just have to find the time to unwrap it and test out the 13 groups and hopefully see something that stands out.

will be looking at a bigger battery pack in the future as at full throttle the pack was cutting momentarily once in a while. Was the only battery we could get quickly before fall/winter.

 

[Comrade]

Who said it was ever 10ah? The no name made in China label? :lol:

 

[jasonahf]

Who said it was ever 10ah? The no name made in China label? :lol:

exactly guess I'll know more once I unwrap it

 

[jasonahf]

The fewer the cells in parallel Jason, the more vulnerable the battery is to lack of capacity because fewer cells to share the load. I think you get the picture. For $250 or so you can a fresh battery with 13amp-hrs or so.

The other thing and this can't be stressed enough. If a battery has known limited capacity and you are still trying to use it, it is a 'fire risk'. Please know that Li-Ion fires are fierce. Worse case scenario. You don't want to be the guy for a couple hundred bucks. I would get rid of that battery personally.

Bike will be parked until I figure out what's wrong with the battery and get it fixed... or replaced.


the guy who sold me it gave me a %50 refund so that was nice... means I only lost $100 if it's totally done.

But given my electronics background I might be leaning on getting some more cells and a better BMS and upgrade it to a 5P battery... if I can find the cause of the current issue first.

 

[docw009]

I ran the bike around the block until the lcd said the max Watts were around 200-300 and very low power. during this the battery gauge on the lcd was showing no bars, but letting off the throttle the battery gauge would come back up to around 3/4 full.

once I got back to the house I disconnected the battery and checked the voltage at the main power leads and it was still reading about 48V.

The battery gauge on ebikes is not as good as a voltmeter but full bars is 52-54 volts and no bars is 40-42 volts. If you're dropping to zero bars, and nominal was 48V, then you have terrible voltage sag of 6-8 volts at a nominal load of 5-6A. That's a woefully inadequate battery. A more typical drop from a cheap battery is maybe 2 volts at 6A and 6 volts at 20-22 amps.

I would say cut your losses and have your son buy a better quality battery. I don't recommend shrink wrapped packs. They're made cheap and are fire hazards. THey use cheap cells and are not worth repairing, because if one cell out of 39 is bad, that's horrible reliability stats, and another will soon fail.

Welcome to the wild and risky world of lithium batteries. Be very careful with them. QUite the fire hazard if mishandled.

 

[jasonahf]

Just a quick update.

So After testing a few cell groups who's voltage showed less than the other groupings in the pack (3.46v rather than 3.6V etc.)
I found that the batteries in this pack are basically crap. I bought a charger with a grading function in order to charge-discharge-charge again and display capacity.
the batteries are all in good condition with low IR... but the capacities ranged from 980mah to 1100mah per cell.
Given that it's a 13s3p battery it's only got about 3 AH... which explained its limited range.

I managed to scrounge a huge pile of 18650 cells from my work from discarded battery packs that were no longer meeting specs. (used for very sensitive equipment so specs are extremely tight). Weeded out a few bad ones but aside from those pretty much all the batteries tested good with low IR and capacities testing around 3000mah
Going to use these to build a 13s5p battery pack for him that should work much better.

the original pack I'm going to re-assemble into a 7s6p pack (24v) to retrofit into a razor scooter for my youngest son. Much lower power requirements so shouldn't have any problems with that... the only issue I have is that I would be 3 cells short for this.
I'm sure it's unwise to have all the cell groups of 6 with 1000mah and then one group with 3 1000mah cells and 3 3000mah cells.

going to try to source out a couple cells with similar capacity I guess.