Battery Question.

[T4KT1KZ]

Not sure if this is in the right area.

So I recently purchased a new Ebike. A 2020 Voltbike Yukon 750 Limited.

The battery it comes with is a 17.5ah (840wh) 48v Reention style battery pack. Made with Samsung 35E cells. Having a background in electrical, as well as being an avid hobbiest for many years i'm well versed when it comes to lithium ion batteries. The Samsung batteries were a factor in the reason chose voltbike.

Voltbike advertises that the included 5A charger can charge a completely drained pack in 4 hours. The charger itself is a brand name charger it says 54.6v max voltage. Long story short. My battery performs fine but takes a long time to charge.. I've been monitoring it the last few cycles. It charges fast up to 53v at which point it ramps down charging current to a trickle. It takes like 2+ hours to charge my pack 1v from 53v to 54v. Where the charger cuts off. Should it not charge all the way to 54.6v? I know that charging to 4.05v(80%) or 4.1v(90%) instead of fully charging all the way to 4.2v (54.6v) can prolong the lifespan of the cells. I'm just concerned I have a bad cell In there and thats why it is taking forever to balance the pack. But why stop at 54v instead of 54.6 as the charger states. Thoughts?

 

[999zip999]

How new is this bike maybe the battery has not been fully balanced you may need to leave it on the charger for many hours so all cells balance. The BMS works very very slow.
So leave it on the charger and the charger should kick back on after it drains the high sell it over time it should bounce the whole pack if pack is out of balance.

 

[T4KT1KZ]

Initially I thought the same thing. That it was just out of balance. I just purchased the bike recieved on July 20th. So it's less than a month old. Only 7 charge cycles (I've kept a log). The last two cycles have both done exactly the same thing. First charge the battery was fully drained. The second charge the pack was half charged. Both times it charges it quickly up to 53v. Then it takes like 3 hours to charge it from 53v to 54v. Light goes green and it says its done. Checking the battery reads 53.9v-54v. Disconnecting and reconnecting the pack does nothing. Charger just shows green light and won't charge it any further.

I know quite a bit about batteries. Having spent many years in the R/C hobby world. I even built my own 20A charging station in a metal briefcase for charging at the races (for R/C Lipo etc)

My ebike came with a 5 amp charger. I'm just not familiar with the BMS systems and how they function. I suppose it could just be that the BMS has a very low balancing current (many R/C chargers have this very limitation) In my experience with multicell lipo packs if its taking forever to balance up its because one cell is out of balance with the rest. Chargers struggle with this because they have to bleed power off the other cells in order to avoid overcharging them while still applying power to charge the bad cell. Atleast that's my understanding. But the fact it seems to do this every time leads me to think it's a bad cell. Or the BMS sucks really hard. I did open it up to check out the BMS but I cannot even figure out anything about it.

The fact It does not charge all the way to 54.6v is what concerns me. The charger states 54.6v output.

I was hoping there were some other voltbike Yukon owner's out there who have the 17.5ah pack that can do a little comparison with me.

Maybe it's built into their BMS as a way to extend the lifespan of the cells. If so I can live with that.
I'm wanting to purchase a https://www.ebikes.ca/product-info/cycle-satiator.html
for exactly this reason. To be able to accurately test capacity, see detailed charge info, customize the charging current and cutoff Voltage. Just wish it wasn't $400+

 

[99t4]

Light goes green and it says its done. Checking the battery reads 53.9v-54v. Disconnecting and reconnecting the pack does nothing. Charger just shows green light and won't charge it any further.

That light might be throwing you off. Mine appears to do similar (note: different cells -- Samsung 30Q) but actually will go up and down a few tenths of a volt for several hours until it finally levels off at max. charge (in my case 67.2V for a 60V pack). Green light during this entire time, fan is off, but the charger stays moderately warm to the touch.

Apparently this is the BMS working to balance the cells. Can take from 4-5 hours to a few days until it settles at max. charge. As 999zip999 suggests, it takes a long time. How long have you left the charger charging?

 

[T4KT1KZ]

Usually I charge my battery during the day as I do not like to leave batteries charging overnight and unattended. So I typically leave the pack to charge for
6-8 hours. I let it fully charge until light goes green and usually its left for atleast a couple hours after it is done and showing green.

On your recommendation I left it plugged in overnight. For atleast 15 hours after it showed green. Stopped at 54v. Won't charge any higher than 54v no matter how long its left plugged in.

It's a brand new pack. Only 8 cycles. Samsung 35E cells. The DC jack from the charger reads 54.2v on my Multimeter. And not the rated 54.6v it states. I guess I need to start by ruling out the charger. Going to contact Voltbike and see what they have to say.