Battery charging questions

[Deacon Blues]

My UC Pro came with two Shark 52c, 880Wh batteries and a WW 10a charger.

It doesn't matter what I set the charging % at (80,90, or 100%) the charger always stops at around 76 to 78% (as seen on the bike's display).
Can someone explain to me why the charger won't charge the battery to a higher percentage?

I also find that the percent numbers on the display are inconsistent. It will show 78%, then drop to 75%, then go back up to 77%, etc.

 

[pushkar]

can you change the display to voltage, and see what the fully charged voltage is please ?

 

[Deacon Blues]

I'll charge the battery back up to 90% and then see what the voltage is.

 

[Deacon Blues]

@pushkar, the display shows 58.4v
I set the charger to 90%

 

[scrambler]

That looks like 100% charge
I believe the shark 52V are 14S batteries (14 in series, 14 x 3.7V = 51.8V)
If so, the max voltage is 4.2V x 14 = 58.8V

 

[Deacon Blues]

Thanks Scrambler. Can you give me a short tutorial on how to read the voltage as I ride?
I understand percentages, but I'm a real noob when it comes to volt readings.
For instance, what would the voltage read at the half-way 'used' point, and what's the 'this is as low as you should go' point?

 

[scrambler]

The difficulty with lithium-ion cells is that the discharge curve is very flat. it drops quickly initially from 4.2 to 3.7, then changes very little for most of the discharge, then drops again quickly at the end.
It looks something like.

This is the individual cell voltage and you have 14 in series, so the battery voltage it 14 times the cell voltage.

So, what you see is that between 80% and 20%, the voltage is going to change very little, and this is why a voltage to % conversion is so tricky.
Each brand / model of cell will have a slightly different discharge curve, so you can't really use one conversion table for all batteries.
Normally the % calculation is optimized for each battery, and only Pushkar can explain what they do on their end to help the precision.

The important part is the max and the min you want to stay in, which is 4.2v - 3V (58.8V - 42V). And if you do not need the whole battery capacity, you will increase the battery lifetime by restricting the max and min further like 4v- 3.2V (56V - 44.8V)

Full charge, but especially deep discharge is what can damage the cells

 

[Lsthrz]

fun fact: I charge my battery to 85% using the Grin Satiator and that’s 56.6v.

 

[scrambler]

Sounds about right

 

[Deacon Blues]

Thanks again, scrambler.