Can anyone recommend a good balance charger?

Hi ESFMs,

I'm experiencing a slow loss to my pack's full charge over the past few months and I suspect am imbalance.

Is there a good balance charger on the market for a 13s pack (48v)?

Clinton

If you find out that you bought some cheaply made batteries. ( not cheep in price cheaply made and/or fake cells )
and
You are using more current than what the batteries are rated for , then it is time for new batteries and a charger.

What e-bike kit do you have ?

What power are you running it at ?
Watts and amps

What batteries are they , brand name and size of pack ( you have 13 in series , how many cells in parallel ? )

You might want to get a 14 s pack for your next pack, depending on where you live and if you ride up hills that take allot of amps or flat riding and faster speeds.

They are sanyo cells. It's a 10 parallel I think. 48v, 35AH pack. And paired with a 30 amp Max controller and a 1200 Watt motor.

It gets a lot of use everyday as I mostly work with it doing between 50-100 kms of riding.

I see a lot of balance chargers on the market but they seem to be only up to 8 series and for lower power levels.

Is there anything on the market for ebike packs?

Balance charger for 13S / 48V.
iCharger is the go to but they are expensive and the highest is 10S / 36V.
You shouldnt buy them cheap rc chargers, takes too long to charge.
You could use a balance BMS on the battery and use bulk charger like the Meanwell's.

BMS can be found on aliexpress for little as $14.
Leaning toward ANN power, as they supply nickle strips
and everything else for DIY, they might have the right
sort of junk to upgrade your pack.

But beware that each cell's shunt can only bypass very
little current, and the BMS will almost certainly get hot.
Nowhere near the normal C rating that you might use
when voltage is safely below full.

So set your power supply a little higher than pack on
Volts, and very low on current. Balance slow, as you
will be relying on that BMS to prevent overcharge of
individual cells. And probably for first time, if not
every time, outside away from anything combustible.

A resistor in series with your supply can lower current
automatically as you approach full charge. But will
depend the voltage difference between the BMS and
the charging supply. Divide by the resistace to figure
the balancing current. I would want this figure to be
less than 50mA, unless you know exactly how much
bypass current your BMS can reliably shunt, and how
hot it might cook adjacent cells when it does.

If you bought your pack pre-made, it might already
have a BMS under the wrap somewhere. Then is just
a matter of setting your power supply and resistor.
Don't overcharge if you are not sure...

So much for my earlier BMS theory. Here's an example that seems to lack dissipative balance.
Not that its a bad 48V BMS. I might even buy it. But never going to balance anything by itself.

https://www.aliexpress.com/store/product/13S-48V-6P-13S-78-holes-battery-holder-nickel-BMS-6P13S-6-13-holder-nickel-BMS/536657_32853669649.html

It just cuts off when any cell is deemed unsafe. I suppose that makes sense, since dissipative
balance can get hotter than you want next to a battery, and not keep pace with fast charge.
But this also puts all responsibility for charge balance on the external charger. And that will
require reliable connections to every individual cell, big enough to handle the shunt current.

The balancer I've built for my own 36V is made to fully shunt away 2A of overcharge, and
at 4.15V per cell, thats 83W! That much heat I want nowhere near a battery, and heatsink
is hefty enough I may leave off the bike. Not like I need full balance every time. Portable
dumb charger may target an average 4V per cell, or some reasonably safe lower number.

Was also working up an active balancer to efficiently and fully wring the full use every cell.
Check schematics in the technical section. I had this sim running on 4 cells, and looks very
plausible from a sim standpoint. But then I get real about it. Do I have the time to layout
such a monstrosity and build the custom 11 wind transformer? Will it squeeze more out of
low end imbalance than the extra weight I'd have to cart around? Might as well balance the
top at the charger, and trust in weight savings and keeping it simple....

I'll attach picture of the BMS in question, assuming the seller's link will eventually expire.
Buyer beware: Not all BMS feature balancing. Maybe for good reason, it depends...

Fastech website --> 18650 holders --> Choose ePacket --> Quick Shipping!

Then choose a known good BMS. Not sure how you'd do that beyond a search.
Best Tech has known good BMS' but if I remember correctly, there is a minimum order quantity (MOQ) of two.
So maybe you could do a 14S pack and get two 7S BMS'

If there is a DIY BMS somewhere, that'd be cool, if there is not too much components to solder.
Might be worth a look.

Here is a good list, came from a search on "DIY BMS"
https://endless-sphere.com/forums/viewtopic.php?f=14&t=92952&p=1394735&hilit=DIY+BMS#p1394735
Adaptto is expensive but reliable, get a charger and bms and more all in one.
Also listed from fetcher on that link is the Speedict, lots of info on es about that unit.

Only way is start from the beginning. Fully charge the battery. Then check each group of parallel cells. On a piece of paper like.

1. 4.15 volt
2. 4.20
3. 4.09

13. Xxx volt
Get us the voltage of your charger.
Give us the voltage of you fully charged battery.
This will tell you and us the state of charge. Don't skip a step. Must write it down.
This is ground zero.
No they don't have a 13s balance charger.

You can find this 13S BMS at site watermarked in the image, or slightly from less from the SuPower store on
Aliexpress. Not saying this is anything special BMS, only that its a convenient picture to illustrate a point.

Here you can clearly see dissipative components to balance each cell at the threshold of overcharge. 47ohm
resistors take some of the heat for the balance transistors, and limit the rate of discharge though the circuit.

Even with these fairly large components: This BMS that claims to allow up to 30A charging current, the balance
rate is only 60mA. If you overcharge faster than 60mA, it cannot dump the excess to balance any cells that are
still weak. It should detect overcharge and shut down. Just going by what the specs say, not saying it actually
safe to rely on those, but lets assume for a moment...

So you are wanting to charge fast up to nearly full, or maybe the pack shuts off. Then charge ~50mA to bring
up the weak cells. There will be no overcharge because dissipative shunts (if they work properly) are bleeding
up to, but not more than 60mA of excess.

If you don't want to watch for the pack to stop the fast charge, and manually reduce to a balance rate,
then you need a series power resistor that slows the charge as pack voltage approaches charger voltage.
Specific value resistor depends your charger's open-circuit voltage.

You cannot balance when battery charge is shut off. Leaving on the high rate will not balance anything.
Might even have to drain a little to allow charge to resume. Then you might sneak your balance charge
in slow, staying well under the threshold of shutoff for as long as possible.

I agree that you need to measure individual cells, and not trust an unknown BMS to stop the charge
until it has proven itself to your satisfaction.

If you have no bms, then use any cheap 50w RC charger to balance. hook up to one group of cells at a time, set the charger to 1s, and charge that cell group. You do not need to charge the full groups, just the ones lower than 4.15v. Over time, all your cells will lose ability to hold 4.2v for long, so inevitably some of your capacity does diminish after a lot of use. So don't sweat trying to get cells to 4.2v, that won't hold them anymore anyway. Just get them all the same, whatever that is.

If you have a bms, do this. Charge, unplug, let sit half an hour for the bms to discharge any high charged cell groups, then charge again. If the charger won't restart, ride around the block and then charge, let sit, then charge. Repeat till your bms has balanced the pack.