How exactly do I know when my cells are balanced?

[Nkh]

I just bought the Commander HT. I'm coming from an 18xl. For context I'll start with the 18xl and cell balancing.

After the light turns green on the charger for the 18xl you can unplug the charger from the wall, except that the headlight will blink once like it's been overloaded. If I wait a few hours before unplugging the wheel, it will beep five times after which unplugging causes no overload. If you power cycle the wheel after that, it will ensure that the bluetooth has been turned of and no power drain will happen. Understand that very little of this was in the manual.

Now for the Commander. I deliver food on this thing, so I can and do frequently discharge this thing a very fair amount. It comes with a generic 3 amp charger with 2 lights on the front. I use the kickstand while charging, i'm assuming it's ok. I've heard that charging on its side is bad, but again, word of mouth info instead of documentation. While charging, the left light will be solid green, the right one red. Eventually both turn solid green. If I unplug the wheel (unplug from wheel first) and turn the machine on while still on the kickstand, EUC World shows 100.8v. If the wheel isn't unplugged it will stay like this for a while then both lights will begin blinking green erratically. I let it sit like that for more than 10 hours once, as this is what someone suggested that I do. After I do this though, the wheel sits around 100.4v or lower. I understand that there will be some sag.

Getting good information seems to be a community trial and error system. I have been told that a blinking red and green light means balancing, but I have never seen the charger do that. It could be that I just missed it, as I don't stare at the charger while its charging. I was also told by the same source as well as other riders that the sporadic blinking green lights mean balancing. It will never (it seems) stop the sporadic green phase though.

I have ordered a faster charger, so maybe it will behave differently. Thanks ppl for listening.

[alcatraz]

Short answer, you don't. Until there are smart bms' used in wheels.

When the packs are relatively new, they usually don't balance because group voltages are stable and well matched. 

When you put a few hundred cycles (or if you have moisture creating corrosion) is when you'll notice the charging time to increase before you reach your 100.8V.

If your voltages drop lets say 1h after you've reached the end voltage, it's a sign that there are slight imbalances developing.

It's fine to have imbalances and let the bms' take them out, but you need to keep a charger connected for a while. The larger the imbalance the longer it will take. 

After a while the imbalance will become greater than the ability of the bms' to handle it.

The worst kind of imbalance is when you have some kind of external damage to a single cell, be it friction/impact/corrosion. It causes an inproportional large self discharge. Bms' don't balance by charging single cell groups. They discharge all the groups that have higher voltage. It means that with one fast discharging group, the bms is essentially useless. There is no way it's going to be able to discharge 23/24 cell groups to catch up to that weak cell voltage.

That's when the end volage after several hours of charging remains below 100.8v. It means one of the packs is damaged. This assumes that the charge cutoff system works. If it doesn't you will see 100.8v after every charge, and the wheel will catch fire eventually. Usually there are warning signs though, like mentioned above. The voltage drops quickly after stopped charging. It shouldn't.

If you want to be 100% sure you cut away the shrinkwrap off all the packs, attach balance leads, and re-heatshrink them. That way you can monitor the pack's cell groups every few months with a voltage tester.

[meepmeepmayer]

As long as

• the wheel charges to full voltage
• you regularly keep the charger in for an hour or two after it has finished, so balancing is ensured

there should be no danger of any cell imbalances. I wouldn't worry too much.

I don't see how charging on the side (or in any position) could make a difference for charging, never heard of that being an issue either.

[Tawpie]

4 hours ago, Nkh said:

the headlight will blink once like it's been overloaded

This is the wheel turning off because its power source (the charger) has been removed, it's not an overload... it's like in the olden days when you turned your TV off the picture would shrink to a dot, which would then blink out. Newer firmware seems to have done away with the 5 beeps though, I miss it.

All the wheels behave differently though, and firmware changes their behavior. @meepmeepmayer has it spot on, do this and ride ride ride!

(I treat "regularly" as if it means "as often as you can manage"—I try to charge+1 or more hours so that I end just before I'm going out riding, you might let it rest an hour after your shift ends and then start a charge+balance cycle so it's all set for the next day. Many people don't like going to bed with their wheels on charger or charging them unattended, so keep that in mind. Daily should be often enough to keep things in great shape)

 

Edited January 25, 2022 by Tawpie

[Boostnsvt]

Its pretty easy to check, you just need to set it up with some accessible connectors, then use one of these digital capacity things. I have an old one i used to use to check each pack (https://www.towerhobbies.com/product/cell-master-7-digital-battery-capacity-checker/INTC23858.html). They might make a bigger one to check each cell (you might need a better bms for that), but I just wanted to verify my packs are good. I equated this to checking the oil in my car and check randomly.

 

I would like to add that some of the higher end chargers have this function built in so you can "balance charge" or balance while charging but I went cheap. Those chargers are 100's more. Ideally, in a perfect setup you would have a balancing capable charger with 4 ports and your Commander would have 4 accessible ports including the balancing cable.

Edited January 25, 2022 by Boostnsvt
chargers can do it too!

[RagingGrandpa]

7 hours ago, Nkh said:

How exactly do I know when my cells are balanced?
If I unplug the wheel [from the charger, after the charger light turns green] and turn the machine on while still on the kickstand, EUC World shows 100.8v

That's exactly how!

Assuming no physical damage, being able to charge all the way to 100.8 is only possible if the cells are balanced. If there was a cell group substantially over- or under-voltage, the EUC will interrupt the charging and you would be unable to achieve >100V after disconnecting the charger.

[alcatraz]

The bms trips the overcharge at around 4.25v from what I've seen. 

It means theoretically you can reach 100.8v with 23 groups at 4.25v and one dead group at 3.05v.

The overcharged cells have a higher rate of self discharge than normal (if this has happened repeatedly) so you'll see 100.8v drop by a volt or two pretty quick after you've disconnected the charger.

That's a bad sign.

[Bone]

I use a power monitor on my outlet, so I can see when the power draw has dropped off.  My stock charger turns green when it's pulling less than an amp from the wall.

[Planemo]

1 hour ago, Bone said:

I use a power monitor on my outlet, so I can see when the power draw has dropped off.  My stock charger turns green when it's pulling less than an amp from the wall.

Good call. Just remember that its still balancing when it drops below an amp. Mine flatlines at about 130mA iirc.

[Nkh]

Thank you everyone for the replies. I feel like I have to be an electrical engineer to feel safe using this thing. The new king song s20 is supposed to have a smart BMS. I'm way by and try to use it just because of that.

[mike_bike_kite]

On 1/25/2022 at 11:50 AM, Nkh said:

I deliver food on this thing, so I can and do frequently discharge this thing a very fair amount.

Just curious but what mileage do you have on the wheel?

[alcatraz]

On 1/27/2022 at 5:56 PM, Nkh said:

Thank you everyone for the replies. I feel like I have to be an electrical engineer to feel safe using this thing. The new king song s20 is supposed to have a smart BMS. I'm way by and try to use it just because of that.

The following is not 100% conclusive but...

Keep the inside of your wheel dry (seal it up if needed) and do the charge test. Get it to 100% = 100.8v. Did it take longer to charge than when it was new? It's the time from 80-100% that is mostly important to compare.

Ensure it's fully charged with the app, then wait 1h and compare that voltage with when the charger was just disconnected.

If charging time is similar to new, and it holds voltage well. There is little reason to suspect pack damage.