Balancing - Time-Consuming?

[boom]

I don't have an ebike yet. I've heard that properly balancing a pack can take all night. True? Thx!

 

[Extreme1]

I don't have an ebike yet. I've heard that properly balancing a pack can take all night. True? Thx!

That’s not true. You won’t even know that the battery is balancing during the charging. Depending on how low your battery is, your charging time will vary.

 

[Marcela]

I charged a couple 72v batteries for the first time, it took longer during the last few percentages and assuming it was balancing, the time was maybe doubled but only by half hour or so.

 

[harryS]

Balancing shouldn't take much time on a quality battery with well matched cells. If you had one where you knew it was taking 6-8 hours to balance, and if it did this every time you recharged the battery, there is something fundamentally wrong,

Only the more expensive batteries have balance capability too, Most low cost packs don't balance, based on what I've seen in my ebike packs.

.

 

[fauconnier]

It's the role of the battery monitoring system integrated into every bike battery to balance the cells. This happens slowly throughout the charges without us realizing it. The longer time at the end of the charge cycle is not the balancing but rather the caution of the charging system which requires more precision to avoid overheating and degradation.

 

[PCeBiker]

,.. The longer time at the end of the charge cycle is not the balancing but rather the caution of the charging system which requires more precision to avoid overheating and degradation.

When a charger reaches maximum voltage (54.6V on my 48V batteries), it switches from constant current to constant voltage charging.
The light turns green on most chargers at that point, but that doesn't mean the battery is fully charged.

The voltage is maintained at 54.6, and the current flow starts dropping, so the battery is no longer charging at the full rated output current of the battery charger.

It can take a Long time for the current to trickle down to 0 amps.

I charge my batteries to 51.6 volts after my ride then top them up to 54.6 volts before my next ride.
It takes about an hour for my chargers to get to 54.6 volts and switch to constant voltage, then it takes well over an hour to finish a full charge.

If I unplug my 3 amp charger as soon as the green light comes on, my battery voltage is only ~53.1 volts.

It's the same thing as voltage sag with a battery under load, but in reverse.
Voltage surge I guess you could call it.

The faster you charge a battery (4 or 5 amps) the sooner it will get to 54.6 V but the longer it will take to fully charge the battery after it switches to constant voltage.

Hopefully the 54.6 volts are equally shared at 4.2 volts across all 13 cell groups, but that all depends on the BMS and whether or not it prevents all cell groups from exceeding 4.2 volts, or if it only monitors the 54.6 volt total.

One or more bad cell groups that don't fully charge can increase the voltage of the good cell groups, then things can become dangerous.

That's where buying a quality battery with quality cells goes a long way towards safety.

 

[Marcela]

When a charger reaches maximum voltage (54.6V on my 48V batteries), it switches from constant voltage to constant current charging.
The light turns green on most chargers at that point, but that doesn't mean the battery is fully charged.

The voltage is maintained at 54.6, and the current flow starts dropping, so the battery is no longer charging at the full rated output current of the battery charger.

It can take a Long time for the current to trickle down to 0 amps.

I charge my batteries to 51.6 volts after my ride then top them up to 54.6 volts before my next ride.
It takes about an hour for my chargers to get to 54.6 volts and switch to constant current, then it takes well over an hour to finish a full charge.

If I unplug my 3 amp charger as soon as the green light comes on, my battery voltage is only ~53.1 volts.

It's the same thing as voltage sag with a battery under load, but in reverse.
Voltage surge I guess you could call it.

The faster you charge a battery (4 or 5 amps) the sooner it will get to 54.6 V but the longer it will take to fully charge the battery after it switches to constant current.

Hopefully the 54.6 volts are equally shared at 4.2 volts across all 13 cell groups, but that all depends on the BMS and whether or not it prevents all cell groups from exceeding 4.2 volts, or if it only monitors the 54.6 volt total.

One or more bad cell groups that don't fully charge can increase the voltage of the good cell groups, then things can become dangerous.

That's where buying a quality battery with quality cells goes a long way towards safety.

Don't think there is any way to check current flow on my setup. How long should a guy leave them charging after the green light goes on using a 3.5a charger on a 20a and 15a 72v battery pack? For the most part I leave them at less than 80%, but occasionally do a full charge, intentionally or by mistake

 

[fauconnier]

PCeBiker I agree, the most important thing is that all cells must be the same from the start. If there is a 48v BMS that manages each cell separately, that's new to me, let's say 52, 65 wires maybe more. Does it exist?

 

[Gionnirocket]

PCeBiker I agree, the most important thing is that all cells must be the same from the start. If there is a 48v BMS that manages each cell separately, that's new to me, let's say 52, 65 wires maybe more. Does it exist?

No... The cells in parallel are monitored as one because they act as a single cell. So a 48v/13S battery pack has 13 monitoring leads.

Don't think there is any way to check current flow on my setup. How long should a guy leave them charging after the green light goes on using a 3.5a charger on a 20a and 15a 72v battery pack? For the most part I leave them at less than 80%, but occasionally do a full charge, intentionally or by mistake

I don't agree with leaving the battery charging after the light turns green for an extended period without clear manufacture instruction or testing as you need to know what your hardware is doing during this time. You could be unnecessarily stressing your battery or you can just be wasting your time.
Many issues of not fully charging on the first cycle are from poorly matched or just inexpensive basic Chargers and BMS'.
And most inexpensive batteries are not balancing and your just topping it off repeatedly which will yes get you a few more tenths of a volt but I don't believe there's any benefit especially when it takes so long and your keeping the battery at the higher voltage which is adverse to its health.

When a charger reaches maximum voltage (54.6V on my 48V batteries), it switches from constant voltage to constant current charging.
The light turns green on most chargers at that point, but that doesn't mean the battery is fully charged.

The voltage is maintained at 54.6, and the current flow starts dropping, so the battery is no longer charging at the full rated output current of the battery charger.

It can take a Long time for the current to trickle down to 0 amps.

I charge my batteries to 51.6 volts after my ride then top them up to 54.6 volts before my next ride.
It takes about an hour for my chargers to get to 54.6 volts and switch to constant current, then it takes well over an hour to finish a full charge.

If I unplug my 3 amp charger as soon as the green light comes on, my battery voltage is only ~53.1 volts.

It's the same thing as voltage sag with a battery under load, but in reverse.
Voltage surge I guess you could call it.

The faster you charge a battery (4 or 5 amps) the sooner it will get to 54.6 V but the longer it will take to fully charge the battery after it switches to constant current.

Hopefully the 54.6 volts are equally shared at 4.2 volts across all 13 cell groups, but that all depends on the BMS and whether or not it prevents all cell groups from exceeding 4.2 volts, or if it only monitors the 54.6 volt total.

One or more bad cell groups that don't fully charge can increase the voltage of the good cell groups, then things can become dangerous.

That's where buying a quality battery with quality cells goes a long way towards safety.

You have it a little backwards.
First phase of charging is CC- Constant Current and as it reaches Full Charge Voltage it changes to CV-Constant Voltage as it slowly ramps down current.


I'm just blown away by the ridiculous amount of misinformation and the continued repeating of assumptive science on this subject... smh...

 

[PCeBiker]

You have it a little backwards.
First phase of charging is CC- Constant Current and as it reaches Full Charge Voltage it changes to CV-Constant Voltage as it slowly ramps down current.

Opps.
I didn't proof read my post, and I didn't have my morning coffee yet.

I will edit my post.

Thanks for proof reading for me.

 

[Gionnirocket]

That vado before coffee will get you every time!

 

[PCeBiker]

That vado before coffee will get you every time! View attachment 199814

That's exactly what happened !!
Then I bought a six pack of beer, so now I got that going on too.
(It's raining today. No riding for me.)

 

[PCeBiker]

Don't think there is any way to check current flow on my setup.

You can buy a watt meter and use it to monitor your charger.

Check the power draw with the charger plugged in but not connected to the battery.
Then check the power draw when you connect the charger to the battery.
Then check it again when the light turns green.

Some fast chargers shut right off after the maximum voltage is reached.
Some continue charging but with decreasing current output.

I'm just blown away by the ridiculous amount of misinformation and the continued repeating of assumptive science on this subject... smh...

In effort to avoid assumptions, I was going to measure the voltages on those 13 BMS wires, but decided against it after realizing I'd have to pull the cell pack out of the aluminum case to get at the BMS, and my cell packs are glued in place,..

I always fully charge and usually almost fully drain my 2 batteries on my rides, so I wanted to be as fully charged as possible before my rides.

Charging until the lights turn green left me more than a full volt below full charge for my ride.

So,..
What I do now is charge up my batteries to 51.6V after my ride AND after letting the batteries cool down.
I use my bench charger set to 51.6V and let it sit until the current drops to almost 0
(I know, that's more than 80%, but I didn't want to have to wait 3 hours to go for a ride after deciding to go for a ride, even starting from 51.6V)

That way, I figure it might be possible to balance my cell groups to 3.97V to help stabilize the battery?
(and as @Gionnirocket mentioned, I don't know what my BMS is doing without measurements?)

I figure that "topping up" the battery to 51.6 volts is not as potentially harmful to my batteries as doing it at 54.6V, and "I may" have the added benefit of balancing the cell groups while doing it?

I don't drive anymore, and I don't really miss it, but I do miss how I could Fully charge my gas tank in less than 5 minutes, including paying for it !!

I Do Not however, have any desire to charge my batteries in 5 minutes.
Too much can go wrong.

 

[Gionnirocket]

The above watt meter may be workable depending on the charger. Some chargers are switching and only output current when connected to the battery. Additionally the reading will be off as most chargers are only about 80% efficient.
And it's not just fast chargers... One of my 2A chargers shuts down at 54.6V and does not output again unless cycled OFF/ON. This is why I say, know/test your hardware as there's a million variants out there and I'd bet most of the DTC bikes the seller doesn't even know.
The meter I use is on the load side of the charger so the reading is actual like that on a desktop power supply.
This all said, unless you have one of the higher end name brand ebikes I doubt very much it has a Balance BMS
So that means for the rest of us... NO Balancing is going on at any point.
It's not the end of the world as a quality pack built with matched cells that is not abused should have no problem lasting 5+ years and the cells will stay within acceptable tolerances. Also remember that balancing isn't going to save a defective cell. There's posts on here of Bosch batteries failing prematurely.

 

[Marcela]

Thanks for all the input! I do have a watt meter for the plug in, I'll have to check it out. My batteries are supposed to use Samsung 21700 cells and the chargers look top notch chinese stuff, the bike came with two chargers since there are two batteries.