How long does it take to balance charge your pack?

[SamTexas]

This is my first experience with a Li-Ion/LiPo balance charger (Supermate DC-6). 2 hours ago I began balance charging my 6S 15Ah pack (half of my actual pack). The pack was almost full (manually charged). The initial cells' voltage were:
4.19 4.17 4.13 4.15 4.16 4.20
After 2 hours, it's still not finished. The cells' voltage are practically the same now, fluctuating between 4.19 and 4.20. The charge current is 0.4 to 0.6A. Total pumped-in energy is reported at 1.216Ah.

How much longer will it take? How long does it take for your charger/battery pack?

 

[Ypedal]

the 4.13v cell is likely your downfall... if it is a bad or not so great cell that is refusing to stay at 4.20v and keeps dropping, the charger may try to keep ballancing until it times out.

At this point you can just terminate the charge cycle and call it good enough tho.. if you got them all to 4.19 the pack is charged, cycle it a few times to see how it goes.

 

[liveforphysics]

Not starting balancing until the top is standard, it's called "top balancing", if you have a setting for "continuous balancing", it can sometimes reduce the time to balance a bit.

100mA balance current shunts from the charger.

If you had a 1Ah difference in SOC, it should take 10hours to correct it.

0.5Ah difference in SOC, it should take 5hours to correct it.

Etc etc.

 

[neptronix]

yup..
That battery is certainly out of wack if it had a cell at 4.13v and one at 4.20.

It will take a while, especially on a charger that has a very low discharge rate. Some of the better chargers discharge at 300ma+, if that's 100ma, then that sucks..

 

[SamTexas]

the 4.13v cell is likely your downfall... if it is a bad or not so great cell that is refusing to stay at 4.20v and keeps dropping, the charger may try to keep ballancing until it times out.

100mA balance current shunts from the charger.
If you had a 1Ah difference in SOC, it should take 10hours to correct it.

Thanks guys. I will try to charge the lower voltage cells individually to see if they can reach 4.20V.

Since the charger can control individual cells, why doesn't it selectively charge the lower voltage cells instead of discharging the higher ones? Or does it do both? What's the pros/cons of each method?

 

[Ypedal]

Most RC chargers have 2 main power wires, and ballance wires...

the Charger does not charge via the Ballan wires, it only discharges from these..

The large power wires being connected to all the cells in series means the charger is charging all the cells equally and draining the higher voltage cells via the ballance leads at the same time.. once all the cells reach 4.20v and the charger is no longer ballancing, and the current ( amps ) drop to a set value, charging ends..

On very badly unballanced packs, i charge individual cells via the ballance leads ( up to 2 amps max.. because of the small gauge wires ) .. this is a much faster way to fully charge a complete pack if any or many cells are way off..

 

[wojtek]

once badly unbalanced cells in a pack are balanced, will they stay in balance once used, or it shows that there is a problem with the pack?

i think the latter

got new turnigy and they are already unbalanced! between 4.04v-4.20v after first balance charge!

 

[liveforphysics]

once badly unbalanced cells in a pack are balanced, will they stay in balance once used, or it shows that there is a problem with the pack?

i think the latter

got new turnigy and they are already unbalanced! between 4.04v-4.20v after first balance charge!

Rest your fears, its not the latter. (Unless you have a bad cell)

 

[wesnewell]

Balanced cells aren't very important. The only thing that is, is that you don't exceed the upper and lower limits of individual cells. I find that when charging, the cells get more out of balance. After discharging to 50-80% they are more in balance. The only problem with unbalanced cells in a pack is that they aren't perfectly matched cells. And one is very unlikely to find perfectly matched cells when using over 6s in a pack. All this balancing hype is just that for the most part. I wouldn't worry about it till it exceeds .06v, and then it's not that big a deal as long as.....

 

[Ypedal]

http://ypedal.com/Cyclone/cyclone4.htm

I recently got 5 zippy packs, 6S, all cells arrived within 0.05 v of each other, took all cells to 4.20v and discharged a whole 5ah from them, cell 2 in pack 2 is the weakest link but kept inline with the rest until 4.9 ah where it drops off the curb first...

so it's not always black and white, you do get good packs, sometimes you don't.

 

[wojtek]

Balanced cells aren't very important. The only thing that is, is that you don't exceed the upper and lower limits of individual cells.

it doesn't make sense. First sentence contradicts with the second one! Unbalanced cells = exceeding limits.
When you bulk charge your batteries, one cell can have 4.10v and another 4.30 - all the charger cares is to get to 4.2v in total.
So unbalanced cells cause exceeding limits.

If one cell lost some capacity for some reason, and you discharge the battery packs, the rest of the cells might have 3.5V or whatever but this only cell can drop badly!

I am checking all cells on a regular basis trying to keep them very balanced. I did 12 000km within last 12 month without BMS , no LVC/ HVC. If cells are healthy, i know i am safe.
Now i have ordered LVC / HVC boards from Geoff - nice and small and will add security - won't hurt!

 

[neptronix]

Balanced cells aren't very important. The only thing that is, is that you don't exceed the upper and lower limits of individual cells. I find that when charging, the cells get more out of balance. After discharging to 50-80% they are more in balance. The only problem with unbalanced cells in a pack is that they aren't perfectly matched cells. And one is very unlikely to find perfectly matched cells when using over 6s in a pack. All this balancing hype is just that for the most part. I wouldn't worry about it till it exceeds .06v, and then it's not that big a deal as long as.....

Sorry to ding you, but that's not true. Different storage voltages make batteries degrade differently over a long period of time. You want your batteries to degrade evenly.

There have been studies about this: http://www.che.sc.edu/faculty/popov/drbnp/WebSite/Publications_PDFs/Web26.pdf

I'd say ~0.06v variance wouldn't be too much to worry about though. Over the super long haul, you do want things as balanced as possible however.

 

[dogman dan]

bit late now to do you much good. Surely they finally balanced by now. But I'd cycle the batts a few times before I started sweating their state of balance. Sometimes a few light discharges will perk up the pack, and then they will tend to charge more balanced and stay that way better. BTW, that's kinda what the charger is doing anyway. Just a LOT slower than taking a ride around the block.

 

[wojtek]

Thanks - i will do further analysis on those weaker cells and make an update! my drama queen state of mind is gone now..

bit late now to do you much good. Surely they finally balanced by now. But I'd cycle the batts a few times before I started sweating their state of balance. Sometimes a few light discharges will perk up the pack, and then they will tend to charge more balanced and stay that way better. BTW, that's kinda what the charger is doing anyway. Just a LOT slower than taking a ride around the block.

 

[wesnewell]

Balanced cells aren't very important. The only thing that is, is that you don't exceed the upper and lower limits of individual cells.

it doesn't make sense. First sentence contradicts with the second one! Unbalanced cells = exceeding limits.
When you bulk charge your batteries, one cell can have 4.10v and another 4.30 - all the charger cares is to get to 4.2v in total.
So unbalanced cells cause exceeding limits.

If one cell lost some capacity for some reason, and you discharge the battery packs, the rest of the cells might have 3.5V or whatever but this only cell can drop badly!

I am checking all cells on a regular basis trying to keep them very balanced. I did 12 000km within last 12 month without BMS , no LVC/ HVC. If cells are healthy, i know i am safe.
Now i have ordered LVC / HVC boards from Geoff - nice and small and will add security - won't hurt!

There is no contradictions. Unbalanced cells do not =exceeding limits. If you never go over 4.2v on any cell during charging, it doesn't matter what the others are. They could be 3.9v and you haven't exceeded charge limits. But if they're off that much then you have a bad cell that needs to be replaced anyway. Still won't damage adjoining cells just because it has more/less voltage than the others. Each lipo cell is a battery by itself. Does it make sense now?

 

[jonescg]

If it's any consolation to the original poster, my 4S packs take 2-3 days to balance if they have been sitting for a long time. But that's cause they are 60 Ah packs

I'm hoping that once they are all within 0.06 V of each other the on-board BMS will take care of top end balancing.

 

[wesnewell]

Balanced cells aren't very important. The only thing that is, is that you don't exceed the upper and lower limits of individual cells. I find that when charging, the cells get more out of balance. After discharging to 50-80% they are more in balance. The only problem with unbalanced cells in a pack is that they aren't perfectly matched cells. And one is very unlikely to find perfectly matched cells when using over 6s in a pack. All this balancing hype is just that for the most part. I wouldn't worry about it till it exceeds .06v, and then it's not that big a deal as long as.....

Sorry to ding you, but that's not true. Different storage voltages make batteries degrade differently over a long period of time. You want your batteries to degrade evenly.

There have been studies about this: http://www.che.sc.edu/faculty/popov/drbnp/WebSite/Publications_PDFs/Web26.pdf

I'd say ~0.06v variance wouldn't be too much to worry about though. Over the super long haul, you do want things as balanced as possible however.

I also want my batteries to last the rest of my life, but that's not going to happen either. At least i hope not. Everything I said is true. See previous post. Yes, it would be nice to have every cell at the same voltage, but it really doesn't mean anything as long as you don't exceed individual cell limits. And you even agreed with me, so that leaves me a little confused too. I don't take much stock in studies. There results are only good for the components used in the study.

 

[neptronix]

wesnewell,

What i disagree with you is that when you said that balanced cells weren't important when the OP was worrying about a pretty big variance of 4.0 -4.2v.

It is important to keep them in balance to a point.. you said the only thing to worry about going over max... no way.
I suppose the context here is important, so read through the first few points to see why i said what i said.

You don't have to take stock in studies either, RC guys will tell you that charging to lower voltages per cell will extend the lifespan of the pack.. well, if you have a disbalanced pack, then your cells wear funny over a long period of time.. so balancing really is important.

No harm no foul, maybe you misspoke and/or i jumped on you for a technicality.

 

[wojtek]

Balanced cells aren't very important. The only thing that is, is that you don't exceed the upper and lower limits of individual cells.

it doesn't make sense. First sentence contradicts with the second one! Unbalanced cells = exceeding limits.
When you bulk charge your batteries, one cell can have 4.10v and another 4.30 - all the charger cares is to get to 4.2v in total.
So unbalanced cells cause exceeding limits.

If one cell lost some capacity for some reason, and you discharge the battery packs, the rest of the cells might have 3.5V or whatever but this only cell can drop badly!

I am checking all cells on a regular basis trying to keep them very balanced. I did 12 000km within last 12 month without BMS , no LVC/ HVC. If cells are healthy, i know i am safe.

There is no contradictions. Unbalanced cells do not =exceeding limits. If you never go over 4.2v on any cell during charging, it doesn't matter what the others are. They could be 3.9v and you haven't exceeded charge limits. But if they're off that much then you have a bad cell that needs to be replaced anyway. Still won't damage adjoining cells just because it has more/less voltage than the others. Each lipo cell is a battery by itself. Does it make sense now?

Teoretically you are right, if none of the cells exceeds 4.2v or go below 2.8v, there won't be any explosion. Where i don't agree with you, is the approach. I don't like the "minimalist" way. I'm on the other side. IT IS IMPORTANT TO KEEP CELLS BALANCED! ESPECIALLY LIPOS!
As it is important to for instance use the RIGHT cable AWG!

Why walking on the thin line between a disaster and "it works like shit but it works"?

There are many people on this forum that are new to this stuff and want to learn things [like me] So i feel responsible not to write anything that can be potentially dangerous.

I gave you example where it could be a disaster to have unbalanced cells [bulk charging with no bms function] , also other members gave some examples why unbalanced cells "work like shit" [Different storage voltages make batteries degrade differently over a long period of time]. Another reason why you want to have your cells balanced - you can get a full capacity of the whole battery pack if all cells are at the highest V.

Another reason - what if you BMS will malfunction? or any other unforeseen event will happen? with balanced cells it is much safer!

 

[999zip999]

Cells can and will full at diffirence states of voltage and dis charge help it or not. There are difference no matter how the manifactoriers will try. Some cells act a little different for god knows why but can work whith in reason high or low voltage. Ask NASA.

 

[Kingfish]

... How long does it take for your charger/battery pack?

15S6P 5Ah 15C starting from 54V, about two hours using my new Meanwells; a 2X improvement over the old Meanwells.
~KF

 

[liveforphysics]

You can only use as much energy from the cells as the highest and lowest cell imbalance permits you to charge and discharge the pack.

For non-safety reasons, this is why balance is important.


In his example with one cell at 3.9v and others at 4.2v, it's true the pack is in no danger, but now during discharge you can't discharge the pack lower than your first cell to run out of charge. If you always stopped when that low cell reached 3.5v (or whatever the safe LVC for the cells happened to be), and always stopped charging when the highest cell reached 4.2v (or whatever the safe HVC for the cells happened to be), then you've still given up around ~30% of the usable pack capacity just due to your cell imbalance. A pack is only as strong as it's weakest cell (or cell group), or it's least balanced cell (or cell group).


If by chance you're discharging this same pack, and you happen to miss the low cell reaching 3.5v, then the rest of the cells that can still supply current drive that cell into reversal, and with LiCoO2 (like these laptop cells are), it means venting gases and/or fire and/or explosion.

So yes, you can function with your cells in random balance if you like, but the usable range of your pack can only be when your highest cell reaches HVC and your lowest cell reaches LVC. This makes it pretty foolish to lug around a bunch of battery that you're not able to use.

Likewise, building a pack from unmatched cells means the same thing, you're whole pack is only as strong as your weakest cell group. If you've got 19groups of cells in series that are all 20Ah, and one group that is 5Ah, you've got yourself a 5Ah pack that has the weight of a 20Ah pack.

 

[999zip999]

A well balance pack always fills to have more power in the seat of my pants. So my ass knows the difference.

 

[wesnewell]

I've checked the balance after charging without balance. Cell voltage varies from 4.2 to 4.13. After discharging the pack by 50-80% all the cells are within .01v. So you really don't loose much of anything. I've checked this numerous times, but you are welcome to test it yourself.

 

[neptronix]

4.13 to 4.2v variation is actually pretty big. You may have some bad/funky cells in there, or they were never balanced to begin with. Or you have a balancing charger that is not doing it's job well.

0.01v difference in the middle of the charge is normal. Check those cells at 3.5v/cell average. The ones that weren't in line with the others at the top will be horribly out of line at the bottom... limiting your depth of discharge quite a bit.

My packs are never +/- 0.02v at the top 4.15v/cell charge, all the way down to about 3.5v/cell.. only because i bought extra lipos, identified the funky ones, and set those aside for other uses ( girlfriend's ebike, 5ah magicshine lipo pack for the pedal bike, mega battery for the gopro HD, 3s booster pack, etc. )