Lipo Balance Charging ? really ?

[Alastor]

Good morning mates ,

My pack is doing something that is making me very happy i just want to share it with you because i am a lipo noob and i am still learning .
I have charged the 12s2p pack i am having like 15 times with bulk charger as a lilo the charger gets each battery at 25 volt approx.
The strange thing the pack dose is that some bricks are kinda unbalanced 0.065 after charge but after i do the series connection and leave the pack to rest after charging like one hour all bricks are perfectly balanced like 0.010 ~ 0.018 differences max is that normal ?

Are the lipos equalizing while in parallel after a while ? even if i don't have the balance wires paralleled ? I know its not an issue but if you want to explain why this happens i will be more than happy

Thanks again and again

 

[dogman dan]

That's a bit odd. It's normal for a charged battery to drop voltage just a bit when taken off the charger. But more typical would be all the cells to drop up to .05v and then the inbalance would still exist.

Well, at least that's what I've seen with the lipo I've had for two years.

Once you discharge some, and get into ther really flat part of the discharge curve, slight inbalance tends to even out some. But you are seeing this at the top of the charge, not at 3.9v.

As for paralelling them causing it, It shouldn't be causing much difference if both packs are at the same total voltage when you connect them. At pack level, no difference would mean no electrons flow from one pack to the other.

 

[Alastor]

That's a bit odd. It's normal for a charged battery to drop voltage just a bit when taken off the charger. But more typical would be all the cells to drop up to .05v and then the inbalance would still exist.

Well, at least that's what I've seen with the lipo I've had for two years.

Once you discharge some, and get into ther really flat part of the discharge curve, slight inbalance tends to even out some. But you are seeing this at the top of the charge, not at 3.9v.

As for paralelling them causing it, It shouldn't be causing much difference if both packs are at the same total voltage when you connect them. At pack level, no difference would mean no electrons flow from one pack to the other.

Probably that's my case man because the voltage differences are between 0.020 ~0.040 for example the cell i was talking about had 0.060 difference from the other cells and after an hour i checked it again and had 0.018 difference.
Yes the grand total of all the packs is the same just slight unbalanced cells that are balancing themselves out.I don't know if it has to do with the fact that i don't over discharge the battery a lot usual i recharge the pack at 23 volt.

Today i discharged the pack at 22.3 and i want to see the cells deference.Another thing i was thinking about is that the cell meters i use might not be that accurate after all i will try cross checking this with my volt meter.

Thanks again man

 

[Punx0r]

I find my lipo's are better balanced when partially discharged than when straight off the charger. 0.06V isn't *that* much anyway, so I wouldn't worry. As always with lipo, keep an eye on it, in case it's the early warning sign of a weak cell.

 

[Jeremy Harris]

As mentioned before, the voltage of a LiPo cell doesn't tell you anything useful about the state of charge, and hence balance of the pack, except under two conditions; either when the pack is being charged and all cells are at the cut off voltage, or when being discharged and all cells are at the low voltage cut off.

Any voltage reading taken at any other time doesn't give you any clue as to state of charge or pack balance, unfortunately, as float charge dissipates at varying rates and cell voltage is a poor indicator of state of charge for all lithium chemistry cells anyway.

 

[Russell]

As mentioned before, the voltage of a LiPo cell doesn't tell you anything useful about the state of charge, and hence balance of the pack, except under two conditions; either when the pack is being charged and all cells are at the cut off voltage, or when being discharged and all cells are at the low voltage cut off.

Any voltage reading taken at any other time doesn't give you any clue as to state of charge or pack balance, unfortunately, as float charge dissipates at varying rates and cell voltage is a poor indicator of state of charge for all lithium chemistry cells anyway.

I have found just the opposite with LiPo; the voltage tells a great deal about the SOC.

I have never seen my LiPo packs "self-balance" however as the OP has.

-R

 

[Jeremy Harris]

As mentioned before, the voltage of a LiPo cell doesn't tell you anything useful about the state of charge, and hence balance of the pack, except under two conditions; either when the pack is being charged and all cells are at the cut off voltage, or when being discharged and all cells are at the low voltage cut off.

Any voltage reading taken at any other time doesn't give you any clue as to state of charge or pack balance, unfortunately, as float charge dissipates at varying rates and cell voltage is a poor indicator of state of charge for all lithium chemistry cells anyway.

I have found just the opposite with LiPo; the voltage tells a great deal about the SOC.

I have never seen my LiPo packs "self-balance" however as the OP has.

-R

Please tell us more.

I've measured dozens of cells, and have yet to be able to accurately determine SOC from cell terminal voltage. The wide variations from cell to cell in self-discharge rate alone make determining SOC from cell voltage very tough, as float charge voltage will drop by maybe 3 to 4% on some cells, yet they will still retain maybe 99%+ capacity.

 

[Alastor]

As mentioned before, the voltage of a LiPo cell doesn't tell you anything useful about the state of charge, and hence balance of the pack, except under two conditions; either when the pack is being charged and all cells are at the cut off voltage, or when being discharged and all cells are at the low voltage cut off.

Any voltage reading taken at any other time doesn't give you any clue as to state of charge or pack balance, unfortunately, as float charge dissipates at varying rates and cell voltage is a poor indicator of state of charge for all lithium chemistry cells anyway.

I have found just the opposite with LiPo; the voltage tells a great deal about the SOC.

I have never seen my LiPo packs "self-balance" however as the OP has.

-R

Probably i took measurements just after the charge and again latter on and i was thinking it was self balance or something .Today i did a lot of measurements and everything was normal.

 

[miuan]

Please tell us more.

I've measured dozens of cells, and have yet to be able to accurately determine SOC from cell terminal voltage. The wide variations from cell to cell in self-discharge rate alone make determining SOC from cell voltage very tough, as float charge voltage will drop by maybe 3 to 4% on some cells, yet they will still retain maybe 99%+ capacity.

Jeremy, I suggest you study some of the discharge charts posted on ES.
My experience has been very predictable with 20C Turnigys.
4.2V = 100%
4.0V = 75-80%
3.85V = 50%
3.75V = 20%
3.6V = 5%

well... to be honest, by accident I also realized the following
4.5V = 130%

This may vary a bit from brand to brand (e.g. Zippy chart is less flat than Turnigy) but with a pile of identical batteries, variation is minimal.

I've been using total voltmeter only as a fuel gauge while riding and all cells have kept perfect balance until as little as 3.7V which is a reasonable no load cutoff voltage for reliable use.

There is also very little of surface charge sensation. The cells really only drop depending on their internal resistance, i.e. the higher charging current the more they drop back after charger is disconnected. After the load is removed, they get back (almost) to their previous fully charged voltage.

 

[Jeremy Harris]

My experience is that you can get lucky and find some cells are well enough matched for this to give a very rough indicator of SOC (and Zippys seem better than Turnigys in my experience, and both are far better than Headway LiFePO4 cells), but it's hit and miss at best and subject to a lot of variation from one brand to another.

If you get to know your pack, then perhaps you can guess at SOC this way, based on experience of that particular pack, but I've seen wide variations between cells (particularly in Turnigy packs) that make me distrustful of suggesting that such a method is in any way useful.

The unreliability of this method of determining SOC, together with me having been caught out a couple of times with packs going flat unexpectedly, was the reason I went to the trouble of building a capacity meter a couple of years ago. I fit one of these simple "fuel gauges" to every ebike now, as it's far more reliable than measuring cell voltage when it comes to determining capacity left in the pack.

 

[gwhy!1]

I got one of these watt meters from HK ( cheaper than the normal watt meter and does a lot more )and I must say all SOC of my lipos show up more or less correct with it, i.e if the meter says 50% and I charge the battery then it becomes fully charged after putting 5ah back into my 10ah battery.

 

[Punx0r]

Probably i took measurements just after the charge and again latter on and i was thinking it was self balance or something

I don't think it is self-balancing, just coincidence in the way surface charge disipates from your cells

 

[Alastor]

Probably i took measurements just after the charge and again latter on and i was thinking it was self balance or something

I don't think it is self-balancing, just coincidence in the way surface charge disipates from your cells

That's what i like to hear

 

[bobc]

Just to weigh into the volts => state of charge debate.....
I found that ON LOAD - i.e. near the battery max, the terminal voltage is very much the same for most of the discharge curve (what jeremy said)
I found that NO LOAD - the terminal voltage was a nice linear function of state of charge.
But that was just one test, one battery. But it may explain some of the different experiences above....??

 

[Hillhater]

I have charged the 12s2p pack i am having like 15 times with bulk charger as a lilo the charger gets each battery at 25 volt approx.

I am confused ? .. how can you charge a 12s 2p pack at 25volts ??
...12s would need 50volt charge,
...so are you splitting the pack into two 6s 2p packs for charging at 25volts ?

 

[Punx0r]

I imagine so. 6S on the LiIo setting on my charger terminates at 24.6V

 

[Alastor]

I have charged the 12s2p pack i am having like 15 times with bulk charger as a lilo the charger gets each battery at 25 volt approx.

I am confused ? .. how can you charge a 12s 2p pack at 25volts ??
...12s would need 50volt charge,
...so are you splitting the pack into two 6s 2p packs for charging at 25volts ?

Hehehehe how else could i do that without splitting the pack to two ?
Lol i confused you for sure......

 

[Hillhater]

Well actually i figured what you were doing,
.. BUT i am sure that some other readers may not have realized that you actually have 2 packs of 6s 2p cells .
A novice reading your OP may have thought that you were recommending charging 12s 2p at 25v !

 

[Alastor]

Well actually i figured what you were doing,
.. BUT i am sure that some other readers may not have realized that you actually have 2 packs of 6s 2p cells .
A novice reading your OP may have thought that you were recommending charging 12s 2p at 25v !

And i thank you for clarifying that out because there is no room for misunderstandings with lipo charging .

Its probably my bad English

 

[fivari]

Just to weigh into the volts => state of charge debate.....
I found that ON LOAD - i.e. near the battery max, the terminal voltage is very much the same for most of the discharge curve (what jeremy said)
I found that NO LOAD - the terminal voltage was a nice linear function of state of charge.
But that was just one test, one battery. But it may explain some of the different experiences above....??

For me the opposite is true. When I drive my scooter and when I am drawing max current (40A), the voltage gives me a good indication of the state of charge, especially in the second half of my battery and definitely near the end of the battery's capacity . However, when I don't touch the throttle and no current is flowing, the voltage does not give any indication about the SOC.