1.Protection Circuit Board for 37V 10S Li-ion and Li-polymer battery pack; 2.PCB applies for 10 cells Li-ion/Li-polymer battery pack; 3.To prevent the battery packs from overcharge,overdischarge,over current, over temperature ,short circuit ; 4.Compatible with both Li-ion and Li-Polymer cells. 5.How balancing function works? after battery pack is fully charged. PCM will detect each cell’s voltage and trim higher voltage down until other cells reach the same voltage level. Therefore, it helps cells have longer service life. http://bestechpower.com/37v10spcmbmspcbforli-ionli-polymerbatterypack/PCM-D223V1.html
The specs of your BMS should tell you when it begins balancing
For example the specs for my BMS (from Battery Supports) state:
Technical Parameters:
Balanced current: 60mA (VCELL = 4.20V when) Balanced for: 4.20 ± 0.05 V
Recently I have only been charging to about 80% (4.00V/cell), which means the BMS is not balancing the cells. The max delta voltage between all 12 cells has only grown from 0.02V to 0.04V after several partial cycles without balancing. Perhaps a good practice would be to go to 4.20V every few cycles to force the BMS to balance
That said, I don’t think charging to 100% each cycle will have any real negative effect on battery life. Discharging too far would be much worse
That’s the Bestech BMS logic, I wonder what would be the Battery Supports one.
Lets state an example:
- Battery pack does not charge full with a brick charger only until 41V
- You forcethe charge with a high powered charger as the one you posted from Amazon
- Battery pack reaches 42V
- At least one individual cell was unballanced, 9 packs have 4.15V and the unbalanced one 4.65V (cell has already being damaged)
- Balancing from BMS starts lowering the unbalanced cell from 4.65V back to a normasl 4.2V and rasing the other 9 packs to 42V
If order to verify this you will need meassure the voltage of the highest pack before and while balancing occurs
To me it seems Depth of Discharge is the biggest factor. As long as you don’t let your battery sit at full voltage for long, charging to 4.20V should not adversely affect the overall battery life
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[quote=“Eboosted, post:23, topic:19302, full:true”] That’s the Bestech BMS logic, I wonder what would be the Battery Supports one.[/quote]
They either begin balancing at 3.90V/cell or 4.20V/cell
I have one from SuPower (aka Battery Supports) and I can’t figure out how to tell which model I have. When I bought it from eBay last year, I could have sworn it said 3.9V, which is what their website claims. But their eBay listing now says 4.2V. Emailing them was not helpful at all
Balancing starts at 3.9V: http://www.batterysupports.com/44v-48v-504v-12s-60a-12x-36v-lithium-ion-lipolymer-battery-bms-p-270.html
Balancing starts at 4.2V: http://www.ebay.com/itm/44V-48V-50-4V-12S-60A-Lithium-ion-Li-ion-LiPo-Li-Polymer-Battery-BMS-PCB-System-/221644780045
If a pack was this far out of balance, charging to even 40v would be a problem.
I agree with this theory. I think it is better to charge to 100% and discharge to %40 than to charge to 80% and discharge to 20%
Not if the brick charger stopped the charge (which was the correct thing to do), but with a high power charger as your it might have continued until it reached 42V damaging all unbalanced packs.
Just a thought, maybe I’m mistaken, but wouldn’t be bad to check the voltage of each individual cell.
It’s really hard to say since it is a hypothedical situation and a very unlikely one at that. Normally if you have an extreme out of balance situation, it will be one cell much lower than the rest.
When my battery only charged at 90%, in my case at least, it was because one of the packs was higher than the rest, BMS shutted down the charging cycle to prevent damaging of the highest voltage cell.
When I checked the voltage of individual packs, only two of them had 4.20V and the other nines were 4.05-4.08V, if you sum them all up you got 40.8V only, brick charger refused to charge more. I’m not sure if it’ll be a good idea to force charge the battery with a high powered charger as yours.
To fix my issue, I individually lowered the voltage of one of the unbalanced packs and after that I was able to charge until 95% again, I’m going to lower the other pack as soon as I have time and I’m pretty sure it’ll go all the way up to 42V after that.
I’m not the owner of the truth, just pointing out my own experience.
If the BMS shut down the charging cycle, it would have done that with either charger. A Lab power supply isn’t really a “high power charger” it’s just a power supply that can be used as a charger while allowing the operator full control of voltage and current and lets you monitor the voltage and current going into the battery. Because the power supply switches to CV mode when the battery is around 90% full, the current output decreases steadily to below 1 amp so the final stage of charge is done at very low current.
You can’t take partial information from a source to suit your needs. That same source states how many cycles more you get from not fully charging @jmasta @Namasaki. The proof is there. If you choose to ignore it then that’s your choice…
This is technical data based on lots of research papers. All of their citations are there. We discussed this recently (yesterday) in some other thread.
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They have a chart for charging and a similar chart for discharging.
So you can increase cycles by under charging or by under discharging.
I’m just saying that I believe under discharging is the better option.
And it’s good that we are getting opinions from both sides so that people who read this can make up their own minds.
Partial Charge or Partial Discharge
Or, you could do both if range isn’t an issue.
@Namasaki It just seemed from your initial post that you were dismissive of life cycle improvement through lower full charge. Yes, you can trim up at either end and ideally at both.
80% DoD gets you roughly 33% more cycles 80% Charge gets you roughly 200% more cycles. Take it however you want.
Yeah, that’s the beauty of this forum.
But whatever is the voltage of the whole pack we choose to charge, we need to have each pack well balanced.
Tomorrow I’ll try to manually discharge/balance the highest voltage pack just to see if the charging capacity increases.
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In order for that to be an equal comparison, you would have to discharge your 80% battery to 0% And I don’t think your gonna want to do that. I think that fully charging and partially discharging is the better option because discharging is harder on the batteries than charging. At Least that has been my experience with Lipo batteries. I’ve seen them get hot and swell during discharge but never seen it while charging them.
I did not believe it at the onset of this discussion but now that I have seen the article, I accept that it is true. 
li-ions hate being at high voltage. That is fact. I discharge my li-ions to 2.5V at work all the time.
You measure the temperature delta while charging and discharging at the same current and tell me which one gets hotter. There’s a reason why the charge current rating is way lower than the discharge rating
My point is that we charge at a much lower current than we discharge. Thats partly why I would rather cut the discharge short than the charge. Besides, as we discharge the voltage drops and more current is needed to produce the same wattage.
As I said, I’ve discharged tens of packs down to 2.5V for hundreds of cycles. Look up the spec sheets, manufacturers do it all the time too. I don’t see the point in cutting it short other than you might over discharge a cell if your cells are out of balance.
I have data. Lots of it. I cannot share it since it’s work related but trust me. You rather trim up top than bottom. The numbers don’t lie.
Good night!!! (It’s 2am!!! 