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Is the theory of not charging to full capacity to prolong the useful life of the batteries as stated by others not correct?

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11 minutes ago, SlowMo said:

Is the theory of not charging to full capacity to prolong the useful life of the batteries as stated by others not correct?

It's correct, the practice is common practice in the EV world to maximize cell lifespan. 

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42 minutes ago, SlowMo said:

 

Is the theory of not charging to full capacity to prolong the useful life of the batteries as stated by others not correct?

 

25 minutes ago, Jason McNeil said:

It's correct, the practice is common practice in the EV world to maximize cell lifespan. 

I'm very confused by this exchange - 

On the one hand Zlymex is saying we should charge fully and leave the charger connected - that is also what appears in the Airwheel instructions - so that cell balancing takes place.

On the other hand, Jason, you're confirming that it is good practice to NOT fully charge in order to prolong battery life. (excuse the split infinitive...)

What am I not understanding?

 

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Both claims are correct: ideally the BMS would have a setting that would allow the owner to set the level at which they are charged, problems occur when cells are topped-up at different levels which is what Zlymex was referring to.  

Edited by Jason McNeil
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Following on from @esaj (as always) excellent post, I'm in contact with one of the most intelligent & knowledgeable suppliers I've worked with to incorporate a toggle 60v/67v toggle switch. Will need some extensive testing, but the concept will be to offer 60v 'regular' daily charging, then once a week recommend that owners use the 67v setting to top-up the cells. 

567986d7b7ca8_VoltageSelector.jpg.e1548e

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Trouble with not 'topping' EVERY cell off is that the imbalance could get worse over a period of time.  If one cell in the pack drops too low to recover when the rest are half way that one cell will be destroyed and the pack no use.

By charging - and then allowing all the cells to reach the same voltage by the electronics 'bleeding' off excess voltage from the full cells to allow all the weaker ones to catch up - you ensure that you start every cell from the maximum, and theoretically at least, they'll all discharge to the same level.

More complex than I can explain and the above posts from esaj and Jason are spot on, just needs a bit more understanding to get the most out of the knowledge provided here ;) .

I suppose ideally you'd give a full 'balance' charge every 10th or 15th charge, and the rest just short of full to really get the most out of a pack.  Then again, you wouldn't want to remove that charge as quick as we do to extend as well - that means not necessarily pushing the top speed like most of us do, and avoiding high inclines.  Then there's keeping them out of the cold and not bouncing them up and down curbs too but how many of us appreciate all these little things which combine to reduce the possible life a battery can offer and just go out to enjoy ourselves :) .

Your battery won't last forever, bank / budget etc. on replacing it every couple of years if occasional 'leisure' users, or may be even more than once a year if regular 'commuter' users?  At least if you're not expecting too much, then most of the time you'll be more than satisfied?

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  General Paranoia, yap that's it .  Don't care what it is called.  After multiple reports of Hoverboard fires, I will stop charging when I'm not around/asleep.  I've got a lazy (cold) day today, so I guess this a "balance" the battery day.  Thank you all for the insight into the charger.  I've had a habit of hovering over the Wheel, waiting for the charger to go green.  Green is for GO. That's exactly what I've been doing.  Now I now it OK to let it set green for a while every so often.  

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I was under the impression that the BMS balancing of lower voltage cells in was separately controlled from the charging and thus continuous in operation.

I agree that if you truly want a fully charged battery, leave the charge plugged in a while after the light goes green; however, the difference will be very minimal.  On the Ninebot, the charger light turns green when current drops below 120mA.  This means that over a 3 hour period as the current continues to drop, you would likely receive ~ 0.25AH which is negligible in comparison to the battery size.  

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@esaj  The problem I have with many of the charts and test that are on battery university is that they don't state all of the test conditions for the results.  And the actual research papers that they get their information from aren't always available without a subscription to the site where the paper is hosted or a single paper purchase option.  A couple of questions I didn't find clear answers to was 1.  What state was the battery in at the beginning of the charging cycle?  2.  What constitutes a discharge cycle in this testing?  3. What is the correlation between charge capacity and depth of discharge?  4. What is the final state of the battery at the end of the rated discharge cycles (percentage of battery decrease)?

The chart for charge levels you referenced is very surprising and I don't know of any manufacturer or charging system I've used for RC LiPo batteries that recommends charging at <100% of the capacity to prolong battery life.  But until I find something that contradicts the table, I will assume it to be accurate.

Charge level(V/cell)

Discharge cycles

Capacity at full charge

Table 4: Discharge cycles and capacity as a function of charge voltage limit

Every 0.10V drop below 4.20V/cell doubles the cycle but holds less capacity. Raising the voltage above 4.20V/cell would shorten the life.

Guideline: Every 70mV reduction in charge voltage keeps 10% of usable capacity vacant

[4.30]

4.20

4.10

4.00

3.92

[150 – 250]

300 – 500

600 – 1,000

1,200 – 2,000

2,400 – 4,000

~[114%]

100%

~86%

~72%

~58%

Also as the article states:  If you are recharging your EU after each ride and not riding until the battery is dead, the longer the battery will last. One should try to avoid full discharges and charge the battery more often between uses. Partially discharging Lithium batteries is fine. 

Depth of discharge

Discharge cycles

Table 2: Cycle life as a function of
depth of discharge

A partial discharge reduces stress and prolongs battery life. Elevated temperature and high currents also affect cycle life.

100% DoD

50% DoD

25% DoD

10% DoD

300 – 500

1,200 – 1,500

2,000 – 2,500

3,750 – 4,700

If you look at both of these, it appears that the Depth of discharge has a greater effect on the life of the battery than the charge level.  For instance if I charge to ~75% of the battery capacity, I'm getting between 1000-1200 discharge cycles.  But if I charge to 100% and then discharge to 25% (using the same 75% of the capacity), I'm getting 2,000-2,500 discharge cycles.  But the article doesn't really state the starting charge OR state the correlation between the two tables so this has some conjecture involved.

@Jason McNeil, your idea of only partially charging your pack is interesting and would certainly prolong life but why limit the range of your EU?  I certainly wouldn't want to become stranded somewhere because I chose not to fully charge my pack.  Perhaps with the really large packs it would not be as big of a concern.  

If you put aside $0.50 each time you charge the batteries you will always have more than enough money to purchase new batteries.  This would be much more appealing to me than knowing that I'm almost always operating at 75% capacity with the benefit of only having to put aside aside $0.20 each time I charge it for new batteries.

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10 minutes ago, Cranium said:

@esaj  The problem I have with many of the charts and test that are on battery university is that they don't state all of the test conditions for the results.  And the actual research papers that they get their information from aren't always available without a subscription to the site where the paper is hosted or a single paper purchase option.  A couple of questions I didn't find clear answers to was 1.  What state was the battery in at the beginning of the charging cycle?  2.  What constitutes a discharge cycle in this testing?  3. What is the correlation between charge capacity and depth of discharge?  4. What is the final state of the battery at the end of the rated discharge cycles (percentage of battery decrease)?

I cannot tell, as the article isn't that clear on them, but I'd guess that the voltage at the beginning of the charge test would be the "cut-off" voltage (whatever that may be for the cell in their example, 2.5V?), a discharge cycle would be from full to empty (full being the voltage the battery was charged to, so in terms of mAh, less than for a more fully charged cell?), depth of discharge tests would use full 4.2V voltage as starting point and for the last one 

Table 2 compares the number of discharge/charge cycles Li-ion can deliver at various DoD levels before the battery capacity drops to 70 percent. 

But, I'm mostly just guessing here. Battery University does have some discrepancies and out-dated information here and there, but it's the best source for general battery information I've found in concise form without going too much into the details like specific electrochemical reactions (which go way above my head ;)). Also, the company (Cadex) that maintains the pages sells stuff like battery testing equipment, chargers and (I think) batteries, so they sometimes might have some hidden agenda... Now I need a tinfoil hat :P 

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2 hours ago, esaj said:

I cannot tell, as the article isn't that clear on them, but I'd guess that the voltage at the beginning of the charge test would be the "cut-off" voltage (whatever that may be for the cell in their example, 2.5V?), a discharge cycle would be from full to empty (full being the voltage the battery was charged to, so in terms of mAh, less than for a more fully charged cell?), depth of discharge tests would use full 4.2V voltage as starting point and for the last one 

If we are going to assume the charge cycle in the table above is from empty and the discharge cycle in the table above is to empty then for the vast majority of people charging should not ever really be a worry.  They typical 1000+ charge cycles would apply.  

Charge it up as much as you like and recharge after your rides! :)

Storage is another story.  With RC LiPo batteries, if you are going to store them for long periods without use (>1 month) then it is best to store them at 50% charge.  My LiPo chargers have a storage setting that will only charge them to 50%.  I don't know what the recommended storage method is for these EU batteries.

 

Edited by Cranium
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So I have this electric outlet timed cutout thing (the power will turn off 1/2 hour / 3 hours / 6 hours after pressing the button) and I'm wondering if I can use that to avoid over charging the EUC. It won't damage anything to just cut the power like that, will it?

Edited by WakefulTraveller

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Out of interest, as I understand it the balancing only takes place whilst the charger is connected because it is needed to complete the circuit through all the cells in the battery packs.

Will this not still happen if the batteries are only charged to 60V but left connected for a few hours for balancing?

The circuits would still be complete to allow the flow to the weaker cells but no further power would be added once the charger voltage and battery voltage were both equalised at 60V.

Edited by Gimlet

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39 minutes ago, WakefulTraveller said:

So I have this electric outlet timed cutout thing (the power will turn off 1/2 hours / 3 hours / 6 hours after pressing the button) and I'm wondering if I can use that to avoid over charging the EUC. It won't damage anything to just cut the power like that, will it?

AFAIK, no, it shouldn't cause any damage. Rationally, if the pack or charger could  be somehow damaged by cutting the power, how would you ever turn it off, since there (usually) is no on/off-switch, you just pull the plug from the wall outlet? ;)

15 minutes ago, Gimlet said:

Out of interest, as I understand it the balancing only takes place whilst the charger is connected because it is needed to complete the circuit through all the cells in the battery packs.

Will this not still happen if the batteries are only charged to 60V but left connected for a few hours for balancing?

The circuits would still be complete to allow the flow to the weaker cells but no further power would be added once the charger voltage and battery voltage were both equalised at 60V.

I guess some BMSs could be "smart" enough to handle the balancing "properly", but from what I've gathered, many use some form of a "bypass" for the cell, so that once the cell reaches the full 4.2V or so, the current won't pass through the cell anymore, but through something in parallel with the cell (like a 4.2V zener or something). It does (sort of) balance the cells (all get charged to 4.2V) when charging to full voltage, but nothing will happen unless you charge it all the way through to around 67.2V (and then keep in charge for some time until the current drops to some really small value, ie. all the cells have reached 4.2V and it's only the current flowing through the bypasses). But, I could be wrong ;)

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I am trusting my "charge doctor" more and more to turn off at 90% but also noted that to balance takes a few hours after led goes green and do this about every 10 or so.

ukj

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My understanding is as @esaj has stated above. Some BMS may be sophisticated enough to keep all of the cells at the same voltage at all points during charge but many seem to simply shunt the charge around cells once they reach 4.2V, and therefore won't completely balance the pack unless the charger is left on for a few hours after charge shows complete. (And will not balance at all if a lower charge voltage is used) However, if the cells go significantly out of balance after less than 10 lower voltage charge cycles the pack is probably on its way out anyway. Cells are damaged by going to too low or too high a voltage, the BMS should protect from a cell getting too high. However a cell that is out of balance low is it most risk of harm if the battery is discharged near fully, so balancing is probably most important before a long run.

Do not lose sight of my original post though. Whilst the risks may well be very, very low, regularly leaving the charger on all night is betting your life that nothing in the charger or BMS will fail while you are asleep. If you must do it in your house at least make sure you have a good smoke detector!

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