How Often Should I Charge My Wheel?

[longjohnsally]

I'm trying to figure out best practices for charging my 16x.  After reading about a number of cutouts below 50% battery as well as potential reduced speed/torque, my intuition is to constantly keep it topped off.  My concern is that I might be shortening the battery life if I'm constantly just topping it off after quick errand rides that only take me down to 80% - 90% battery.  Is it better to let it get lower before charging  in order to establish a better battery memory or preserve the overall life of the battery?  Is that even a factor with EUC's?

Sorry if this topic was discussed elsewhere.  I couldn't find anything on it.

[gr8ps]

I think it depends. If you are riding near cutout speeds then it will be worthwhile to charge to 100%. Any additional charge/discharge cycles you get by partially charging your battery will be outweighed by damage to you and your wheel when it cuts out. 

I'm a casual rider with just the occasional need for speed. I usually stay below 30 mph and my wheel can do probably around 40 mph with a full battery. I use a power outlet timer to try and get the battery between 80% and 90%. I will charge to 100% maybe 3 or 4 times a year for the long rides and to balance the batteries. If I rode more frequently I would balance it more frequently but with <1,000 miles on the wheel since the last 2.5 years, I'm a low mileage kind of guy. 

[meepmeepmayer]

Don't worry about battery life and just enjoy the ride

Things you should avoid:

• Unbalanced cells. Regularly charge to 100% and keep the charger in a few hours to balance the cells. Once a month or so is easily enough.
• Keeping the battery at very cold (freezing) or hot (car in the summer sun) temperatures.
• Storing (for weeks and months) the battery at 100% or at very low charge percentage. Apparently that wears them out.

The rest is more or less irrelevant and up to you. Trust your intuition and don't overthink/waste your time.

Don't forget safety (more battery % = safer, though 100% vs 90% won't make a difference) and convenience (nothing worse than deciding to go for a longer ride and then the wheel isn't charged up enough!!)

So keep doing what you are doing, and if you need a good conscience, charge to 90% instead of 100% if you only go for shorter rides and charge after each ride (and top up to 100% for balancing purposes occasionally). Whether that actually improves you battery life or doesn't really matter is another question

(No such thing as battery memory.)

[longjohnsally]

3 hours ago, meepmeepmayer said:

Don't worry about battery life and just enjoy the ride

Things you should avoid:

• Unbalanced cells. Regularly charge to 100% and keep the charger in a few hours to balance the cells. Once a month or so is easily enough.
• Keeping the battery at very cold (freezing) or hot (car in the summer sun) temperatures.
• Storing (for weeks and months) the battery at 100% or at very low charge percentage. Apparently that wears them out.

The rest is more or less irrelevant and up to you. Trust your intuition and don't overthink/waste your time.

Don't forget safety (more battery % = safer, though 100% vs 90% won't make a difference) and convenience (nothing worse than deciding to go for a longer ride and then the wheel isn't charged up enough!!)

So keep doing what you are doing, and if you need a good conscience, charge to 90% instead of 100% if you only go for shorter rides and charge after each ride (and top up to 100% for balancing purposes occasionally). Whether that actually improves you battery life or doesn't really matter is another question

(No such thing as battery memory.)

Thanks for all the great info! 

I'm a person of habit, which means that I've been coming home after each ride and just recharging back to 100%.  I bought a fast charger, so I don't even think about it.  If I'm riding every 1-3 days (again...mostly shorter trips like 3-10 miles) is this fine then? 

My charger has a setting to only charge to 80% or 90%.   Would I be better off just recharging each day to 90% and then doing the occasional 100% charge for balancing?

[meepmeepmayer]

3 hours ago, longjohnsally said:

I'm a person of habit, which means that I've been coming home after each ride and just recharging back to 100%.  I bought a fast charger, so I don't even think about it.  If I'm riding every 1-3 days (again...mostly shorter trips like 3-10 miles) is this fine then? 

My charger has a setting to only charge to 80% or 90%.   Would I be better off just recharging each day to 90% and then doing the occasional 100% charge for balancing?

Both options are fine. If partial charging starts being a mental load, just charge to full and forget about it. Or charge only if you end up below 80% (unless you might risk not having a fully charged wheel when you need one) so maybe after every second ride.

If you want to do partial charges, do these.

It really barely matters from all real life experiences here on this forum (= people do all kinds of things and nobody noticed any capacity loss), so whatever works for you

Personally, I charge to ~90% if I have no idea when I'll use the wheel next (and it may stay like this for a week or two... or over the winter), and I charge to 100% (or top up the day/night before) on all other occasions just to be sure to have a full battery when I want one. Nearly 8000km and the only range loss I notice is because I' ride faster than I used to

Edited June 21, 2020 by meepmeepmayer

[longjohnsally]

4 hours ago, meepmeepmayer said:

Both options are fine. If partial charging starts being a mental load, just charge to full and forget about it. Or charge only if you end up below 80% (unless you might risk not having a fully charged wheel when you need one) so maybe after every second ride.

If you want to do partial charges, do these.

It really barely matters from all real life experiences here on this forum (= people do all kinds of things and nobody noticed any capacity loss), so whatever works for you

Personally, I charge to ~90% if I have no idea when I'll use the wheel next (and it may stay like this for a week or two... or over the winter), and I charge to 100% (or top up the day/night before) on all other occasions just to be sure to have a full battery when I want one. Nearly 8000km and the only range loss I notice is because I' ride faster than I used to

Perfect, thank you.  Exactly what I needed to know. 

[Ed in San Diego]

How do you limit the max charge? Is that a wheel controller setting (set via the app)?

[longjohnsally]

39 minutes ago, Ed in San Diego said:

How do you limit the max charge? Is that a wheel controller setting (set via the app)?

I don't know how others do it, but I purchased a rapid charger from eWheels and it has a setting for 80%/90%/100%.  I didn't realize what the setting was for before posting this thread.  The charger also has a readout to tell you current voltage of the cells as well as current rate of charge in amps. 

I expect there are other ways to do partial charges if you don't have the rapid charger.  Maybe putting some kind of voltage meter in the loop?

[meepmeepmayer]

2 hours ago, Ed in San Diego said:

How do you limit the max charge? Is that a wheel controller setting (set via the app)?

Either your charger does it, or you have a timed outlet, or you can use a charge doctor or similar device:

[longjohnsally]

For anyone still reading this thread...I found this very helpful article on charging posted by other forum member.  Good stuff to know.

https://eunicycles.eu/en/module/blocknewsadv/news?id=wszystko-o-bateriach-li-ion-w-monocyklach-elektrycznych

[mrelwood]

A single person’s experience doesn’t mean much in terms of general guidelines, but I’m definitely not the only one being bitten in the behind by 80-90% charging.

I had a habit of charging my 16S to 80-90%, and balance charging for at least 2-3h about every 10th charge. Result: First pack developed a dead cell group at 4000km / 6 months / 100 charge cycles. After replacing the dead cells, the second pack died at 8000km.

 There are several threads on early battery deaths if charging only to 80-90%, some as soon as 2000km at 4 months. A dead cell group is a failed battery, with the power and range of less than 50% of original, added with a great risk of a spontaneous cut off. In comparison, aging cells only lose 20-30% of their capacity at 300 cycles / 20000km.

 Balance charging only every 10th charge is not enough for EUCs. The balancing current on the BMS is just too low. For my MSX I took the habit of balance charging practically every single time. At 12000km / 2 years, the only capacity drop I see can be linked to faster and more aggressive riding, just like @meepmeepmayer above.

I would store the wheel at 40-80% if not ridden for a few days or more. Other than that, I recommend balance charging for a few hours after the charger turns green, at least on every fifth charge. Even every single charge.

Aging cells are not an issue on a large battery EUC. Even extending the drop to 80% capacity from 300 cycles to 1500, is a difference of about 10-15% at 20000km. Only a small handful of riders will ever get a single wheel that far anyway. Risking even the slightest of balancing issues because of that is just not well informed practices.

 Always keep balanced, both the rider and the batteries!

Edited June 23, 2020 by mrelwood

[meepmeepmayer]

2 hours ago, mrelwood said:

and balance charging for at least 2-3h about every 10th charge

Maybe 2-3h is too short for balancing? Longer should work, right?

[Planemo]

18 minutes ago, meepmeepmayer said:

Maybe 2-3h is too short for balancing? Longer should work, right?

Difficult to say without plotting the charger being used. On my PM Battery 6A, the green light comes on at about 750ma and after 2.5hrs its down to 100ma which I believe is below what any balancing would require. I therefore don't see any point in going longer (on my charger anyway).

[Chriull]

54 minutes ago, Planemo said:

Difficult to say without plotting the charger being used. On my PM Battery 6A, the green light comes on at about 750ma and after 2.5hrs its down to 100ma which I believe is below what any balancing would require. I therefore don't see any point in going longer (on my charger anyway).

+1! 100mA is (for most modern "high" capacity) already trickle charging, which is unnecessary stress for the li ion cells.

As rule of thumb (according to batteryuniversity.com) at about 3% of the rated charge current one should stop.

So many 3500mAh are specified to be charged at 0.5C = 1750mAh. For a 6p this would lead to about 3%*6*1750mA=315mA.

1 hour ago, meepmeepmayer said:

Maybe 2-3h is too short for balancing? Longer should work, right?

So this 1-2h after the green light comes on should be some nice time to finish balancing.

[meepmeepmayer]

1 hour ago, Chriull said:

+1! 100mA is (for most modern "high" capacity) already trickle charging, which is unnecessary stress for the li ion cells.

So you shouldn't keep the charger in for too long? Balancing by having a full battery but without charger?

[Planemo]

19 minutes ago, meepmeepmayer said:

So you shouldn't keep the charger in for too long? 

That's they way I understand it, yes. The charger itself never 'shuts off', and the only overcharge protection is via the BMS but that doesn't usually engage until 4.25+v is reached AFAIK, which is a bit over what we really want. I seem to remember someone saying (Chriull?) that current never stops flowing though, which I don't really understand given the 4.25v 'cutoff'. Maybe the current just continuously bleeds after that point, generating nothing but heat. Either way, it's not ideal to just leave the charger in for hours and hours after the batts are saturated.

[Chriull]

28 minutes ago, meepmeepmayer said:

So you shouldn't keep the charger in for too long? 

From https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

"Full charge occurs when the battery reaches the voltage threshold and the current drops to 3 percent of the rated current. A battery is also considered fully charged if the current levels off and cannot go down further. Elevated self-discharge might be the cause of this condition."

"Li-ion cannot absorb overcharge. When fully charged, the charge current must be cut off. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To minimize stress, keep the lithium-ion battery at the peak cut-off as short as possible."

33 minutes ago, meepmeepmayer said:

Balancing by having a full battery but without charger?

Balancing happens just by a paralleled resistor once a cell reaches 4.2V. So every cell above 4.2V gets charged a bit slower. With something around 4.2V/(70...?150? Ohm)=60..28mA less charging current...

So the only thing that happens without charger is all cells above 4.2V get discharged to 4.2V again. Also some kind of balancing.

So if one lets the wheel on the charger with low currents (let's stay with the ~100mA) the cells at or above 4.2V get overcharged with some ~50mA and the cells with voltages below get very very very very very slow charged (100mA == 0.03C charge).

Once the first cell reached 4.24..4.25V the BMS cuts off the charger - so again no balancing once this happens. No idea if this protection circuitry resets automaticly once this cell is discharged again by the balancing resistor and charging continous?

I personally assume this is not worth the risk of "plating and compromised safety"!

So my recommendation if one wants to "enforce" balancing is to do full saturation charges (~1h after green led), ride until ~ 9x% (measured after a rest!) and do a full charge again. And discharge and repeat...

So one stays more or less within the constant voltage stage where balancing happens. Imho minimum stress with maximum balancing.

28 minutes ago, Planemo said:

I seem to remember someone saying (Chriull?) that current never stops flowing though, which I don't really understand given the 4.25v 'cutoff'.

As you wrote - the charger never stops. He just signals with the green led.

Charging current stops with this 4.25V cutoff. If the charging voltage is "perfect" 67.2V, 84V or 100.8V and the cells are in balance it never stops, as this single cell overvoltage protection can never kick in.

28 minutes ago, Planemo said:

Maybe the current just continuously bleeds after that point, generating nothing but heat.

Plus plating, as i cited above