Fast charging is not (always) good for 340Wh battery and smaller

[jbwheel]

I have a Gotway MCM4 which is using Panasonic NCR18650PF battery cells, like lots of recent Gotway and Kingsong wheels. I have found these informations which indicate that fast charging (5A or 3,5A - 4A using 2 chargers) may not be good for 340Wh and smaller battery packs.

General NCR18650 series : cell at 10°C or below : charge at 0,35C = 1,89 A (2P / 340Wh)   ----  MAX charging is 0,7C = 3,78A (2P / 340Wh)

NCR18650PF : standard is 0,5C = 2,7A  between 10°C and 45°C

For general information as I dont know if these are used in wheels : NCR18650B (used before 18650PF) : 0,25C at 10°C and below, MAX is 0,5C (same apply for NCR18650F)

So it would be recommended to check a wheel battery cell specs before applying a higher charge current as wheel as the room temperature. And maybe do not put to charge just after riding if it too hot or cold outside.

 

[Jason McNeil]

That's why in my post-sales email, have this disclaimer: " Please note that the fast-charger is designed for the King Song 840Wh Wheel ONLY. Using this with other Wheels may result in permanent damage or even the risk of fire!" 

Those PF reference cells are old-hat, the LG & Samsung cells that are used in the top spec Wheels support 4A fast-charging. 

[Keith]

6 hours ago, Jason McNeil said:

That's why in my post-sales email, have this disclaimer: " Please note that the fast-charger is designed for the King Song 840Wh Wheel ONLY. Using this with other Wheels may result in permanent damage or even the risk of fire!" 

Those PF reference cells are old-hat, the LG & Samsung cells that are used in the top spec Wheels support 4A fast-charging. 

As can be read between the lines in @Jason McNeil's reply, fast charging has nothing whatsoever to do with the size of the pack. What matters is the 'C' rating of the cells. An 840Wh 16s pack actually has parallel cells of over 14 Amp hour. In my view, fast charging is anything more than 1 'C' and personally for the best life I'm happier charging at 1/2 'C' I.e. two hour to charge empty to full (plus a bit for balancing). There is absolutely no significant advantage in charging at any lower rate than that. If I remember correctly the "Fast" charger for the KS-14C 840Wh is 5 Amps, that is around 1/3rd 'C' and really isn't in anyway stressing those cells, or indeed truly "Fast" Charging Them

On the other hand, the "standard" 2 Amp charger is dumping 1C into a 130Wh pack, nearly 3 times as fast as a 5 Amp charger on the bigger pack. Put a 5 Amp charger on a 130 Wh pack and you are going well over 2C, not good for the health of anything but the best quality cells, that you don't often see in 130Wh packs!

[jbwheel]

21 hours ago, Jason McNeil said:

That's why in my post-sales email, have this disclaimer: " Please note that the fast-charger is designed for the King Song 840Wh Wheel ONLY. Using this with other Wheels may result in permanent damage or even the risk of fire!" 

Those PF reference cells are old-hat, the LG & Samsung cells that are used in the top spec Wheels support 4A fast-charging. 

For the most recent wheels, the question would remain only for the KS16 340Wh version (still using NCR18650PF like KS14 ?). Kingsong France / Gyroroue shop is selling 4A charger for 340Wh KS...

 

15 hours ago, Keith said:

As can be read between the lines in @Jason McNeil's reply, fast charging has nothing whatsoever to do with the size of the pack. What matters is the 'C' rating of the cells.

For one cell, C "=" cell capacity but for a battery, you can have C "=" number of pack * cell capacity = battery size / average voltage (ex : 60V) = number of pack * (pack size / average voltage)

 

[Keith]

1 hour ago, jbwheel said:

For the most recent wheels, the question would remain only for the KS16 340Wh version (still using NCR18650PF like KS14 ?). Kingsong France / Gyroroue shop is selling 4A charger for 340Wh KS.

@jbwheel, you titled this thread: "Fast charging is not (always) good for 340Wh batteries and smaller". That statement is simply not true, pack size has nothing to do with it.

A fast charge rate of (say) 1C will have the same effect on ANY CAPACITY battery pack made with the same specification cells. Actually a 340Wh KS pack is made up of 16S2P cells of 2.9 Ah. Cells are improving all the time and it isn't unusual now to find cells that can support 2C charging with minimal degradation.

the Rechargeable Lithium Ion Battery INR18650 MJ1 3500mAh Document you originally linked to states a standard charge is 0.5C and max charge is 1C. These are not the cells used in the 340Wh batteries, but assuming at least similar specs for modern good quality cells (as @Jason McNeil stated the best LG and Samsung cells can handle 4Amps per cell - the 340Wh pack has 2 cells in parallel) then 4 Amps is well below the 1C rate for that pack which would be 5.8 Amps. and should be fine.

Pitched correctly, without specific reference to small pack sizes, which is a red herring, I would agree with you:

* It is not a good idea to charge packs at low temperature (below 10 degrees Celsius) If you must do so then a charge rate of less than 0.5C is strongly advised.

* A safe Standard charge rate is 0.5C, this should give a good balance of life against practicality. 

* As long as you or the supplier are sure the cells are of a quality to handle it, fast charging at up to 1C is acceptable. Ideally use 0.5C when you are not in a hurry. Don't forget the BMS and charge leads also need to be specified to handle that current.

As jbwheel stated above, the 1C rating for any pack can be found by dividing the Wh rating of the pack by the nominal voltage. The nominal voltage, if not stated, can be found by: number of cells in series x 3.7V

For example: a KingSong 340Wh pack is 16 cells in series so: 340/(16x3.7) = 340/59.2 = 5.74 Amp hours (actually 2 off 2.9Ah cells in parallel for a total capacity of 343Wh.) For this pack a 1C charge would be 5.8 Amps and 0.5C would be 2.9 Amps.

[jbwheel]

@Keith My title is a "shortcut" which seems to be true for commercially available wheel and because people often do not know their cell reference and therefore the max charging value. I removed the LG MJ1 because it would be a 420Wh battery for 16S2P so over the 340Wh value.

I guess everybody has got the right picture now and it would be more useful to list which wheel with 340Wh or below do accept fast charging.