Fast Charging

[Jason McNeil]

There hasn't really been any discussions/debates on the topic of Fast Charging, which is a bit odd. Besides the known/recognized benefits of multiple battery-packs—more power, less stress per cell, higher speed potential, less prone to voltage sag, reduced low-battery threshold—possessing more parallel packs is also hugely beneficial to charging. 

With something like the King Song, with a 4p16s pack (sorry Esaj, I know it's against convention but I prefer the parallel value prefixed  ), in theory the pack should be capable of charging from 10-80% in under an hour with a 8A charger (PLEASE DO NOT TRY THIS, I've been told a KS engineer that the BMS is not compatible with this rate of charge). Using the more conservative 4A charger that we're providing with every King Song 800W/680Wh, it's absolutely terrific to be able to get around the same ride time as charge time.

I wonder why no decent manufacturer has yet to recognize, even as an option, the value of fast chargers. In the first tech specs that were put out by Ninebot this time last year, they mentioned a 250W charger, but never brought it out, why?  

Images of the 4A fast charger below. 

          

Edit: Vee73 is of course the exception: in another post he has a setup which consists of 2x 2000W special chargers for his custom LiPo packs, I think he said was capable of fully charging in 8 minutes!  

[esaj]

1Rad Werkstatt sells 8A (500W) charger for the a bit over 1kWh MSuper -packs, but it also requires the charging-connector to be changed (I understood it comes with the packs, if you so wish), as the original cannot withstand the high current:

The unicycle gets a new high-current charging socket and in addition can be charged with a special charger from us with 8A charging current (500W).
Is thus charged after about 2 hours again and ready for use.

The charging socket is retrofitted and is not absolutely necessary. 
The original charging socket should be charged no more than 4A / excessive heating of the interior (the Wheel) connector.

[Jason McNeil]

Yes, those guys are great! Charge times of 6+ hrs is simply crazy for the likes of the MSuper, faster = better. Are the pin-outs (3 pin) the same? To prevent people from burning up their 132Wh Airwheels, I think it should be physically incompatible. 

[esaj]

Are the pin-outs (3 pin) the same?

I think they use a completely different connector for it, some sort of bullet-connector with 2 pins only (as the 3rd pin is unnecessary even in the original connectors), judging from the pictures. There isn't a picture of the charger, so this is just an assumption, but I don't think it even could be similar as the original/typical charging connector used in wheels, since they say it cannot withstand that high current.

[Chrisxr2]

6 hours to charge, bloody hell. What's considered fast charging then?? Mine takes 2 hours to full.

[esaj]

6 hours to charge, bloody hell. What's considered fast charging then?? Mine takes 2 hours to full.

Your wheel probably hasn't got 680/850/1035Wh batteries like the MSuper options?   If it's a Solowheel Xtreme, it's more like 200Wh.

[Jason McNeil]

The original Solowheels with the 26650 LiFePo4's had the potential to fully charge in 12 minutes. Lack of capacity could have been mitigated by fast-charging; what we had was the worst of both worlds, slow (2A) charge + low capacity, IMO a lost opportunity there.... 

http://www.a123systems.com/Collateral/Documents/English-US/A123 Systems ANR26650 Data Sheet.pdf

[Cloud]

I want a fast charger! 6 hrs is killing me especially when i want to ride twice a day on a weekend. With 6 hrs charging it becomes very hard, the only option is to charge overnight.

i am not an expert on electrical ( even though i work in the energy field), but i always wondered just from a layman's prospective and understanding, why if you have more than 1 battery pack, it cannot be charged in parallel to save time. 

@Jason McNeil , this fast charger is what Kingsong will now be providing or is this something youve come up on your end? I assume this charger can be used with a 2 month old units like mine? Can i get one from you?

thanks!

[Jason McNeil]

@Jason McNeil , this fast charger is what Kingsong will now be providing or is this something youve come up on your end? I assume this charger can be used with a 2 month old units like mine? Can i get one from you?

Yeah, it's an advantage of our 'special relationship' with King Song, most of my reasonable  change requirements get implemented. From what I understand, we, WheelGo.com are the only distributor who offer this...

[Cloud]

Thank you, great, its fantastic that you are able to convince them to implement your suggestions. They are lucky to have such a knowledgeable and objective reviewer as yourself.

 

[esaj]

i am not an expert on electrical ( even though i work in the energy field), but i always wondered just from a layman's prospective and understanding, why if you have more than 1 battery pack, it cannot be charged in parallel to save time. 

If I undestand correctly what you mean, the packs ARE charged in parallel, if you charge a 4-pack wheel with a 2A charger through the single charge port (all the packs are in parallel behind that port), the charging current per pack will be 0.5A (2A / 4 packs = 0.5A per pack). If those are 3Ah packs each, it will take 6 hours (3Ah / 0.5A = 6h). In real life, it will take actually a bit longer, because the charging current will start to drop when the charging enters the constant voltage -phase...

Usually it's safe to charge a 18650-cell at or below 1C-rate (so for 3Ah pack, 3A charging current = 1C), so in theory you could charge four 3Ah-packs with 12A charger, but the connectors and wires in the charging-side of the wheels aren't designed for that high current (they may overheat & melt), and the BMSs of the packs may not be suitable for that high charge current (you don't want to burn your BMSs either ).

Fast charging (= high charging current) stresses the cells, so your battery will start to drop in maximum capacity sooner than with slower charging. Same goes for high discharge rates.

 

[Cloud]

If I undestand correctly what you mean, the packs ARE charged in parallel, if you charge a 4-pack wheel with a 2A charger through the single charge port (all the packs are in parallel behind that port), the charging current per pack will be 0.5A (2A / 4 packs = 0.5A per pack). If those are 3Ah packs each, it will take 6 hours (3Ah / 0.5A = 6h). In real life, it will take actually a bit longer, because the charging current will start to drop when the charging enters the constant voltage -phase...

Usually it's safe to charge a 18650-cell at or below 1C-rate (so for 3Ah pack, 3A charging current = 1C), so in theory you could charge four 3Ah-packs with 12A charger, but the connectors and wires in the charging-side of the wheels aren't designed for that high current (they may overheat & melt), and the BMSs of the packs may not be suitable for that high charge current (you don't want to burn your BMSs either ).

Fast charging (= high charging current) stresses the cells, so your battery will start to drop in maximum capacity sooner than with slower charging. Same goes for high discharge rates.

 

ok i see, so the wires and connector and bms would need to be uprated to take more amperage from the fast charger. 

But why would high current stress the cells? If you compare a unicycle with one battery pack, i understand that the battery experiences the same high current with regular 2A charger as the the uni with 4 battery packs charged with a 8A charger?

[esaj]

ok i see, so the wires and connector and bms would need to be uprated to take more amperage from the fast charger. 

But why would high current stress the cells? If you compare a unicycle with one battery pack, i understand that the battery experiences the same high current with regular 2A charger as the the uni with 4 battery packs charged with a 8A charger?

I don't understand the electro-chemical reactions behind it, but all I know is that the faster charge (= higher charging current) you use, the faster the battery will "wear out". With current Li-Ion cells, which are usually above 2Ah (2000mAh), typically 2.2-3.5Ah, charging at 2A per cell (or 2A per series of cells, so 2A per pack), shouldn't be "too high" or stress them too much. So 8A for 4 packs (especially if the cells are at or above 3Ah) should be still safe and not stress the cells too much. Then the limiting factors are the connectors, wires, and the BMSs. Most wheels even with 4 packs seem to skimp on the BMSs, so that they can even be behind a single BMS. Custom packs usually have their own BMS per pack, and when using high-current connectors & wires, charging at higher current isn't usually a problem.

http://batteryuniversity.com/learn/article/ultra_fast_chargers

The article's a bit out-dated on some details (it seems current NCA Li-Ion cells produce about 260-280Wh per kg, and can discharge at about 3C continuously, and 6-7C at peaks), but mostly I believe this is correct. I'm not a battery "specialist", I mostly just know what I've read from multiple sources  

The maximum charge current a Li-ion can accept is governed by cell design, and not the cathode material as is commonly assumed. The goal is to avoid lithium-plating on the anode and to keep the temperature under control. A thin anode with high porosity and small graphite particles enables ultra-fast-charging because of the large surface area. Although these so-called Power Cells can be charged and discharged at high currents, the energy density is low. The Energy Cell, in comparison, has a thicker anode and lower porosity but this battery should be charged at less than1C. Some hybrid Cells in NCA (nickel-cobalt-aluminum) can be charged at 4C with moderate stress.

Figure 2: Cycle performance of Li-ion with 1C, 2C and 3C charge and discharge Charging and discharging Li-ion above 1C reduces service life. Use a slower charge and discharge if possible. This rule applies to most batteries.

 

[Jason McNeil]

I agree that some of the info on batteryuniversity has been overtaken by developments. In the near future, I see some enterprising Chinese company produce a cheap programmable fast-charger where you can set the charge point, 80% (4.05v cell) or 100% (4.2v cell) & a range of supportable charge currents, it already exists for eBikes.ca, just a matter of time before a less specialized & cheaper one is made for eWheels.

One question that I have not seen satisfactorily answered yet, is what is the consequence of fast-charging (say the max of mfgs recommendation) to 80% capacity for cycle life. Do you still get the 4x improvement in lifespan? Or is the same or worse as regular 1C charging to 100%.  

[checho]

 

I don't understand the electro-chemical reactions behind it, but all I know is that the faster charge (= higher charging current) you use, the faster the battery will "wear out". With current Li-Ion cells, which are usually above 2Ah (2000mAh), typically 2.2-3.5Ah, charging at 2A per cell (or 2A per series of cells, so 2A per pack), shouldn't be "too high" or stress them too much. So 8A for 4 packs (especially if the cells are at or above 3Ah) should be still safe and not stress the cells too much. Then the limiting factors are the connectors, wires, and the BMSs. Most wheels even with 4 packs seem to skimp on the BMSs, so that they can even be behind a single BMS. Custom packs usually have their own BMS per pack, and when using high-current connectors & wires, charging at higher current isn't usually a problem.

http://batteryuniversity.com/learn/article/ultra_fast_chargers

The article's a bit out-dated on some details (it seems current NCA Li-Ion cells produce about 260-280Wh per kg, and can discharge at about 3C continuously, and 6-7C at peaks), but mostly I believe this is correct. I'm not a battery "specialist", I mostly just know what I've read from multiple sources  

Figure 2: Cycle performance of Li-ion with 1C, 2C and 3C charge and discharge Charging and discharging Li-ion above 1C reduces service life. Use a slower charge and discharge if possible. This rule applies to most batteries.

 

Here is an untested idea, based on http://batteryuniversity.com/learn/article/ultra_fast_chargers they talk about ultra fast charger where the charge should only reach 70%.

This charger here:

http://www.ebikes.ca/product-info/cycle-satiator.html

has a 95% efficiency and it is programmable however it can not be used to charge a unicycle properly since it does not reach the voltage 67.2 volts, however it does reach 63 volts as a max, at 63v  for 16 cells that's 3.94V per cell max, that means the max it can charge it is about 70%, but at 8Amps and being programmable it fits the definition of an ultra fast charger, good for when on the road and needing a very  quick charge.

It would be needed to check for a unicycle that the cables can handle the charge, if the cables are to thin they can be upgraded.

So that's my idea for a fast charger, you will not get a full charge, at most 70% charge but very fast.

The key to prevent the batteries to wear out quickly when fast charging is to charge slowly when deeply discharge, and only charge quickly between certain voltages, voltages to low or too high should be avoided with a fast charger.

The problem is that most chargers are cheaply made and for that reason there is the belief that quick charging wears out the batteries, it is true when using a cheap charger, but with a good charger the additional wear on the batteries should be minimal if you avoid fast charging when the voltage is either too low or too high, the charger I mention can not charge too much since it is outside its range for the upper voltage, and for the low voltages it could be programmed to trickle charge for very low voltages, and only do the 8A charging after a certain safe voltage is reached.

I am new in regards to euc I recently purchased a airwheel q3 waiting for delivery, the one I like is the gotway m 18 high torque, but thats for later after I learn to ride, the Q3 seems to be better for learning.

In regards the satiator charger I will post some results later after I get my euc.

Correction, the max watts that the satiator can handle is 360w, at 63volts, it is basically a 5.7A charger not 8A, so a good cycle could be to trickle charge from 32V to 43V, and the fast charge at 5.7A to 63 volts, it will not go beyond 63V.

For a large battery pack like for example 840Wh, this could help a lot, in a rough approximation 3.94V is like a 65% charge based on the chat at batteryuniversity, 65% of 840Wh is 546Wh, at 360W/h it would take 1.5 hours to reach a 65% capacity, which the 2A, charge that is about 130W, it would take 4.2Hours. So an strategy could be to use the satiator to reach 65% capacity very quickly, and then use the slow charger, or use the satiator when on the road.

[Chris Westland]

Here is a great article on the Samsung battery explosions with caveats on fast charging....http://www.allaboutcircuits.com/news/why-samsungs-lithium-batteries-explode-and-how-they-could-change-electronic/?utm_source=All+About+Circuits+Members&utm_campaign=5a64219bdc-EMAIL_CAMPAIGN_2016_11_03&utm_medium=email&utm_term=0_2565529c4b-5a64219bdc-266723477/