How many mAh in 24 18650 batteries 6.4Ah total?

[broken_card]

I have 24 batteries, labelled US18650V (which I can't find online), from an older 250w Bionx kit.

The battery pack is labelled with: 22.2v, LiMn. Based on online research, I believe this pack has 6.4Ah capability (it's a small battery pack).

To get 22.2v, I figured out that there are 4 sets of 6 batteries in series, each of the 6 battery sets put out 22.2v.

I wish to replace these LiMn batteries.

How can I calculate how many mAh the replacement batteries should be?

 

[cycborg]

Simple answer is 4 cells in parallel for 6.4 Ah would be 1.6 Ah each. But what is your plan, exactly? Do you want to replace all the cells but keep the case, BMS, connectors, etc? Have you extracted the old cells? Will you need to solder or weld the new pack?

doctorbass sells returned Makita battery packs that have these type of cells for $1/cell plus shipping, but you need to put in some effort to extract the cells from the packs and identify the bad ones.

Or you could upgrade to higher capacity cells; modern cells have twice the capacity but since the voltage-SOC profile is similar they ought to work with the existing BMS. It would take twice as long to charge unless you also upgrade the charger.

 

[broken_card]

Thanks for your response Cycborg! How did you get to the 1.6mAh?

By 4 cells in parallel are you referring to: 6 cells @ 3.7v each, connected in series - 22.2volts

This is repeated to make 4 sets (since there are 24 batteries), then connected in parallel produce the same voltage (22.2).

So what math did you do to come up with 1.6 milliamp hours per battery?

To answer your other questions, I just want to replace all 24 batteries with the same batteries to make things simple. I don't think I can just switch to lithium ion (can I)?

However, to order the batteries I need to know how many milliamp hours they are rated at.

 

[cycborg]

Well, I said Ah, not mAh. So 1600 mAh if you prefer.

If the capacity is 6.4 Ah, then each of the 4 parallel strings is 1/4 of this, or 1600 mAh. Each cell in the string also has this capacity - stringing them in series multiplies the voltage but gives the same "ampacity".

Your cells are Li-ion. LiMn is one Li-ion variety; others have some combination of Ni, Co, Mn, and Al. They all have similar V-SOC relationships so you can use a Li-ion BMS interchangeably with any of them. Non-Li-ion varieties you might see are LiFePO4 and lithium polymer (Lipo) which need different BMS settings.

But for a straight swap, 1600 mAh is the number you need.

 

[broken_card]

Wow, that's great info Cycborg.

Apart from ripping apart Makita power packs, have you ever found a cheap source for new 18650 Lithium Ions? I know I can get them from China for pretty cheap, but they don't have soldered tabs on the tops and bottoms, meaning that I have to find some way to solder tabs on myself. I've read that soldering will likely damage the cells unless you do it very quickly with high heat.

 

[cycborg]

A lot of the Chinese battery suppliers will build a pack for you in the configuration you want - maybe try contacting them with photos of what you have now and ask if they can replicate it.

 

[broken_card]

Yeah, I'm trying to communicate with a Chinese company now; but "communication" seems to be the challenge here.

BTW: some batteries say they are protected, others are not. I guess the non-protected versions rely on your charger/controller to sense the battery's charge so as to not overcharge and blow them, correct? I'm guessing that the Bionx charger and circuit board inside the battery case look after all that and therefore I can get regular non-protected batteries, yes?

 

[riba2233]

You must use non-protected cells, protected ones are just for usages when there's only one cell used.

This is good site for new cells, non-chinese:

http://eu.nkon.nl/rechargeable/18650-size.html


They have export site if you are outside EU. They offer some cells with welded tabs, but for more money. Yeah, you shouldn't solder, welding is preferred way for connecting cells. I offer spot welder if you want, you can see it in my signature.

 

[broken_card]

I checked out that website but they do not appear to provide the 1600mAh batteries with tabs.

Thanks for the info re soldering iron; I'd prefer finding batteries with tabs already welded on if possible.

Funny thing: I've been having communication with a Chinese battery manufacturer but they keep telling me that I'm not giving them enough info. I'm saying all I need are 18650's at 1600mAh and 3.7v with welded tabs. They keep saying: what brand, what model??? I must have a half dozen emails like this by now. I guess there are high end and low end batteries even though they have the same basic specs. Seems that the SONY Konion are some of the most talked about batteries for this type of application, but I haven't found these with tabs.

Is it safe to just go with a more popular 2200 or 2400mAh battery, or could these cause problems?

 

[riba2233]

It wont, just put some newer batteries with bigger capacity. Oh yeah, there are many different cells with same capacity. Quality ones are Panasonic (Sanyo), LG, Sony, and Samsung.

 

[broken_card]

Perfect, thanks for your responses!

 

[Cephalotus]

I hope that you dind't have bought any cells yet!

---

The green Sony US18650V cell in your BionX battery was the first "high energy" cell that was called "Konion" in some places of the world.

The most special thing about those cells is that you can use them without a battery management system connected to each cell and without a balancer for many years.

It is VERY(!) important that you use similar cells and not just "some 18650" cells to replace them, because those BionX batteries don't have a balancer built in.

I do recommend the Sony US18650V3 which is the 3rd generation of that type of cells. It offers 2200mAh vs 1600mAh of your actual cells, so a bit more range for the same size/weight.

It is a cheap and good quality cell that does not need balancers.

You could also buy Sony US18650VTC4 or Sony US18650VTC5 which offer similar functionality plus less internal resistance but cost several times more money (be aware, that there are many fakes of these two cells, so if you find a cheap supply it is most likely a fake cell and that can get _very dangerous_ in your battery pack without a BMS that knows individual cell voltages!)

You also need cells to make a 6s4p pack that will survive 25A current and 6-10A recuperation current from your BionX setup.

If you have built your new battery pack (without setting something on fire) you need to recalibrate your BionX battery. With software versions 5.9 or older charge the battery until it is full and than press and hold power on the console for at least 30 seconds. (light will switch on/off for some cycles when doing so).
Empty the battery until power significantly fades and charge full again and the battery gauge should be more or less accurate.
With CAN tools and hacked software (i.e. TinyCAN and bikeinfo) you could reprogramme your battery electronics for 2200mAh cells, otherwise the battery gauge will show empty a bit to soon, but imho this is ok.

For BionX software 6.0 and later there is no way for software calibration, you have to use it for a few full cycles and hope that it will adjust itself to the new capacity...

best regards

 

[riba2233]

The green Sony US18650V cell in your BionX battery was the first "high energy" cell that was called "Konion" in some places of the world.

The most special thing about those cells is that you can use them without a battery management system connected to each cell and without a balancer for many years.

It is VERY(!) important that you use similar cells and not just "some 18650" cells to replace them, because those BionX batteries don't have a balancer built in.

I do recommend the Sony US18650V3 which is the 3rd generation of that type of cells. It offers 2200mAh vs 1600mAh of your actual cells, so a bit more range for the same size/weight.

Most new 18650 cells will also stay in balance. It's probably just the tight manufacturing tolerance, not some "self-balancing" magic. I used pack made of vtc4 cells in a drill, and it got out of balance, because at the higher current tiny differences are more pronounced.

 

[Cephalotus]

Most new 18650 cells will also stay in balance. It's probably just the tight manufacturing tolerance, not some "self-balancing" magic...

I do agree, its just the quality of the cells nd not some magic.
But long term experience is missing with most cells and if you are not able/willing to control the cells regularly I would use what has been proved 1 million times. (i.e. Bosch 36V fatpacks used 1100mAh "Konion" cells without balancers and those are very high power applications)
Bosch also used Samsung cells. I used some Sanyo UR18650E (2100mAh each) without balancers for more than 3 years and around 300-400 half cycles in a 10s3p configuration and they are still nice in balance and have more than 90% of their initial capacity.

That said, I would keep my recommendation for Sony US18650V3. Cheap, good, proven (by ebikes at least) to be useable without balancers...

Btw, imbalances at high C-rates could be a side effect of different cell temperatures in the pack. The "inner" cells get warmer than the outer cells which let them age quicker and leads to higher self discharge = slightly lower voltage/imbalance.

 

[broken_card]

Hey Cephalotus, thanks for the info. No, I still haven't purchased any batteries. I had some other non-bike priorities to deal with the last couple weeks and I'm just getting back to my ebike.

So, based on what you're recommending, I can order something like Ebay item number 221249723161, correct?

Or, do you have an online seller that can provide these batteries with tabs for a better price?

BTW: since my batteries are 1600mAh, can I just replace maybe 8 of the 24 batteries with 2200mAh's or is it all-or-nothing?

Cheers!

 

[999zip999]

I would replace all cells. If you tell them what it's for and send a picture. You should be able to find a Chinese company that can match your pack. More ah the better.

 

[broken_card]

Ya, I found a couple, like Apollo and Joy....I sent them requests for info.

BTW: I noticed a number of comments including warnings by manufacturers about how dangerous these batteries are. I can understand if you short circuit them it might cause problems, but if you wire them up in the same parallel/series pattern then I trust I shouldn't have any danger issues, yes? BTW: should a battery blow while going up a hill or something, won't the Bionx plastic case hold in the damage (unless it catches fire, of course). I just don't want to injure myself while cycling....

 

[riba2233]

Don't worry, modern 18650 cells are pretty safe, even if you short them.

 

[broken_card]

Thanks.

 

[markz]

These Sony Konion US18650VTC4 cells look interesting.

I do not get your math.....

You also need cells to make a 6s4p pack that will survive 25A current and 6-10A recuperation current from your BionX setup.

max. discharge current: 30 A Vtc3 and vtc4.

I thought if thats the absolute max for discharge. Then thats the max for each series circuit. 30A in this case. If using a 29E, then it would be 10A for each series string.
Then for each parallel circuit/string added, you just start adding up the amperage. So 4P = 120Amax, and probably 80Acont. for a 30A cell.
But I doubt each cell will ever get that high. 30A.
Depending on the series cell count, lets make it easy at 10S4P, then each cell in a series string is cranking out 1A to make a 10Acont. per series string. Times 4P = 40Acont., that might be enough for your controller and motor setup. Then perhaps you go up a hill, and need 80Amax for a short time. Then each cell is cranking out 2A.

So 3.6V 2100mAh (15C) 30A, and you are using 2A at most ever, then you are only using 1C out of your 15C battery.
I assume, from reading other forum posts, that this would dramatically increase the cycle life. As most cycle life tests are done at very high C rates.
It could also decrease the voltage sag, then if you were to be cranking out the full 30A from each cell, but that wouldnt make much sense if the series string is limited to only 30A. How could the series string crank out 300A, then collect all parallel together and crank out 1200A? Its not logical atleast not in my mind.

Currently Sony Konion US18650VTC4 3.6V 2100mAh (15C) is 2.75euros. It packs a bigger punch in terms of C rate then the 25r, but the VTC4 has lower capacity (Ah). Not much though. 2100, 2500mAh.
I would hazard a guess that without doing much math, that both the 25r and vtc4 would be running in the 1-2 maybe tops 3C range.

The 25r is 3.40euros.
LG 18650HE2 2500 mAh 20A IMR 2.95euros. Which is almost the same as the VTC4 price 2.75euros.

 

[riba2233]

VTC4 is fine cell, but still lower energy density and it's NMC, not NCA chemistry. It has great cycle life, but calendar life...

 

[markz]

VTC4 is fine cell, but still lower energy density and it's NMC, not NCA chemistry. It has great cycle life, but calendar life...

Energy density as in the chemistry abd/or wh/kg or wh/size.
So NMC is lower energy density, great cycle life.

but calendar life...

Meaning not good calender life? because low energy density?
And NCA is higher energy density, hence good calender life, b/c of higher energy density?

 

[riba2233]

VTC4 is fine cell, but still lower energy density and it's NMC, not NCA chemistry. It has great cycle life, but calendar life...

Energy density as in the chemistry abd/or wh/kg or wh/size.
So NMC is lower energy density, great cycle life.

but calendar life...

Meaning not good calender life? because low energy density?
And NCA is higher energy density, hence good calender life, b/c of higher energy density?

No, no

You got it all wrong, these thing are not connected at all.

NCA has best calendar life of all cells, while NMC is worse, you can see it in that 1 hour video.

Sony vtc4 and V3 have great cycle life, but that doesn't mean that other NMC cells has it two! Cells with same chemistry can have different performance.

Energy density and cell life are not connected in any way. It was only my observation about cell itself.

 

[broken_card]

Bought the Sony batteries as recommended, soldered them all together, tested 22.2 volts just fine. Put it in the bike and the controller powers up but no power to the wheel. If I put it on "G" it does grab the rear wheel meaning that it's trying to return power back to the battery, but in "A" mode, it doesn't assist at all.

Any thoughts on how to test what's going on? BTW: when I put my voltmeter on the pins of my charger, I don't get any readings. I put the black on the ground of the plug and then tried all 4 pins with the red probe but nothing comes up. Is that normal?

btw, I also tried the 30 second reset and it does flash off/on with an internal LED light I guess, but that's about it. It shows the battery as being empty.

 

[broken_card]

It's running!!!

Gosh, I connected the battery to the charger overnight and nothing. Now, I connected the charger to the battery WHILE the battery is connected to the controller and VOILA!!! It works!