Building a small A123 Battery Pack

[banbury frank]

Hi Have yo seen these 96 pieces £200 delivered
all they need is tags welding on ask them for a price

2.2Ah 18650 Li-NiCoMn Cylindrical Battery Cells 1Box 96Pcs - BMSBATTERY



Frank

 

[jerrysimon]

Thanks Frank at first glance I thought you had found something, until you look more closely at the specs

Maximal Continuous Discharge C-Rate: 0.8C(1.76Amps).
Maximal Discharge C-Rate: 1C(2.2Amps).

Even with the 180 watt Tonxin I pull continuous at 5amps and probably peak around 15amps!

I guess you could parrallel them up, but that is a lot of cells to configure and solder up. You can probably buy a ready made battery for less given all that hassle/buying other bits needed.

What I like about my DIY A123 pack is its all simple i.e. no BMS and easy to fix if you need to swap a cell or two out after a couple of years, like I have just done.

I will continue to point out though, that this pack has a limited application and is certainly not the solution for all ebike requirements.

Regards

Jerry

 

[Scottyf]

Thanks D8veh I thought you was using a couple of the cheaper Lipo packs.
Reviews of the C rating and total capacity on most sites says they don't deliver the full 20c bust or 15c continous. But as most Ebikes barely pull over 2c (On faster setups) they should be fine.

Also pulling the lower C rate should increase the capacity of each cell.

I'm hoping there ok as you could effectivly buy a 10ah 44v battery for £120 delivered. Which is a fantastic buy for Lipo. Also very cheap for buying a single battery (5200mah 6s 22.2v) for £30 delivered.

I suppose if your really bothered you could always buy a load of Lipo and a BMS and permanently parallel the batteries up to 13s (From BMS Battery) and buy a charger from them also at the correct voltage and then you've got a safer system.

I still like the A123 batteries for a more robust setup with in theory a longer lasting cycle life.

 

[Deleted member 4366]

T

I'm hoping there ok as you could effectivly buy a 10ah 44v battery for £120 delivered. Which is a fantastic buy for Lipo. Also very cheap for buying a single battery (5200mah 6s 22.2v) for £30 delivered.

I suppose if your really bothered you could always buy a load of Lipo and a BMS and permanently parallel the batteries up to 13s (From BMS Battery) and buy a charger from them also at the correct voltage and then you've got a safer system.

That's what I've done. I have two 44v packs and just received the bulk charger (54v I think). I've also got a couple of their smart (not actually so smart) BMS for 12s lipos, but I haven't fitted it yet to see if it all works as plug-and-play. I've lost interest a bit since I got my 20aH Ping, which means I can have effortless cycling for as far as I want to go. Maybe after I've done the next mods to my Cyclamatic I might come back and sort the lipos. I've no idea about their actual C rating because, as you say, we only use them at between 0 and 2C, which is nothing for them.

 

[Scottyf]

Let me know how you get on with the "Not so" Smart bms. I have a BMS for a 36v setup (10s) that I no longer need but works perfectly. I think that only cost me £5 from Sunlova when replacing my old one.

I would like to see how you get on though as your clearly more teccy than myself.

I think If I had a 20amp battery I might get a bulk charger but for now it takes 2.5 hrs for a 10amp battery using a balanced charge but I can see the need for a larger bulk for more than say 8 lipo's.



How many rough cycles have you compelted with the cheaper lipo setup?

 

[jerrysimon]

As luck would happen another cell has now failed but this time in the other 6s1p pack. At least now I know how to replace it correctly

I had noticed over the last few weeks that the voltage of this cell has been trailing slightly behind the others. It will be interesting to see how long the packs now last with these new cells or if this is the beginning of the end for this two year old pack.

This will be my last spare cell that I purchased when I first got these packs.

With other two new packs, my daughter's and the one I just purchased I will balance them every few months or so.

With this original pack I never really balanced it after it was first constructed and pretty much stop checking cell voltages after six months as they never really went out of balance.

Regards

Jerry

 

[Scottyf]

Thats pretty impressive really. I would have thought a failure would have occured much more quickly.
I constantly balance lipo. The cells being in parallel seem to help each other support and stay in balance. But the 2 min it takes me to pull the pack apart i'm never that fussed.

Don't think i've ever bulk charged or fast charged them.

Still it just shows how much A123 cells seem to take as thats a fair amount of abuse really from a pack without BMS or any management what so ever.

 

[jerrysimon]

Yes Scott not bad and I think I have had my monies worth. They were always bulk charged after the initial balance when I first built them. They might even last longer now I have replaced two cells, but I suspect the other cells will slowly fail one by one.

With these new packs I will treat them a little better and balance them every few months or so

Regards

Jerry

 

[daniel.weck]

I charge my A123 pack (2x 6S packs in series) using the same Turnigy Accucel-6 balancer, but with a cheap generic 12V 5A charger...which recently died (I opened its guts but I can't see any obvious circuit board damage), so I bought a new one for the princely sum of 4.89 GBP from eBay.

Now, the Turnigy Accucel complains when I attempt to charge at 2.5A ("wrong input voltage"), but it works fine at 2.0A. Going through the options on the LCD display, I can see that there is a significant voltage drop on the cheap 12V charger, which isn't surprising after all.

I don't mind waiting for the pack to charge, but I am interested to know what charge intensity you draw from your computer PSU? I imagine that you can afford to crank it up above 2.5 Amps on the Accucel, right?

Cheers, Daniel

 

[Scottyf]

I use an Xbox 360 Power Supply 203w @ 12v. I used it becasue it was spare at the time and to be honest it was cheap as there simple to modify.
It outputs a good 185w that I can use before it shuts its self down with its protection circuit.

Not as good as meanwell supplies but again didn't cost anything. They can even be brought for a tenner on Ebay.

I use it in conjunction with a GT Power A6 10amp charger (Pretty much a Turnigy clone) thats a 200w lipo charger.

This allows me to charge at 7.3amps
Which is ok at charging 6 packs of 6s 5000mah lipo bricks.

I'd like it to be quicker if i'm honest but it would require me bulk charging of buying a better charger.

 

[Scottyf]

Ps Isn't the Accucell charger only a 50w lipo charger?
Which means it won't go past 2amp max really.

 

[jerrysimon]

My DIY PC power supply outputs 5 amps if I recall. I am pretty sure my Accucell charges at 5 amps as well, though I don't usually charge my A123s at more than 1C i.e. 2.3amps.

I am at work so can't check until I get home.

Just to say since I have replaced the two cells the pack seems to be performing well again

It is clear that to get the most out of these packs you should DOD them to empty, though having said that I did it for two years before I had these problems.

Regards

Jerry

 

[Scottyf]

That charger has a 50w max limit.
So regardless of the amp selected it will tone it down to 2amps.

Heres the logic...

50w / 25.2v = 1.98amps
Alot of these chargers usually operate at slightly higher than there rated max.
This is for a 6s Lipo brick.

If your getting a good 2.3amp then is operating slightly higher at...
25.2v x 2.3a = 57.96watts

Even if you set it to do 5amp it won't do it.
5 x 25.2v = 126watts

Hence why on my 200w charger much the same as the above but has an operating max of 10amp will actually only charge at...

200w / 25.2v = 7.93amps
My power supply at that voltage with the losses only safely runs at 7.3amps which isn't far off its max.

 

[daniel.weck]

Ps Isn't the Accucell charger only a 50w lipo charger?
Which means it won't go past 2amp max really.

max 6A charge
(so it says on the label)

 

[daniel.weck]

I don't usually charge my A123s at more than 1C i.e. 2.3amps.

The full 12S pack has a nominal capacity of approximately 2.6Ah, right?

26650 Lithium Ion Cell - A123 Systems Products

CROSS THAT! (brain fart)
--- So for each 6S pack that's 1.3A @ 1C charge rate, not 2.3A ---

Each 6S pack obviously has the same capacity as the total 12S configuration
(only the voltage is divided by two)

I'm currently charging one of my 6S packs at 1.8A (the pack that supposedly has an undervolted faulty cell).

Cheers, Dan

 

[Scottyf]

Doesn't mean it will do it at 25.2v though... ;-)
Check for yourself... Or read the instructions for the charger it says so there.

It'll do the 6 amp charge with the following combinations :-

60 Watt Max Charger (As they circuit protected)
2s = 8.4v @ 6amp = 50.4watts
3s = 12.6v @ 6amp = 75.6watts Actual Max 4.7amps
4s = 16.8v @ 6amp = 100.8watts Actual Max 3.5amps
5s = 21v @ 6 amp = 126watts Actual Max 2.8amps
6s = 25.2v @ 6amp = 151.2watts Actual Max 2.3amps

 

[jerrysimon]

Each cell has a 2.3Ah capacity (written on the battery) thus 1C = 2.3Amps.

My bulk charger charges the 12s at 1.6amps but when I stick eack 6s pack on my Accucell I charge/balance them at 2.3Amps.

All that said you can charge them at 10Amps I think if you want.

Regards

Jerry

 

[daniel.weck]

On my Turnigy Accucel, A123 cells in 6S configuration charge until 21.6V is reached (3.6V per cell).

The first charging phase is Constant Current (CC) - in my case 1.8A - during which my cheap 12V charger sees approximately a -1V voltage drop, at 19.8V constant output from the Accucel. That's theoretically 19.8*1.8=35.64W (not accounting for any loss), so that's about 3A draw from my cheap chinese charger which is rated 5A. Safe margin

The following Constant Voltage (CV) phase doesn't require much (if any at all) current, so the 12V charger sees no voltage drop. This is when balancing occurs, at approximately 20.6A => note that this figure varies, as the capacity is distributed amongst cells until 3.6V is reached for each cell...or in my case never (because I need to cycle my cells a bit more for the proper balance to be achieved)

I guess the figure you quoted (25.2V) applies to LiPo, not nanophosphate technology (LiFePO4 et al.), right?

Cheers, Dan

Doesn't mean it will do it at 25.2v though... ;-)
Check for yourself... Or read the instructions for the charger it says so there.

It'll do the 6 amp charge with the following combinations :-

60 Watt Max Charger (As they circuit protected)
2s = 8.4v @ 6amp = 50.4watts
3s = 12.6v @ 6amp = 75.6watts Actual Max 4.7amps
4s = 16.8v @ 6amp = 100.8watts Actual Max 3.5amps
5s = 21v @ 6 amp = 126watts Actual Max 2.8amps
6s = 25.2v @ 6amp = 151.2watts Actual Max 2.3amps

 

[daniel.weck]

Each cell has a 2.3Ah capacity (written on the battery) thus 1C = 2.3Amps.

Sorry, brain fart!
Each 6S pack obviously has the same capacity as the total 12S configuration
(only the voltage is divided by two)

A123 quotes 2.5Ah capacity per cell, but I totally trust your judgment / observation.

26650 Lithium Ion Cell - A123 Systems Products

 

[Scottyf]

Yes sorry I applied it to Lipo rather than Life.
Either way the charger will not hit the full 6amp limit.



If you parallel charge the 12s batteries into 6s2p you could charge them a bit quicker. Turning the amp limit up on the charger to 5ah (If each battery is 2.5ah capacity). It will also help the cells balance a bit better too. As more cells in parallel help each other to balance.