Building a small A123 Battery Pack

[daniel.weck]

Note that the Turnigy Accucel-6 is factory-configured at 19.8V for 6S (3.3V per cell) which is the nominal A123 voltage, not the rated charge voltage (3.6V).

3.6V *nominal* is often quoted for Li-ion cells (unlike 3.6V *charge* for A123).

LiPo chargers use 4.2V per cell, thus (I guess) the 25.2V figure quoted in your previous post.

Dan

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

 

[Scottyf]

Thats correct.
But my poke at it was that the charger is limited to 50w max output. So regardless of the power supply it simply will not charge any higher than that 50w limit (Although most let up to about 60w).

Based on the 50w Life Chemistry the max charge rates for that charger are :-

50 Watt Max Charger
2s = 7.2v @ 6amp = 43.2watts............Full 6amp Allowed
3s = 10.8v @ 6amp = 64.8watts..........Actual Max 4.6amps
4s = 14.4v @ 6amp = 86.4watts..........Actual Max 3.4amps
5s = 18v @ 6 amp = 108watts.............Actual Max 2.7amps
6s = 21.6v @ 6amp = 129.6watts.........Actual Max 2.3amps

 

[daniel.weck]

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.

I see, thanks!

I actually only use my Turnigy Accucel-6 (limited to 6 cells) charger/balancer for my 2x A123 6S packs. No generic non-balancing charger.

As for balancing the cells...I am now at a stage where I must discharge both 6S packs to figure-out whether they can achieve better distribution. I won't use the built-in discharge function on the Accucel, I prefer to go for several rides out, and to monitor the cell voltages in between each run. I want to get them as low as possible without reaching critical voltages (Depth Of Discharge), and then give them a good charge/balance.

First I need to fix my controller though

Cheers, Dan

 

[jerrysimon]

Going for a three or four mile run, coming back, using your bulk charger then balancing with the accucell usually works.

Testing your battery cell voltages after the run will also tell you if the dodgy cell has whimped out again

Regards

Jerry

 

[daniel.weck]

Going for a three or four mile run, coming back, using your bulk charger then balancing with the accucell usually works.

Does the cheap generic charger cut-out automatically when full-charge is reached, or is there an LED going from red to green?

Testing your battery cell voltages after the run will also tell you if the dodgy cell has whimped out again

Lucky me (so it seems)!!

http://www.pedelecs.co.uk/forum/electric-bicycles/6956-diy-stage-9-a123-nano-battery-pack-photos-3.html#post123408

 

[jerrysimon]

Yep there is a red and green light as you say which shows green when the charge is complete.

Once the 12s1p pack has been balanced a few times, the the generic charger works well and cells stay in balance.

My advice however would be to rebalance every month or two depending on how much you use it.

Fingers crossed for you pack then

Regards

Jerry