DIY stage 9: A123 "nano" battery pack [photos]

[jerrysimon]

Glad you got it sorted Dan. As I said I have not used my charger/balancer since I first built my packs.

I do use the cellog just occasionally to check them. Recently they have been down to barely 12mv out

Regards

Jerry

 

[daniel.weck]

Say hello to my second cheap chinese 12V 5A charger
(actually even cheaper, 4.89 GBP instead of 7 GBP)

The first one died, I should probably not have used 2.5A as the charge current on the Turnigy Accucel-6 (for each 6S A123 pack). I am now using 2.0A or below, which means I just have to wait more...

I also have a dead A123 cylindrical cell (which could actually have contributed to the charger's demise...and actually my 36V 250W eCrazyman controller is also faulty so it could all be related)...so I have to dismantle the pack, replace the cell and solder the balance tabs...unknown territory to me, but I am sure jerrysimon will be able to help

Cheers! Daniel

 

[jerrysimon]

No problem Dan. My DIY A123 pack post has all the details. Feel free to email me if you have problems or if you send it to me I will do it for you, though at the moment I have no spare A123 cells.

Regards

Jerry

 

[daniel.weck]

Thanks

That being said, the pack containing the (supposedly) faulty cell is now charging fine...I am puzzled. One cell (out of the total 6) initially registered a little over 1V on the Turnigy Accucel (the other cells registered normally, that is to say over 3.2V), but after a few seconds it rose to 3V and is now aligned with the other cells! I suppose this could be just the charging voltage, so perhaps as soon as I use/discharge the pack, the (faulty) cell will "collapse" back to a low voltage? I guess I will try and see. It would be nice if the cell "self-repaired" magically If it appears to discharge abnormally again, then I will try the "revive" technique (single-cell charge with higher voltage...I'm looking for tips on the rcuniverse, rcgroups and endless-sphere forums).

As it turns out, my other 6S pack needs a good discharge in order to bring the cells to balance. Right now, some of them get to about 3.6V during charge, whilst others remain at a little over 3.3V. The Accucel doesn't seem to be able to balance them when they are nearly fully-charged, I need to "empty" the cells more in order to allow the balancer to do its job properly.

Thanks again for offering your help! I will let you know how it goes.

/Dan

No problem Dan. My DIY A123 pack post has all the details. Feel free to email me if you have problems or if you send it to me I will do it for you, though at the moment I have no spare A123 cells.

Regards

Jerry

 

[jerrysimon]

Dan I had two cells go down to 1V. They will recharge to full voltage/capacity but will fail again under load/before the battery has discharged.

You could try and see what happens but I suspect it will need replacing.

Re balancing I find that a bulk charge (with my el cheapo 36v 1.6amp charger) followed by a balance on the Accucell usually brings them into balance but can take an hour or two!


Regards

Jerry

 

[daniel.weck]

Dan I had two cells go down to 1V. They will recharge to full voltage/capacity but will fail again under load/before the battery has discharged.

You could try and see what happens but I suspect it will need replacing.

Yeah, I'm not too optimistic about that

Re balancing I find that a bulk charge (with my el cheapo 36v 1.6amp charger) followed by a balance on the Accucell usually brings them into balance but can take an hour or two!

Remind me: is that a Lead-Acid (SLA) 36V charger? Li-ion has a different CC/CV/float-trickle charge pattern, I remember reading that A123 cells can be charged confidently in Lead-Acid mode (assuming the cells do not get overcharged, of course).

 

[jerrysimon]

Yep 3 stage lead acid charger

One of these

Battery Charger 36V 36 Volt 1.6A Electric Bike Scooter | eBay

Or better looking one

New 36 Volt Automatic 3 Stage Bike Battery Charger 36V | eBay

I have both which work fine. The second is more compact and looks more robust.

Ps you will have to change the charge plug to suit.

Regards

Jerry

 

[Scottyf]

Any at 48v ? ;-)

 

[daniel.weck]

Good news!!!!

Dan I had two cells go down to 1V. They will recharge to full voltage/capacity but will fail again under load/before the battery has discharged.

You could try and see what happens but I suspect it will need replacing.

Guess what? So far so good! I loaded up to 10A repeatedly, first by braking whilst the motor/wheel was spinning, then I went for a hilly ride. The voltage sag of the hole pack was clearly visible on the Cycle Analyst (from 40V to just under 36V), but the individual A123 cell is still going strong. Last time I tried riding the bike, the was an unmistakable loss of power due to the cell voltage collapsing under load, and the Cycle Analyst was reaching the low voltage cut-out threshold.

During those tests, I must have discharged the whole 12S pack by about 60%. I recharged both 6S packs to check individual cell voltages, and there are the usual unbalanced discrepancies but no dead cells! I guess time will tell, but this has certainly given me a happy boost!

Wait, there's more: I opened-up the (supposedly) faulty controller after I tried a spare identical one, and guess what? Everything works as normal!!! There was no obvious signs of component damage on the circuit board, so I gave it a good dusting and decided to try it again ==> no cut-out, no problems at all! Very strange...but I am not complaining!

 

[daniel.weck]

Ah, one A123 cell in my 6S pack is now "properly" dead.
(~0V)

Should I attempt to replace the cylindrical cell? (I have basic soldering skills, but the metal tabs look spot-welded, or something like that) I know Jerry Simon has tons of experience with self-made battery packs, thoughts?





Otherwise, my other pack is healthy (shown charging):

 

[jerrysimon]

Hey Dan nice to see you posting. They are simple to change as long as you take care when cutting out the dead sell. My build thread shows this (when one of my cells failed) together with using a replacement cell that already has tabs spot welded onto it. You should be able to get one of those cheaply.

I guess you could solder directly to the cell ends but would need to take care so as not to apply heat directly for too long.

Regards

Jerry

 

[daniel.weck]

My build thread shows this (when one of my cells failed) together with using a replacement cell that already has tabs spot welded onto it.

Ah yes! Thank you for the tip.

 

[daniel.weck]

Ah, I really just need one A123 cell, but given how expensive a single one is (AMR 26650 M1-A 2.3Ah, or even worse: the more recent M1-B 2.5Ah), I thought I might as well purchase another pre-built pack (6S1P) from sz_ohmygod @ eBay (Hong Kong):

http://www.ebay.co.uk/itm/200919174943

http://www.ebay.co.uk/usr/sz_ohmygod

This means ~42£ (inc. postage) for 6x A123 cells (£7 per cell), including spot-welded tabs, balance wires + 6-port JST-XH connector, and AWG14 silicon discharge cables with female Dean connector.

I'll just keep the other 5x A123 cells as spares for other projects

Meanwhile (2-3 weeks delivery waiting time...), I'm using my LiFePO4 10Ah pack:

http://www.pedelecs.co.uk/forum/threads/diy-stage-2-received-li-ping-lifepo4-battery-photos.4734/page-2#post-216434

...and the little Tongxin is still alive

http://www.pedelecs.co.uk/forum/threads/my-e-brompton-tongxin-nano-pulling-steady-at-360w.6724/page-2#post-216677

Ah, one A123 cell in my 6S pack is now "properly" dead.
(~0V)

Should I attempt to replace the cylindrical cell? (I have basic soldering skills, but the metal tabs look spot-welded, or something like that) I know Jerry Simon has tons of experience with self-made battery packs, thoughts?





Otherwise, my other pack is healthy (shown charging):

 

[daniel.weck]

...I might as well purchase another pre-built pack (6S1P) from sz_ohmygod @ eBay (Hong Kong):

http://www.ebay.co.uk/itm/200919174943

http://www.ebay.co.uk/usr/sz_ohmygod

This means ~42£ (inc. postage) for 6x A123 cells (£7 per cell), including spot-welded tabs, balance wires + 6-port JST-XH connector, and AWG14 silicon discharge cables with female Dean connector.

A bit cheaper here by the way, but not in my layout configuration unfortunately:

http://www.a123rc.com/goods-165-Free Shipping 6s 2300mAh A123 Battery Pack - Craft.html

Dan

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