Discussion A123 cells - my experience..

[retiredVTT]

Ordered my Dewalt pack of 10 A123 cells a month ago from an ebay supplier and got the pack disassembled last night and much to my shock the entire pack read 6.94 volts rather than around 33 to 36 volts ...

this pack left the factory in Feb and here we are in November....had it died...?

I separated a four pack from the 10 cells, hooked it to a Wattage PF12 charger set on Nicd and gave it a 1.2 amp charge for two hours removing it after it took in 2200 mah and showed 14 volts on the meter.

After 11 hours standing....this pack reads 13.42 volts with the cells reading 3.37,3.29, 3.37, 3.37

The next pack of four cells is about to be charged and right now the pack reads 9.90 volts, with the cells at 2.42, 2.50, 2.37, 2.59 volts.

The last two cells read 0.79 and 1.11 for a total of 1.90 volts.

later edit .. (the cells actually increased in voltage AFTER they sat awhile, DISCONNECTED from the balance circuitry, leading one to think that a small drain may occur when they sit for months on the shelf)

Bill

[retiredVTT]

1st 4S pack after 90 minute charge..

[retiredVTT]

I tried charging the 2nd 4S pack on the Apache Smart Charger, and had to "trick it" by setting the jumper for a three cell pack to get it to start.

However 15 minutes later it shut down with the pack only at 12.5 volts. Maybe with a LipoDapter in series with this charger it might work.

So I've put the 2nd pack on the Pf12 charger to bring it to 14 volts ...

(later edit..) After several hours at rest pack #2 is at 13.5 volts with cells at 3.37 3.38 3.38 3.38

Bill

[RC Man]

Does anyone besides A123 Systems make packs using M1 cells?

[everydayflyer]

If they do it remains a secret .

http://www.rcgroups.com/forums/showp...66&postcount=1

Unless you are looking for A123 cells in SPTs.

http://www.modelelectronicscorp.com/...t.html#sptkits

Note weight is incorrect on that site.

[retiredVTT]

The remaining two cells which had a combined voltage of 1.9 volts have been given a couple bumps with 2 cell lipo packs fed through the Astro Wattmeter so I could see what was happening and eventually the voltage came up to 6.2 which was high enough for them to be "recognized" as a 2S pack by the Apache Smartcharger. They are now on it, receiving a low 700 ma charge, and each cell reads 3.35 volts and the pack has taken in 1000 mah.

So, bottom line so far is that ALL cells have "awakened" and taken a charge.

Bill

[Gene Bond]

This is another thing that disturbs me about these packs...

The balancer circuits are apparently contiuously connected, with some leakage, albeit low. The fact that the cell voltages increased once removed from the DeWalt package, IMO confirms this.

These packs could all be dead after some undetermined storage life, if kept in the OEM package...

[retiredVTT]

..here we have the 2 cells that were "at rest" showing 1.90 volts (combined!) now showing 7 volts after being on the Apache charger for a couple hours at a charge rate of 700ma. As the voltage went to 7 and with over 2200 mah being replaced in the "pack" the current showed a slight increase to 720 ma and I pulled the plug..!
Both cells read identical voltage of 3.39 volts each.

I'll run some loads on these tomorrow and see where that leads....I ordered some balance connectors and will install them later....not sure what to balance them with since Blinky will not do it unless you deliberately overcharge them to start with ....they say the Hyperion LBA unit will work ok.

Bill

[retiredVTT]

Originally Posted by Gene Bond

This is another thing that disturbs me about these packs...

The balancer circuits are apparently contiuously connected, with some leakage, albeit low. The fact that the cell voltages increased once removed from the DeWalt package, IMO confirms this.

These packs could all be dead after some undetermined storage life, if kept in the OEM package...

I just saw your post Gene...and maybe you just got the BINGO.....makes sense that a continuous drain over NINE months would lower the pack!
I wished I had read the voltage the moment I took the pack from the box, instead of AFTER I dismantled it. Sure had me worried for awhile. I'm just surprised that I had not read of anyone else experiencing this low votage when initally getting the pack.

Anyone else want to chime in on this?
As shown above the cells seem to have recovered.

Bill

[RD Blakeslee]

Gene, would voltage leakage back through the balancer cause the cells to sink to such widely divergent voltages - most near full charge, one or two way down?

Bill, several people have reprted large variances in A123 cell violtages in DeWalt packs bought on eBay, causing me to speculate about why.

http://www.rcgroups.com/forums/showp...94&postcount=4

- RD

[retiredVTT]

Well, you might have something there..but what I read seems to indicate that when used, these cells tend to huddle around the fire at very similar voltages...!

It's all pretty new stuff, and we modellers are right there in the forefront, so I guess a number of possabilities exist .....but I feel confident that Gene has hit this one out of the park....because initally I had 6.94 volts total but after cutting four cells loose, an hour later I had about nine volts in the second group of four cells, so in that hour they were coming alive..!

Bill

[INewton]

Originally Posted by retiredVTT

Well, you might have something there..but what I read seems to indicate that when used, these cells tend to huddle around the fire at very similar voltages...!

It's all pretty new stuff, and we modellers are right there in the forefront, so I guess a number of possabilities exist .....but I feel confident that Gene has hit this one out of the park....because initally I had 6.94 volts total but after cutting four cells loose, an hour later I had about nine volts in the second group of four cells, so in that hour they were coming alive..!

Bill

I found that these cells like saphions recover from low voltages without a problem. But they will short circuit if reverse biased - For example if you run a 10S cell down to 20V... One or two cells can be destroyed if they are the first to be fully discharged to 0V then reverse voltage.

[Gene Bond]

RD: The leakage current spec on most devices is not as 'critical' of a spec for final testing, so variances could well happen. It would be interesting if the cells in a certain position tend to be the ones thare always low... would make sense as well, depending on what's actually in the potted cuircuit

And, yes, when I have had almost any Li cells discharged too low due to a very light load (like leaving the BEC plugged in), recovery was pretty quick and painless. I believe one of the 'big guys' like Fred or Bob even suggested a very light charge current to wake them back up...

[RD Blakeslee]

Bill,

Just got my toolset from Harbor Freight and opened up a DeWalt pack.

Voltages on each cell, reading from one end of the 10-cell array to the other:

2.886
2.888
2.888
2.850
2.902
2.902
2.863
2.890
0.383 (!)
2.861

If our packs were stolen from stores-
http://www.rcgroups.com/forums/showp...6&postcount=27
-the thieves had an uncanny ability to pick bad packs.

- RD

[INewton]

Originally Posted by RD Blakeslee

Bill,

Just got my toolset from Harbor Freight and opened up a DeWalt pack.

Voltages on each cell, reading from one end of the 10-cell array to the other:

2.886
2.888
2.888
2.850
2.902
2.902
2.863
2.890
0.383 (!)
2.861

If our packs were stolen from stores-
http://www.rcgroups.com/forums/showp...6&postcount=27
-the thieves had an uncanny ability to pick bad packs.

- RD

BTW, there's no difference between .38 v and 2.8v in capacity. They are all the same and fully discharged. Why would you think .38V is any worse than 2.8V for a 3.3V cell?