LiFePO4 32600 (D size) failure

[SteveTheReaper]

I bought these D size LiFePO4 cells and this charger. I shrink wrapped the cells together into a 4 cell stick pack and put them on the charger. They were apparently almost fully charged already, as the light on the charger turned green after a couple minutes.

I put the pack in my HID Mag and ran it for a while. After that, I put the pack on the charger and left it for a while. When I took it off the charger, I found the pack had 0 voltage.

I took apart the pack, and found that the two end cells have 0 voltage, but the two middle cells each have 3.3 volts.

The first thing I suspect is the charger, because I looked on batteryspace.com and saw that the LiFePO4 charger they sold me appears to be the same as this lead acid charger. The charger I have even has the 6V/12V switch covered with a sticker.

I also used a rather powerful magnet on the negative end of the pack to hold the alligator clip on. Could the magnet have caused the problem? Is it the charger? Did I just get defective cells? Does anyone know what the problem is?

 

[lolzertank]

Does your HID Mag have undervoltage protection? If not, the two cells were probably destroyed through reverse charging.

By the way, the charger you linked to is not a very good charger; Series packs of Li cells of any type should be charged with a balancing charger.

 

[SteveTheReaper]

Does your HID Mag have undervoltage protection?

Yes, it will shut off when the input drops below 9v.

 

[luckybucket]

the numbers on that charger do seem somewhat incorrect. i saw a chart a long time ago that showed 3.6 volts as a good cutoff for lifepo4 cells. after that the current dropped dramatically. if this charger stops at 13.8v, then the cells will only be at 3.4 each. that seems a little low. i found that chart by just doing a search for a123 cells, but that was 2 years ago and now i cant find it again.

 

[luckybucket]

since u have 2 cells with 0v then it sounds like bad cells. i charge 2 a123 cells in series with one of their chargers and it works just fine. after they run my 5761 for twenty minutes or so, they normally measure around 2.8v. im curios if they are just duds because i want those cells for my next purchase along with 3 of their 36900's. please keep us up to date with what u find.

 

[SteveTheReaper]

While, the problem is that I'm an idiot. Beacause the ballast I used is rated for 9-16v, I assumed it would just cut off at 9v. I tested it, and it turns out the ballast will continue to run down to about 7v.

 

[luckybucket]

HI,

I'm curious how you like those batteries? I want to buy some and started to do my research and found out that the documentation doesn't make sense. On batteryspace website it states they are 3Ah, but when you download the the documentation it states 2.6Ah. I may as well get 26650 with the same capacity. Did those come with any papaerwork?

 

[McAllan]

By the way, the charger you linked to is not a very good charger; Series packs of Li cells of any type should be charged with a balancing charger.

Yes optimally. However LiFePO4 can be used without but of course it's not how to get the most from your cells. A balance every 10-20 charge is recommended though. The easy way to do it is to charge every cell individually until they reach same voltage. For the last topping up you can parallel them - then they are 100% same voltage. (just don't parallel them with too much different voltage or a great amount of current will flow between them)

At least that's what it says in the assembly document for my ELV LiFePO4 "LIFE4" charger.
In many respects LiFePO4 are quite different from other LiIon chemistries.

 

[luckybucket]

I agree because my 2 cell series charger does not charge correctly. I get 3.8v from one cell and 3.3 from the other. I'm going to order a single cell charger on my next purchase.

 

[SteveTheReaper]

HI,

I'm curious how you like those batteries? I want to buy some and started to do my research and found out that the documentation doesn't make sense. On batteryspace website it states they are 3Ah, but when you download the the documentation it states 2.6Ah. I may as well get 26650 with the same capacity. Did those come with any papaerwork?

I don't use them very heavily, but they're working fine for me so far. They didn't come with any paperwork, but the wrapper on the cell does say 3000mAh. I selected this size just for the ease of fitting them into a D size mag lite.

 

[luckybucket]

I did some research and found a website that showed discharge graphs of the 3.2Ah batteries from battlepack.com and the A123 graphs as well. Both are 26650 in size but one is supposed to have higher capacity with reduced current draw limits. The graph only got 3/4 of the way before it started dropping voltage drastically. My limit is 2.7 volts for the driver I want to use and that meant the difference would only end up being around .4Ah between the two. I chose to buy genuine A123 because I know they will last and can be used in anything if I need them to.