50% is not good

[Danny Fenton]

I received two 5S 5000mAh packs fresh off the boat.

 

In one pack, one of the cells was down to less than a volt. The other pack had 4 of the 5 cells at less than 1 volt!!! Not very good really.

 

Anyway the usual stance is that the packs useless. However I thought I would charge each individual cell, and made up a small two pin connector that will straddle adjacent pins in the balance connector. I then used my charger set to a setting that would charge the cell. As soon as I had enough voltage >3v I changed the settings to LiPo, single cell. Each cell took roughly an hour but eventually they came up to 4.2 and have all held good after 24 hours.

 

I am going to give them a good load of 70+ A and see how well they hold up.

 

If you are not comfortable with what I have explained then don't try it yourself, but it's worth a try before condemming them as long as you are careful.

 

Before anybody asks, I couldn't send them back as I had foolishly already split the connectors. Lesson here, measure the cell volts as soon as they arrive, at least then you can send them back.

 

Cheers

Danny

[Vecchio Austriaco]

I did the same once on a 3-cell lipo which arrived with cell voltage so low that the automatic charger refused to charge them. It worked, but in the end the battery was not one of my favorites and went after one year into the bin.

 

Also I have learned and have a small power meter / cell tester which does the work in a second for me...

 

 

[Danny Fenton]

Hi Vecchio, Lipos don't seem to last long with me anyway, which is why I prefer A123 but lipos are currently so cheap and the range of capacities so great, its difficult to choose otherwise.

I too have a cell tester that displays cell voltage one after the other, and cell 3 was showing 3.81 when the others were all 4.19 I tried it on another pack and the same cell, cell 3 was 3.81......... the cell tester was faulty giving a constant WRONG reading for cell 3. So there is a moral here, check your testing equipment with a good meter every now and again.

 

Cheers

Danny

[Peter Beeney]

I did some experiments on some of the very first lipos when they first appeared, they were very small single cells then. One such destructive measure was to reduce the voltage right down to much lower than recommended and find out if they would recover. They duly did, but subsequently they soon gave up the ghost and each succeeding discharge was noticeably weaker. However, newer lipos are a different breed, and I have seen others recently which seem to be faulty, i.e. won’t balance etc., however, when they’re made to do it they perform as well as all the others. So it may be a bit of pot luck!

From the experiences of these and other cells, I would personally not put these in a position where the result of a sudden failure could have a catastrophic effect, such as powering a UBEC to drive the radio. This may not absolutely guarantee an undamaged landing in the event of such an occurrence, but no radio power in the same situation I think would virtually guarantee a damaged one.

Re the faulty cell tester, yes indeed, as I’ve said somewhere in a previous post, I learnt a long time ago that if you get a sudden erroneous reading always check the test equipment first! And that’s not always the easiest thing to get your head round, particularly when everything else is also falling apart around you!

PB

 

Edited By Peter Beeney on 01/05/2011 16:12:05