safe discharge level for NIMH cells?

[red_robby]

a couple of monthes ago i puchased some NIMH cells on ebay, they showed up 3 monthes later and they all test at 0.6 volts
and some are actually completly drained ( 0 volts ).
are these cells still good ?

 

[vcal]

What I would do with those:
The .6V should go into a smart charger right away.

The .OOV ones may have to be "jolted."
First, put them into a charger. If they start charging, let 'em charge normally. If they do NOT start charging, take each one singly and connect it into a closed series circuit with at least TWO other strongly charged cells-but with the dead cell's polarity REVERSED. Usually about 5 seconds of connection will do the job, allowing the other two cells to jolt the dead cell back into electrical activity. -at least enough to take a charge.

Prognosis on the "dead" cells: about half of them will wind up being serviceable.

At least, on the internet, replacement NIMH cells are cheap these days. /ubbthreads/images/graemlins/tongue.gif

 

[red_robby]

Thanks for the quick reply Doug, i'll try that with the 0.0V
cells and see what happens.
theses cells are supposed to be new 1800mAh NEXcell, would you consider these cells to be "new" ?, they show a capacity of no more then 300mAh...

 

[vcal]

Re:

Are you using something like a Lacrosse or Maha unit to measure that 300 or so...?

Doesn't sound very good, but as you know, cells that are really new are chemically "stiff" and need to be put into several "use" cycles to realize their maximum capacity..

FWIW-I've never had great luck with Nexcells /ubbthreads/images/graemlins/frown.gif ...but maybe they've improved in tha last 3-4 years. YMMV

 

[red_robby]

Re:

i was using the Lacrosse, the maha was charging the cells too hot.
i just spoke with the seller and he tells me the cells were actually discharged by him before shipping /ubbthreads/images/graemlins/thinking.gif, only god knows why he would do that.

 

[SilverFox]

Hello Red Robby,

When NiMh cells have been allowed to self discharge all the way down (which takes about 1.5 years) they generally have lost some capacity. They usually require some "forming" cycles to get some of that capacity back.

300 mAh out of a 1800 mAh cell is not good. You need to discharge the cells (down to 0.9 volts), then charge them at 180 mA for 14 hours. After about 5 cycles of this, they hopefully should give you more than 1620 mAh of capacity at a 0.25 A discharge rate.

Good luck.

Tom

 

[SilverFox]

Hello Red Robby,

You posted before I finished my post.

If the cells were "just" discharged prior to shipping, they should come right back. The way they are acting suggests that they have been in the discharged state for "some time."

Just put them in the La Crosse charger and select the refresh mode. Come back in a day or so and see how they are doing.

Tom

 

[red_robby]

Thanks tom,
i doubt the seller discharged these cells before shipping, it just makes no sense, i think these cells have been sitting around for a long long time.
I'll try the refresh mode and see what i end up getting.
First i'm off to ebay to leave some feedback ( not the good kind )

 

[koala]

red_robby (hooded)?,

Does your ebay NiMH has any brand?

vince.

 

[red_robby]

Vince,
yes, they are NEXcell 1800mAh brand.

 

[VidPro]

i had some nexcells , , HAD. only 2 left out of the bunch, and they sure didnt make it 300 cycles.
i will never buy them again, even if they improve thier methods. burn me once.

 

[JonSidneyB]

it wasn't me....I don't discharge cells before shipping

 

[red_robby]

[ QUOTE ]
JonSidneyB said:
it wasn't me....I don't discharge cells before shipping

[/ QUOTE ]
that would not have even crossed my mind!, you are not even in the same ball park as this freakin idiot...
BTW after refreshing the cells in the la crosse charger i'm getting just over 1400mAh cpacity.