Empty battery showing high voltage ?

[vlad777]

I have Ni-Cd battery 14,4V (12 elements)
(battery pack for aku drill)
that is bad and empty but it still
shows 16V on volt meter.
It gives low current on max load.
It gives 1.7 Amps short circuited.

How do you explain that?

(Maybe bad/old battetry overcharged?)
Thanks.

(BLDC Fan)

 

[Hero999]

What's the capacity?

It could have gone high impedance but that woudn't explain why the voltage is higher than normal.

 

[crutschow]

A recently charged NiCd cell can measure >1.3V, more than its nominal voltage of 1.2V, which would give about 16V for a 12-cell, 14.4V battery. But after a short-circuit test I would expect it to drop to its normal voltage.

 

[vlad777]

I have opened the pack and it's
filled with 12 sub c size batteries.
I dont know the capacity but it's
at least 1Ah.
10 of them give 3-4.5 amps short circuited.
2 of them give 200-400 mA short circuited.
All of them have 1.27-1.29 volts.
So I guess they are full but two of them have
"gone high impedance".
I am not familiar with "gone high impedance"
or battery failures so could you point me to
some links.

Thanks.

(BLDC Fan)

 

[Chippie]

I have opened the pack and it's
filled with 12 sub c size batteries.



So I guess they are full but two of them have
"gone high impedance".
I am not familiar with "gone high impedance"
or battery failures so could you point me to
some links.

Thanks.

Why bother...the pack has had it...buy another and move on...

Treat your battery packs carefully and they might last a bit longer

 

[kinarfi]

Take each cell and hit it a charger or power supply with up to say 16 vdc and with up up to about 15 amps for just one second. This will kill it's memory and it will go back to work for a while, sometimes, quite a while. NiCads develop a memory of how far down they get drained and won't go below that point.
Kinarfi

 

[unclejed613]

two other ways to remove battery memory, 1) hard freeze the battery for 24 hours (below 0F) this breaks up the crystallization that causes battery memory. 2) repeated hard charges and discharges through near short circuits. the internal heating also breaks up the crystals that cause battery memory.

 

[smanches]

They are all dead if short circuiting them isn't blowing them up. A sub-c nicad cell is usually 1200-1400mAh and should be supplying at least 50A in a short circuit. Do not short circuit batteries to test if they are good. Put them on a known load.

 

[BrownOut]

Why bother...the pack has had it...buy another and move on...

Treat your battery packs carefully and they might last a bit longer

Those packs are effing expensive. When I tried to buy new packs for my portable power tools, they were more expensive than I originally paid for the tools! I've given up on cordless tools till they come up with reasonably priced replacment packs.

The Battery Store offered to rebuild the packs, but they were also expensive. I looked into rebuilding them myself, but the bus bars are spot welded to the batteries, and I don't have equipment to do that.

 

[kinarfi]

two other ways to remove battery memory, 1) hard freeze the battery for 24 hours (below 0F) this breaks up the crystallization that causes battery memory. 2) repeated hard charges and discharges through near short circuits. the internal heating also breaks up the crystals that cause battery memory.

I didn't know about the hard freezing! Wonder how well it would work if I went to the welding supply shop and got a thermos of liquid nitrogen to bathe them in, something 300 below.
Kinarfi

 

[creakndale]

I rebuilt a 4 year old worn out 3000mAh 15.6V (13 cell) NiMH Battery pack with higher capacity 3800mAh tabbed cells after finding that the least expensive replacement pack was ~$90 with shipping. I purchased the tabbed cells from an eBay store for 1/2 the price. They have all types and sizes of cells.
eBay Store - All-Battery Center: Battery Charger Kits, 8.4V, Nimh Nicd Batteries

I'm an electronics technician and it took me 4 hours to take apart the old pack and rebuild it. You have to be so careful not to accidentally short out any cells. I drew an arc once while soldering 2 cells together when the soldering iron touched something it shouldn't have. I used a small piece of mylar to keep from melting the plastic directly below the tab areas.

Here's a pic of 12 cells soldered together.

creakndale

 

[BrownOut]

I rebuilt a 4 year old worn out 3000mAh 15.6V (13 cell) NiMH Battery pack with higher capacity 3800mAh tabbed cells after finding that the least expensive replacement pack was ~$90 with shipping. I purchased the tabbed cells from an eBay store for 1/2 the price. They have all types and sizes of cells.
eBay Store - All-Battery Center: Battery Charger Kits, 8.4V, Nimh Nicd Batteries

I'm an electronics technician and it took me 4 hours to take apart the old pack and rebuild it. You have to be so careful not to accidentally short out any cells. I drew an arc once while soldering 2 cells together when the soldering iron touched something it shouldn't have. I used a small piece of mylar to keep from melting the plastic directly below the tab areas.

Here's a pic of 12 cells soldered together.

I wasn't sure that soldier would stick to the plated battery terminals. Maybe I'll try that with my pack. I saved the plastic shell in case I got inspired to try to replace the cells.

creakndale[/QUOTE]

 

[Mr RB]

Here's a pic of 12 cells soldered together.

I wasn't sure that soldier would stick to the plated battery terminals. Maybe I'll try that with my pack. I saved the plastic shell in case I got inspired to try to replace the cells.

creakndale

[/QUOTE]

The battery bodies will always solder easy once you scratch them with sandpaper, I use one of those sandpaper type disposable nail files.

Sometimes the tag lead is stainless steel and almost impossible to solder but you can just cut them off and solder a new wire to the battery casing if the tag is one of the hard to solder types.