Charging NiCads?

[Pommie]

I have a 24V Dewalt drill that is about 5 years old. In the last month the Dewalt charger has decided that my two batteries are no good and refuses to charge them. This morning the charger decided to charge one of the batteries and I got around half hour use out of it. It now refuses to charge it again.

I have now put the worst of the batteries on my lab supply and have had to turn it up to 29V in order to get a 400mA charge going into it. I'm guessing this is due to a cell or two getting charged in reverse.

Anyway, my question is, can these batteries be rejuvenated by cyclic charging? Has anyone had any luck doing this? I would buy two new ones but they are not available in Australia - Dewalt didn't release the 24V series. Is it worth unpacking them and doing the "high current whisker blasting" on each cell using a car battery?

Any advice, stories, anecdotes appreciated.

Mike.

 

[mvs sarma]

I have a 24V Dewalt drill that is about 5 years old. In the last month the Dewalt charger has decided that my two batteries are no good and refuses to charge them. This morning the charger decided to charge one of the batteries and I got around half hour use out of it. It now refuses to charge it again.

I have now put the worst of the batteries on my lab supply and have had to turn it up to 29V in order to get a 400mA charge going into it. I'm guessing this is due to a cell or two getting charged in reverse.

Anyway, my question is, can these batteries be rejuvenated by cyclic charging? Has anyone had any luck doing this? I would buy two new ones but they are not available in Australia - Dewalt didn't release the 24V series. Is it worth unpacking them and doing the "high current whisker blasting" on each cell using a car battery?

Any advice, stories, anecdotes appreciated.

Mike.

Yes Pommie.
They can be rejuvenated. Generally these cells under question develop a short circuit. You have to access each cell and recod the voltage and of "0" check for short circuit. The selected cells for short circuit can be handled like this.

you can device a rig to pump a heavy current of say 5 or 10 amps as short pulse of say 500 mS. each time you push a button.this would repeat.
with few pulses, the short developed inside would fuse and the cell would then show 1.2 or little more.

repeat the process for other faulty ones. Now put the battery on charge at a low rate as you did not use it for long time. after say 20 hours the battery would have been charged,
Try to have 2 cycles of charge discharge at permitted rate.

By these steps, i was able to restore some cells earlier. For future, perhaps you may wire a LOW voltage sensor and cut off the load.

 

[audioguru]

Ni-Cad is a very old technology. They are 5 yers old but might have spent another 5 years or longer waiting to be sold.
Replace them with a less toxic (cadmium is deadly) Ni-MH battery.

 

[Pommie]

I thought of replacing the C cell size NiCads with AA size NiMH batteries and they would easily fit. My worry is that I may do this and the "intelligent" charger supplied by Dewalt may refuse to charge them.

I've now found a supplier of replacement batteries. I guess I'll blow $200 on two new ones. Actually, I should buy one and play with the older two. They have a chip in them, I wonder what it is?

Mike.

 

[mvs sarma]

I thought of replacing the C cell size NiCads with AA size NiMH batteries and they would easily fit. My worry is that I may do this and the "intelligent" charger supplied by Dewalt may refuse to charge them.

I've now found a supplier of replacement batteries. I guess I'll blow $200 on two new ones. Actually, I should buy one and play with the older two. They have a chip in them, I wonder what it is?

Mike.

Pommie, other day I saw 4500mAH sony AA cells in the indian Market
they said Indian Rs.450/- per set of 2
of course Indian Rs40/- = us $ we get AA to D type cell converter interface in India
I doubt whether C type would suite
It may not be that difficult to make a pic based battery charger. however please see one such design at oshonsoft.com

 

[Pommie]

Pommie, other day I saw 4500mAH sony AA cells in the indian Market

Wow, the largest capacity AA cells I can get here are 2800mAH. Are you sure they are genuine?

Mike.

 

[mvs sarma]

Wow, the largest capacity AA cells I can get here are 2800mAH. Are you sure they are genuine?

Mike.

They appear genuine and marked CYCLE ENERGY

WHAT IS YOUR LOCAL TIME SIR AWAKE SO LATE IN NIGHT , I WONDER

oH. IT IS MOORNING 07-30 FOR YOU
GOOD MORNING TO YOU

 

[audioguru]

Sony-Canada's website lists AA Ni-MH cells:
Ones that have ordinary self-discharge are 2500mAh and ones with much less self-discharge are 2000mAh.

 

[Pommie]

They appear genuine and marked CYCLE ENERGY

WHAT IS YOUR LOCAL TIME SIR AWAKE SO LATE IN NIGHT , I WONDER

oH. IT IS MOORNING 07-30 FOR YOU
GOOD MORNING TO YOU

It's currently 2AM here and I should go to bed. What time is it there?

Mike.

 

[mvs sarma]

It's currently 2AM here and I should go to bed. What time is it there?

Mike.

it is 21-30 Thursday, as we are at UTC + 5-30

 

[shokjok]

Is there a Dewalt distributor in Australia? Do they sell Li-Ion batteries for their tools?
If no luck there, you could try other tool suppliers - what about Dick Smith Electronics? Are they still around?

 

[Krumlink]

The problem with high capacitance cells like that, is that they have a very High ESR rating, so you would not be able to pull very much power out of them. NIMH used to have this problem but now they can outperform NICAD's in some cases. NIMH are way better.

 

[Pommie]

Just to update this thread, I managed to get the batteries to take a charge by forcing them on my lab supply. I then discovered that the Dewalt charger has a discharge/cycle button. I have now cycled both batteries a number of times and they appear to be almost back to full capacity. Moral of the story, find out what that extra button on the charger is for.

Mike.

 

[mvs sarma]

Just to update this thread, I managed to get the batteries to take a charge by forcing them on my lab supply. I then discovered that the Dewalt charger has a discharge/cycle button. I have now cycled both batteries a number of times and they appear to be almost back to full capacity. Moral of the story, find out what that extra button on the charger is for.

Mike.

CONGRATS Mike !

If possible, try to upload a schematic of the "Dewalt charger", we can also enjoy the result of the research done by you. It is nice. I hope you might have even restored the shorted cells.