bring NiCd accus back to live

[case-sensitive]

Hi,

is there any truth to the story that one can revive NiCd accus? I got an accu drill, and after 2 years the accus go flat within a few days. I read one could charge them and discharge them on the spot using a resistor. This will reduce the size of the crystals.

Cheers,

Case.

 

[audioguru]

Old Ni-Cad batteries, when over-charged for a long time or are discharged for a long time develop spikes of crystals that penetrate the insulation inside and short-circuit the battery. You can burn out the spikes by feeding a battery cell a high current for a few seconds (without a resistor) but the spikes of crystals develop again in a few days.

Ni-MH batteries do not develop these spikes of crystals but their maximum current might be less than Ni-Cad. A Ni-MH battery the same size as a Ni-Cad battery has about 4 or 5 times the capacity so a charge lasts a lot longer under load.

 

[case-sensitive]

thats good-bye then to the accu drill? Well for now it still works for some time, straight after charging. Suppose pulling the battery packs apart and putting Ni-MH cells in is not an option?

 

[MrAl]

Hi,

Only if you use a different kind of charge mechanism.

An alternative is to use a lead acid battery and decent gauge wire.

I've revived NiCd's in the past but they start going dead again pretty fast. It's not worth the bother. I used a large electrolytic capacitor charged up to generate the current pulse.

The Li-ion based portable drills are supposed to be better now but i dont actually have one yet so i wont comment too much on this. The batteries are easier to work with though.

 

[dr pepper]

You could dismantle the battery pack and re-stuff it, you can get pretty much most sizes of cells, not too difficult if your handy with a solder iron and a screwdriver.

 

[MikeMl]

You cannot solder directly to NiCad cells without damaging them; either buy cells with solder tabs spot-welded on, or you will have to make your own spot-welder

Recent thread on NiCads

 

[audioguru]

You cannot solder directly to NiCad cells without damaging them

Many people solder Ni-Cad cells together even when they have plastic insulators inside.

 

[case-sensitive]

its 2 18V packs, thats 30 cells, half the price of a new cheap one. Maybe just find the dead cells.
And NiMh needs different chargers?

 

[Nigel Goodwin]

You cannot solder directly to NiCad cells without damaging them

While it's obviously preferable not to, I've soldered many over the years - and never damaged a single one.

You can also buy them with solder tags on, for making your own battery packs - but I've mostly used just normal cells (as they are more easily available).

 

[audioguru]

A Ni-Cad charger will not detect that a Ni-MH battery is fully charged and might over-charge it.
Ni-MH cells might not provide the very high current of Ni-Cad cells so they might not do the job.

My new Energizer AA size Ni-MH cells provide 9A of current. My old ones provide a few hundred mA.

 

[Nigel Goodwin]

its 2 18V packs, thats 30 cells, half the price of a new cheap one. Maybe just find the dead cells.

You should NEVER mix old and new cells, always replace them all - and with identical cells.

And NiMh needs different chargers?

It does unless it's just a crude trickle charger.

 

[case-sensitive]

do Lithium ion ones live longer, seems the way to go in professional equipment? As the drill was a cheap one, the accus still last a while and it may die soon anyway?

 

[audioguru]

Lithium batteries pack high power with long duration into a small battery but are expensive. A charge lasts a long time without a load.
Laptop computers, cell phones, my electric radio-controlled airplane models and the Chevrolet VOLT car (I don't know about the new Nissan electric car) use them.
Lithium is dangerous and might explode or catch on fire if it is not charged and discharged properly.

A Lithium battery is destroyed if its voltage drops to less than 75% of a full charge voltage.
A Lithium battery is damaged if it is stored with a voltage that is at full charge.

 

[case-sensitive]

hm, sound like some everyday use tradie stuff, would not like to sit in the shed for 3 months and run empty