Bringing Dead Ni-Cad Batteries Back To Life!

[transistor495]

It is nothing about an interesting article bringing dead Ni-Cad cells back into life by surge zapping, just found on instructables(little late). Wanna give it a try.

**broken link removed**

CAUTION:
Can be dangerous if attempted without any patience.
Only for Ni-Cad lovers with a handful of dead ones(Others just skip it).

**broken link removed**
old_bass_mastasays: Dec 4, 2008. 3:55 PM

Question, Can you accidentally electricute yourself with this? (Fatally?!) ihave a bunch of batteries that need it but i'd be afraid.

**broken link removed**
Plasmanasays: Dec 6, 2008. 3:36 PM

That is the only thing you need to worry about, getting shocked... I have not heard any reports of people being killed by a camera, but they reported it hurts bad if you get shocked...

 

[audioguru]

Instructables are designed by people who know nothing about electronics.
It is crazy to use 300V to zap an old Ni-Cad battery cell.

Years ago when I used Ni-Cads (I use modern better Ni-MH cells now) I zapped them with a 15V supply that has a 4700uF capacitor at its output.

There are many crystals that grow and short the cell but a zap blows out only one. Then the next string of crystals shorts the cell soon.
I don't think modern Ni-MH cells develop crystals.

 

[JKF1000]

When the internal chemicals are broken down and crystalizing its time to bite the bullet and retire them, costs of replacements are more than reasonable now and it will be worth it for the gain in milliamphour you get from the new NiMh cells.

 

[Willbe]

If the zap is free and the inconvenience is negligible, zap!
We used a current-limited supply, 1.5A max. It took one second or so of suspense. Wear face protection.

 

[audioguru]

Then zap again tomorrow, and the next day, and ...

 

[transistor495]

Guruji,
I know MiMH is better than Ni-Cd when considering overall. But have a look here:
Advantages of Ni-Cds:
1. Low self-discharge rate(1%) comparing to 5% of NiMH. So NiMH are not suitable for low current drawn applications which is important.
2. Stable terminal voltage during discharge period where an NiMH loses its voltage like a normal cell.
3. Higher discharge rate for rapid current drawn applications.NiMH fails here.

I can see NiMH is environmental friendly and comparatively higher capacity than Ni-Cads which needs more charging time.

 

[Leftyretro]

Guruji,
I know MiMH is better than Ni-Cd when considering overall. But have a look here:
Advantages of Ni-Cds:
1. Low self-discharge rate(1%) comparing to 5% of NiMH. So NiMH are not suitable for low current drawn applications which is important.
2. Stable terminal voltage during discharge period where an NiMH loses its voltage like a normal cell.
3. Higher discharge rate for rapid current drawn applications.NiMH fails here.

I can see NiMH is environmental friendly and comparatively higher capacity than Ni-Cads which needs more charging time.

Point #2 is in error. Show source of this statment if you think I'm wrong.
Here is an extract from Wikipedia:

Sometimes, voltage-sensitive devices won't perform well because the voltage of NiMH batteries is lower than fresh disposable batteries at equivalent sizes, particularly at light loads. Even though the nominal NiMH voltage is lower, it sustains for the length of the discharge cycle, because the low internal resistance allows NiMH cells to deliver a near-constant voltage until they are almost completely discharged. Alkaline discharge voltage drops more towards the end of the discharge cycle.


Lefty

 

[dknguyen]

Yes, point #2 is false. NiCds falter under load more than NiMH does. The reason people put an extra NiMH in series is to make up for the fact that NiMH has a lower nominal voltage than NiCd, not because it's voltage drops more!

 

[audioguru]

Why is everybody wrong? simply look at the datasheets for the different battery cells.

The voltage of a Ni-Cad is exactly the same as a Ni-MH cell. But the Ni-MH cell has 4 times to 5 times the capacity of a Ni-Cad cell.

The voltage from the rechargeable cells stays flat until the charge is gone. The voltage from an alkaline cell continues to drop as it discharges. Therefore the voltage from the "1.2V" rechargeable cells is actually higher than the voltage from the "1.5V" alkaline cell for most of the discharge.

New Ni-MH cells are pre-charged and keep a charge for 6 months to 1 year.

 

[Leftyretro]

Why is everybody wrong? simply look at the datasheets for the different battery cells.

The voltage of a Ni-Cad is exactly the same as a Ni-MH cell. But the Ni-MH cell has 4 times to 5 times the capacity of a Ni-Cad cell.

The voltage from the rechargeable cells stays flat until the charge is gone. The voltage from an alkaline cell continues to drop as it discharges. Therefore the voltage from the "1.2V" rechargeable cells is actually higher than the voltage from the "1.5V" alkaline cell for most of the discharge.

New Ni-MH cells are pre-charged and keep a charge for 6 months to 1 year.

"Why is everybody wrong? "

OK, I'll bite, where was I wrong?

Lefty

 

[audioguru]

OK, I'll bite, where was I wrong?

Lefty

You forgot to provide proof like I did why we are correct.

 

[Leftyretro]

You forgot to provide proof like I did why we are correct.

Ah but I did provide a reference to my statement that point #2 was in error, even highlighted in blue. So there.

oh yea, get off my lawn

Lefty

 

[Roff]

The voltage of a Ni-Cad is exactly the same as a Ni-MH cell. But the Ni-MH cell has 4 times to 5 times the capacity of a Ni-Cad cell.

Then how come the time scales are identical?

 

[Leftyretro]

Then how come the time scales are identical?

Because the current draws shown are different.

 

[audioguru]

I use Energizer Ni-MH AA cells rated at 2500mAh. My Chinese solar garden lights came with Ni-Cad cells rated at only 400mAh and 600mAh. A charge on the Chinese ones does not last long.

 

[transistor495]

Oops! #2 is wrong.
I'm using 4 x 700mah Eveready Ni-Cad cells in my TA7368P rechargeable ipod audio amp. Battery lasts too long. Maybe the IC was superb
Is it possible to get 3000mah and more in NiMH AA. What is the upper limit.

 

[audioguru]

I have 2500mAh Energizer AA Ni-MH cells. Somebody said that the highest available is 2700mAh.

Your Toshiba TA7368 amp IC has an output at clipping of only 0.2W into 8 ohms with your 5V battery. No wonder your very old Ni-Cad battery charge lasted a long time.

 

[transistor495]

I got 5.5V when the battery charged to maximum(10Hrs at 70ma). I got a very strong audio upto around 4.8V. But has taken a bit long duration. When I got a total distortion the whole voltage was only 1.8v(.45v per cell). But I've tested the IC with two Zn-Cl fresh battery. Got good audio. It'll take a while to reach down to 1.8V where the IC fails to operate normally.
You've to make that amp. Performance is superb through my 4ohm 4" whole range speaker. Good overall frequency response.

Ericgibbs has helped me a lot to build the LM317 charger for my amp. It is working fine now.

 

[Roff]

Because the current draws shown are different.

D'oh.

Why the frick do I need to post at least 10 characters?

 

[audioguru]

I got 5.5V when the battery charged to maximum(10Hrs at 70ma).

It is not charged to max because charging has losses. It needs 14 hours at 70mA for a full charge if the battery was completely discharged.

I got a very strong audio upto around 4.8V.

Hee, hee. Do you live in a drawer? The output power of the Toshiba IC at clipping into 4 ohms with a 4.8V supply is only 0.3 Watts which is almost nothing. With the loudest parts of music at 0.3 Watts then the average power is only 0.04W.