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Ni-Cad battery experts!

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NutmegCT

NutmegCT

Great Pumpkin
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I've replaced the 10 year old ni-cad batteries in an old screwdriver.

The original five batteries were each 1.2 volt, 180mAh.

The new batteries are 1.2 volt, 2500mAh.

Voltage is the same - 6 volts.

The old charger is rated at 25mA output.

The old 180 battery amperage is about 14 times "less" than the new 2500.

Using the same charger, will it take 14 times longer to recharge the batteries?

:crazy:

(Edit: Old batteries would recharge in about 24 hours - but lose their charge within about five minutes use. I charged the new batteries for 24 hours, but they lost their charge even faster, in about two minutes. Maybe I just didn't charge them long enough?)
 
My guess is 25ma will not charge those batterys at all. Years ago the rule of thumb was charging ni-cads was 10 percent. so with a 2500mah cell that would be 250ma. I'm not sure with more modern cells but 25ma is only 1 percent. What is true is that when fully charged, your new batterys should last 14 times longer!
 
It will take much longer to fully charge the new batteries; but it sounds to me like you've got something else going on. Try charging the new batteries for a week and see what happens. But I think you're going to find there is something sucking the battery down, like binding in the motor.

Any way you could get an ammeter in series with the battery pack?
 
My last business was heavily batteries. NiCad, then NiMH, never Lithiums.
You're telling me you went from 180MAH to 2500 MAH? Gotta be SubC cells. In NiCads, about the only way to get that high.
25MA charger will charge them up in 100 hours, plus a fudge factor. NiCads are very forgiving, at 10% "normal" charge they are designed for "continuous overcharge", if I recall my Sanyo Engineering Manual correctly.
It is one helluva jump, 180 to 2500.
Buy a "smart" charger. It will do NiCad and NiMH, sense voltage (number of cells), and shut down when done. The ones I use are about 800MA charge rate. Just find a new plug or graft the old one on.
Dave
 
Thanks gents. The "issue" is that the batteries (sub-C) are inside the unit (an old B&D), and the charger (really just a transformer) just plugs in to the charging point. I can't just put the batteries "in a charger".

The charger is marked:

Input 120v, 3 watt
output 15v AC

I didn't know the old batteries were 180mA until I pulled the paper covers off. Then I couldn't find 180mA batteries anywhere, so went with the more available 2500. Don't know where to find another AC output charger to plug in to the unit. Obviously there's a diode (?) inside to take care of the AC input.

Hmmm - maybe remove the diode, then jerry-rig a standard smart Ni-Cad charger to plug into the charge point? If so, what amperage output should I look for? 800 mA? 1100 mA? 2500mA?

Thanks.
Tom
 
Didn't say to plug the batteries into a charger. Buy a new high-output charger, with either a new plug to fit or whack the old one off and splice it.
If two sleeves (inner and outer), they are called DC Coaxial Power Plugs, generally 21.mm X 5.5mm or 2.5mm X 5.5mm, altho there are others.
I use 2.5mm plugs.
Centre is generally hot (positive) but you can determine that before whacking by measuring with a voltmeter.
Personally, I cannot recall ever seeing 180mah cells in SubC.
The 1/3A units (short, stubby things) were 600mah.
I started out with 1300mah SubC packs, went to 1400, then 1500, then 1700 (skipped 1600's), then 1800, then 2000, now I can get them in 3300 for the guys who still use NiCads and only want them.
180mah, driving a drill motor, will last about......4-5 minutes.
I do believe yours are 1800's.
The wall wart better not be AC output. I've not seen that. Those "chargers" are only a fixed rate of DC. I have about six Radio Shack units for caboose battery charging. AC in, DC out.
Double check the wall wart tag.
Dave
 
Oh, and on your edit....that's exactly what happens with old NiCads. First thing they won't hold a shelf charge...next, they just puke after a short time.
Typical.
Honest.
I do this.
 
Thanks Dave. Just checked the charger (transformer) output. Definitely 15 VAC. (Edit: measured 15 VAC with a DVM.) That's why I'm afraid to plug in a "battery charger" - which to me look like they all produce direct current that goes directly into the batteries. (right?)

But if I remove what looks to be a diode (between one side of the charger output and one battery terminal - maybe I could use a charger like you're describing?

Edit #2: it's not a screwdriver. Fumble brain strikes again. It's a hand vac with rotating brush attachment. B&D DustBuster Power Brush. Label on back: CORDLESS VAC, Cat No. 9338/9339 Type 2, 6.0 VDC.

The charger label: input 120 VAC, 3 watt; output 15 VAC.

Tom
 
Most likely you can just charge the batteries right through the diode; depending somewhat on what kind of charger you use. The charger produces DC, which the diode conducts continuously, so no problem. The only possible issue might be if the charger is picky about the 0.7 volt drop through the diode, but most of them aren't.
 
NutmegCT said:
:crazy:

(Edit: Old batteries would recharge in about 24 hours - but lose their charge within about five minutes use. I charged the new batteries for 24 hours, but they lost their charge even faster, in about two minutes. Maybe I just didn't charge them long enough?)
Click to expand...
25ma charge, that's 100ma in 4 hours. 1800MAH cells will charge with 25ma in 72 hours, 800MAH in 24. Let me call my battery supplier.
 
No 180MAH SubC's he or I have ever heard of. 1100 is about the smallest. They wouldn't have bothered with 180MAH.

Find a smart charger that will handle 5 cells. Wire it directly into the shoe. Remove the diodes, once you are certain the polarity is correct.
 
Thanks for all the research. I'll hunt up a smart charger this week. I'm assuming I can figure out the polarity, as I can tell the positive from the negative on the batteries, and how they're placed in the unit relative to the charging terminals.

By the way, here's what one of the old batteries looks like. Note the size, and the positive end showing "180" stamped twice around the top. That why I guessed each was a 180mAh cell.

View attachment 27419

View attachment 27420

Edit: note also that I just assumed the amperage of the charging transformer, based on the input (120 VAC, 3 watts) and output (15 VAC).
 
Actually....the 180 is just leftover Mini thermostats they used for top plates on the batteries. Left the 180 degree markings on them...got them cheap....
 
Victory! I got a Tenergy universal smart charger 6-12 volt. Removed the diode (?) from the battery pack unit, checked polarity, plugged in the charger.

In one hour (at 2 amp setting) the charger completely recharged the pack. Runs better than ever.

Also left a recommendation for Tenergy in the vendor forum.

https://www.britishcarforum.com/bcf/showthread.php?90939

Thanks all.
Tom
 
A lot of my batteries come from Tenergy. Major supplier. Cordless Renovations in Iowa is the direct supplier.
 
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