nimh replacement batteries for nicad cordless drill

[inetquestion]

I had a craftsman 14.4v cordless drill that was in good shape except
for the ni-cads losing their charge capacity. I jolted each one of
the cells a few years ago and got great results at that time. Now
that the problem resurfaced...I tried it again with no luck. Since
NiMH cells were available, I decided to replace all the cells with
these. For some reason both of the two packs never seem to get much
of a charge. Is there something special these type packs need in
terms of charging? Or is there something inherently missing by using
a nicad charger on a NiMH battery pack?

-Inet

 

[Jim Yanik]

I had a craftsman 14.4v cordless drill that was in good shape except
for the ni-cads losing their charge capacity. I jolted each one of
the cells a few years ago and got great results at that time. Now
that the problem resurfaced...I tried it again with no luck. Since
NiMH cells were available, I decided to replace all the cells with
these. For some reason both of the two packs never seem to get much
of a charge. Is there something special these type packs need in
terms of charging? Or is there something inherently missing by using
a nicad charger on a NiMH battery pack?

-Inet

NiMH requires a different charging system.
Most NiCd chargers use a thermal sensor in the pack to cut off charge when
the pack nears full charge,but that doesn't work with NiMH.
You may have permanently damaged your NiMH cells.(ruined them)

 

[Phil Allison]

"inetquestion"

I had a craftsman 14.4v cordless drill that was in good shape except
for the ni-cads losing their charge capacity. I jolted each one of
the cells a few years ago and got great results at that time. Now
that the problem resurfaced...I tried it again with no luck. Since
NiMH cells were available, I decided to replace all the cells with
these. For some reason both of the two packs never seem to get much
of a charge. Is there something special these type packs need in
terms of charging? Or is there something inherently missing by using
a nicad charger on a NiMH battery pack?

** So you bought 12 NiMH cells - what size, brand and what mAH capacity ??

Do ( or did) the cells get warm during charging ??

How did you connect them all up ?

Apply a hot soldering iron to them, maybe ??




........ Phil

 

[inetquestion]

"inetquestion"




** So you bought 12 NiMH cells - what size, brand and what mAH capacity ??

Do ( or did) the cells get warm during charging ??

How did you connect them all up ?

Apply a hot soldering iron to them, maybe ??

....... Phil

The nicads were replaced with 12 - 3500mah sub-c nimh cells with
solder tabs. Connected in series...yes they were soldered.

They don't seem to get hot during charging that I've noticed.

 

[Phil Allison]

"inetquestion"
"Phil Allison"

The nicads were replaced with 12 - 3500mah sub-c nimh cells with
solder tabs. Connected in series...yes they were soldered.

** Those tabs are meant for spot welding - but soldering them is OK.

Long as you know how to solder.

They don't seem to get hot during charging that I've noticed.

** No-one here can give any sensible advice as the problem is unique to you
are the charger you own.

Normally what you SAY you have done works.



........ Phil

 

[Dave Platt]

NiMH requires a different charging system.
Most NiCd chargers use a thermal sensor in the pack to cut off charge when
the pack nears full charge,but that doesn't work with NiMH.

Hmmm. In my readings of the literature from battery manufacturers, it
appears that a thermal-sensing cutoff is actually _preferred_ for NiMH
(as long as it's properly designed and calibrated).

NiCd chargers sometimes use a thermal cutoff, and often use "negative
delta V" detection circuit (the battery terminal voltage rises during
charge, and then drops slightly after full charge is achieved and the
battery warms up).

The negative-delta-V system isn't very good for NiMH batteries,
though, as the voltage doesn't drop as much after full-charge is
achieved, and the battery can suffer a significant overcharge before
it occurs. I've read in several places that *this* is the reason that
chargers originally designed for NiCd batteries are often ungood for
NiMH charging.

The cutoff regime that manufacturers seem to recommend, is a primary
cutoff based on rate-of-temperature-rise (absolute-temperature-rise is
also usable but not as sensitive), with a secondary cutoff based on a
zero-delta-V detection (i.e. peak voltage), and a tertiary cutoff
based on a timer.

 

[TT_Man]

SNIP

** Those tabs are meant for spot welding - but soldering them is OK.

Long as you know how to solder.




** No-one here can give any sensible advice as the problem is unique to
you are the charger you own.

Normally what you SAY you have done works.



....... Phil

I agree, it should work fine for your purposes...
Try charging them twice...leave a few hours between charges.
Try measuring the terminal voltage after a charge. You should see about
1.4 - 1.5 V per cell

 

[Fred Bloggs]

I had a craftsman 14.4v cordless drill that was in good shape except
for the ni-cads losing their charge capacity. I jolted each one of
the cells a few years ago and got great results at that time. Now
that the problem resurfaced...I tried it again with no luck. Since
NiMH cells were available, I decided to replace all the cells with
these. For some reason both of the two packs never seem to get much
of a charge. Is there something special these type packs need in
terms of charging? Or is there something inherently missing by using
a nicad charger on a NiMH battery pack?

Sounds like your charger is on the blink, and there was nothing wrong
with your NiCd pack...

 

[Phil Hobbs]

Sounds like your charger is on the blink, and there was nothing wrong
with your NiCd pack...

IIRC nickel hydride cells don't have the peak capacity of a similar
NiCd, so they're not as well suited to things like drills, where you
need lots and lots of torque for brief periods.

Cheers,

Phil Hobbs

 

[Phil Allison]

"Phil Hobbs"

IIRC nickel hydride cells don't have the peak capacity of a similar NiCd,
so they're not as well suited to things like drills, where you need lots
and lots of torque for brief periods.

** Very far from true, nowadays.

The OP has used 3500mAH sub-C size NiMH cells.

These have extraordinary performance compared to any Ni-Cd ever made of the
same case size.

Ask any RC modeller.



........ Phil

 

[Fred Bloggs]

IIRC nickel hydride cells don't have the peak capacity of a similar
NiCd, so they're not as well suited to things like drills, where you
need lots and lots of torque for brief periods.

Cheers,

Phil Hobbs

I'm not sure about that, they were designed as a less toxic replacement
for the NiCd market, they certainly come in large capacities and battery
packs for tools. The only notable downside to the NiMH chemistry that
I'm aware of is the relatively high self-discharge rate, but this is now
overcome, see the Rayovac "hybrid" NiMH technology for example, right
now available only in AA and AAA size.
This seems like a fairly comprehensive comparative survey and summary of
NiMH power tool performance:
http://www.eeb.org/activities/waste...r-tools-NiMH-and-low-temperature-Sept2004.pdf

 

[Fred Bloggs]

IIRC nickel hydride cells don't have the peak capacity of a similar
NiCd, so they're not as well suited to things like drills, where you
need lots and lots of torque for brief periods.

Cheers,

Phil Hobbs

See Annex 2 Behnke, German EPA, 2001, Summary of discussion with power
tool suppliers (Makita, Panasonic,
Bosch, Black & Decker, Metabo) additions by S. Karcher, 2004, says "high
current approximately the same."

 

[Phil Hobbs]

See Annex 2 Behnke, German EPA, 2001, Summary of discussion with power
tool suppliers (Makita, Panasonic,
Bosch, Black & Decker, Metabo) additions by S. Karcher, 2004, says "high
current approximately the same."

Good to know, thanks all. One of the many things I've been out of date
on, obviously.

Cheers,

Phil Hobbs