Charging NiMH battery pack

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Jim Wilkins

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Jun 17, 2021, 7:53:00 AM6/17/21
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I bought a $35 pair of replacement battery packs for my 14.4V DeWalt drill
that contain NiMH instead of NiCad cells like the original. Amazon reviews
claim the original DW9118 charger handles them without problems, but having
been a battery test tech I wanted to know more.

DeWalt says their chargers need a true sine input so for remote job site
solar+battery use I bought a 300W Bestek inverter which gets decent reviews.
Mine shows a nice 113V sine wave on a scope and cuts off at 350W. Some users
wrote that a modified sine inverter blew their charger's fuse or worse. The
AC input feeds a capacitor rather than a transformer.

I recorded the voltage and current while charging the old NiCad and found
that the charger ignores the small negative steps as each cell tops off and
begins generating oxygen, instead it cuts off the current once a minute and
measures the battery voltage. Charging ends when the zero-current voltage
reaches 17.0V, or ~1.42V per cell. The charging current of 1.3A raises the
voltage almost to 18V before the individual full-charge cell drops begin,
ending at 17.65V. When the NiCad pack was new (or new-old-stock) it measured
17.13V at full charge.

Internet sources suggest without firmly stating that constant-voltage
charging to 1.4V~1.45V per cell is acceptable, though the last part of the
charge is slow.

So does anyone have hands-on experience with replacement drill battery packs
that use NiMH cells instead of the original NiCads?

John Doe

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Jun 17, 2021, 3:13:01 PM6/17/21
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Also post to an electronics group...

You can use sci.electronics.design, labeled "OT: ..."

Or sci.electronics.basics

Good luck.

Clifford Heath

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Jun 17, 2021, 7:35:40 PM6/17/21
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I can't answer your main question, but I avoid NiMH because they go flat
too quickly when not used, and after three months cannot be charged
again. They're hella expensive to replace usually as well.


CH

David Billington

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Jun 17, 2021, 7:55:32 PM6/17/21
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I can't help with your query but last year I converted my 14.4V Bosch
NiCd battery pack to Lithium. I found 4 18650 Li cells was close at
14.8V and fitted beautifully in the Bosch pack, 3 fore aft, and 1
across, these were tabbed cells so I made a simple PCB to couple them
and hold them together, on top of the PCB I mounted a supervisory board
for over charge, over discharge sensing and wired to the standard
battery pack contacts. For the charger I used a 4 cell Lithium charger
wall wart and gutted the original NiCd charger to just leave the bare
PCB and charging contacts with leads to those and a socket to connect to
the Li charger plug with its lead going into the original charger in
place of the mains lead. I've had no problems and it has revived a
useful tool and the new pack is 3.6Ah as opposed to the original 1.2Ah.

Jim Wilkins

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Jun 18, 2021, 7:08:00 AM6/18/21
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"David Billington" wrote in message news:sagndj$cm2$1...@dont-email.me...

On 17/06/2021 12:52, Jim Wilkins wrote:
> ...
> So does anyone have hands-on experience with replacement drill battery
> packs that use NiMH cells instead of the original NiCads?
>
I can't help with your query but last year I converted my 14.4V Bosch
NiCd battery pack to Lithium. I found 4 18650 Li cells was close at
14.8V and fitted beautifully in the Bosch pack, 3 fore aft, and 1
across, these were tabbed cells so I made a simple PCB to couple them
and hold them together, on top of the PCB I mounted a supervisory board
for over charge, over discharge sensing and wired to the standard
battery pack contacts. For the charger I used a 4 cell Lithium charger
wall wart and gutted the original NiCd charger to just leave the bare
PCB and charging contacts with leads to those and a socket to connect to
the Li charger plug with its lead going into the original charger in
place of the mains lead. I've had no problems and it has revived a
useful tool and the new pack is 3.6Ah as opposed to the original 1.2Ah.

Thanks. Were you able to determine the battery discharge rating and the
tool's current draw?

The tabbed 18650s I've collected are in outdated cell phone chargers, so
they may not have a high enough discharge current capacity, maybe only 2C. I
bought them to refurbish old laptop batteries and since a few had dropped
slightly below 3V and self-disabled, I recharged them directly with a lab
power supply, as I learned to do at Segway. Unlike a smart charger, a
current-limited power supply will try to recover a fully discharged battery.

I suppose I could measure the drill's stall current with a 20A power supply
or 12V battery and the 18650's max output (outdoors) with my 1 Ohm 1000W
rheostat.

I stopped testing the NiMH in the DeWalt charger when the voltage rose above
19V. They came at 16.5V and charged reasonably quickly at 17~18V 0.5A from a
power supply, to the endpoint of 0A drawn at 17V. Anderson PP45s fit
directly onto the battery contacts and I wired the charger contacts to
external PP45s.
https://www.powerstream.com/NiMH.htm

Jim Wilkins

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Jun 18, 2021, 8:05:26 AM6/18/21
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"Clifford Heath" wrote in message
news:168982c86c6e8452$1$1356503$70dd...@news.thecubenet.com...

On 17/6/21 9:52 pm, Jim Wilkins wrote:
> ...
> So does anyone have hands-on experience with replacement drill battery
> packs that use NiMH cells instead of the original NiCads?
>

I can't answer your main question, but I avoid NiMH because they go flat
too quickly when not used, and after three months cannot be charged
again. They're hella expensive to replace usually as well.
CH

------------------

Many brands of these non-OEM NiMH packs had lots of very negative reviews. I
chose a more expensive version with mostly good reviews.

For years I've let NiCads in tools I rarely used self-discharge flat and
then brought them up when needed with a lab-type power supply until the
charger would accept them. In contrast I try to top off my lead-acids
monthly and my lithiums once or twice a year.

https://en.wikipedia.org/wiki/Nickel%E2%80%93cadmium_battery
"In fact, Ni–Cd batteries in long-term storage are typically stored fully
discharged."

Clifford Heath

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Jun 18, 2021, 8:16:22 AM6/18/21
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I did a similar refit using 4 26550's on a Ryobi pack that had has 11
sub-C NiCd. I still use it every day, but one cell in particular is
becoming weak:

<http://polyplex.org/electronics/ryobi_lifepo4/index.html>

CH

Bob F

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Jun 18, 2021, 2:13:04 PM6/18/21
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On 6/18/2021 5:05 AM, Jim Wilkins wrote:
> "Clifford Heath"  wrote in message
> news:168982c86c6e8452$1$1356503$70dd...@news.thecubenet.com...
>
> On 17/6/21 9:52 pm, Jim Wilkins wrote:
>> ...
>> So does anyone have hands-on experience with replacement drill battery
>> packs that use NiMH cells instead of the original NiCads?
>>
>
> I can't answer your main question, but I avoid NiMH because they go flat
> too quickly when not used, and after three months cannot be charged
> again. They're hella expensive to replace usually as well.
> CH
>

The "pre-charged" NiMH are not supposed to have that problem.

David Billington

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Jun 18, 2021, 6:12:35 PM6/18/21
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I worked out the peak current by measuring the motor resistance and
selected suitable new cells from a vendor which could supply them with
tabs already welded on. With the cost of the cells and a few other bits
it might have been better to buy a new drill as it might not have been
much more expensive but it was interesting to do it. I've only done the
one pack at the moment but have all the bits ready to do the 2nd just
need to get the soldering iron out.

Jim Wilkins

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Jun 19, 2021, 12:26:20 PM6/19/21
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I stripped a dead battery pack for its connector, which I mounted on a
dowel. It had been spot-welded to the (-) end of a NiCad. For part of the
fitting I completed an adapter to clamp a Dremel in a lathe tool holder, and
wish I'd done it years ago, it's so handy!

David Billington

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Jun 19, 2021, 2:30:09 PM6/19/21
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My neighbour has done the same so he can mount his Dremel on his Myford
for various operations. Needed for one job and then found to be useful
for many others. Similarly I can mount a couple of my die grinders on my
lathe. Some years ago I introduced him to my new to me linisher and he
found it so useful he kept popping round to use it, in the end he bought
his own and got it at a good price I guess as the auction finished
Sunday lunchtime when the football was on.

Jim Wilkins

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Jun 19, 2021, 4:43:24 PM6/19/21
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"David Billington" wrote in message news:sald3g$iv1$1...@dont-email.me...
----------------------

Somewhere I have a laminate trimmer head with a 1/4" collet I bought cheap
intending to mount on the lathe. It won't be as easy as the Dremel which
already had an adapter for my small lathe that could be quickly modified.

Jim Wilkins

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Jun 19, 2021, 5:13:28 PM6/19/21
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"David Billington" wrote in message news:saj5oh$he0$1...@dont-email.me...

I worked out the peak current by measuring the motor resistance and
selected suitable new cells from a vendor which could supply them with
tabs already welded on. With the cost of the cells and a few other bits
it might have been better to buy a new drill as it might not have been
much more expensive but it was interesting to do it. I've only done the
one pack at the moment but have all the bits ready to do the 2nd just
need to get the soldering iron out.

---------------------------

After wiring the battery connection adapter I measured the fully On
resistance as 4.8 Ohms, likely that high because it has an electronic
variable speed control. Restraining the chuck with my hand as best I could,
the 20A power supply current-limited and dropped to 4V, and a (very) quick
check on the last half-decent NiCad peaked at 35A.

The drill has plenty of torque on a 12V lead-acid which may be how I power
it to raise the head of my sawmill between logs.

Jim Wilkins

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Jun 19, 2021, 5:48:47 PM6/19/21
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"David Billington" wrote in message news:sald3g$iv1$1...@dont-email.me...


...Some years ago I introduced him to my new to me linisher and he
found it so useful he kept popping round to use it, in the end he bought
his own and got it at a good price I guess as the auction finished
Sunday lunchtime when the football was on.

-----------------------

After I ordered some 1/2" x 12" sanding belts for an auto body air sander I
began seeing ads for the same size belts in very fine grits for a sharpener.
I also have a 1" x 30" belt sander with some unsupported space above the
platen that I use for freehand deburring. Do these sound like good
candidates for "linishing"?

The blacksmith/knife maker whose class I took had a large and powerful
shop-made 3 wheel belt sander for shaping blades. I tried it, but I'm
experienced enough with a 7" angle grinder to remove metal as fast and
reasonably neatly, with the work in a vise so it doesn't burn my hand.

David Billington

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Jun 19, 2021, 6:34:10 PM6/19/21
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Sounds like we have some of the same kit, I too have a 1/2" x 12"(12mm x
300mm) air belt sander and the linisher, maybe you'd call it a vertical
belt sander, sounds much the same though is 25mm x 1065mm (1" x 42").
The bit above the platen does get the most use, the platen not so much.
I refurbish glass blowing jacks occasionally and reshape the parts built
up freehand with an angle grinder, one can do surprisingly fine work
with care and the right choice of discs.

Jim Wilkins

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Jun 19, 2021, 9:32:12 PM6/19/21
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"David Billington" wrote in message news:salrd0$cmn$1...@dont-email.me...

...
I refurbish glass blowing jacks occasionally and reshape the parts built
up freehand with an angle grinder, one can do surprisingly fine work
with care and the right choice of discs.

------------------------

I bought a batch of name brand saucer disks for my 7" angle grinder cheap,
then found that they were rejects whose hubs hadn't been staked securely
enough, so I machined a hub that screws tight to salvage them. Lathe time is
good time when making metal take whatever shape I imagine. The saucer shape
is nice for grinding welds flat because it continues to cut only at the
outer rim as it wears down, and thus guides itself to make a flat surface.

Jim Wilkins

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Jun 19, 2021, 10:01:18 PM6/19/21
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"David Billington" wrote in message news:salrd0$cmn$1...@dont-email.me...

Sounds like we have some of the same kit, I too have a 1/2" x 12"(12mm x
300mm) air belt sander and the linisher, maybe you'd call it a vertical
belt sander, sounds much the same though is 25mm x 1065mm (1" x 42").
The bit above the platen does get the most use, the platen not so much.

--------------------

My Delta 1" x 30" belt sander is a light-duty hobby machine whose main
virtue is that it's compact and light enough to occupy shelf instead of
bench space when not in use. I think yours is the better choice if there's
serious work to do.

Snag

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Jun 21, 2021, 9:03:52 AM6/21/21
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I bought 2 aftermarket NiMH batteries for my 18V DeWalt , the 9118
charger worked fine . Until a couple of weeks ago when I let the magic
smoke out of it . Probably moisture in/on the PCB . The new aftermarket
unit will only charge batteries that have the 3rd contact on the center
fin , so 3 of my batteries are now useless .
Snag
Race only matters to racists ...

Jim Wilkins

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Jun 21, 2021, 5:15:39 PM6/21/21
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"Snag" wrote in message news:saq2nm$m02$1...@dont-email.me...

I bought 2 aftermarket NiMH batteries for my 18V DeWalt , the 9118
charger worked fine . Until a couple of weeks ago when I let the magic
smoke out of it . Probably moisture in/on the PCB . The new aftermarket
unit will only charge batteries that have the 3rd contact on the center
fin , so 3 of my batteries are now useless .
Snag

----------------------

The DW9118's no-load output is 45V. On Amazon it's described as being only
for 7.2V to 14.4V NiCds. I'm still investigating how to fully charge a NiMH
by measuring the voltage rise at zero charge current, which the DW9118
appears to do briefly once a minute. I've seen hints that the DW9118 and
similar fast chargers use the curve of voltage rise to determine the battery
voltage and state of charge, but I haven't found many specifics.

https://lygte-info.dk/info/batteryChargingNiMH%20UK.html

My homebrew LM350 solar-powered variable linear regulator charges the NiMH
pack to 17V pretty well. 18V at zero current is within the suggested safe
range.



Tester1

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Sep 30, 2021, 12:15:22 AM9/30/21
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Testing reply. Is this working?

--
For full context, visit https://docker.test/homepower/charging-nimh-battery-pack-115860-.htm

Bob F

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Sep 30, 2021, 12:29:16 AM9/30/21
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On 9/29/2021 9:15 PM, Tester1 wrote:
> Testing reply. Is this working?
>

No.

Jim Wilkins

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Sep 30, 2021, 6:19:13 AM9/30/21
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"Tester1" wrote in message
news:16a97e6702d85199$1$2558138$4226...@news.newsgroupdirect.com...

Testing reply. Is this working?

---------------

The original DeWalt NiCd charger isn't rated for NiMH replacements but I
found an aftermarket version that works.

default_admin

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Jan 31, 2022, 2:02:10 AMJan 31
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This is a test reply, it goes here

--
For full context, visit https://docker.test/homepower/charging-nimh-battery-pack-2243069-.htm

Jim Wilkins

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Feb 9, 2022, 6:18:09 PMFeb 9
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"default_admin" wrote in message
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