Charging NiMH battery pack

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?
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Also post to an electronics group...
You can use sci.electronics.design, labeled "OT: ..."
Or sci.electronics.basics
Good luck.
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On 17/6/21 9:52 pm, Jim Wilkins wrote:

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
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"Clifford Heath" wrote in message
On 17/6/21 9:52 pm, Jim Wilkins wrote:

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
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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."
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On 17/06/2021 12:52, Jim Wilkins wrote:

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.
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"David Billington" wrote in message
On 17/06/2021 12:52, Jim Wilkins wrote:

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
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On 18/6/21 9:07 pm, Jim Wilkins wrote:

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
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On 18/06/2021 12:07, Jim Wilkins wrote:

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.
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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!
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On 19/06/2021 17:26, Jim Wilkins wrote:

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.
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"David Billington" wrote in message
On 19/06/2021 17:26, Jim Wilkins wrote:

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.
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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.
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"David Billington" wrote in message
...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.
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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.
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On 19/06/2021 22:48, Jim Wilkins wrote:

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.
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"David Billington" wrote in message
... 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.
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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.
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"David Billington" wrote in message
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.
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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.
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"David Billington" wrote in message
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.
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On 6/17/2021 6:52 AM, Jim Wilkins wrote:

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 ...
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"Snag" wrote in message
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
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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.
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On Monday, June 21, 2021 at 6:03:54 AM UTC-7, Snag wrote:

Sounds like time to repair a charger. It's do-able, cheaper than two aftermarket batteries...
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"whit3rd" wrote in message
On Monday, June 21, 2021 at 6:03:54 AM UTC-7, Snag wrote:

Sounds like time to repair a charger. It's do-able, cheaper than two aftermarket batteries...
----------------------
https://blog.adafruit.com/2016/06/30/teardown-of-a-dewalt-dw9118-7-2v-14-4v-battery-charger-with-macro-die-shots-of-components/
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