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Lithium ion tool power packs


jay1028's Avatar
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05-18-17, 12:04 PM   #1 (permalink)  
Lithium ion tool power packs

I recently purchased a Ryobi weed eater and a Dewalt leaf bower. Both run on Lithium ion packs. The Dewalt pack gets pretty warm, warmer than I would like, when charging in the DCB115 charger. Probably due to its fast charge capability. After doing some research, I have noticed that when a pack fails, it is always due to one or two bad cells in the pack. I am wondering if these chargers use cell balancing when charging. It is leading me to beleive that these chargers are just charging and not minitoring or balancing each cell so that they all get the same charge.

Does anyone have any input on how these chargers operate and your experiences?
Thanks

 
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05-18-17, 12:08 PM   #2 (permalink)  
Welcome to the forums.

Most of the tool battery packs run the cells in series and don't monitor each one individually.

I've changed cells in ni-cad and Ni-Mh packs but not any lithium cells yet.


~ Pete ~

 
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05-18-17, 01:06 PM   #3 (permalink)  
Most chargers for lithium cordless tools are smart and monitor the charging voltage, rate/amperage and many also monitor the batteries temperature. They are doing it for safety as lithiums are very unforgiving of improper charging.

The battery packs don't always fail due to a bad cell. Sometimes it's a simple matter of the charger no longer "recognizing" the pack because the pack's voltage is out of range. Most often this happens when using a battery in a flashlight as many flashlights are dumb and don't include the same low battery protection that the power tools do. Repeatedly trying to use a power tool that has a dead battery can also cause the voltage to drop below where the charger will recognize it and the charger simply says "bad pack". Before tearing your packs apart I would check them with a volt meter.

And "yes", sometimes it is a bad cell that causes a bad pack. If you attempt to re-build a lithium pack be very careful to polarity and shorts. Hooking up an alkaline, NiCd or NiMh backwards or shorting out briefly may make a minor spark without much harm done but lithiums can dump a tremendous amount of current very quickly. Reversed polarity and shorts can immediately be very bad especially with cells that are charged.

 
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05-18-17, 02:01 PM   #4 (permalink)  
Understand about LI-ion cells. I have converted some older Makitas to 18650 cells and also used Lipo. Didn't stick with the Lipo. Nice power, but they are too unforgiving and puff up at the slightest overdischarge. You can't always hear the voltage monitor alarm go off when the tool is in operation. Strange the Ryobi 18V One + only has three terminals on the pack. Must be some electronics in the pack. These cost too much money to be mishandling them and I have a fear of what the chargers are doing. There are recycle bins full of these packs at Lowes and HD. I use an RC type charger to charge my converted drills and can control the charge current and end voltage and have all cells balanced at the same voltage level - matched. This way, all of them drain at a very close rate and the likelyhood of one cell going south first is almost elliminated.

I just don't trust idiot lights on chargers. I would rather see a small digital display and pay $2 more for it than LEDs that just tell us that it's cooked.

 
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05-18-17, 05:07 PM   #5 (permalink)  
Similar minds... I too use my RC programmable chargers for many tasks. It's also nice to see how much charge is going back into a pack.

 
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05-19-17, 03:43 PM   #6 (permalink)  
Got into the Ryobi pack and found all kinds of circuitry. Looks like they are stepping up their game.

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