do you know about tool lithium batteries?

e9999

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So I got an older Toro lithium battery with a busted hedge trimmer. The motor on the trimmer burned up at some point so could well have drawn some big amperage, don't know.
I'm trying to test the battery to see if it's good. It's a 24V battery. It seems to charge fine, shows 24.5V no load.

However, and this where I'm wondering, I was trying to test it to see its capacity. Since I don't have any Toro tool, I put a 100 ohm resistor on it with a power meter. It draws 6W and 1/4A. So it should really not tax a biggish battery like this one. Yet, after just a few minutes running at 6W (with the voltage staying above 24.2V) it shuts down completely and abruptly (as in less than a second). Shows 0V (as in a couple of millivolts). It's like the BMS (or something) shut it down deliberately.

Seems pretty odd. First time I've seen that. Any chance that the BMS does not like a small draw for some reason, or maybe a thermal protection gizmo is going crazy despite the low draw? That seems farfetched to me, but eh, I may be wrong on that.

Thoughts before I take that thing apart and starts digging in?
 

LandLocked93

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Hadn't thought about tool batts...how's this coming?
Sudden qs:
Are you saying there is a BMS built into the battery?
Could it be shutting off because it's spent after a couple mins @ 6W?
If it's old, wouldn't this performance be typical?
 
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What does it do after shutdown ? or does it lose voltage ? If it goes back to normal it would seem there is a temp cut out , wether it is working properly or got fried when tool shorted is anyones guess.
 

e9999

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I haven't looked at it seriously yet, so don't know much. Will check.
 
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How many cells? Lithium Ion batteries, the bottom voltage should be 3.1 volts, max should be 3.7 volts.

If it's an 8 cell battery, it should be min 24.8, max 29.6. If it is 8 cell, you're hosed. Voltage is too low. I'm betting it's a seven cell though.

Most of the tool batteries have a cutoff built into them. If the voltage drops too low on a given cell, it'll shut down the pack. Lithium ion/poly/fe batteries can turn into chemical bombs in a hurry when the chemistry gets too dicked up.

The consumer grade chargers are terrible, so they have to build in some fail safes. A good charger costs way more than the average cordless tool, and you still have to get a power supply.


I only know any of this from RC planes and racing RC cars. The batteries are stupid expensive and have a huge impact on performance if not charged and stored correctly.
 

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