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Thane_Bitter
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join:2005-01-20

Thane_Bitter

Premium Member

Li-Ion battery charge question

I have a cordless screwdriver that has been less than reliable, and while I have it apart and charging I have been checking the voltage on the battery contacts.

It is a 3.6v Li-ion battery, last I checked the terminal voltage was around 4.27v which struck me as somewhat high. The tool has some sort of shutoff system that stops charging, I have no idea what it is set/designed for.

Bottom line I just don't want the thing to go off like an incendiary while the cover is off it.

shdesigns
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join:2000-12-01
Stone Mountain, GA

shdesigns

Premium Member

4.3v voltage is the full charge voltage. Fully discharged is about 3V.

3.6v is point of about half charge.

Jason
Stowage Class Traveler

join:2001-01-24
38.2967 Lat

Jason to Thane_Bitter

to Thane_Bitter
Yeah, Li-xxx has a different charging schema than Ni-xx

With lithium, the charger will current-control the charge rate, initially. It will push whatever voltage is needed to provide the current that that battery can accept, until a certain voltage is achieved. (usually ~4.2V)

Once the cell voltage has reached 4.2, then the charger switches over to voltage control. It will deliver whatever (now slowly going down) current as required to maintain the 4.2 volts. Once the current has dropped to whatever the threshold for that charger / battery is, you get the green "charged" light typically. Some chargers give the green light when it switches to CV, or when the battery is ~80% charged.

The charging methodology for Lithium, is called "CC/CV" (constant current / constant voltage)

A lot of "smart" chargers for Ni-xx use something called a "delta-V peak detection" charging schema, that would seriously piss off any lithium cell, but thats outside the scope of this discussion.

4.27V is getting close enough to uncomfortable as to take notice, but if the charger is on the ball, and the cell/s are even somewhat healthy, it should be fine.
TheMG
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join:2007-09-04
Canada
MikroTik RB450G
Cisco DPC3008
Cisco SPA112

TheMG to Thane_Bitter

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to Thane_Bitter
As with all batteries, the voltage rating on it is the nominal voltage. Fully charged voltage will be somewhat higher, and fully discharged somewhat lower.

For example, a 12V lead-acid car battery will actually settle around 12.5-13V when it is fully charged (with the car not running and no load).

Different battery chemistry will of course have different charged and discharged cell voltages and different charging schemes, but in all cases this will be different from the nominal rated voltage.
lutful
... of ideas
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join:2005-06-16
Ottawa, ON

lutful to Thane_Bitter

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to Thane_Bitter
said by Thane_Bitter:

Bottom line I just don't want the thing to go off like an incendiary while the cover is off it.

You can plug their AC adapter on a timer set for 8 hours.

P.S. Accidentally shorting the terminals while checking voltage of Li-Ion battery pack has caused many fires.

Thane_Bitter
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join:2005-01-20

Thane_Bitter

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Thanks,

Well it seems that aside from the torque sense being borked the charger cut off is a well, it will not stop charging. Spins faster as the battery is overcharged but still cuts out with the slightest resistance. Made in China PoS.

Next stop for it, the recyclers.