Replacing Nickel metal hydride by Lithium ion.

[dimitristephan]

Hello people,

My old black and decker electric screwdriver had lost a lot of torque and speed after a

couple of years of use, so I decided to replace the 3 x AA batteries that were connected in

series by one 18650 lithium Ion battery of the same voltage rating but higher

capacity. However, since the battery is not protected against overcharging/discharging,

leaving it on the charging base has actually caused the battery to get overcharged to

around 4.6 V. The nominal voltage of such a cell is 3.6 V, but are generally charged to 4.2

V. For some reason, the charger is not stopping the charge at 4.2 V. Could it be that the

battery has a lower internal resistance than 3 AA's in series? There is a serious risk of fire

and/or explosion if I do not find a way to limit the terminal voltage to 4.2 V. Is there any

way I can do so? Your input is much appreciated.

Thank you!

 

[(*steve*)]

It is not charging properly because the charger is not designed for LiPo cells.

You're lucky you didn't start a fire.

Get a LiPo charger.

Note that the protection of LiPo cells doesn't protect the cells, it protects you. The cells are still likely to be damaged, but they probably won't burst into flames.

 

[CocaCola]

but they probably won't burst into flames.

Keyword "probably" They could still have a major meltdown even if flames never materialize...

 

[dimitristephan]

It is not charging properly because the charger is not designed for LiPo cells.

You're lucky you didn't start a fire.

Get a LiPo charger.

Note that the protection of LiPo cells doesn't protect the cells, it protects you. The cells are still likely to be damaged, but they probably won't burst into flames.

I already have a Li-ion charger, but the thing is, the base has its own circuitry that converts 12

V AC into 12 V DC since the external AC adapter cannot charge the battery on its own.

Also, I cannot get any voltage reading when placing the leads of my DMM on the charging

pins of the screwdriver.

Should I remove all the inner components and re-wire everything so that i can directly plug

in a 4.2 V DC charger?

Thanks!

 

[(*steve*)]

Should I remove all the inner components and re-wire everything so that i can directly plug in a 4.2 V DC charger?

That would probably be the safest thing to do.