Electronics > Projects, Designs, and Technical Stuff

Hotspot battery getting overcharged

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drummerdimitri:

--- Quote from: NiHaoMike on May 15, 2020, 02:40:33 pm ---
--- Quote from: drummerdimitri on May 15, 2020, 12:54:58 pm ---Will be using two diodes back to back to drop the voltage to around 4.2V but currently only have Schottky diodes that drop the voltage by 0.17V so the battery will only be charged to 4.11V thus reducing the effective capacity.

--- End quote ---
That's close to perfect! If you need more capacity, buy a slightly bigger battery.

--- End quote ---

Theoretically speaking, yes close to perfect but now that I have it installed it's far from perfection!

It is reading 23% charged and wont go above that with the diodes in the circuit and it dies when it drops to 0% so I basically cut my capacity in 4  |O

Not sure why that's the case since the voltage drop when the battery is fully charged (4.2V) is only 0.6 V!

Maybe I'm doing something wrong here. A circuit diagram might be useful in this case  :-//

NiHaoMike:
Where did you get the new battery from? A lot of the cheap ones are rejects with low capacity. Try bypassing the diodes for a test.

drummerdimitri:

--- Quote from: NiHaoMike on May 15, 2020, 03:48:58 pm ---Where did you get the new battery from? A lot of the cheap ones are rejects with low capacity. Try bypassing the diodes for a test.

--- End quote ---

It's a 900 mAh battery and I tested it's capacity and it was around 900 mAh so right on the money until I find a suitable replacement for the original capacity of 2930 mAH.

Works fine without the diodes so they're definitely the culprit here.

Peabody:
Does the charger have to read the battery voltage at any point during the charging process?  It seems it would have to do that at the very beginning to make sure it's above 3V before applying full charging current.  And then after it terminates charging it will initiate charging again if the battery falls below 4.05V or so.  Diodes would block any reading of battery voltage.

NiHaoMike:
The ESR of a much smaller battery could result in the usable capacity being greatly reduced if there's a high discharge current.

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