Hi,
I've been using Lipo batteries in a few jobs, specifically these ones:
https://www.sparkfun.com/products/8483
2000mAh, 4.2V (max voltage). Along with the MCP73832, the charging circuit used is taken directly from the microchip datasheet:
https://www.electro-tech-online.com/custompdfs/2012/11/21984e.pdf
I chose the 4.2V option, '2AC'.
Now, this is the same chip used in the sparkfun charger, albeit with an open-drain status output (doesn't change functionality). However, in my design the battery is permanently connected to the circuit, which can drain a constant 9mA, or 30mA if there is a fault and it doesn't sleep.
Often the battery's built-in protection circuit kicks in, due to low battery voltage. This can happen if it is not charged for a while, the constant drain lets the battery drop to <~2.9V so the internal FET disconnects it. Of course the only way to reset this condition is to start charging it, and this is a bonus because it means the battery is protected.
Now, the problem I have is, in two cases, I will leave the battery charging over night with the charging current set to 300mA (this has been measured). Twice after several hours the battery has disconnected itself, and once put back on charge the battery voltage was 2.9V. The charger of course now indicates its fully charged (or not charging) because it connot detect a battery present. Has anyone experienced anything similar?
I do not understand why the battery would drain so significantly *whilst* on charge. The charging power supply is more than enough to provide the current the circuit draws, and whilst it takes a while (2000mAh battery, charging at 300mA) this current was set to reduce the heat dissipation of the charging chip.
Unfortunately, the battery has to sit on top of the charging board, which, taking in 5V, and providing 3-4.2V to the battery @ 300mA warms a bit. (0.6W heat dissipation max) and this warms the battery. Only to maybe 30C.
The only thing I can think of is.... the charging chip determines the 'end of charge' state when the current drawn from the battery (with circuit attached!) drops below 7.5% of the set charging current., In my case thats 0.075 * 300 = 22.5mA. With the circuit drawing 9mA, that means that the battery stops charging when it draws less than 13-14mA. It appears this is too low, but I don't see how such little ammount of current, trickling into the battery, can cause the internal circuit to shut down, AND make the battery voltage drop to <3v.
If anyone has experience of 'dodgy batteries' or this particular charging chip I would appreciate any quirks/problems that have been encountered. I am hoping is it simply a dodgy battery, but if it turns out its my design, a complete overhaul would be required.
A very worried, BT
I've been using Lipo batteries in a few jobs, specifically these ones:
https://www.sparkfun.com/products/8483
2000mAh, 4.2V (max voltage). Along with the MCP73832, the charging circuit used is taken directly from the microchip datasheet:
https://www.electro-tech-online.com/custompdfs/2012/11/21984e.pdf
I chose the 4.2V option, '2AC'.
Now, this is the same chip used in the sparkfun charger, albeit with an open-drain status output (doesn't change functionality). However, in my design the battery is permanently connected to the circuit, which can drain a constant 9mA, or 30mA if there is a fault and it doesn't sleep.
Often the battery's built-in protection circuit kicks in, due to low battery voltage. This can happen if it is not charged for a while, the constant drain lets the battery drop to <~2.9V so the internal FET disconnects it. Of course the only way to reset this condition is to start charging it, and this is a bonus because it means the battery is protected.
Now, the problem I have is, in two cases, I will leave the battery charging over night with the charging current set to 300mA (this has been measured). Twice after several hours the battery has disconnected itself, and once put back on charge the battery voltage was 2.9V. The charger of course now indicates its fully charged (or not charging) because it connot detect a battery present. Has anyone experienced anything similar?
I do not understand why the battery would drain so significantly *whilst* on charge. The charging power supply is more than enough to provide the current the circuit draws, and whilst it takes a while (2000mAh battery, charging at 300mA) this current was set to reduce the heat dissipation of the charging chip.
Unfortunately, the battery has to sit on top of the charging board, which, taking in 5V, and providing 3-4.2V to the battery @ 300mA warms a bit. (0.6W heat dissipation max) and this warms the battery. Only to maybe 30C.
The only thing I can think of is.... the charging chip determines the 'end of charge' state when the current drawn from the battery (with circuit attached!) drops below 7.5% of the set charging current., In my case thats 0.075 * 300 = 22.5mA. With the circuit drawing 9mA, that means that the battery stops charging when it draws less than 13-14mA. It appears this is too low, but I don't see how such little ammount of current, trickling into the battery, can cause the internal circuit to shut down, AND make the battery voltage drop to <3v.
If anyone has experience of 'dodgy batteries' or this particular charging chip I would appreciate any quirks/problems that have been encountered. I am hoping is it simply a dodgy battery, but if it turns out its my design, a complete overhaul would be required.
A very worried, BT