charging lipo batteries

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mrburnette
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Re: charging lipo batteries

Post by mrburnette »

There are identical formfactor cells that are rechargeable

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GonzoG
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Re: charging lipo batteries

Post by GonzoG »

mrburnette wrote: Sat Oct 23, 2021 5:46 pm There are identical formfactor cells that are rechargeable

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I know it's an old topic, but I have to write this.

In most cases you CANNOT use rechargeable li-ion cell batteries (eg. LIR2032) instead of primary lithium coin batteries (eg. CR2032).
CR2032 is a 3V battery, fully charged LIR2032 has 4.2V.
ervinjason12
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Re: charging lipo batteries

Post by ervinjason12 »

I am thinking in terms of pulsing a P channel mosfet and charging the li-ion battery. STM32's adc can monitor voltages at the terminals.
When the mosfet is off the input would be the open circuit voltage of the solar cells and the other end the residual voltage of the battery. Kind of a 'pwm'.

When the mosfet is on assuming a short circuit, the voltage would drop to the residual voltage of the battery.
Below 4.2v, I can pretty much leave it to change.
GonzoG
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Re: charging lipo batteries

Post by GonzoG »

@ervinjason12
Charging Li-ion batteries is much more complicated.
1. You cannot exceed maximal voltage, so power source must be limited, you cannot simply connect solar cell and use low frequency PWM to "control" voltage. It does not work like this.
If you won't limit voltage output, battery will charge to PWM maximal voltage.
With simple PWM you can only achieve control over average power output, not voltage.

2. You cannot exceed maximal current, so you need to measure current.
ag123
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Re: charging lipo batteries

Post by ag123 »

for solar cells, i think the output for each cell is about 0.7v. But some modules have a number of them connected in series that give those higher voltages.
If indivitual cells can be used, 4.2v is about 6 cells in series. This would likely make it more managable, e.g. one could connect exactly 6 cells in series to charge the LiPo battery. A thing is this would likely be pretty slow. I think most lipo chargers use higher voltages when the lipo battery is at lower voltages 'constant current' mode, then about 3.6v, it switches to 'constant voltage' mode i.e. charge up to 4.2v and cap it there.

accordingly, for safety. one'd need to monitor battery temperatures during charging, but it seemed the 'cheap' chargers, battery banks etc simply ignored this requirement and simply used 'charger' chips. battery temperatures is hardly monitored.

Another way, the 'lazy' approach is to use something like TP4056
https://dlnmh9ip6v2uc.cloudfront.net/da ... TP4056.pdf
this would allow using more than 4.2v to charge the battery as TP4056 is a charger chip, which would top it off at 4.2v.

i'd think using PWM with a p-channel mosfet is still feasible as well, just that now STM32 is playing the role of that lipo charger chip, and so it'd need to switch off the mosfet once battery voltages reach 4.2v.
GonzoG
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Re: charging lipo batteries

Post by GonzoG »

ag123 wrote: Sat Jun 04, 2022 3:39 pm for solar cells, i think the output for each cell is about 0.7v. But some modules have a number of them connected in series that give those higher voltages.
If indivitual cells can be used, 4.2v is about 6 cells in series. This would likely make it more managable, e.g. one could connect exactly 6 cells in series to charge the LiPo battery. A thing is this would likely be pretty slow. I think most lipo chargers use higher voltages when the lipo battery is at lower voltages 'constant current' mode, then about 3.6v, it switches to 'constant voltage' mode i.e. charge up to 4.2v and cap it there.
In theory and ideal world this would work. Unfortunately real world isn't ideal. 0.7V pre 1 solar cell is it's maximum output and usually you don't get this much so you need more cells to get at least 4.2V or you would be able to charge battery only in full sun and for 2-3h when sun shines directly at solar cell.
ag123 wrote: Sat Jun 04, 2022 3:39 pm accordingly, for safety. one'd need to monitor battery temperatures during charging, but it seemed the 'cheap' chargers, battery banks etc simply ignored this requirement and simply used 'charger' chips. battery temperatures is hardly monitored.
When you charge with low current, you don't have to worry about temperature.
ag123 wrote: Sat Jun 04, 2022 3:39 pm Another way, the 'lazy' approach is to use something like TP4056
https://dlnmh9ip6v2uc.cloudfront.net/da ... TP4056.pdf
this would allow using more than 4.2v to charge the battery as TP4056 is a charger chip, which would top it off at 4.2v.
It was mentioned in this thread before, but OP wanted to do Li-ion charger by himself using STM32.
ag123 wrote: Sat Jun 04, 2022 3:39 pm i'd think using PWM with a p-channel mosfet is still feasible as well, just that now STM32 is playing the role of that lipo charger chip, and so it'd need to switch off the mosfet once battery voltages reach 4.2v.
Not with PWM.
You could charge Li-ion battery, monitor voltage and disconnect when battery reaches 4.2V, but this would be only 1 phase of charging - Constant current (CC). But you would get not fully charged battery. The higher the current and the higher battery internal resistance, the lower state of charge you get.
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