Electronics > Projects, Designs, and Technical Stuff
UPS - Charging a Li-ion battery whilst also powering a load?
Ionforbes:
I'm trying to build simple 12v UPS poweredd by 2 18650 cells in series. I was thinking of a sort of topology where the normal 12v source would go to straight into the charger IC. The output of the charger IC would connect to both the li-ion cells and the input of a boost converter in parallel like the 1st image '2S charger block diagram 1' (sorry I can't work out how to embed images). Under normal conditions, the battery would feed the converter to power the load whilst the charger ic from the normal 12v input would keep the battery from discharging. When the 12v onput is disconnected, the battery would feed the converter and discharge (I'll also have some undervoltage protection). When reconnected, the charger would recharge the battery whilst also feeding the converter as I would charge the battery with more current than is being drained from it.
However it seems thaty designs for similar goals instead prefer to go for a different approach where they switch between the regular input source and battery+converter as in the image '2S charger block diagram 2.' Why is this 2nd desitgn the one thaat's commonly used (or is not)? Would the first idea work? Which would be the better route to go down and why? Any help much appreciated.
-Thanks, Ion
SiliconWizard:
Not 100% sure of what exactly you envisioned, but basically constantly trickle-charging a Li-ion battery (unlike with other chemistries) is a big no-no.
jbb:
Hmm
You could look at the Texas Instruments battery charger chips with Narrow Voltage DC (NVDC) feature. But some messing around will be required.
If currents aren’t too high, it might be better to use the LiIon cells in parallel, as this simplifies battery protection and removes the need for battery balancing. (At cost of reduced efficiency.)
NiHaoMike:
--- Quote from: SiliconWizard on March 21, 2020, 11:04:38 pm ---Not 100% sure of what exactly you envisioned, but basically constantly trickle-charging a Li-ion battery (unlike with other chemistries) is a big no-no.
--- End quote ---
It works perfectly fine if the voltage is limited to 4.1V/cell or less.
Ionforbes:
The battery would be hooked up to a dedicated charging IC so if the coltage rose too much the charger would just allow it to discharge and effectively hold it at 4.2V
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