Lipo percentage guidance

B

brokeattack

Member
I'm making a wearable that includes a teensy 4.0 and a 2000mah lipo battery. I wanted to have a way to check the percentage of the battery without having to use a multimeter, but since the teensys pins are only 3.3v tolerant, I'm not sure how I'll be able to do so. I was thinking at first to maybe use a level shifter but I can't get the battery's highest voltage so that won't work. If it helps I'm using a lipo amigo to charge it.
 
Is a lipo in use measurable? In other words is the voltage only dependent on the % or more on temperature etc...?

A resistor divider with high resistance (thus very low current) and a helper capacitor to make readings fast (between midpoint and ground), would be my first suggestion as BriComp already poited to.
 
100k : (100k || 100nF). divider would be me choice, half the LiPo voltage to about 2V, 30uA drain.
 
Hi you may need a pinMode(<pin>, INPUT_DISABLE); also.

In the past I got info that on the 3.x series there was a internal capacitor of 10pF used. So even a few fast readings wouldn't affect the 100nF much on those. Don't have the info on the 4.x series.
 
Thank you all so much for the help, I've been away from my electronics all weekend so I haven't been able to do anything but I'm going back later today so I'll be able to post an update on how it goes soon. Have a great day :)
 
As @AlainD indicated using the voltage to measure LiPo charge level is normally a bad appraoch. 5% charge at 20 C and 80% at 10 C can give you the same voltage. If you want to go that route and want any sort of accuracy then you should also include a temperature sensor and factor the battery temperature in to the calculation.

The best way to do this is with a battery gas gague or coulomb counter IC. The self discharge for the batteries is very low so the best way to measure charge level is to measure the charge going in and then measure if going back out. This does require that the battery is charged in unit or has the charge counter IC included in the removeable battery pack.
 
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