Lithium Ion Batteries for Dummies

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speed711
 
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Lithium Ion Batteries for Dummies

Post by speed711 »

I'm currently making a light that uses batteries for my apartment. the only problem with this is that I'm somewhat new to using batteries and I'm used to working with AC current so please forgive me if I'm just doing something stupid. The light that I am making uses about 11 watts of power and so when I originally did the math I thought the 3.7 volts 2500mAh lithium-ion polymer battery (Product #328) would be a good fit. I also purchased one of your lithium ion chargers (product #259). I didn't realize until after I got the battery in the mail and redoing my math that this battery was to small, but I figured I might as well see if I can get any power into this light so I went and wired everything up.

This is the part where I'm not sure about the problem. I wired the given 2-pin JST cable into my circuit and inserted it into the "load" port. putting my battery in the "battery" port, I put the charger to charge and waited. The red power ("pwr") light was solid and so was the yellow charge light ("chrg"). When I came back to it about 4-hours later, I unplugged it and switched the circuit on, nothing happened. when I timidity plugged it back in the battery was still cold (as it was when I first unplugged it) with the same bright yellow charge light. I switched the ion battery from the "battery". I'm not sure if I'm wrong in thinking that this charger works as a sort of inline charger where you don't have to unplug the battery from the circuit to charge it. however, I'm sure that there was no charging of the battery, even when I disconnected the charger from the circuit and just had the battery plugged into it. I know I need a new battery and I was going to purchase the 3.7v 6600mAh battery from Adafruit I just want to be sure that is the only thing I might need and not a different charger.

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adafruit_support_bill
 
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Re: Lithium Ion Batteries for Dummies

Post by adafruit_support_bill »

The light that I am making uses about 11 watts of power and so when I originally did the math I thought the 3.7 volts 2500mAh lithium-ion polymer battery (Product #328) would be a good fit.
A common error. mAh is not the same thing as mA. That cell is rated for a 0.5C discharge rate, which would be 1250mA. And 1.25A * 3.7v = 4.625 Watts, which is not enough for your 11 watt light.

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I wired the given 2-pin JST cable into my circuit and inserted it into the "load" port. putting my battery in the "battery" port, I put the charger to charge and waited. 
What was connected to the cable plugged into the Load port? On that charger, the Load and Battery ports are wired in parallel. Any current drawn by the load is current that does not go to charging the battery. In fact, if the current drawn by the load exceeds the maximum charge rate of the charger, the remaining current comes from the battery and you will end up with a net battery discharge.

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