Pro Micro Li/Ion battery questions


(Simon) #1

I am hoping to buy some cheap lithium ion batteries to power a handful of Pro Micro boards. I have found these beasts on line and have a few questions that some of you hardware boys will be able to answer or at least give me the right questions to ask the supplier.

  1. The battery comes with overload protection. Can I hook the +ve and -ve batteries straight up to the 5V from a USB port?

  2. Most of the batteries are 3.7V whereas the pro micro and the RGB LEDs (a string of 5050 RGB WS2812B) I want to power off it are 5V. Will these work at 3.7V or should I be looking for a battery with a higher voltage? I know this sounds like a dumb question, but I know the effective operating range for WS2812B is supposedly 3.3 to 5V.


(Holmes) #2

Batteries are so complex, so please correct me if I am wrong… But don’t you need to step up the voltage to 5v in order to ensure the board operates at the correct MHz? To do that, you need a booster, I think they are called, which also could be used in some fashion to help charge the battery, as well.


(Simon) #3

Thanks for the response.

I guess that is really my question but since posting I remembered that I can get a 3.3V Pro Micro - albeit it runs at 8mhz instead of 16mhz but that is no problem for what I am doing.

The original charging question still remains.


(Kevin) #4

The onboard circuit only protects it, it does not provide charging. You need another circuit that you would hook up to those wires.

What the charging circuit does is sense the internal resistance of the battery and match the charge voltage just above nominal and also limits the current as well.

https://www.adafruit.com/category/575

These or anything based on these.

This is the same what is on the arduboy.


(Simon) #5

Ah OK … I looked at these and was not sure if I needed them or not. That answers that question. Thank you all!


(Shawn) #6

Technically according to the datasheet, yes you need a minimum of 4.5V to operate at 16MHz (any lower and you are overclocking out of spec), however in practice I’ve never had a problem running an atmega32U4 at 3.3V and 16MHz (though obviously this is not guaranteed to be stable for all operating conditions).


#7

What exactly does that protection mean? if it doesn’t protect against over charging. you need a charger module.

If you have the patience these are pretty cheap.

running Pro micro and the WS2812B at 3.7V shouldn’t be a problem. In case the Pro micro would act odd. you can lower the clock by software or use the built in 8MHz RC osc (but full speed USB is off the table in the latter case). For the WS2812B make sure the data lines and supply voltage are the same (ie don’t power them by 5V and control them by a 3,3V or 3.7V powered Pro Micro)

When connecting the battery (with charger module) to Pro Micro 5V pin and you also want to use USB while it’s running of the battery. You’d better remove the voltage regulator of the Pro micro.


(Kevin) #8

The specific protection the battery has will be over voltage, undervoltage, short circuit protection and sometimes thermal protection but not common on single cell batteries. In any of these conditions are sensed, it opens the ground connection through a mosfet.