I’m looking at powering a Pro Mini 3.3V board and I plan to play around with batteries to find the better option but I’ve a few questions.
The RAW pin can except 3.3v upwards, which is ideal for a 3.7v lipo battery and I was going to connect it via a tp4056 module, to avoid over discharging. From memory, the lipo battery can run as low as 2.3v, or there abouts, what will happen to the Pro Mini, just tun the battery down to that or just cut out once the volts drop below 3.3v into the RAW pin?
Another option would be to use two rechargable AA batteries, but directly into the RAW pin. I guess the same question applies, what will happen once the volts drop beliw 3.3v?
I was just going to have a go and see what happens but I’d rather not damage a lipo battery in the house.
No, the RAW pin can not accept 3,3V and upwards. It needs around 250mV extra.
Just use the 3v3 pin directly. The whole voltage range of a LiPo is just fine for the Arduino. Which doesn't get that low, at 3V you should really stop using it.
I’m looking at powering a Pro Mini 3.3V board and I plan to play around with batteries to find the better option but I’ve a few questions.
The RAW pin can except 3.3v upwards, which is ideal for a 3.7v lipo battery and I was going to connect it via a tp4056 module, to avoid over discharging. From memory, the lipo battery can run as low as 2.3v, or there abouts, what will happen to the Pro Mini, just tun the battery down to that or just cut out once the volts drop below 3.3v into the RAW pin?
Another option would be to use two rechargable AA batteries, but directly into the RAW pin. I guess the same question applies, what will happen once the volts drop beliw 3.3v?
I was just going to have a go and see what happens but I’d rather not damage a lipo battery in the house.
Thanks
If you use LiPos then you should turn them off at 3.0v, 2.3v is very low and how safe this is depends on how lucky you fell.
Most all 3.3V Pro Minis have the brownout reset set at 2.8v, go down to that or below and the pro Mini resets.
Two rechargeable AAs, will on average be 2.4V, which is not enough voltage really.
Should be; Most all 3.3V Pro Minis have the brownout reset set at 2.7V.
septillion:
You could measure battery voltage and put it to deep sleep when it goes below. But a over discharge IC is the nicer option.
This is the module I have
It states that the over discharge protection is at 2.5v. I assume everything will shut down at that point, will have to try it out. Will double check the IC on the board
srnet:
Most all 3.3V Pro Minis have the brownout reset set at 2.8v, go down to that or below and the pro Mini resets.
The typical Vbot level is 2.7 V, not 2.8 V. Of course, the minimum is 2.5 and the max is 2.9, so it might well be 2.8 V, but we usually refer to the 2.7 V number when talking about BOD.
Also be aware, in case it makes any difference in your application, that after the protection chip shuts down at 2.5V under load, the battery, which is no longer under load, will "recover", and voltage may reach the point where the protection chip will turn things on again, if only for a little while. This can go on through a number of cycles until the battery can no longer recover sufficiently.
The other issue is that I believe your charging module does not have a "load sharing" circuit which allows the power source for the charger to also supply power directly to the Pro Mini. That usually means you cannot operate the Mini while charging the battery because charging would never shut down, which you can't do with lipos.
Thank you for the input people. You’ve given me direction and I can go and have a read further, regarding fuses and brownouts.
You’re correct, the boards won’t charge whilst the load is connected, which is okay for this particular application, thanks for pointing that out, as I’d planned to try a solar panel with these, which would not work.