Electronics > Beginners
Need cheap USB power bank with "always on" instead of "auto off"
sokoloff:
Similar experience here, though I tried to only draw them down to 3.5V before changing.
A Li-Ion battery at a 5-hour discharge rate or lower (0.2C) is going to stay above 3.6V for about 90% of the discharge curve.
Peabody:
@elektrolitr, I was hoping to find a power bank that already had both USB connectors in a nice case. But at this point I only know of one like that which is also "always on", and it's $30. If I can't do better than that, I'll have to resort to modules.
But I'm surprised that so far I have not even found one single-module solution that's a combination LIPO charger and boost converter with load sharing. It seems the module kings of the Far East could build a combination module like the one you referenced, but using the MCP73871, which has load sharing built in, instead of the TP4056, which doesn't. Or use the TP4056 but add the mosfet, diode and resistor needed for load sharing. I don't understand why there is no such module available on Ebay.
With respect to just using a battery, I too have done that for an IR remote control using an 8MHz Pro Mini. But that won't work for all projects. In addition to the processor speed issue, there are many peripherals such as sensors, SD cards, and so forth that need to operate at a specific voltage - some at 3.3V, some at 5V, but many may not work at 3.5-4.2V. So powering directly from a LIPO may work fine for some projects, but not for others.
Anyway, I still think the world needs an "Arduino powerbank" for a lot less than $30.
sokoloff:
You might be able to run the AVR directly off the LiPo and use the micro to enable/disable an LDO that drives a stable 3.3 for peripherals. (That doesn't help at all for +5V sensors and peripherals, of course.)
Peabody:
--- Quote from: sokoloff on January 28, 2020, 05:22:31 pm ---You might be able to run the AVR directly off the LiPo and use the micro to enable/disable an LDO that drives a stable 3.3 for peripherals. (That doesn't help at all for +5V sensors and peripherals, of course.)
--- End quote ---
You can provide 3.3V that way to power the peripheral, but if you power the AVR at 4.2V, its GPIO pins will be trying to communicate with the peripheral at 4.2V, which is probably half a volt above the peripheral's absolute maximum voltage on any pin - based on Vcc + 0.3V, or whatever. So I think once you get beyond things like LEDs, you start running into these kinds of problems, and a regulator is going to be needed. Of course some things will work even if they aren't supposed to, but you don't want to be pressing your luck too much.
elektrolitr:
--- Quote from: kjr18 on January 28, 2020, 01:39:24 pm ---This TP4056 module is probably based on MT3608 boost IC or something like that. Those chips have enable pin, but they are hardwired to enable position. With this one is one possibility of overcharging.
--- End quote ---
Nope
TP4056 is a chip made specifically for Li charging. It should have all bells and whistles needed including the current cutout at the end of charge. See the attached picture.
I can check the behavior of the module a bit later, though.
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