Electronics > Beginners
Need cheap USB power bank with "always on" instead of "auto off"
Peabody:
I just wanted to report that after two months, and a refund from the seller, I finally received the single 18650-based power bank I referred to above that looked like the one Julian Ilett reviewed. But my suspicions were confirmed that the circuit has been completely changed, and most of the parts have been replaced by a single chip that does both the charging and the boost conversion, and that chip has "auto-off" built in. The datasheet doesn't say what the minimum stay-on current is, but I stopped testing at 20ma, which produced a shutdown after 18 seconds. So that's a fail.
So I'm still looking for an inexpensive power bank or module that could be used as a UPS for an Arduino project, preferably 18650-based, one that stays on no matter how little current the powered device draws. So it would have a micro- or mini- USB power input, type-A USB output, and would include the charger circuit, a boost converter, and a load-sharing circuit that allows powering the load while charging the battery. If anyone knows of one, please let me know.
The circuit would basically look something like the attached.
sokoloff:
Could you just drive your Atmega328p directly from the Li-Ion battery (3.7V nominal)? The part is 1.8-5.5V qualified, so it depends on your specific peripherals, but for two Halloweens in a row, I ran our costumes directly off a single 18650 for several hours of being "LED stick figures". I saw no unusual behavior across 6 people and probably 6+ hours of runtime per person.
We didn't charge the batteries while wearing the costumes, but I see no reason to think that couldn't also be done.
Peabody:
Yes, that would work, but only at 8 MHz, and any peripherals used in the circuit would also need to tolerate that voltage swing. I also wanted to be able to power it from an AC USB charger if available.
elektrolitr:
If you don't mind a caseless solution
either go with this module which combines battery charging and step-up:
4056 module
This module doesn't have a battery protection so it's a good idea to pair with protected battery. I like to use cell-phone batteries which I salvage across my relatives, but you can as well buy a li-po battery with protection circuit on ali or ebay.
I've just checked and it stays on for long (>10 min) with only multimeter connected, seems not to have power off feature at all
For unprotected batteries, go for this charging/protection module:
charging and protection module
and add a step-up of your choice (like this one). Separate step-up modules tend not to have a "green mode", they just deliver the output as long as input is in spec.
kjr18:
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. TP4056 might have problems with termination of charging. I did module like this some time ago, I added one p channel mosfet, one gate resistor and one lowdrop diode. I made it that way: when there is no external voltage source connected, transistor is open and boost is powered through it. When external source is connected, gate of mostet is pulled high and boost is powered through diode. That way battery is disconnected from boost, and charger can terminate properly.
And about powering straight from battery: once I tested one of my small projects: neopixel based random colour flashing leds. My arduino pro mini was happily running @16MHz and about 2,5V.
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