Electronics for a battery->USB (aka external USB battery)

Mar 7, 2016
121
9
18
Boston
I can't find a USB brick I really like. The biggest problem is that all units I tried (~7) have the same problem. Depending on how own-charge or to-be-charged power goes away they stop charging the USB device at some point. They have a "power button" that you have to press to get them back to power their connected USB device. (disconnecting and reconnecting works, too, but that doesn't do the job for me, I want unattended operation)

Another concern is that I want to use battery cells of my own choice.

So I'm looking for just the charging electronics. And it should be like an always-online UPS.

Any ideas?
 
Mar 7, 2016
121
9
18
Boston
power->brick->phone

You turned on phone charging, all is good.

You disconnect power. When power reappears most bricks will not charge the phone until you either press the button or disconnect and reconnect the phone.

That, or the other way round, connecting a phone doesn't charge it until the brick's button is pressed.

I have some bricks that work OKish but still, I want to take matters into my own hands now.
 
Mar 7, 2016
121
9
18
Boston
Third review:

"Note that this unit will not charge from the USB output while being plugged in and charging itself, as I had hoped, and as some of the other battery packs are able to do, working as higher powered USB hubs. I did not see this mentioned in any other reviews, so I hope it is helpful."
 
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andrewbedia

Active Member
Jan 11, 2013
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The only thing the switch does is manually switch it on (never had to do this? it's automatic!) or off manually (also never had to do this, it's automatic...). Idk why it has the button except to check battery charge when nothing is plugged into it. I have no idea why you would want to charge a device connected to it at the same time as you're charging the battery pack. Just seems idiotic and the current flow is going to drop so it's just going to take forever to charge the battery pack. Just... buy a multi usb charging brick. Problem solved. Lower cost, less headache, no need to waste valuable time building something that doesn't need to be built.

Just my two cents.
 
Mar 7, 2016
121
9
18
Boston
Sorry but what you don't care about is the core feature for me. Of course I want the battery charged at the same time as it charges a device.

Even outside this project. Even for everyday use. There is nothing worse than such a USB brick that cannot do both when you come to a hotel room and cannot charge both the brick and the phone. Or in a car with only one USB charger.

For this project I also need it to always power the device when there is battery or charging power, without it ever disconnecting the device while the whole combo runs unattended. Like what every UPS does.