this post was submitted on 09 Oct 2023

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Is there a device that makes my multiple USB powebanks work together? (self.asklemmy)

submitted 1 year ago* (last edited 1 year ago) by Smokeydope to c/asklemmy

15 comments fedilink hide all child comments

My current means of powering things is USB rechargable batteries. I have a about five of them that range between small 3000-5000mah ones to a big 20000mah interstate battery jump starter pack. Is there a device that lets me add all their power together into a centeral power source so I don't have to keep swapping them out?

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[–] Zak 10 points 1 year ago (1 children)

I'm assuming you mean USB powerbanks.

I'd be surprised if there was such a device. It would require somewhat sophisticated electronics to work well, and the market for it would be small. A design that didn't result in power cutting off during the switchover would need to keep at least two powerbanks active at a time, and that could negatively impact efficiency since the electronics in the powerbank consume power when active even under light loads.

[+] testfactor -13 points 1 year ago (2 children)

Or, I mean, it could just wire all the positives together and all the negatives together and hook that right into your target device.

It'd be the same output voltage regardless. A little less internal resistance, and lower step down in the later phases, but neither should make a difference in what you're powering.

Kinda like how there were those converters for the GameBoy back in the day that let you put C batteries into it. Same principle.

[–] Zak 18 points 1 year ago (3 children)

It's probably not possible to do that safely because USB power supplies aren't just dumb batteries. They actively communicate with the device receiving power about how much current the device wants, and should only supply 500mA if they fail to do so.

USB-A ports aren't supposed to receive input power, which is effectively what would happen in that arrangement after a powerbank shuts off to prevent over-discharge of its batteries. The resulting behavior is, as I recall unspecified and might result in damage to the powerbank. Worse, it could interfere with the over-discharge protection and damage the batteries. Charging damaged Li-ion batteries is bad, where bad may include fire, explosion, and/or emission of toxic gas.

[–] testfactor 5 points 1 year ago

Yeah, I should work on my reading comprehension.

I deff read the prompt as having a bunch of rechargeable AA style Li-ion batteries, and how to utilize them without having to swap out to a new pair or whatever.

Deff don't want to do this with a bunch of disparately sized smart batteries providing power over USB. Very different problem.

[–] Smokeydope 2 points 1 year ago

Thank you for the great reply!

[–] [email protected] -1 points 1 year ago (1 children)

You can still just crack open the banks and wire the cells together in parallel or series (depending on your needs), then hook them up to one of the controllers. I bet they're just a bunch of 18650s

[–] Zak 4 points 1 year ago

Sure, but you probably shouldn't build a DIY battery pack out of salvaged 18650s of varying brands, capacities, and conditions unless you really know what you're doing because that's dangerous if you get it wrong.

[–] Smokeydope -1 points 1 year ago (2 children)

So I could actually get a couple of old short usb cords together cut the ends off, strip the positive and negative wires and hook them in series without it changing the output voltage?

[–] [email protected] 9 points 1 year ago

No...please do not do this.

The voltages of the output ports are probably not all exactly the same and you could end up damaging the device (or worse, starting a fire). They MIGHT have reverse current protection on them, but I've seen some pretty sketchy power banks.

You can't just wire them in parallel. USB has communication pins that help boost circuits in the battery change voltages levels. Even if it all works, you're going to get extremely poor charge times.

I don't believe it's out of the realm of EE to design something that allows you to plug in multiple power banks though, but I've never seen any

[–] [email protected] 3 points 1 year ago

The fact that you're having to ask means you shouldn't do it.

You need to take a minute to research before you burn your house down.

[–] [email protected] 5 points 1 year ago

What you need is a communist dictatorship. That ought to make them work together.

[–] Godnroc 3 points 1 year ago (2 children)

Plug the charging port of one into the next one?

[–] Zak 9 points 1 year ago

That can work, but since the batteries are at roughly 3.0-4.2V depending on state of charge and standard USB power is 5V, that's a whole lot of steps up and down. Each one takes an efficiency hit. The last one in a series of five would likely waste the majority of its energy.

[–] davidgro 2 points 1 year ago

They typically won't provide power while taking in power.

[–] solrize 1 points 1 year ago

Just get a few big ones and put aside the small ones for portable/mobile use.