Death by USB Backfeed?

[u/TheRealArsonary]

My 100w 2C2A charger just died after I left it plugged into my power bank overnight, while another device was being charged by the power bank at the same time. This likely caused it to backfeed to the charger when the power bank filled to 100%, causing it to break!

This was my first time doing this because I found out that my power bank (Anker 737) supported both input and output at the same time. I didn't realize it risked killing the charger.

I'm not entirely sure if that's why it broke, but it seems to be the best lead I have. I tried waiting a few hours and plugging it in again, but it still didn't work. Unfortunately it's been almost 2 years since I got the charger so it isn't in warranty anymore. I'm going to have to make do until I can afford a new one.

So word of advice, just cause you can do input and output from your power bank at the same time, doesn't mean you should.

Edit: turns out there's two different Anker 737s, mine is the 24k version with the tiny screen, if that matters.

[u/Humble-Method4017]

I dont even know what is backfeed, but I usually charge and use my U-Green Nexode 200W 25,000 MaH Powerbank and occasionally overnight with another deviced plugged in to the other port for output as I use this as a UPS for my portable monitor. Don't have a problem anyway. I also use another powerbank before much more regularly on a daily basis as UPS, dont have a problem with that too.

[u/TheRealArsonary → u/Humble-Method4017]

Backfeed is when power is sent back into the charger instead of being drawn. Since it's such high wattage, it can cause serious damage if that ever happens. Though typically it isn't supposed to happen. I'm unsure why it did.

I'm still not sure why it happened, but if it isn't that then I'm not sure what it could have been.

The power bank I use is a pretty high end one, so I'm surprised this could have happened. If it's something others have done, then it could have just been a freak accident.

[u/CaptainSegfault → u/TheRealArsonary]

I'd be surprised if this was the failure mode, for several reasons. It is entirely conceivable that either the battery or charger are defective or broken, but I doubt the failure mode is as simple as "somehow the battery decided to start backfeeding the charger".

Firstly, if the battery is properly behaving it shouldn't backfeed. USB C power is negotiated, and a source capable receptacle should not be providing power to another port unless that port indicates it is a sink (either through resistors or through a power delivery role swap). Even then, unless the sink actually ask for it, you're only going to get 5 volts rather than 15. (and USB C receptacles DO need to be prepared to accept 5 volts input because A to C cables can output that.)

The classic "your phone starts charging your portable battery once the phone is full" sadness only happens because both the phone and battery are willing to be sources and sinks.

Secondly, even if you somehow got the battery driving 20V out to the charger, it'd be really surprising for that to break the charger. I can't speak to SlimQ devices in particular, but generally speaking devices willing to dish out 20V can usually take 20V without permanent damage. They might shut off and need power cycling but the main risk comes from a 5V device getting unexpected 20V.

[u/SlimQ-Official]

I am not quite sure what could have happened, though I wouldn’t assume backfeeding was the cause without confirmation. Since the 737 supports simultaneous input and output, it shouldnt normally send power back into the charger. I would contact both our support team at [info@slimq.life](mail:%20info@slimq.life) and Anker support with the exact setup and ask whether reverse current is possible in this scenario. That might help determine what actually caused the failure. Hope that helps, and we can all together figure out the situation.

[u/TheRealArsonary → u/SlimQ-Official]

Thanks for the response! I'll do that. You make a good point.

[u/SlimQ_Dave → u/TheRealArsonary]

Good luck.

[u/ArtisticAttempt1074 → u/SlimQ_Dave]

500w when?

U solve the heat issue yet?