Started a power bank. Charging it is so slow! Help!

4 posts / 0 new
Last post
JoeRodge
Offline
Last seen: 5 months 3 weeks ago
Joined: 01/04/2018 - 23:13
Posts: 119
Location: United States
Started a power bank. Charging it is so slow! Help!

So I was bored the other day and made a power bank at work. I still need to make a case for it and streamline it buy it works. The only issue I’m having is that it charges so slow through the micro usb! It’s the usual style 1S setup. But I decided to use 20 cells in parallel.

So my questions are: 1.) Are any of those fast charge circuits on eBay promising QC3 real? That’s more about the output. But some promise “fast charge input” but even then I feel like 2 amps isn’t quick enough. Are any true QC3.0 that are legit?

2.) Should i make a port to connect it to a fast/smart charger? Any that someone could recommend for 1S that won’t break the bank?

will34
will34's picture
Offline
Last seen: 8 hours 2 min ago
Joined: 12/18/2012 - 00:12
Posts: 4112

QC 3.0 tops out at about 18W (12V 1.5A). So even at full speed and 85% conversion efficiency you’re looking at 4A max charging current. You have 20 cells in parallel And assuming an average capacity per cell of 2,000mAh per cell we are looking at 40,000mAh, which should take about 10 hours in the CC phase, in best case scenario of course pushing maximum permitted power through a micro USB port.

If your cells are old or are mixed cells with some of them having high internal resistance, this will drastically lower the charging current and will extend the CV phase, or worse never finish it.

The cheapest option for fast charging would be using a 4.2V 10A power supply, they often come in the buck regulator type needing 12V+ DC at the input side. I haven’t tried those yet so I cannot comment on the charging algorithm.

I normally advise against DIY powerbank unless you really have to do something with a lot of cells laying around. Finished products are cheap enough and they come with the convenience of never having to worry about the safety aspects of li-Ion, and of course much higher overall energy density than anything one could build at home. For about $30 you can buy a 20,000mAh powerbank with QC 3.0 input / output support, high quality 18650 cells, compact size, and full of safety features. A DIY board with these functions will cost you about $10, so technically you’re paying just $3 per 3,350mAh 18650 cell. And this is without the case, assembling and warranty. It’s a no brainer.

JoeRodge
Offline
Last seen: 5 months 3 weeks ago
Joined: 01/04/2018 - 23:13
Posts: 119
Location: United States

Can’t I just use one of those smart chargers like the one twneegy makes? Just bypass the microusb port.

will34
will34's picture
Offline
Last seen: 8 hours 2 min ago
Joined: 12/18/2012 - 00:12
Posts: 4112

I’m not familiar with the tweeny charger (did you meant tenergy?) but as I said yes you can use a 4.2V DC adapter to charge your cells directly via a dedicated port (5.5mm, XT60, DC5 or whatever connector that can handle the current), a cheap hobby charger is a good option to achieve higher amps. There are pretty decent ones for around $20.

If you go with a generic 4.2V DC adapter I would recommend installing a PCB protection board just for safety.