Saturday, December 6, 2014

USB Battery Backup Unit

When I returned a modem I was renting from my ISP, the company didn't want back the battery backup unit that came with it. Don't let that $129 retail price fool you, these go for at best $30 on eBay. I'm not really one for selling stuff on eBay anyway, so I thought I'd come up with a little project.

The battery backup unit has an output of 3A, 12V. Taking a page from my previous 12V effort, I thought I could easily convert the 12V to a 5V USB connection and use it as a backup power supply for my wife and my phones. The battery is 7.2 Ah, so somewhat similar to this much smaller Anker battery backup. Although I don't think you can charge the Anker and my phone simultaneously off AC like my unit will do.

In addition to the Belkin battery unit, here's what I used:

12V plug socket, $6
Dual USB car charger, $8 (Although, I should have got this 3A one instead)
Heat shrink tubing, $9
Solderless wire terminal and crimping tool, $13

Here's what I did. I'm sure it isn't best practice.

First, I chopped off the output lead on the power supply. I wasn't sure which of the two wires was positive or negative so I tested them with a multimeter and labeled them.

Here's the 12V terminal. I clipped off the eye terminals after I took this photo.

I stripped the ends of the wires and connected the corresponding leads on the power supply and 12v terminal using the butt-couplers.

I covered the couplers with some shrink tube and added some strain relief with some cable ties.

Here is the USB adapter in the 12V terminal. As I noted above, this is a 1A version. The power supply is capable of 3A output so it would be better to use a USB adapter capable of doing the same. I'm going to get a 3A version and toss this one in my luggage or something.

The smart thing to do here would be to test the USB output. I wasn't sure how to do that so I plugged in an old USB device, in this case my wife's old iPhone 3 that my son plays on occasionally. He probably get's too much screen time anyway.

Hey, it's charging! Right now the power supply is plugged into an AC outlet

In this configuration I unplugged the power supply and the iPhone is charging off the backup battery. Success!

I haven't decided where I want to put this yet. I was thinking I would hide it near my charging station and always keep the phone chargers plugged into it. In the event of a power outage, our phones would still charge up.

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