A long while back I bodged together a USB charger.
One of these charger outputs failed on the last day of my trip.
In this case the one on the left died. I did a quick diagnostic on it but nothing obvious seemed to be amiss with it. Honestly even if something was buggered up I doubt that I would fix it since it’s cheaper to replace.
I built that back in 2011. Things have moved on since then. I used two discrete packages since at the time since there wasn’t any high current chargers at the time.
This time around I picked up a Scosche 2x12W charger that I figured would require less hacking.
Before I voided the warrantee I made sure things worked.
Sure enough it does.
A quick search on the K34AB part number turned up nothing. From looking at the parts though it looks like a standard buck downconverter with a bit of decoupling on the front-end. There’s a big tantalum cap next to the brains, and on the other side there’s a massive SMD inductor.
Quickly I chopped off the input connections. I didn’t trace the circuit all the way out, but both positive and negative went to two different connections. Odd. I made sure to keep that and just spin them together.
I checked this and it worked fine. (check out the glowing blue led)
This seemed fragile though. I had an old stick of Loctite Magic Steel kneadable epoxy. I checked the spec sheet for the stuff and it’s an insulator. Score.
I molded some up as a strain relief for the connection. I know that a simple solder joint isn’t enough to hold up to actual stress.
I took some random tubing I had in the shop to make up a light pipe for the led:
Wrapped up in some silicon tape and Bob’s your uncle!
The reason I really wanted to not use the cigarette connector is twofold:
- The connection is pretty dodgy in my tank bag.
- The socket for the connector is huge when looked at in the tank bag. It looks small in your car’s dashboard, but out by itself it’s pretty big. Especially in a limited space environment.
The other side of the wire in a standard SAE connector. It’s the same one that I can use to hook up my air compressor or my Battery Tender. It’s wired in through a 10A fuse straight to the battery.
The nice thing about the SAE connector is that it’s built for a lot more reliability than the cigarette lighter. In the end the original design was just to heat up something to light a cigarette — reliability wasn’t a concern at all.
I think the end result looks pretty good.
And it’s smaller than the old one it’s replacing!