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.

Warrantee: voided.

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:

  1. The connection is pretty dodgy in my tank bag.
  2. 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!