Cheap USB Power Socket on the bike

This is one of those things

You know how it is. The eTrex Legend C GPS runs for a very long time on two rechargeable AA batteries. Power really isn't a problem. Especially as a normal cigarrette lighter power cable cost about £20. Twenty pounds is really a bit too much. On top of the price, I'd have to hack it into pieces as a) My bike doesn't have a normal size cigarrette lighter socket. b) I'd like it permanently mounted.
Still it was bothering me from time to time that I either had to stop and change the batteries, or that I just simply ran out of juice. Funnily you never run out of juice on your way out on the trip, but on your way home or close to your destination. Good reason to fix a permanent power source.

Luckily the eTrex Legend C charges via its USB socket. That's a "Good Thing" (tm) because Garmin doesn't sit on its proprietary connectors anymore (like the "plain" eTrex series), and I can use "any" power that comes through to a USB connector. To the Batmobile..!

eBay to the rescue

I checked eBay for cheap USB chargers and I can tell you, there's a huge bunch of them there. I picked one that was designed for the Sony PSP, mainly because it looked like it had the right small USB socket. Price was cheap, postage reasonable; Under £5 in total. A week or so later it arrived from China. Result. I tried it in my car on the way home from work and it looked like the cable was a bit dodgy. No prolems as I was going to butcher that cable anyway. It also worked with my O2 XDA which also charges through the USB socket. Perfect!

First steps; Preparing the charger

USB Cigarrette Lighter Charger - Opened up, Click here to view larger image (NaNkb)

The first thing to do after testing the charger in the car was to destroy it. Unscrew the tip and pry it open. Then I soldered the "power cables" on. The positive one is the "tip".

The first thing I did when I got home was to "repair and butcher" the supplied cable. As the cable was for a Sony PSP, it had two plugs in one end, one USB and one for the PSP power socket. The cable was also a bit dodgy so I just cut the connector bit in the middle out and soldered the USB part back on. The cables are quite thin so this gets a bit fiddly. When the cable worked I was happy to proceed to butchering the actual charger.
Unscrew the top of the plug and the rest should just fall apart. I then soldered a power cable onto the connectors that would usually touch the walls of the female power socket. The cable I used was about 15 cm long, I'd recommend a bit longer one, just in case. Solder the positive cable onto the tip of the cigarrete ligher plug, the negative onto the side-connector.
I then put everything back into its shell, and wrapped it in some electrical tape for waterproofness and used my "Trusty glue gun" (tm) to seal the tip where the cables exit. I left the USB socket at the back of the plug untouched.
Ready for next step.

Assemble it on the bike

As my bike is a BMW K1200R I don't have many places to stick the charger. Normally on a faired bike you'll have tons of nooks and crannies where you can find a dry spot to stick the charger.
I opted for the left front "fake" air-intake panel. It's easy to remove and it's close to the battery that's in front of the petrol filler cap. It's also just next to where I've mounted the GPS; to the left of the clocks.
It's easy to remove the pane; just unscrew the indicator and the screw on the tank and slide the panel forward.
Using some double sided tape I attached the charger on the topmost spot fairly far back to give it as much protection as possible. Admittedly there's not much protection here, but at least it won't be submerged in water. I'm hoping the low power, electrical tape and position will give it protecion enough.
I then added some more tape just to try to secure it and give it just a tad more protection. I used cable ties (of course) to position the cable to the GPS. Make sure you add a bit of extra slack; it's very useful when you need to plug and unplug the GPS.
To get the power from the bike I'm "stealing" 12V from the original BMW GPS plug that's located just in front of the battery. I pulled a cable from this plug to near the charger and then I crimped some connectors on these. This allows me to remove the panel without too much hassle.
When it's all connected, the rest is just tidying the wires up and put the panel back in place. Remeber to try the GPS before you put everything into place.

USB Cigarrete Lighter Socket Charger - in place in a bike fairing., Click here to view larger image (NaNkb)

Here's the charger hiding in one of the K1200Rs panels, the LHS fake air intake one, to be precise. It's stuck in place with some double sided tape.

USB Cigarrette lighter charger, all taped up., Click here to view larger image (NaNkb)

Here you can see the charger taped in a bit more, a few cable ties and we're almost done.

Taking power from the BMW K1200R's original GPS power socket., Click here to view larger image (NaNkb)

I'm "stealing" power from the original BMW GPS power socket. This turns on with the ignition and off after about 30 seconds after you've turned the ignition off.

Cables for the USB Charger., Click here to view larger image (NaNkb)

To be able to remove the panel without too much hassle, I created a two-piece cable that goes from the power outlet to the charger. The cable can be unplugged in the middle for removal. Note that the panel is upside down and back to front.

...and that's it!

For about five pounds (£5), I've now got the GPS permanently powered whilst on the bike. I've done about 1,000 miles since the install, sometimes through rain and I've had no problems at all. The charger is of course of quite a low quality, but it's good enough for this task. For my next long trip, I'm toying with the idea of giving my tail-pack 12V plus 5V USB power which would mean that I could have the phone turned on and blaring MP3s into my ears all the way on the boring but necessary motorways. And for £5 I don't really think I have any reasons to hold back.

Cockpit view of the BMW K1200R with Garmin eTrex Legend C GPS and Geodesy speed camera detector., Click here to view larger image (NaNkb)

Here's the view from the riders perspective. The powered R.A.M-mounted eTrex Legend C to the left, and the Geodesy speed cam detector to the right of the clocks. No too bad for a "naked" bike.

This just in...

I've been alerted (by Paul W - Thanks!) that there might be a problem with some chargers as they apparently use "buck/boost switching regulators" this can cause the CAN-bus to stay live, which in turn can draw 100mA - this can lead to your battery being drained over several days. On a CAN-bus BMW this can be detected by the dead battery (hehehe), or that the hazard light switch stays lit for a long time after the ignition has been turned off. On a "traditional bike" I guess the symptons are limited to the dead battery..?! Anyway, apparently one solution is to either unplug everything when you leave the bike, and another one is to add a 1kohm resistor on the output of the charger.
I'm not a very experienced "electickerian", so this all is going into woodoo territory for me, but if your battery begins to die on you, this might be the reason. My bike and charger combination seems to work fine just as they are, so I've got no problems with this.
"Mileage may vary" as they say. Have a peek at the UKGS:er thread about the issue for the gory details.