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Hooking Up A Usb Port To My Vtr - Help With Fuses/wiring

Discussion in 'Maintenance and Servicing' started by cameronp, Nov 24, 2012.

  1. G'day chaps,

    I've just picked up one of the Burnsmoto USB gadgets that Greydog and a couple of others mentioned in a recent thread. While I've got a decent understanding of electronics, my practical knowledge of car/bike electrical systems is pretty much nil. I've got the USB port mounted easily (hoorah for cable ties) and ran the cable around the tank and under the seat. I was going to hook it up straight to the battery, and then I realised that it didn't have a fuse - or rather it did, but it was all the way up at the USB port end which wouldn't help if e.g. the cable got damaged and shorted out.

    Is there a "standard" way to add extra electrical bits and bobs like this to a fused circuit on a motorbike?
  2. Funnily enough I also ordered a usb port after that same thread (though I went with a cheap Chinese one off eBay).

    Personally I was just going to piggyback off the headlight circuit since in my case it's switched to the engine being on, rather than just the ignition. I also figure the small amount of power drawn by my GPS (less than 0.5A) will be well within the tolerances manufacturers build into everything (it's a 120W circuit for a 60W bulb) :).
  3. Cheers jd. Does that mean that the USB socket would switch off when you put your high beams on or is there an easy way to get to the headlight circuit before it goes through the high beam switch? (I was imagining wiring it up in parallel to the bulb itself, inside the headlight casing bit at the front of the bike...)
  4. A common way would be to run a fused line straight from the battery, through a relay, and have the relay switched on by one of the other circuits (eg. lights etc). Make sure the fuse is as close to the battery as possible.

    If you do it that way, you'll be able to power other accessories such as heated grips, gps, wheel lights, and whatever else you want, and not have to worry about teeing them all into existing accessory lines indivudually...
  5. With my bike there's just the one power lead going to the high-low beam switch, which is then obviously directed to one of the light bulb filaments. So as long as I splice into the power before the switch, it should mean power to the USB with either beam (just not with the engine or ignition off).

    Don't know if the VTR is the same or not though. You'd need to check the wiring diagram.
  6. I ended up picking up an inline blade fuse holder, some crimp connectors and a crimping tool (hilariously labelled "Easy Stripper") from Jaycar this morning... half the challenge is knowing that these things exist. Job done!

    Hooked it straight onto the battery because the stock wiring for lights etc looked like a pain to get to. I figure the quiescent current of a voltage regulator over a few days shouldn't be enough to drain the battery, and if I'm leaving the bike for longer I can always pull the fuse.
  7. As stated, the common way to do this is to either buy a fuse that you can connect in line between the device and the battery or alternatively, connect to a spot which is already fused e.g. horn.

    However Burnsmoto state "Contains a built in automatic fuse that resets itself".

    As I have a glove box I hooked mine up directly to the battery rather than through the ignition so I can charge up at lunch stops if needed with my phone locked away in the glove box. Seems to work well.

    I wouldn't have thought the current drain wouold be very great, however a friend who used one to charge his phone each night said that after a couple of days his bike didn't want to start.

    Anyone know what the actual drain on the battery would be?
  8. Devices aren't supposed to draw any more than 0.5A through USB (though some do). So just look at the amp hour rating of your battery and do the math based on the worst case scenario.

    For example, a 12 amp hour battery being drained at 0.5A would be dead flat in 24 hours. Other option is to look at the mAh rating of the phone battery, and the time it usually lasts between charges to work out its amp hour rating - then use that to guess the drain on the battery.

    Either way a phone flattening a bike battery to the point a bike won't start after a few days is definitely plausible.
  9. The built-in fuse would only protect against faults inside the USB adaptor. If e.g. the insulation on the cable to it somehow melted or broke and the wires touched, the fuse inside the adaptor wouldn't help. Fuses should be as close to the battery (or mains) as possible...

    I didn't end up measuring the quiescent current. I think it should be possible to do by pulling the fuse and touching multimeter probes to fuse holder contacts, so I might give that a shot and report back.

    Back of the envelope calculation for current draw when charging: an iPhone battery is 1420 mAh @ 3.7 V = 5.25 mWh = 438 mAh @ 12V. A typical voltage regulator e.g. LM7805 is about 50% efficient, so that would make about 900 mAh to charge a completely flat phone. (Minus a bit because the phone battery probably wouldn't be completely flat, plus a bit because there'd be some further inefficency in the phone's charging circuit.)
  10. Minor pedantry: USB provides power at 5V, so 0.5A @ 5V is 0.2A at 12V (but when you take into account the inefficiency of cheap voltage regulators, you're looking at more like 0.3-0.4A, which is near enough). Most phones will happily suck more current from a USB port if they can get it. The iPhone needs 1A to charge while switched on (source), and an iPad more like 2A.

    Anyway, your conclusion is quite correct.
  11. Thanks guys
  12. Ah yes, good point. Still I have heard of devices pulling up to 1.5A despite the supposed limit, and frying the USB ports of laptops as a result.

    Of course then you have those people who just can't resist seeing how far you can take things :)
  13. Ive got two USB ports on my bike, one at the back, one at the front.......then theres the UV lights for the wheels, and the aux lights...........all except the UV lights is connected to the battery, with its own fuse and the aux light has its own switch.....................what im saying is that it really depends what your using it for.

    Id say, the best way would be to connect to the battery to limit f***** up other components, cut and move the fuse closer to the battery, and for a USB port just run it without a switch...............
  14. some USB ports constantly drain power, mine dose so i added a small on/off switch
  15. So how do you know if it is constantly using power or only using when something is plugged in?
  16. A multimeter; on the A setting; in between the 12v of the battery and the 12v power feed to the usb port will tell you how much current is being drawn from the battery.

    If you don't get a reading on the A scale, switch to mA..
  17. Ta. Provided I can find the power feed in the USB port.
  18. Jaycar 12v socket, $2.49. Centre pin +ve.

    Solder on a length of cable of your choice and, if you want to be really tidy, add shrink-wrap over the socket sleeve where the cable goes in.

    Solder or crimp an inline fuse holder to the +ve line at the battery end. Shrink-wrap soldered cable joints.

    Crimp on two ring terminals. Attach to battery. Job done.

    I added a tiny on/off switch on the +ve line at the socket end (another $1 to Jaycar) cos I know that my little USB adapter has a light on it, and flicking the switch off is easier than pulling the fuse.
  19. I used a cigarette lighter type socket on my vstar, with a usb adapter that fits into the socket. The socket is "always on" via a fused link directly from the battery, but does not drain any power when nothing is in the socket. I use this setup because I can blow up mattresses when camping using the cigarette lighter socket, and then charge up my SENA and phone afterwards. I connected a positive wire deirectly to the battery, put in an in line fuse within about 10 cm's, and then ran the wires to where I wanted the socket. Earth doesn't need a fuse.

    What I did not realise is that if I leave the usb adapter, which is a little bud type thing that disappears almost entirely into the lighter socket, then it does drain power. Enough to flatten the battery after two weeks. I had left it in after a camping trip, and ridden the other bike a few times, and found it flat as a tack. The only give away when I recharged the battery was a glowing red LED when I looked at it in the dark.
  20. Easily overlooked. Hence why I fitted a small on/off switch. :D