Powering a Quest 12 to 5v?

I want to wire up my Quest to the bike perminantly so I thought I'd butcher the second mains powered cradle, but the Quest is meant to run off 5v.
I'm not bothered about audio and I'm too tight to pay £30 for a proper mounting kit - when I have cable ties...
Can I put a resistor in series to reduce the voltage? If so how do I work out out the right ohm rating? Will the resistor get too hot (Err P=R*I^2?)
My physics is bit rusty, can anybody help?

Try a search in the this section for '5 volts'.

http://www.seetron.com/an_vpwr1.htm

http://www.elecfree.com/electronic/12v-to-5v-power-supply-regulator-by-lm317-and-lm337/

or read to understand

http://www.ukgser.com/forums/showthread.php?t=86209

You can use the power supply from the Quest car cradle with a Ram mount for the Quest. The Ram mount comes with a tiny torx key that fits the screw holding the contact pad on back of the car mount. Undo this from the car mount and transfer to the Ram mount. Then rig up an adaptor so that you can plug the Garmin ciggie lighter plug (complete with speaker etc) into a ciggie lighter socket on your bike - try Hein Gericke, they sell one for about a fiver with a BMW style plug on one end and a ciggie lighter socket on t'other.

I've had my Quest running like this for 12 months or so without problems. The Quest speaker/ciggie socket etc fits under the seat on the 1200GS (wrapped in a poly bag held on with cable ties), and there's enough lead to run up under the tank cover to the RAM mount which I have attached to the bar above the instrument panel.

HTH
TC

TUNED IN said:

http://www.seetron.com/an_vpwr1.htm

http://www.elecfree.com/electronic/12v-to-5v-power-supply-regulator-by-lm317-and-lm337/

or read to understand

http://www.ukgser.com/forums/showthread.php?t=86209

Click to expand...

Some good links there...

FWIW, I use a 7805 regulator to power an MP3 Jukebox on my bike based upon a simplified version of the circuit in the first link. In that schematic, D1 is irrelevant if you're wiring to a known polarity source, and D2 (the zener diode) is junk too. Frankly, if your charging circuit is that poor on regulation then you've got bigger problemls than blowing up a Quest GPSR... C1 need only be 0.33uf, while C2 can be junked too (D3 and R1 are noted as not necessary for a 7805 circuit anyway).

I use no additional heatsink on the regulator which happily supplies 1 amp for as long as you like. OK, you wouldn't want it in your trouser pocket, but it does OK in a pretty enclosed space with minimal ventilation. For higher current I would use a heatsink though. HTH