Afternoon all

You've had more than enough time off without a daft question of car electrics so it's time once again to get the old locost forum brain cells going.

If I wanted to wire a sat nav into the car without using a cigarette lighter socket how would I go about it? the unit is 5v so I can't just wire it in can I?

I'm thinking I need a resistor or something else to drop the voltage to 5v so what is the easiest/best way of doing it so someone daft can get their heads around it.

Nice simple laymans answers greatfully received

as always thanks for time and patience

A resistor will get hot so you are better off using the lead that came with it.
A cigar socket would be your best and tidy option, even if you hid it away under the dash

[Edited on 8/2/2010 by nitram38]

I would have said the same.
It's hidden under the dash so it's tidy and it will have the right resistor etc already

Dan

Would agree with wiring in cigarette lighter socket, fitted one in mine and it then gives you the option for sat-nav, phone charging, mini air compressor, wheel nut gun etc. Only a few quid on the 'bay

Or.... go to maplins/rapidelectronics/rswww.com and buy a 5V voltage regulators... its a 3 pin chip... easy enough to wire up.... gives you a stable 5V... usually up to 1A from a 12V source...(worth noting that the regulator will draw current even if the satnav is switched off!)

But... as they say above... fit a lighter socket under the dash somewhere..... will be useful for other things... even solar trickle charging if its wired in right

[Edited on 8/2/10 by tegwin]

This is a pic from when i had just wired mine in.Tucked it up at the front under the dash so it is out of the way and do find it useful.



11/10/05 3

Lighter socket it is then, many thanks.

For my tomtom, I cut the lighter adaptor off the end, and bought an LM7805 from Radio Spares, and a small Jack/Socket which I've mounted out the way. I plan on doing the same in the fury, with both 5 and 12v outlets tucked around the car for mounting cameras, chargers, sat navs and other low power devices.


Rob Collingridge has done something similar i think, buggered if I can find his write up of it though.

A simple resistor is useless as a way of dropping voltage, since the voltage drop will vary with current drawn i.e. get the voltage drop correct with TomTom running, and you'll blow it up when you switch it off as voltage will rise way above 5v.

The three terminal regulator such as LM7805 are more useful, but they aren't automotive grade parts, which means they are not rated to take the large voltage spikes often found in car eletrical systems. That said, they do seem to survive ok. Note that it's important to use the correct bypass capacitors mounted as close to the device input pin as possible, failure to do so can cause the device to oscillate at high frequency.

Also note that linear regulators work by converting voltage drop to heat, just like a resistor. Sat Navs can pull a fairly high current, so ensure any regulator has a sufficiently large heatsink e.g. 500mA @ 5v would give a regulator power dissipation of ~ (14-5)*0.5 = 4.5 Watts which is plenty of heat to get rid off from a small device.

The regulators built into the cigarette lighter plugs for Sat Navs are switching regulators which do not suffer from this high power dissipation.

Edit: Beaten to it!
You should not use a 7805 in cars, a lm2940 has the same pinout but can cope with load dump (80v spikes), and has a lower dropout voltage.
Thanks
Darren

[Edited on 8/2/10 by turbodisplay]

Why not open up the Lighter socket plug, extract the circuit and hard wire it in behind the dash with a suitable socket (2.5mm DC socket?) through the dash?

lot easier just to get the correct car voltage adaptor from Maplin.