[aprssig] In car power solution for GPS 18

[Dave Baxter]

Hi...

>From personal experience...

Use a "Wet" type motorcycle battery, fix it down, and run the vent out
through a hole in the floor, if "inside" the passenger compartment.

Use a standard type split charge relay, with a 21W bulb in series with
the charge feed to the new battery to act as some sort of current limit,
not forgetting a fuse (5A max) on the vehicle, or "Hot" side.  99.9% of
the time, you wont see any glow, let alone light, unless you let the
battery run way down, then start the car to charge it, then maybe only
for a minute or so...  A smaller fuse too, on the feed to the GPS supply
of course.

You then have a simple indipendant low power supply for GPS and alarms
etc that stay's up when the engine is off.

Low voltage cut off systems are available to protect the battery from
deep discharge, but are just as easy to make yourself.  Use a P type
power FET, or latching relay as the "switch".

Jelly cells.  Not recommended without special charge regulators, as they
need much more careful charging than a car alternator will give them,
hence use a wet (flooded) cell battery.

Or, one of the commercial switched mode 12V to 12V chargers, but that
starts to get very expensive, though is the "ultimate" solution.

There was a link to a US company listed on here a while back, that makes
all sorts of DC input SMPS battery chargers, 12V "UPS's" and cut outs
etc...  http://www.powerstream.com/ I think.

Of course, you could put another car type battery in there (minus the
lamp, and with a larger charg fuse) with the split charge system, then
have all the radio's, PC's, GPS's and other gadgets indipendant of the
car system.  The biggest problem, is usualy finding space to physicaly
fit another battery of that size in modern cars.

I've seen several instalations of this type to keep alarm systems
running for extended "off" periods, one even had a solar charger as the
"off" times were months!  It doesn't take much current drain over a few
weeks to make even the biggest battery struggle to start an engine...

73...

Dave G0WBX.

________________________________

	From: Andrew Rich [mailto:vk4tec at tech-software.net] 
	Sent: Saturday, August 12, 2006 10:58 AM
	To: TAPR List
	Subject: [aprssig] In car power solution for GPS 18
	
	
	Gudday
	 
	When I jump in my car, my GARMIN GPS18 (5volt version) takes a
while to lace up on the sats. (because it has been off)
	 
	I am wondering if I can throw a gell cell battery in there and
charge it while the car is running. (and GPS going when the car is off)
	 
	Now I need to know 
	 
	1) Should there be a diode in line ?
	2) Should there be a resistor to limit current to battery on
charge ?
	3) Any low voltage cutout ideas ?
	 
	Cheers 

	-----------------------------------------
	Andrew Rich
	Amateur radio callsign VK4TEC
	email: vk4tec at tech-software.net
<mailto:vk4tec at tech-software.net> 
	web: http://www.tech-software.net
	Brisbane AUSTRALIA