Re: GPS Power



Pieter Litchfield wrote:

I have found a couple of places that have simple plans for 12vac to 12vdc rectifiers. I have built one to run a strobe light on a work sled that required 12 vdc from a lighting coil that produces only 12vac.

http://www.allaboutcircuits.com/vol_6/chpt_5/6.html

Yup, that's how it's done. I grabbed a bridge rectifier and filter capacitor out of a scrap TV - much higher ratings than required for the application, but that doesn't matter.

Note that the rectifier circuit has no regulation - you'd get very high DC voltages (and probably a spectacular capacitor failure!) at full throttle if you connected it direct to the sled's lighting coil. I'm assuming my sled has a regulator to keep voltages to the bulbs down, even though it has no battery - but I'll be taking a run with my meter hooked up so I know what I'm dealing with before taking any risks with my new GPS!

If you attach a "12 volt power outlet" (aka cigarette lighter socket) to the rectifier output, you can use the original GPS power cord to reduce the voltage to the correct level.

I could, but it won't last long outdoors - problem is the 12v adapter supplied with the GPS unit has the speaker and audio amp for route announcements integrated with the DC-DC converter and the cigarette lighter plug all in one plastic casing. There's no attempt at moisture proofing at all - it's clearly designed for use in a closed vehicle only.

Another possibility would be to take along a smallish 12 volt dc battery and power the GPS as a "dead loss" system. Some of the small cheap booster battery/cable packs sold by Wal-mart and Sears have a 12 volt power outlet included. My snowmobile has a weak battery charging system, so I power accessories off a removable jump starter battery pack which I charge in the house between uses.

Certainly an external battery is an option, but I'd much rather power the GPS direct from the sled while riding. To that end I assembled a simple DC-DC converter (again from bits out of the dead TV) which delivers 4.9v DC out from 12v DC in (rising to 5.1v out from 24v DC in, didn't test it past that).

That leaves me with just a cradle problem. The GPS unit has flat brass buttons on the back for power in and audio out, and there's no way to make reliable electrical contact without clipping it into a cradle with spring loaded contacts - and the only way to get the right cradle is to buy another car adapter for $$$.

I'll visit my favourite electronics stores later in the week and look for 4-pin inline plugs and sockets - that will allow me to cut the car adapter cable close to the speaker/DC converter box and install a plug and socket so the speaker can stay in the car while the cradle and mount go with me on the sled - plugged into a matching socket leading to the DC-DC converter on the sled.

Sunny

"Sunny" <sunny@xxxxxxxxxx> wrote in message news:LZmpf.988$1Y4.45285@xxxxxxxxxxxxxxxxxxxxxxxx


Dennis Mayer wrote:


Sunny wrote:


Bought myself a Christmas present today - a Garmin Quest GPS.

I got it because I often use lakes as 'transport sections' to reach
trail systems that are otherwise too far away for day trips, but I
sometimes get lost on the ice.

I've been playing with the software, plotted my favorite lake routes on
the map and transferred them to the GPS unit - looks like it will do
what I want, i.e. show me the route I plotted vs where I am right now.

My question is ... do I have to run it on battery while riding, or can I
power it from the sled?

The GPS came with a cigarette lighter adapter, but the speaker for
announcing route directions is part of the adapter and doesn't look like
it was designed for outdoor use - and my sled doesn't have a battery,
let alone a cigarette lighter socket.

Can I power the GPS off the lighting coil on the sled? If so, what's the
best way to hook it up?

Thanks,

Sunny 



 Generally speaking about Garmin units....    the cigar plugs takes in
12V DC...

but the Garmin Cigar Power cord reduces the voltage to 3 V DC..... 

Thanks for pointing that out!

The manual says 13.8v, but that didn't seem right for the GPS unit itself.

It turns out both the AC adapter and car adapter output is 5v DC, and the GPS 'threshold' voltage (the voltage at which it detects external power and turns itself on) is 4.5v.


You should not hot wire 12V DC from the sled to the Garmin GPS....... 

Definitely not!

There was a dead TV on the curb today - so I hauled it in, pulled a suitable power transistor and zener diode, and built a DC-DC converter. My converter's output is 4.9v, and it runs the GPS just fine from a car battery.

Next step is to find out if my sled has a rectifier (sled is at the cottage, I'm stuck in the city this weekend), if not I'll need to add a bridge rectifier and filter capacitor ahead of the DC-DC converter - already pulled those from the TV in case I need them.

However, I guess I'll still have to buy a second car adapter ($$) since I don't see a way to get a reliable connection to the power buttons on the GPS unit without using Garmin's cradle - unless someone has a cheaper idea...

Sunny 



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