Need help from some of you electrical weenies out there.  I have a Garmin etrex type GPS and would like to hardwire the unit so that I do not have to worry about it shutting off on me when the batteries get low.  I realize that there are more rugged GPS units out there but the etrex works well because it is small and fits easily on my bars.  I can buy an accessory 12v adapter power cord that will run the unit from a car's 12v cigarette outlet.  One end of the cord has a "micro USB" connector which is what plugs into the GPS to power it.  I don't trust the micro USB connection to handle the vibration from the bike so I am thinking about cutting off the micro USB plug and soldering the power wires directly to the battery contacts inside the unit.  Can I get away with this without damaging the GPS?

The GPS is designed to run off 2 AA batteries in series so the battery contacts normally see only 3.2v or so.  The spec for micro USB is 5v + 0.25v, so if I cut off the micro USB plug and connect to the battery contacts would I be subjecting the unit too much voltage?  I realize the unit can handle the 5v if it comes in thru the micro USB port, but again,I would be applying the 5v directly to the battery terminals.  Would I be circumventing some step-down circuitry that takes the 5v to 3v?

In a bit over my head - any help would be greatly appreciated.

I use a Garmin GPS 76 and an Oregon, both have 18 hour battery life on a pair of AA batteries.  Dirt bikes have notorious bad power that I'm not willing to subject to sensitive electronics.  I do carry  spare  batteries but that is more for a back up in case I need to abandon the bike in the woods and hike out. During the past three years I've only once needed to replace batteries because I wasn't keeping track of hours.  So why bother with the hassle and risk to the GPS of connecting to bike power?

If I were doing that, I'd wire directly to the terminals where the 5v USB feed goes to the board.  However, the point about regulating and conditioning the power feed is not one to be shrugged off.  Even a YZ450 has enough spare energy to run a GPS, but the extra complexity of regulators and rectifiers would put me off.  Personally, I've done stuff like replace soldered-in batteries on small circuit boards before, but I'd rather not if it can be helped.

chuck4788, on 12 March 2012 - 07:30 PM, said:

Been there, tried that with the spare batteries.  Started out using fresh duracells on each ride and it was a 50-50 chance that the GPS would make it 5-6 hours without crapping out.  Switched over to lithium cells and appeared that the problem was solved until my last ride.  Went three hours, had to put in a fresh set of lithiums.  Second set made in another three hours then crapped out.  Thinking I may have an intermittent short that is brought on by vibration.  Really this is a last ditch effort to salvage this unit.  I am one step away from hucking it at the neighbor's cat next time I catch him crapping in the bushes.  Figured if I could feed the GPS constant full voltage then it might be happy and work a little while longer.

grayracer513, on 12 March 2012 - 09:33 PM, said:

That was my first thought but I can't access the internal board without destroying the unit.  Don't want to risk damaging the micro USB port or then I won't be able to upload/download to it.

I wish Garmin would come out with a ruggedized externally powered version of the etrex because the small size really works well for me.  Really only use the thing in compass mode to keep me on my planned routes or find waypoints.

My old eTrex Legend goes a long time before the batteries go bad (12+ hours??).  I've heard from somewhere that using the electronic Compass really draws down the batteries quickly.  Mine doesn't have the electronic compass so I can't say this for sure.  Not ever having the electronic compass, I can't imagine what you would use it for.  I just follow the tracks.  I do trailwork, so I do find bringing a regular old compass along sometimes helps.

Wiring a GPS to a bike is common but I've never tried it.  I would guess that if you went to ADVRider.com, you would be overwhelmed with info on how the Adventure Bike folks to do this.  Note that it is common for GPS's to go bad when riding with the batteries installed because the heavy batteries vibrate at a different frequency than the lighter GPS.  All of the fretting of the contacts messes them up.  I even had a similar problem with my battery powered ICO dual sport computer of all things.

Edited by NemadjiMan, 13 March 2012 - 10:02 AM.

NemadjiMan, on 13 March 2012 - 09:55 AM, said:

That gives me something to investigate.  I sometimes find my old 60cs has shut down for no apparent reason in the middle of a ride.  It has an external power jack on it, but I ride a YZ450, so there again...

NemadjiMan, on 13 March 2012 - 09:55 AM, said:

I have the HCx with the electronic compasss, I believe it gives you true north versus magnetic north, if you need that kind of precision.  I don't.  I always make sure the compass is tuned off and still I have power issues.  My power is bleeding off somewhere, not sure where it goes, but that is why I want to hardwire.  Give the darn thing all it can eat and maybe it will work for a while longer.

NemadjiMan, on 13 March 2012 - 09:55 AM, said:

I am also aware of this issue, it was particularly bad on the older etrex models with soft spring contacts.  You could see the black pitting marks on the contacts after a few rides.  My unit is only 2 years old and Garmin really beefed up the battery compartment so that the batteries are in there snug.  I even go one step further and put a wrap of self-amalgamating tape around the batteries just to make sure they can't vibrate.  When I pull out used batteries I have to gently pry them out with a small screwdriver to "unstick" them from the case.  The things are damn near glued in there.  I still inspect my contacts periodically with a loop and can see no evidence of pitting or fretting as you call it.  Really not sure what the problem is, just not ready to toss $200 at the neighbor's cat just yet.

I know this doesn't help solve the battery draw of your etrex but from my experiences with three different GPS units I think vibration damage to batteries and battery life are not that common. I use my Garmin GPS units on three different bikes, two with XR engines, one that vibrates so badly that the hand grips buzz your hands at 5500rpm. Never had a battery problem.

I don't know about the etrex compass power draw but I always have the compass' on in my two 76s and Oregon. I'm just leary about connecting a GPS to bike power with out installing good filtering. And I always carry backup batteries  in case I have a long hike out.

Try this: http://www.cycoactiv...PS-Cables-Cases

I just googled "hardwire etrex motorcycle" and eventually came up with this.  I got the "Cycoactive" website info from a "Thumpertalk" Forum thread.  Go figure.

Edited by NemadjiMan, 16 March 2012 - 06:14 AM.

Thanks Nemadjiman!  I just sent them an email to see if they make a power cable for my particular unit.  I was getting ready to try and make my own 12v-to-3v regulator but not worth the effort if these guys have already done it, assuming the price is reasonable.

I've had three Etrexs over the years and they all have cut out on battery power due to vibration. I've used NiMH and Alkaline batteries, but it doesn't matter. Once I powered my Etrex from the bike, the problems ended immediatley. It's great having the display backlit all day and for night riding. On my ATV with the same engine as the WR450F, I've had the Garmin cigarette lighter adapter under one of the fenders. Never a problem after years of use this way. I couldn't find any room for the cig adapter on my WR450F, so I bought a "Garmin Nuvi Hardwire Cable (Mini-USB connector) for Garmin Nuvi Sold by Semsons & Co. Inc. on Amazon $20 (shipped). I just mounted it last weekend and tested it, but I have no time on it yet. The genuine Garmin hardwire adapter had a 90° USB connector that faces the wrong direction for the Etrex, so I bought this other one instead. They're both made in China anyway.

I prefer to wire it directly to the battery (with fuse) so the GPS will continue to log one giant track all day even when you shut the bike off. You have to remember to pull the fuse or install a switch or else the 5vdc transformer will continue to draw from the battery after you put the bike away.

I've also used a Duracell Powerhouse on my 2-stroke because there's no bettery power available from the bike. I've used the Duracell Powerhouse for years now. It works great, but you have to charge it up.

rpyfz450, on 20 March 2012 - 09:12 PM, said:

Thanks for the info.  I am also mounting the GPS to a WR450 so good to know that you have had success in doing it.  After thinking about the problem some more, I have got a plan that should work.  I found a vendor on ebay that sells the 12v to 3v power cables for the older gray scale etrex units for $11.  The cables are rated for an input of 12-32v, fused, and appear to have that ferrite bead thingy to suppress RF interference - all good signs of a quality design.

http://www.ebay.com/...=item483d1506a9

I will attach some small wire leads to the battery contacts in the GPS and drill a small hole in the back of the cover to bring them outside the unit.  I plan to do it in a way that will still allow me to use batteries in case I want to use the unit for hiking, etc.  I will leave about 6" of wire length and terminate the leads to one end of a small two pin connector (e.g. Molex).  This connector will allow me to take the GPS on and off the bike easily without having to undue the wiring.  The other end of the two pin connector will be attached to the power cable, after I cut off the unneeded e2plug that it comes with.  Then I will stick the bulbous 12V cigarette adapter end under the seat and wire it to the bikes battery terminals.  May have to extract the voltage regulator circuitry from the plastic housing if it is too big to fit, but I'll make it work somehow.

I'm not sure if anyone still cares, but a garden variety 7805 or low power 78L05 voltage regulator is all you need. Either one will regulate from 12V down to 5V. The 78L05 is good up to 100mA, which is probably enough for small battery powered devices. You can add some filter caps for good measure. The 78L05 is 45 cents in single quantity from Digi-Key:

http://search.digike...CPFS-ND/1049368

I've got a bunch in the man cave if you have trouble getting them.

If you want 3V you can use this one:

http://search.digike...9830-ND/1510725

Edited by msiddalingaiah, 28 March 2012 - 03:02 PM.

msiddalingaiah, on 28 March 2012 - 02:59 PM, said:

Appreciate the offer msiddalingaiah and I would take you up on it if I needed to design my own circuit from scratch.  Was lucky enough to score an original Garmin 12v-to-3V adapter cable from ebay for less than the decent looking knock-off I was about to buy.  The bulbous cigarette plastic case comes apart with no tools and you can harvest the regulator circuit card and fuse for repackaging.  The card is about the size of a poker chip and I plan to stick it in a water tight enclosure and foam tape it to the underside of my headlight cowling - even simpler than mounting under the seat, and easier to get to.  Will try to post some pics when I'm done.

msiddalingaiah, on 28 March 2012 - 02:59 PM, said:

So could I use that 5v regulator to run something like a trail trech bike computer off my battery on a dirt bike?

Edited by alexisfire51, 29 March 2012 - 09:27 PM.

alexisfire51, on 29 March 2012 - 09:26 PM, said:

Sure. If you need more than 100mA, use the 7805, it's good up to about 1 amp.