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 Post subject: GPS and solar cells
PostPosted: Mon Jul 14, 2008 2:53 pm 
Brotherhood of the Golden Paddle

Joined: Mon Apr 18, 2005 3:40 pm
Posts: 1080
Location: isles of scilly UK
For quite a few years i have been powering my Garmin 76 direct from a 12 volt 6.5 w folding solar cell through the Garmin cable that will connect the GPS to the cig lighter in a car, and it works, the owners manual say,s one of the power sources can be 8-35vdc as these folding cells probably supply 12 - 14 volts all seems ok and there is no apparent problems, Now comes along the Garmin 76csx it says up to 36vdc but when trying it with the solar cell it "flickers" from the solar cell power to the batteries, i know nothing about electronics or electric in general, i am thinking of going up to a larger solar cell and i think they are still 12 volts but about 12w. I suspect the problem is the map and color which are not in the old GPS. The 76csx works ok from the cig lighter in the car. Before i try a larger solar cell does anyone know if it would destroy the Garmin 76csx.


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 Post subject: Re: GPS and solar cells
PostPosted: Tue Jul 15, 2008 1:38 am 
The voltage of my solar charger is steady - 3V, 6V or 12 V, depending on connenction. Not that I find it useful - it is small, low-power, takes forever to charge AA batteries, and 2AA in my 76 CS (not X) last more than 10 days, if I only check my location once in a while to make sure I'm on the right course. If you keep GPS ON all the time, then of course you need a solar panel, but I don't - less gear, makes life easier.

Back to the electrics: AC voltage is steady, but the current in Amps (i.e. power in W) can vary depending on the received sunlight amount. Your solar panel should be the same - check the specs, if it's 12V, than it's 12V (give or take 1V may be). You can't destroy the GPS by 11-13V AC supplied to its 12V AC input socket, or am I missing something? The fact that it switches to the batteries while connected to solar panel, shows that it's not getting enough power - the circuit reacts to insufficient power same way as if there were no external power at all.


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 Post subject: Re: GPS and solar cells
PostPosted: Tue Jul 15, 2008 11:59 am 
Site Admin

Joined: Thu Apr 14, 2005 12:34 pm
Posts: 1718
Location: Southeast Michigan
That's DC voltage, not AC.

Most nominal 12volt solar arrays deliver about 18-20v "open circuit"- that is, with nothing attached to them. As the load- the demand for current- increases, the voltage drops. At rather current, they supply 12-14v. But if you exceed that, the voltage will drop.

A 6.5watt panel will deliver 6.5 watts under direct full sun, but that will drop as the panel ages. New, 6.5watts translates into 540ma at 12v. But that panel might be delivering sigificantly less power under normal operating conditions.

I couldn't find a spec on the Garmin site for current draw, but I suspect you intuition is correct- the new model draws more current, and the panel isn't sufficient to supply the needed power.

I sometimes use a 12watt solar panel for powering electronic devices in the wild, but I have a 7amp-hour gel cell wired in parallel with the panel. The penl continuously charges the gel cell at a rate low enough to prevent overcharging, and when extra current is needed, the gel cell supplies it. As you generally don't run your GPS or other electronics continuously, this allows you to bank power for when you do need it.

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Michael Edelman
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 Post subject: Re: GPS and solar cells
PostPosted: Tue Jul 15, 2008 1:50 pm 
Yes, sorry - it's DC ccurrent. It's a good idea, - to keep a reserve battery permanently connected to the solar panel. I'm surprised how people are able to have a reliable power supply with the solar panel alone, of the size that double kayak can handle. The boat turns, or sun moves, or sets lower, - and the power drops; cloudy skies - zero power at all. In a single kayak it's just not worth the trouble - unless in exceptionally long wilderness trip, 1 month or longer. Probably - even 6 weeks trip still doesn't warrant carrying a panel and reserve battery (over 2 lb for the whole kit, I guess), when you can carry 6 or 8 spare AA batteries.

Cost savings are negligible too. Once I pondered on small solar panel fountain for patio, but as it turned out, the cost of running a small pump from 110V socket, 12 hours a day, was about 30 cents a month - and solar fountain only works in direct sunlight.


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 Post subject: Re: GPS and solar cells
PostPosted: Wed Jul 16, 2008 4:05 pm 
Site Admin

Joined: Thu Apr 14, 2005 12:34 pm
Posts: 1718
Location: Southeast Michigan
True. It's usually easier to carry batteries. I bought the panel to run a 20 watt amateur radio, which would have otherwise required a lot of large batteries.

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Michael Edelman
FoldingKayaks.org Webmaster


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 Post subject: Re: GPS and solar cells
PostPosted: Sun Jul 20, 2008 11:25 pm 
knight of the folding kayak realm
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Joined: Sat Jul 14, 2007 12:53 am
Posts: 396
Location: Phoenix AZ
mje wrote:
True. It's usually easier to carry batteries. I bought the panel to run a 20 watt amateur radio, which would have otherwise required a lot of large batteries.


Ham?

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Gerry
PHX AZ

Long Haul Mark I
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 Post subject: Re: GPS and solar cells
PostPosted: Mon Jul 21, 2008 12:30 pm 
Site Admin

Joined: Thu Apr 14, 2005 12:34 pm
Posts: 1718
Location: Southeast Michigan
Yes, with mustard, please.

;-) w8mje

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Michael Edelman
FoldingKayaks.org Webmaster


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 Post subject: Re: GPS and solar cells
PostPosted: Tue Jul 22, 2008 11:39 am 
knight of the folding kayak realm
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Joined: Sat Jul 14, 2007 12:53 am
Posts: 396
Location: Phoenix AZ
mje wrote:
Yes, with mustard, please.

;-) w8mje


Smaaart guy 'eh?

k7lro here. I used to operate a fair amount of qrp - even built one of the early Elecraft radios - what a great radio. Haven't been active for a while - no time but I do plan to pick it up again later. I earned the first 1000-mile per watt award for psk31 years ago. Make a 5,000 mile contact into Salvador Brazil running a simple antenna and 5 watts.

dit dit

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Gerry
PHX AZ

Long Haul Mark I
Impex Assateague


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 Post subject: Re: GPS and solar cells
PostPosted: Tue Jul 22, 2008 10:29 pm 
Site Admin

Joined: Thu Apr 14, 2005 12:34 pm
Posts: 1718
Location: Southeast Michigan
Cool. I used top operate QRP with a 5 watt Ten-Tec. Worked Europe on SSB w/ 2watts... using a dipole.

Portable rig is SGC 2020. 20 watts.

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Michael Edelman
FoldingKayaks.org Webmaster


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