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Old 07-17-2013, 04:38 PM   #1
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Cheap solar worth it?

First off, yes, I know there's tons of threads already on Solar. Most of them have very good information on what I would need if I ever decided to boondock, but as the Wife insists on A/C, that's not likely to happen.

All I'm looking for, is to keep my battery from draining when I have the TT parked in storage and I leave the battery connected in order to keep the fridge running due to back to back trips over adjacent weekends.

The several hundred dollar options aren't worth it just to be lazy and not unload a fridge. However this $85.49 deal at Amazon might be:

Sunforce 50033 15-Watt Solar Charging Kit : Amazon.com : Automotive

I know it's probably not enough to maintain a battery over long periods, and it's definitely not enough to maintain while boondocking, but I think it might be just enough to keep the parasitic loads from draining me dry if I'm in storage for 1-2 weeks. Any longer then that and I'll probably just hit the disconnect and empty the fridge anyways so the food gets used before it expires.

For those of you with experience, what do you think?

Thanks,

Mike
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Old 07-17-2013, 04:45 PM   #2
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"Keep the fridge running" - I assume this means you have a 3-way fridge with a DC only option. What is the wattage when running on DC only?

I will try to find out for you but a make and model would help. Remember that you only get a fraction of the wattage possible and you have to replace ALL of what has been used all day in a 5-6 hour charging window.
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Old 07-17-2013, 04:56 PM   #3
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For example if you have an RF60 TRi-Mode fridge https://docs.google.com/viewer?url=h...%2FRF60_EN.pdf The unit draws 110 watts (9 amps at 12 volts) when running on battery (only - no gas).

Even if the unit sits in full sun for 6 hours a day an 85 watt panel will not replace 100% or even 75% of the amps used per day. While it will certainly make your battery last longer, without a good battery monitor system (capable of monitoring capacity remaining) installed you might just show up to go camping and find a mess and a dead battery.
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Old 07-17-2013, 04:57 PM   #4
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Nope, just the regular 2 way fridge. I found out the hard way between the first and second camping trip that the fridge won't run on Propane if the Battery Disconnect is pushed in. So the fridge will be running on propane, and the only parasitic loads should be the CO-detector, the fridge (running on propane) and any others I don't know about.

I don't have specific model numbers for the appliances yet. All that information is stored in the TT. (I know, I should make a copy for home.) It's a Dometic fridge and it's the CO/LP detector with the built in battery disconnect. Most likely whatever was standard in 2012.
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Old 07-17-2013, 05:01 PM   #5
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I would not trust my beer to just running on battery and propane.
If the propane runs out; the beer gets skunky...

Seriously, with propane as expensive as it is I would be emptying the fridge.
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Old 07-18-2013, 09:49 AM   #6
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it won't be nearly enough. that 15 watt rating is based on perfect conditions...perfectly clear sky, Sun at 90 degrees to the panel & at optimum temperature, like 70 degrees or something like that. That's a rare day...especially here in central PA.

Basically, a 15 watt panels will keep a battery from self discharging, but only if a battery disconnect is used.
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Old 07-18-2013, 10:26 AM   #7
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Thanks for the help. Looks like I won't wont' probably bother then until:

a) Solar comes down more in price and
b) I change the fridge to a Tri-mode with DC.

For reference though, after a run out to the trailer this morning, the model numbers for anything with a parasitic load should be:

Fridge: Dometic Dm-2652-LBX
CO2/LP: Safe-T-Alert 35-742
Radio: Genesis GT-2.0

Though with the radio I had assumed I can pull a fuse and cut that load.

Thanks again,

Mike
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Old 07-18-2013, 03:56 PM   #8
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OK, so after much, much, much more research. I've learned a few things:

1) Nobody has an exact value for the load on the fridge. It varies often enough that I'll only find mine by measuring. Quoted values are anywhere from 0.21A to 4A.
2) The fridge's 'climate control' is supposed to be a power hog. If I don't open the unit (and void the warranty in the process) to remove this feature then I'm going to be at the higher end of that scale. (Aside: I have to wonder who's idea it was to make a device less efficient by putting a heater in an appliance meant to cool things?)
3) Assuming a 30% efficiency with the Solar panels (as per another thread on here) and a few other assumptions regarding 24 hour use, 12V panels, etc... I've solved the various calculations i was using to determine solar needs down to:

Solar Panel Size in Watts = 40 x Average Load in Amps

So, if I have say, 2A parasitic load total, I'll need 80W of panels total to cover, give or take depending on conditions. The 15W panel I first referred to would only cover about 0.375A.

Thanks for all the help,

Mike
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Old 07-18-2013, 04:47 PM   #9
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You've discovered why solar isn't for everyone. It's just not cost effective. I have it, I love it. My family and I made changes to the way we camp in order to adapt to solar limitations. Even with 360w of solar and 245AHr of battery, we still need to be mindful of usage and the weather. ----too much usage and cloudy forecast means trouble in the future. We can camp places that many can't or won't because we have solar.
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