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Old 06-13-2012, 03:50 PM   #21
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50 watt $95. shipped 2.89 amp
100 watt $179 shipped 5.75 amp
Might go with the 100 watt
Still need to know avg cable length everyone use and cable wire size for
50 watt
100 watt
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Old 06-13-2012, 04:25 PM   #22
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50 watt $95. shipped 2.89 amp
100 watt $179 shipped 5.75 amp
Might go with the 100 watt
Still need to know avg cable length everyone use and cable wire size for
50 watt
100 watt
Do you have a link for that 100 watt panel? That is better than the price I found on Amazon for an 80 watt.
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Old 06-13-2012, 04:29 PM   #23
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At full sun w/50 watt panel I assumed 3A. current.
Your voltage loss for 20 ft (double wire) of 18ga copper wire is 3/4v. For 16 ga the loss is 1/2 volt, and 14 ga is about 1/3 volt. Everything is linear so if you go to 100 watt you will double the current and double the resulting loss. If you halve the wire length you halve the loss. I would use 16 ga for the 50 watt and 14ga for the 100 watt. As long as you keep the polarities strait, hardware store lamp cord will work or even an old extension cord. Raz
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Old 06-13-2012, 05:13 PM   #24
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Link for 100 watt solar WSolar 100 Watt Solar Panel 12V UL | eBay
Link for Controller Amazon.com: HQRP Solar 10A Charge Power Controller / Regulator 12V / 24V 10 Amp with LED Indicator plus HQRP UV Chain / UV Radiation Health Tester: Patio, Lawn & Garden
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Old 06-13-2012, 05:13 PM   #25
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I looked at it a little differently than Raz, looking at wattage wasted as heat.

For the 50 watt with 50' wires you waste about 2 watts in heat with 14 gauge, 1.3 watts for 12 gauge and 0.84 watts for 10 gauge.

This assumes I calculated it right. I used the formula that Power = Amps (squared) times resistance. I looked up the resistance of copper wire on line.

As Raz noted, it is all linear so a 100 watt panel doubles this, a shorter wire set halves it, etc.
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Old 06-13-2012, 06:44 PM   #26
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I have the controller at the panel and 10 ft of cable that connects to the battery. I calculated with 20 ft of cable to be conservative. Fifty feet seems a tad distant but maybe I am missing something.
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Old 06-13-2012, 07:24 PM   #27
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I don't mean to highjack this thread, but does anyone know how large a panel etc. I would need to run something like this ? Whynter 45 Quart Portable Fridge / Freezer - Sierra Expeditions
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Old 06-13-2012, 08:24 PM   #28
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power

This may give you a feel for the requirements and it depends on how much sun you get and the amp draw on the cooler. But I Just got back from the outer Banks of NC. Stayed for 6 nights at Ocracoke NPS campground (no electricity)and ran my ARB 50 Qt (which is supposed to be a little more efficient) as a freezer as an experiment on 150 watts of solar. Never got below 60% on my battery monitor which was checking on 2 T605 210 Amp hr Trojans in series. one day was cloudy all day, two were full sun and the rest were Partly Cloudy . Had Movie night 2 evenings when I was pulling about 6 Amp Hr for 2 hours. I suspect running as a fridge will use less and Movie night is a drag on the batteries with the inverter and all running.
Michael J
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Old 06-13-2012, 11:21 PM   #29
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Thanks for those links, both are pretty good prices. I'm going to do a little measuring of both the camper roof and my TV roof rack (never use it for anything else) I like the 100 watt and it's a good price but... moving anything 4 ft long in and out of a 13ft camper is a chore. It's a pretty big item to store when not in use.


I checked out some of the other items that seller had and I figure a pair of 40 wattt panels would be $154 @ $77 each. Those are 26" x 21" and I'm thinking I could use one for weekend rustic camping, it might not keep battery at 100% but would be a 14 ah a day supplement. If I was going to be out for a week take both panels.... and don't count on wife coming with.


My furnace does not use electric so I'm really only running at most two lights when getting ready for bed and recharging camera & laptop batteries, maybe the Kindle e-reader. Grandsons game thingies if they are along.
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Old 06-13-2012, 11:51 PM   #30
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Don't skimp on wire size especially if you are thinking about longer runs to escape the shade. I would not use less than a 12 guage extension cord. Wire is one of the most critical parts of your system. Voltage drops of less than 1/2 a volt can result in less amp hours stored in your battery and ultimately sulfation and shorter battery life. Jumper cables, welding cables and surplus scrap wire from metal yards could also be used.
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Old 06-14-2012, 03:03 AM   #31
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Let's see. There is the internal resistance of the battery. The internal resistance of the panel. The contact resistance of the clamps. Most wire resistance tables assume 20*c. Being in the sun the temperature is higher so the resistance values and thus the losses will be higher. Then there is the increased minority carrier concentrations in the silicon, lowering the panel output.......
With a fifty watt panel producing about 3 amps max, we might want to use something even thicker to make up for all those losses, or just use some 16 ga. zip cord that's light and flexible and expect to take an extra 1/2 hr. or so to charge the battery.
Now if the government is paying for it........ Take care, Raz


p.s. again, make sure the polarity is correct.
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Old 06-14-2012, 05:10 AM   #32
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This may give you a feel for the requirements and it depends on how much sun you get and the amp draw on the cooler. But I Just got back from the outer Banks of NC. Stayed for 6 nights at Ocracoke NPS campground (no electricity)and ran my ARB 50 Qt (which is supposed to be a little more efficient) as a freezer as an experiment on 150 watts of solar. Never got below 60% on my battery monitor which was checking on 2 T605 210 Amp hr Trojans in series. one day was cloudy all day, two were full sun and the rest were Partly Cloudy . Had Movie night 2 evenings when I was pulling about 6 Amp Hr for 2 hours. I suspect running as a fridge will use less and Movie night is a drag on the batteries with the inverter and all running.
Michael J
Thanks Michael, I appreciate the info.
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Old 06-14-2012, 06:01 AM   #33
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I have the controller at the panel and 10 ft of cable that connects to the battery. I calculated with 20 ft of cable to be conservative. Fifty feet seems a tad distant but maybe I am missing something.
As the controller is temperature compensating for the battery and its output voltage can't compensate for wire resistance losses downstream, wouldn't it make more sense to mount the controller right next to the battery? Also, voltages downstream from the controller are lower, thus wire resistance losses are higher, reinforcing the case for installing the controller right at the battery.

I didn't mean to suggest that 50 feet was a recommendation, but rather was trying to quantify losses within a range. Again, since it is all linear, if the OP uses a 10 foot cord, all he has to do is divide the losses by 5, etc.
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Old 06-14-2012, 06:34 AM   #34
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I was thinking the same thing about size of 100 watt panel and where to store it. The 50 watt panel is a better size to store but half the the power.
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Old 06-14-2012, 02:15 PM   #35
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RogerDat
I was thinking the same thing about size of 100 watt panel and where to store it. The 50 watt panel is a better size to store but half the the power.
Yep there is the rub. I'm pretty sure I have seen two into one MC4 connectors on Amazon. My thought was use a connector like that close to the controller. I would only pack a second panel to plug into the "extra" MC4 connection if I thought it would be needed. Or it turned out a single 40 or 50 watt panel just did not do the job.

I don't have enough real data on my energy consumption in the scamp to know if I need 100 watts or if half as much will do just fine for long week ends and such that will be our typical usage.

Since I can't "make it right" I was thinking I would aim for making it adjustable using a second panel.
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Old 06-14-2012, 03:27 PM   #36
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I think before purchasing more than one panel you determine your needs per day and start there in making decisions. I recently ordered a solar panel and did several calculations in making my choice. First and utmost is what are my daily 12v needs and just as important, what is my daily capacity. These 2 numbers are important for several reasons. If my needs can be such that my capacity can meet them, then my solar should be sized to replenish my needs. If my solar is beyond my storage capacity, then it is wasted.

For example, if I need 30 ah per 24 hour period and I have 50 ah storage in my battery
( group 27 battery with 120 ah @ 40%) then my solar size needs to meet my daily use. A 50 watt panel should give you 4 amps per hour for approximately 6 hours or a 24 ah replenishment. So my net loss is 6 ah per day from my storage which means I can go about 8 days before having to plug in. Your water use will make you move before then!!
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Old 06-14-2012, 05:25 PM   #37
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I checked out some of the other items that seller had and I figure a pair of 40 wattt panels would be $154 @ $77 each. Those are 26" x 21" and I'm thinking I could use one for weekend rustic camping, it might not keep battery at 100% but would be a 14 ah a day supplement. If I was going to be out for a week take both panels.... and don't count on wife coming with.


My furnace does not use electric so I'm really only running at most two lights when getting ready for bed and recharging camera & laptop batteries, maybe the Kindle e-reader. Grandsons game thingies if they are along.
If thats all you are using and if the lights are LED you will not need more than one 40 watt panel to keep the battery fully charged no matter how long you are out for
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Old 06-14-2012, 05:39 PM   #38
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I think before purchasing more than one panel you determine your needs per day and start there in making decisions.....

....So my net loss is 6 ah per day from my storage which means I can go about 8 days before having to plug in. Your water use will make you move before then!!
Since I don't yet know my 12 volt usage (only camped with AC available so far) I do think I will purchase one modest sized panel but wire to make a second panel an easy option. The 10 amp controller does provide room to expand.

I agree beyond 4 or 5 days of 12 volt is a capacity I probably don't need. That capacity might depend on how often wife plugs blow dryer into inverter eh? Or if I add a fan powered roof vent and doze off with it running.

As you pointed out I could add battery capacity or solar capacity to meet my requirements as they are discovered.

On the wire I'm a fan of doing just what others have suggested, bigger is better. If nothing else it's a pretty inexpensive insurance that the problem is not the wire if you do find yourself coming up short of expected results.

My thinking is about 20 - 25 ft of 10 ga would work well.
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Old 06-14-2012, 05:50 PM   #39
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[QUOTE=RogerDat;314883
I agree beyond 4 or 5 days of 12 volt is a capacity I probably don't need. That capacity might depend on how often wife plugs blow dryer into inverter eh? Or if I add a fan powered roof vent and doze off with it running.
[/QUOTE]

If you add a fantastic fan it uses very little and falling a sleep with it on isnt going to kill the battery. The other items in your Scamp that will use power are the water pump & the shower pump if you have one - in my case the furnace in my Scamp does eat power for its fan - actually eats a lot of power so I use it sparingly when dry camping - otherwise I get by with plugging in a much smaller than 40W panel ever couple of days - that includes using a lap top, charging phones and camera etc.
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Old 06-14-2012, 05:57 PM   #40
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If you add a fantastic fan it uses very little and falling a sleep with it on isnt going to kill the battery. The other items in your Scamp that will use power are the water pump & the shower pump if you have one - in my case the furnace in my Scamp does eat power for its fan - actually eats a lot of power so I use it sparingly when dry camping - otherwise I get by with plugging in a much smaller than 40W panel ever couple of days - that includes using a lap top, charging phones and camera etc.
Well that gives me a good reason to go modest for a start. Don't have water pump.

I was just here to pass on a link to the storage idea thread. I really like you wall bungee set up for storing your solar panel and thought the others here might find it of use to consider as a storage option.

About half way down first page Carol posted a picture of a her way to store a solar panel. Going to measure trailer wall now.

http://www.fiberglassrv.com/forums/f...ler-52496.html
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