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Old 05-21-2020, 12:09 PM   #1
Travelling Three
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Solar Panels

We have a 2017 Montana 3661RL, 40', 5 slide outs with a large 2 french door-1 freezer door Samsung refrigerator. How many solar panels would I need to keep the battery charger charging and providing enough power to the AC inverter thereby keeping the batteries charged and the fridge working when I lose power? How much power does each solar panel provide and how physically large are they? Thanks!!
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Old 05-21-2020, 01:42 PM   #2
AZ Traveler
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If all you are looking for is the ability to keep your reefer going after power loss the answer is a bigger battery bank vice solar.

If instead, your desire is to camp for days without shore power solar should be part of the solution. To sort that out you need to build a power budget listing all you want to run (not just your reefer) and then size your solar based on needs.
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Old 05-21-2020, 11:35 PM   #3
gjennings
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I have 1200 watts installed on my roof and 400ah battery bank and I ran my trailer a couple weekends ago for 3 days without having to start my generator. Going out this weekend again for another test. That was with the heater running all night as well.
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Old 05-22-2020, 11:36 AM   #4
jcurtis934
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Solar panels come in various sizes, depending on their wattage rating. Solar panels charge battery bank directly, while the inverter would get its power from the batteries. The onboard battery charger built into the converter would not be running if you had no external source of 120vac power. So, as noted above, the fridge powered by the inverter could run for a certain time period based on the size of your battery bank. You never want to draw the batteries below 50% power as that shortens their life and a lot of batteries aren't that well designed and built to start with. Basically, the fridge will draw a max of 30 amps of 12vdc without the icemaker running. Minimum power draw depends on how it is loaded, temperature inside the trailer as influenced by the outside weather, and how much you are opening the fridge or freezer. IF you only had one crappy group 24 battery installed when you got the trailer, it would be somewhere about 65 amphr max and you can only draw out 32 amphrs before you shorten the life of the battery OR about an hour of fridge time IF it was drawing its max wattage draw of 360 watts. I run two group 31 agm batteries in my bank, so I have at least three hours if the fridge were drawing max current all that time...which it doesn't. If you want solar to not have to worry about how long your batteries can run the inverter and you will not be running anything else off the batteries, then a smaller solar farm would suffice...like one 1000 watt panel. But if you want to start adding in the requirement to run things like powered vents, lights, running awning in and out...then you need to figure out how much 12vdc wattage you are going to be using before you can size the solar panel requirement.
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Old 05-22-2020, 11:57 AM   #5
gjennings
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Quote:
Originally Posted by jcurtis934 View Post
Solar panels come in various sizes, depending on their wattage rating. Solar panels charge battery bank directly, while the inverter would get its power from the batteries. The onboard battery charger built into the converter would not be running if you had no external source of 120vac power. So, as noted above, the fridge powered by the inverter could run for a certain time period based on the size of your battery bank. You never want to draw the batteries below 50% power as that shortens their life and a lot of batteries aren't that well designed and built to start with. Basically, the fridge will draw a max of 30 amps of 12vdc without the icemaker running. Minimum power draw depends on how it is loaded, temperature inside the trailer as influenced by the outside weather, and how much you are opening the fridge or freezer. IF you only had one crappy group 24 battery installed when you got the trailer, it would be somewhere about 65 amphr max and you can only draw out 32 amphrs before you shorten the life of the battery OR about an hour of fridge time IF it was drawing its max wattage draw of 360 watts. I run two group 31 agm batteries in my bank, so I have at least three hours if the fridge were drawing max current all that time...which it doesn't. If you want solar to not have to worry about how long your batteries can run the inverter and you will not be running anything else off the batteries, then a smaller solar farm would suffice...like one 1000 watt panel. But if you want to start adding in the requirement to run things like powered vents, lights, running awning in and out...then you need to figure out how much 12vdc wattage you are going to be using before you can size the solar panel requirement.

Not sure they make a 1000 watt panel and if they do I would think it would be to big for a trailer.... lol
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Old 05-22-2020, 01:32 PM   #6
Rod Spohn
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Batteries

Batteries are a huge part of this equation. That and the amount of sunshine you will get. The more amp hours the more you can run and for longer periods of time, There are a lot of variables In determining What is needed in different conditions. So I feel there isnít one good answer to your question. Overkill would probably be a good thing in solar system. One cloudy day can throw a wrench in things.
Do a lot of research and ask a lot of questions
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Old 05-23-2020, 11:25 AM   #7
jcurtis934
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Yeah, the largest wattage panel was 415 watts released in 2019 and it was 78 x 52 inches. But there are all kinds of panels now in the 300-400 watt range if you wanted to limit the number of panels on the roof. And, if lithium iron phosphate batteries weren't so costly, that would be the ultimate battery since they have high current charge/discharge rates and you can draw them down without killing them like lead/acid designs. I just figured that if we lost power for too long, that I would just connect to the tow vehicle and let it help maintain my batteries.
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