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Old 07-08-2019, 06:35 AM   #1
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Location: Florida
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Solar thinking

I have a residential refrigerator draws 10 or 12 amps plus all the usual draw.
I also have 480 watts or 40 amps of solar on the roof and 450 ah battery bank. All hooked up to a victron 100/50 mppt controller. I plan going out west from Fl. In a couple of weeks and doing a lot of boondocking . Here’s my question? Is it worth the expense for a portable 100 watt or 8 amps solar panel also the effort of hooking and putting it out all the time. Thanks
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Old 07-08-2019, 09:41 AM   #2
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Depending on the weather on your trip you should be good with only limited generator usage. Probably an hour or two mornings and nights.

More solar is always better. But I doubt the portable will change that scenario all that much.

We found in cool temps that we could turn our inverter off at bedtime and wake in the morning with nearly 90% SOC and the fridge would still be good and cold.
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Old 07-08-2019, 09:55 AM   #3
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If your 450 ah battery bank is lithium, I'd think it would be plenty without the extra portable panel. Even on cloudy days, your current solar setup should be able to replenish them.

Even if your batteries are FLA or AGM, I wouldn't bother adding anything. Sounds like a decent off grid system as is.
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Old 07-08-2019, 10:55 AM   #4
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And, be sure to report back on your experience. A lot of folks are asking about this issue. Have a good trip.
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Old 07-14-2019, 06:14 PM   #5
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Is that a 10A draw at 110VAC for what I consider a normal residential refridge? This could be the draw of a residential refrigerator. If this is the case you 12VDC could be as high as 100A±. Considering a 50% run cycle in desert conditions you do not have sufficient battery capacity. so please define 10 or 12 Amps!
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Old 07-14-2019, 09:25 PM   #6
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Charles is about right I think. A good guess is just over 120AH per 12 hour night time run for only the fridge and then add the inverter idle and loss.

The only way to know for certain is a battery monitor system, Victron etc. or put the Fluke or other clamp meter to use. It's easier to use a battery monitor for most and necessary to monitor boondocking.

My GUESS is probably around 650AH of battery and about that much or more of solar. The answer will come from the battery monitor or testing. Anything else is just like my guess. The reason for the high guess is folks are living in the rig 24x7 as well, not just the fridge.

Residential fridge draw depends on size etc. but you could use a kill-a-watt to prove it or read the sticker on the fridge and convert that to dc amps. 10 amps is probably close but what is the duty cycle? My little 12VDC compressor fridge draws far less amps - still a battery hog but far less hungry.

The battery monitor will tell you how many amp hours total you are taking from the batteries, SOC. 450 sure sounds like enough but you have that nagging thought until you know.

I wouldn't bother with the portable.
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Old 07-14-2019, 09:47 PM   #7
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12 Amps?

12 Amps on 120volts is 1440 watts! That must be a big refrigerator. One of our motorhome AC units only draw 14 Amps and that includes the blower fan.
I definitely would check it with a Kill a Watt unit. Amazon $25
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Old 07-15-2019, 09:14 AM   #8
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Your question has multiple parts to an answer. As a residential fridge owner and solar user, my experience breaks this problem into parts. 1) how much power you use, including parasite and daily usage inanition to the fridge. 2) what type of batteries you use 3) how much solar you will need.

First, your power consumption needs to include the fridge and the other items you use. Must of us are at the 20 amps. That is without considering things like the microwave or TVs. Now think about how many hours you will be using that. You need these numbers to start.

Second. Are you using AGM or Lithium batteries. AGM can only be drawn down to 50%. Lithium down to 10%. So you need almost twice as many amp hours of AGM as you do Lithium. Also, the Lithium charges faster, which talks to how long you will need active sunlight to charge

Third, the usual response is 600-800 watts of solar at a minimum, and with AGM even that may not be enough depending on the amount of sun you get.

My advice, go to a professional like am solar or precision solar had have them help you map out a system
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Old 07-15-2019, 09:48 AM   #9
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Lots of small points that will also change the answers, even though we don't think of them. Constant drag on the batteries is something we don't look at sometimes. What type of lighting and how you are trained is another. LED lighting and turned off unless absolutely needed will get you a lot longer than older lighting with sloppy usage. Do you leave a stereo, radio, or TV on much of the time? How about the computer? Any of those can change the answer a bunch. Just simple things like how many times and how long the frig door stays open will add to the question.
For my purposes, I would not try to add enough to make it a totally dry-camp trip as it takes longer term use to really get the figures. I would go with the plan of doing the dry camp but with experience on how each of us actually operate, planning in advance is pretty iffy due to how we each do use the power.
I would go and try it but with the backup plan in mind to maybe have to sweat out a few hours without power or go to a campground for power as certainly a better option that buying lots more than needed due to having poor estimates.
Campgrounds are not cheap but will not run into the thousands of dollars that a poorly thought out retrofit may cost.
Get some better info before investing? If it's only a one time trip, forget the retrofit.
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