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Old 03-06-2016, 08:25 PM   #1
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Solar panels for charging batteries.

I have a 2015 coachman 5th wheel with a residential refrigerator and a 1000 watt inverter. While boondocking last fall the batteries would go low enough to shut down the refrigerator in about 5 hours or less. I hate running the generators 24/7 just so I can run a refrigerator and a CPAP machine. Ive been considering a solar panel to keep the batteries charged during the day and run generator till lights out. Any suggestions on how big I need would be appreciated.
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Old 03-06-2016, 11:11 PM   #2
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I basically have the same question. I have a CPAP machine on a separate marine battery. When dry camping I have 2 nights before I need to recharge. I can run refrig, etc. on propane, but the CPAP is a problem.

I know nothing about solar panels. Where do I begin?

Sorry about piggy backing on your question

Karl in Washington
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Old 03-06-2016, 11:31 PM   #3
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Originally Posted by kwjamison View Post
I basically have the same question. I have a CPAP machine on a separate marine battery. When dry camping I have 2 nights before I need to recharge. I can run refrig, etc. on propane, but the CPAP is a problem.

I know nothing about solar panels. Where do I begin?

Sorry about piggy backing on your question

Karl in Washington
I've run a cpap (no humidifier) for 6 nights on a group 24 battery without recharging. If you use it with a heated humidifier try it without heat. If you run it using an inverter the inverter may not be efficient enough. Inverters waste energy just running themselves.
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Old 03-06-2016, 11:33 PM   #4
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I will have the same dilemma soon when I pick up my TT on 3/23 and start using it.

First, I would start by figuring out your power draw. Look at the data plates of any of the devices you want to run off the battery through the inverter. Amps= Watts/Volts. Add up all the Amps. Assume you come up with 8 Amps.

Second, figure out your battery capacity, Amp-Hours, Ah. I read in somewhere in this forum, you don't want to drain battery but to 50-70% of its capacity. So, of you have a 100 AH battery, you can use 50 Ah to 50%, or 30 Ah to 70%.

Divide 50 AH by 8 A, and you will get 6.25 hours or 30 AH by 8 and you will get 3.75 hours. So, that means you will have 3.75 to 6.25 hours to get to 70% and 50%, respectively.

Amp management is key.

Solar panel will work only in the day, and all else the same, should buy you more time, during the day. If you go to bed with a full battery, then solar won't help.

Anyway, a few things to think about to give you a better idea.
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Old 03-06-2016, 11:36 PM   #5
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At a 10 cm water pressure setting a CPAP which draws 2.5 amps would need 20 amp-hours in 8 hours.
At a 20 cm water pressure setting a CPAP which draws 4.5 amps would need 36 amp-hours in 8 hours.


Fridges do not use a lot of 12v power except some have a heat strip that is used to defrost the refrigerator and can kill a battery quick. Heat strips can be easily disconnected.

You should run a fridge on propane to reduce electricity load. It isn't practical to use solar to run a fridge on a/c power.

I personally feel if you are going to go solar you should go large. I would not go smaller than a 400 watt system and 400 amp-hours of battery capacity.

Four 6 volt golf cart batteries from Sams Club for 85/each will provide 400 amp hours of capacity for a reasonable price.

With 400 amp of battery you actually have about 200 amp-hours usable. You do not want to go below 50% battery capacity because it will shorten battery lifepsan cycles a lot if you do.

I recommend a Renogy system and amazon has good prices on them.

You'll want to install an auto transfer switch so that inverter power from batteries does not power the converter that recharges the batteries. You also want to isolate the ac fridge power line for the same reason so it is only hooked up to generator power to prevent accidental usage of inverter a/c power to run the fridge.

Running a fridge on propane for my fridge uses about 1.5 lbs of propane a day on high. I usually run the fridge on high cool when generator is running and then switch to a warmer setting overnight.
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Old 03-07-2016, 06:00 AM   #6
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As the others have said, boondocking requires power management. Unfortunately, there isn't a lot you can do about CPAPs and residential fridges. Putting in a Trimetric system or similar will do a lot to help you mange your power and know what the current draws are of various devices.

Get a CPAP designed to run on 12V to reduce losses through the inverter and CPAP. Turn off the heated humidification.

For the residential fridge, ensure the condensing coils (on the back of the fridge) have good air flow. If the air around the coils is warmer than the rest of the RV, the air flow is not good enough. Ideally, the condensing coil air space should be vented to the roof, with an intake vent in the floor or low in the outside wall. You want a natural chimney effect over the coils. Another trick to reduce power usage by your fridge are to keep it full of stuff - bottles filled with water take up air space and will help the fridge hold its temp. And of course minimize door openings.

Make sure the inverter does not power general AC. And set up an auto-start tied to the fridge that turns the inverter off when the fridge is not running. An idling inverter can be a power hog for no good reason.

Now some calcs to get you in the ball park. On a sunny day, without tracking the sun by adjusting the panels, most panels will average 60% of their rating over a 6 hour period. Which means a 100 watt panel will give you about 30AH into your batteries - on a good day.

A 160 watt fridge is drawing 15 amps out of your batteries when it is running (allowing for inverter and wiring losses). If your fridge is on a 33% duty cycle, it's using 120 AH per day. So you need 400 watts of solar panels just to keep up with the fridge. And it needs to be sunny every day.

Reality with a CPAP and residential fridge is that you need at least 600 watts of solar panels to keep things going without a generator. And you need a battery bank with at least 300AH usable (600AH total).

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Old 03-07-2016, 01:50 PM   #7
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I am looking at buying a 200 Renogy set up because we are going to be boondocking at Big Bend. I have a Resmed cpap and just looked at batteries for it. I saw costs from 300+ to 700+. I could can get the 200w to start our solar system than I can for the battery. I would still need some type of power to recharge the battery. Thanks for the heads up for turning off the humidifier. I will have to ask my DME if they have a loaner battery.
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Old 03-07-2016, 02:24 PM   #8
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Originally Posted by Harleyman 1955 View Post
I have a 2015 coachman 5th wheel with a residential refrigerator and a 1000 watt inverter. While boondocking last fall the batteries would go low enough to shut down the refrigerator in about 5 hours or less. I hate running the generators 24/7 just so I can run a refrigerator and a CPAP machine. Ive been considering a solar panel to keep the batteries charged during the day and run generator till lights out. Any suggestions on how big I need would be appreciated.
You have some very good advice here from the other members. We installed a a Solar Elite package with a 2000 watt inverter from GoPower and it is working fantastic. We have been boondocking for months on the Baja this winter. The only thing I will change is adding a second bank of batteries.

For you I think you should run the fridge on solar during the day and on propane at night, add a package like The Solar Extreme 480 watts and it comes with a 3000 watt inverter.

I'm sure you have changed all your lights to LED.

Good luck,
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Old 03-07-2016, 03:35 PM   #9
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My wife has a CPAP with the humidifier. If you look at the power converter it changes the 120 vac to 12 vdc. I found an old power cord from a computer that fit the CPAP and wired it directly to a 12 volt source in the TT, with an inline fuse and it has been working for two years with no problems. I have a Renogy 100 solar system and it keeps my batteries charged while boon-docking
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Old 03-07-2016, 03:39 PM   #10
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I have a 19 foot Rockwood Roo, we outfitted with two 6 V batteries and a 1500W inverter, and we utilize a 200 watt Zamp system we bought on sale from Solardealz. Absolutely love it, and we can use everything except the AC. No problem using the microwave, coffee maker, TV, stereo, etc. Keep in mind that Microwave usage is fairly brief, properly managed is no problem. Also, there are very efficient ways of heating, such as using "Little Buddy" heaters that can greatly increase comfort while saving your batteries.

We primarily dry camp, and the system keeps me fully loaded with very heavy usage. I highly recommend.
The techs at Solardealz are terrific to work with and will help you properly size your panel needs based on your projected usage. Give them a call, they were most Helpful.

Also, check out https://handybobsolar.wordpress.com/ and read everything he has to say. Very informative and entertaining. You will be well educated when finished.

Plus, remember that you get a federal tax credit for everything you spend on solar, 30% tax credit for everything involved, not just the solar panels.
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