Solar & Battery performance ?

ky-newbie

Member
Hi all,
I've got a few questions about Solar performance and capacity. I don't see these specifically addressed on the forum already. I have seen the posts pointing to calculators for designing a system. I'm just trying to get a feel for battery performance.

Let's say I have two 6 volt golf cart batteries and one 100 watt solar panel.

1) I have a nice sunny day and a "full charge" in the batteries. I disconnect the solar panel. Could I expect my refrigerator to stay up (just on electric) for 24 hours? Longer? How long? Assume there is no other load on the batteries at all (for discussion purposes).

2) If it turns cloudy for a day or two, could I recharge the batteries via a generator or my vehicle wiring somehow? If so, would it be an easy connection, or would it have to be a "professional modification", wired up beforehand?

3) What is typical battery life - how often do you have to replace them?

4) Are two or four 6 volt batteries the preferred setup? Is there a better combination for everyday use?

As always, thanks for the valuable feedback!

Lannie
Soon-to-be Full-timer (hopefully!)
 

boatdoc

Well-known member
The fridge works on either 110VAC or propane. It does need a 12VDC source also. It will only work without shorepower on propane. So the answer to your 1st question is a long time as you will be using propane without being on shore power. 2nd is just plug the trailer cord into the genny and let the onboard battery charger fill the battery/batterys back up. 3rd is 6VDC batterys last a good long time if taken care of. I've had them go 7 years and others have gone longer. 12VDC not nearly as long of lifespan. As far as 6VDC pairs, this is up to you how you use your rig. If you do lots of boondocking and don't want to run a genny that much 2 sets of 6VDC would be best but can get spendy and the weight gets up there also. On our 3670 I run 2 sets of 6VDC and the one OEM 12VDC battery.
To use 110VAC without being connected to shore power you will need an inverter and this is where 2 sets of 6VDC batterys is nice. I still wouldn't run the fridge on 110VAC from the inverter as the fridge eats up 110VAC power fast. I tried it, didn't work very long.
Good luck
 

ky-newbie

Member
Thanks, but one clarification...

Thanks, boatdoc, for the info. Now, just clarify one thing for me - you say "the fridge eats up 110VAC power fast". That's what I'm looking for. Are we talking 5 minutes, four hours, or overnight? Just a general number, for my thought process.

Where I'm going with this is, "OK, the refrigerator will last one hour on batteries only. That means I would have to be prepared with propane, and also to run the generator if I'm boondocking, etc."

I'm being laid off in a couple of months. I'm considering doing some mission work in the Appalachian area after the layoff for several months. There aren't a lot of RV hookups in these areas, so I plan on a solar setup, and generator if necessary.

Thanks again.
 

wdk450

Well-known member
Running refrig. on 110VAC from 12 V. via inverter

I looked at a refrig manual on the "tools" tab trying to get a current draw rating. All I could find is that it has a 5 amp fuse for 110 VAC. Lets work with that.
5 amps at 110 VAC roughly equals 50 amps at 12 VDC. 50 amps draw for an hour equals 50 amp/hours. The group 24 deep cycle has about 200 amp hours capacity. I don't know what the capacity of your golf cart batteries is, but you can do the math.
 

rick_debbie_gallant

Well-known member
just a thought: Have you given any thought to super insulating your ice box with a layer of bubble wrap insulation on the inside or somethint more on the outside of the box? also the more you are able to shade the box side of the rig from the sun may help? May even try a combo of wind power and solar power. or you could even build human powered generator with a bike and a generator or alternator. again just some more thoughts.
 

boatdoc

Well-known member
Thanks, boatdoc, for the info. Now, just clarify one thing for me - you say "the fridge eats up 110VAC power fast". That's what I'm looking for. Are we talking 5 minutes, four hours, or overnight? Just a general number, for my thought process.

Where I'm going with this is, "OK, the refrigerator will last one hour on batteries only. That means I would have to be prepared with propane, and also to run the generator if I'm boondocking, etc."

I'm being laid off in a couple of months. I'm considering doing some mission work in the Appalachian area after the layoff for several months. There aren't a lot of RV hookups in these areas, so I plan on a solar setup, and generator if necessary.

Thanks again.

The fridge will NOT run on batterys alone, UNLESS you have an INverter to supply 110VAC and this would kill batterys fast. My time frame when first tried on the INverter was maybe a couple of hours and the batterys were down to a point I didn't like. We now NEVER run the fridge on the INverter power, propane only or shorepower, be it from the power company or genny. I guess one could run the fridge off an INverter if and only if you were charging the batterys going down the road or had enough solar feed to keep up with the draw.

Hope this helps. I'm not the greatest at explaining things, so I've been told, but I do know how this stuff works.
 

jbeletti

Well-known member
I've been told by friends who have done it and who know class A owners who have a standard house refer (110 VAC only) and they say they can go 3 to 4 days on an inverter fed by 2 batteries.

Only what I've been told - no personal experience here.

Jim
 

2010augusta

Well-known member
That might be the case for a "standard household type" fridge, but they work on a completely different thermodynamic principle than the absorption type units we have in the fifth wheels and trailer. The standard fridges are running a small compressor motor, the RV unit are powering a good size heater.
 

boatdoc

Well-known member
That might be the case for a "standard household type" fridge, but they work on a completely different thermodynamic principle than the absorption type units we have in the fifth wheels and trailer. The standard fridges are running a small compressor motor, the RV unit are powering a good size heater.

Yup, thustly eating up 12VDC batterys changed into 110VAC by an INverter. :eek:
 

branson4020

Icantre Member
Lannie,

Is there some particular reason you would NOT want to run your refer on the built-in propane system when boondocking? That is, after all, the normal method of operation for which your system is designed.
 

ky-newbie

Member
Let me clarify

All,

I apologize - I obviously wasn't clear in my original post. The question was only theoretical - it has nothing to do with any existing setup. (I don't even own an RV yet!) I was just trying to get someone to say "You can run an RV refrigerator for about four hours on batteries". That's the info I needed. Now I know the rough capacity of a couple of 6 volt batteries with a 100 volt panel. (I understand there are dozens of other variables that come into play in the real world - light use, LCD television vs. tube, cloudy days, etc., etc. That all would have to be factored in.)

The point is, if I were to get stuck in a boondocking situation, and run out of propane, I could shut everything down, and the popsicles would still be frozen for a couple of hours. :D

Thanks, and sorry for any confusion! :eek:
 

boatdoc

Well-known member
I guess what I have been trying to state is You can't run the fridge WITHOUT 110VAC in some form or another if you choose to NOT to use propane. If you are OUT of propane and you have NO source of 110VAC you will NOT be able to keep the icecream frozen for very long.
 

62cwil

Active Member
Is their any amp hours used by refrigerator if you are using propane. I am trying to figure out smallest solar panel I can get by with
 

evolvingpowercat

Well-known member
Re: Running refrig. on 110VAC from 12 V. via inverter

Corrected post: The AC heating element in the smaller Dometic 3 way refrigerators is 175 watts and in the large ones 325 watts. However, the DC heating element is smaller the Dometic Service Manual says the DC is only capable of holding temperature of an already chilled unit not cooling it down. The DC heating element ranges from 150 watts to 215 Watts (12.5 to 18 Amps) depending on refrigerator size.

I feed enough current from the tow vehicle to my Edge M21 thru the 12V pin on the 7 way connector to shut off the LP valves and let the fridge heaters switch to 12 Volt. When fridge is on and is cooling on LP gas, it will draw less than 0.5 Amps.
 
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evolvingpowercat

Well-known member
Note that when sizing solar panels, their watts output are full sun, for example I have a 80 watt panel that will push 4.3 amps into the charge controller in full sun. But the real amount will be less due to sun angle not being optimal the whole day, clouds, etc. Good rule of thumb would be to design at 50% of panel output x 10 hours for example my 80 watt solar panel setup can be expected to replace an average of 20 Amp Hours of battery use a day. The fridge in LP mode will use about 10 Amp Hours of that amount per day.
 

jlb27537

Member
Is their any amp hours used by refrigerator if you are using propane. I am trying to figure out smallest solar panel I can get by with[/QUOT

The answer is YES. The RV refrigerator has a control board that is powered by the house battery and will draw about 1/2 amp. To make the frig actually get cold you need a heat source. Either 120vac or as you mention LP. In the LP mode, the control board has to provide voltage to the solenoid in the LP line and also provides the spark to ignite the flame. It has to monitor the flame and should the flame go out, it has to shut the LP flow off. Once the frig gets cold and and requires no further cooling, the flame is turned off by the control board. Then when cooling is needed again, the cycle is repeated, open LP valve, spark, monitor flame, etc.

Jim
 

jlb27537

Member
The fridge works on either 110VAC or propane. It does need a 12VDC source also. It will only work without shorepower on propane. So the answer to your 1st question is a long time as you will be using propane without being on shore power. 2nd is just plug the trailer cord into the genny and let the onboard battery charger fill the battery/batterys back up. 3rd is 6VDC batterys last a good long time if taken care of. I've had them go 7 years and others have gone longer. 12VDC not nearly as long of lifespan. As far as 6VDC pairs, this is up to you how you use your rig. If you do lots of boondocking and don't want to run a genny that much 2 sets of 6VDC would be best but can get spendy and the weight gets up there also. On our 3670 I run 2 sets of 6VDC and the one OEM 12VDC battery.
To use 110VAC without being connected to shore power you will need an inverter and this is where 2 sets of 6VDC batterys is nice. I still wouldn't run the fridge on 110VAC from the inverter as the fridge eats up 110VAC power fast. I tried it, didn't work very long.
Good luck

Possibly some bad advise here??? 2 sets of 6vdc and 1-12vdc. IF all 5 batteries are connected to create one battery bank? you never want to mix battery types, capacities or age. 2 sets of 6vdc (golf cart) would be 4 batteries of the same type and would be fine. Add in a 12vdc is just not good practice. All batteries in a "bank" also need to be the same age.

As for solar capacity, rule of thumb is for each amp hour of battery you need 1 watt of solar. Most GC2 batteries (golf cart) are 220 amps. So when you connect 2 in series you get a battery bank of 12vdc @ 220 amp hour. Thus you should have a couple of 100 watt panels.

The following is not accurate, but the general idea is there. I am not figuring in the fact that most inverters are 90-95% efficient. You need 325 watts of 120vac to run the frig heater. 325W/120vac =2.7amps@120vac. Now for simplicity sake, you can add a "0" and move the decimal to the right. So now we need 27amps @ 12vdc. Figure a 50% duty cycle so 12 hours @ 27amps=324 amp hours+ the 12 amps the control board uses for a total of 336amp hours @ 12vdc.

Your battery bank of 2x6vdc batteries have a total of 220amp hours in them. You never want to draw down you house batteries past 50% so you have effectively 110amp hours to use. 336amp hours/24hours in a day=28amp hours per hour to run your frig on battery power.

Now since you have 110 amp hours available, 110amphours/28amphours=3.92 hours you can run your RV frig off a couple of GC2 batteries.

But if you were to run your frig off LP, the control board using .5a would be 12 amps per day. 110amp hours/12amp per day=9.1 days you could run the frig off just 2 GC2 batteries.

A side note, If you are looking at a battery for a house battery and it has cranking amps listed on it, as a lot of marine/rv batteries do, it is a compromise battery designed for 2 different uses in one box. You would be better off with 2xGC2 batteries. (Sam's Club about $81 each) and will last about 5-7 years if maintained.

Jim
'96 Safari, 300 CAT, 520W Solar
 

DuaneG

Well-known member
Lots of good info. Thanks for taking the time to document all this. Not ready for solar,.but will go that route in the future so it is nice to learn about it and what others are doing or considering.

Sent from my cell phone. Please forgive typos and spelling errors.
 
Well I am trying to gain as much stuff as possible for solar energy. and this discussion would be another great source for that.
 

danemayer

Well-known member
Well I am trying to gain as much stuff as possible for solar energy. and this discussion would be another great source for that.

Hi JordenLouis,

Welcome to the Heartland Owners Forum. There's lots of useful information here along with a great bunch of friendly and helpful people. Feel free to ask questions.
 
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