Propane fridge -- how many watts per day on propane?

We just did a 4 night boondock, with 2 or 3 hours of driving around while there which helped with charging. Started with 2 full batteries and never went below 75% charge, 100 watt solar panel providing about two amps of charging most of the days (never saw more than 3.5 A). We used the furnace a little on two rainy mornings. The Fantastic fan ran on low while cooking. Our fridge is not particularly large and has no fan or defrost feature.

On trips like this last summer, with no solar panel, we hit the dreaded 50% charge level about the fourth day.

That looks like a snazzy controller.

Sadly I had to cancel the trip. Funeral. Will try again later.

At 250 watts of solar I would consider a Bogart sc2030 pwm and their trimetric. You will be able to see power out and power in. You can expand later if needed. I think you will do fine at 250.
I agree with Handybob, add the trimetric monitor and always know what is going out and into your batteries. Later the sc2030 solar controller can be mated via a rj14 phone cable and they interact forming a very good system. IMO.

Read Handybob as he has full timed on 345 watts.

Found a good thread on this subject. They echo the problem with the parasitic draw from the solenoid valve, and it's in the neighborhood of 1A. Some fridges are 100% LP-only and have an advantage if you do a lot of boondocking. I'm not serious enough about it yet to swap a fridge, so I'll make do for now.
http://www.hybridexplorer.com/forum/index.php?topic=88010.0

They also mention that DSI water heaters use a similar solenoid. It's a normally-closed solenoid, which is great for safety concerns, but tough on the battery. I think I'll be keeping the water heater off most of the day.

Given everything I've learned, looks like a 2nd battery and 250W of panels are the minimum I'd need. If I can do 2x6V golf cart batts as 2oldman mentioned that'd be great; just not sure if there will be an imbalance between the first group 27 batt and the array of 6V batts? One might drain to the other, etc.? Likely I will just grab a second group 27, stash it under the rear seat, and call it good.

SunElec.com has 125W panels for around $100 delivered. They've always had good prices on panels and have built a good reputation. Add a cheapie PWM controller and I'm set. (Maybe MPPT some day?) For around $400 I'm good to go. That price difference pays for around 30 nights at a popular full hookup campground nearby, so I have to balance that out. I've been wanting an off-the-grid "cabin" for emergencies, so maybe it'll be a good investment? And if I go boondocking three more weeks over the next few years it'd pay for itself :)

Thanks all!

2oldman wrote:
You'll be living like a hermit.

Used to it.

2oldman wrote:
I figured 12ah.

I saw, but did you account for the gas valve solenoid? 12thgenusa claims that's 1A.

On the positive side, if you're right about 12AH, since you accounted for a 100% duty cycle it'll be much less in practice.

You'll be living like a hermit.

FYI I am OK with skipping the fridge and going with ice or backpacker food.

cdevidal wrote:
If the fridge uses 35AH/day that's almost an entire battery per day just on the fridge alone, which absolutely demands I get a 2nd battery.

I figured 12ah. Ambient temperature and being parked facing the sun will be factors.

You have to be very judicious using one battery, and nobody I know dry camps with one. 2- 6v will get you 220ah.

pianotuna wrote:
Hi,

Duty cycle is about 2:3 therefore about 1 amp per hour X 24 hours = 24 amp-hours X 12 volts = 288 watt-hours.

There are other parasitic loads, so the 'rule of thumb' is about 35 amp-hours per day.

I've got a single group 27 battery with I-forget-how-many-AH but let's say it's the average of 100. I shouldn't let the charge drop below 50%, so I've got 50AH to play with. If the fridge uses 35AH/day that's almost an entire battery per day just on the fridge alone, which absolutely demands I get a 2nd battery.

Does that sound right to everyone? Seems a bit much. I was thinking it'd be closer to 12thgenusa's 20AH stated figure. I read all the time of people making it through a day or three on a single battery, but with the fridge using up most of the load there seems to be a discrepancy.