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Old 07-22-2013, 02:36 PM   #1
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Adding Stanley PC809 Inverter

I have a Dometic Refrigerator (RM1350) 4 door unit
It can runs off of propane or 120 volt AC.
The controls are 12 volt DC
In the next year I will be taking a long trip and one very long ferry ride which all propane will be shutoff for the full trip. (Est. duration between 12 and 18 hours). I will not be in the motoprhome at all during the ferry trip. If you want to know it is the long ferry to Newfoundland Canada

I don't want to lose any food so I have decided to add a power inverter for the trip. The only thing the inverter will power is the 120 volt, 430 watt electric heater (resistive load) in the refrigerator for cooling. My two 12 volt house batteries should be in good shape and able to handle that little load as far as I can guess.

I'm considering buying a Stanley PC809 800 watt inverter because it has a led screen that shows wattage used as well as battery voltage.
The 800 watts should easily handle the single load of the refrigerater.

It will only be hooked up in a temporary mode so that is not an issue.

Here is what the inverter looks like.
Have I missed anything I should consider?
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Old 07-22-2013, 02:54 PM   #2
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Iggy,

Make SURE everything but the fridge is off and you should be OK.

Not sure how many amp hours your battery bank is (if I knew I could calculate your battery life with a 430 watt load. Heaters are resistance loads, I believe (electric motors are inductive).

So a 430 watt load will draw about 36 amps from the battery bank when heating. Since you will have the door closed the entire time (barring excessively hot temperatures in the car park area), the full 36 amp hit will only be on (probably) 15 minutes or so per hour.

As you can see from the chart, deep cycle batteries have a hard time giving up that much power (each). The capacity hit is 50% if it all comes out of one 12 volt battery. Shared over two 12 volt batteries, (18 amps each) the capacity hit is only 30%.

PM me with specifics of your system (AH and battery type and voltage) and we can juggle some numbers.
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Old 07-22-2013, 03:38 PM   #3
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Thanks Herk
It will be the only thing plugged into the inverter.
And yes my goof it is resistive load not inductive. Not sure why I said that.
My two batteries are typical Series 27 12 volt car batteries but I can't tell you anything about amperage.
Must be low because they were OEM Marine batteries installs by Forest River.
My battery charger is a 70 amp max output.
I just may have to test it out in real life at the house and see how long the batteries last.

Hope you had a great 4th of July vacation in PA. Was it as much fun as you expected?
Iggy
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Old 07-22-2013, 06:43 PM   #4
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Iggy,

(We had a great time; thanks for asking).

I was talking about what is using the batteries and not the inverter. The load on the batteries is the only thing that matters when dealing with battery life driving an inverter. The inverter will definitely be the highest amperage draw on the camper when working. Shared between the two batteries is a plus for battery life as that graph showed.

OEM Group 27 batteries are about 100 amp hours so the graph is gonna be perfect to show the effect of the inverter on battery capacity. (amp hours).

A 100-amp-hour, 12-volt battery will run a 5-amp motor (or a 60 watt light) for 20 hours, and a 200-amp-hour battery bank will run a constant 10-amp (120 watt) load for 20 hours.That’s the theory. In fact, if a 100-amp-hour battery is discharged at a rate greater than 5 amps, it will not deliver all the advertised amp-hours before it goes dead. (see chart)

On the other hand, if you discharge it at a steady rate of less than 5 amps, you’ll get more amp-hours than the manufacturer’s rating shows—not a whole lot more, but some.That principle applies to most lead-acid batteries found on RVs — the faster the discharge rate, the fewer amp-hours delivered. The more slowly energy is taken from a battery, the longer it will last.

In your case, with 200 amp hours (about) of capacity, and running the fridge's ammonia heater about 25% of the time, (but pulling 20 amps when you do), you should get 24 hours or so before the inverter alarms.

Lots of guesswork here, but I would not be surprised if it is close.

OH, BTW - Just cause the camper's battery dies does not mean the food is immediately bad. Your ice cream will still be frozen a few hours after the batteries give up the ghost.
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Old 07-22-2013, 08:28 PM   #5
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Thanks Lou.
I know I really don't have much to worry about. I will do a test in the next few weeks and see if my present batteries are up to the job.
By nest year when I really need it for the trip I may even buy a new set. The heat here in Arizona kills batteries a lot quicker than cooler places.
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Old 07-23-2013, 02:15 PM   #6
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make the cables from the batteries to the inverter as short as possible and size for voltage drop!
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Old 07-23-2013, 02:40 PM   #7
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Quote:
Originally Posted by RPAspey View Post
make the cables from the batteries to the inverter as short as possible and size for voltage drop!
Thanks for the suggestion. Will do.
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Old 07-23-2013, 05:44 PM   #8
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It might be easier and cheaper to buy a $100-200 ice chest and pack your food in it. Given that you'll be in a cool climate, a good ice chest should easily keep your frozen foods frozen for the duration of the trip.
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Old 07-23-2013, 08:40 PM   #9
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Quote:
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It might be easier and cheaper to buy a $100-200 ice chest and pack your food in it. Given that you'll be in a cool climate, a good ice chest should easily keep your frozen foods frozen for the duration of the trip.

That is a great suggestion and I will consider that and it can just work.
Thanks.
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Old 07-23-2013, 10:57 PM   #10
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The kids sent us a big Styrofoam case of Omaha Steaks when the DW had her knee done. During the Gettysburg Trip I packed it full of frozen water bottles and they were still mostly frozen 4 days later.
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