| [GMCnet] Refrigerator Advice [message #312006] |
Tue, 10 January 2017 20:10 |
glwgmc
Messages: 1014
Registered: June 2004
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My real world experience with quality battery monitors in both our coaches is a bit different from the conventionally accepted wisdom. Two to three hours per day of running the Onan and charging with a PD three stage smart charger (or equivalent) is enough to recharge a reasonable size house battery bank (~200 or more amp hours) with normal daily draw use. It won’t bring one back from fully depleted in that amount of time, but it will keep you going way longer than your water and holding tanks will last in normal dry camping use. The only way you are going to know for sure with your coach, your battery bank and your charger is to install and use a good quality battery monitor. Those come with an accurate shunt to directly measure amps in and out of the battery bank over a given period of time. Such monitors cost $150 to $250. The cheap ones that just measure voltage or the $30 wonders with what passes for a shunt will not tell you much of value at all. It takes several charge/discharge cycles to calibrate the monitor to the real amp hour capacity of your battery bank. Do not rely on or believe the battery manufacturers amp hour rating until you confirm it for yourself. There are way too many ways to game the rating system.
Here are some real world estimates using the battery bank, charger and generator in our 77/94 Clasco that might be helpful. These come from the presentation at GMCWS at the October 2016 rally in Coos Bay, OR on how to run your Onan on either gasoline or propane at the flip of one toggle switch:
The GMC finished coaches and the Royales have 62 pound propane tanks. Propane weighs 4.2 #/gal so a full tank will hold 14.8 gallons of propane if properly filled. The tanks are marked 20 gallons, but that is the capacity if they were filled with water. The tanks are designed to run less than 80% full of propane. My 6kw Onan will consume 0.2 gallons of propane per hour while generating 1kw. The consumption is quite linear all the way up to generating 4kw consuming a bit over 0.8 gallons per hour. I had no way to create a reliable load greater than 4kw so could not really test consumption at 5 or 6KW but have no reason to believe it would be anything other than linear in that range, too.
Normal battery charging (batteries discharged to no less than 50%) takes 40 to 50 amps DC initially but tapers down to 10-20 amps DC. That averages around 3-4 amps AC, or less than 1kw. So, an average 3 hour battery charge will consume less than 0.6 gallons of propane per day. Running one typical roof air conditioner will take less than 2kw. Starting will take nearly twice that but only for a short time. If the air conditioner draws 8.3 amps at 120vac it will consume 1kw, if 16.6 amps, 2kw.
Running at an output of 1kw a full tank of propane will run the Onan for 74 hours. Running at 2kw a full tank will run the Onan for 37.5 hours. The way we live in the Clasco (showers every day, no anal water conservation, etc.), a full water tank and empty black/gray tank will serve us for about three days. Two days if we are really sloppy with water use and maybe four days if we really try. The Royale with its separate black and gray tanks will go about a day longer in most cases if we are able to drain gray water safely or pump it into the black tank when necessary.
Heating water from cold in the electric only hot water heater in the Clasco takes running the Onan for about 15 to as much as 25 minutes - more the time it takes to make the morning coffee using an electric coffee pot. Heating water and cooling the refrig. in either coach on propane is hard to really measure because the draw is so low. The propane furnace will consume a lot of propane if it is really cold (those things in our coaches consume around 30,000 to 40,000 btus per hour of operation) and a gallon of propane contains 96,000 btus.
Hope this helps frame the discussion.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
glwork@mac.com
http://jerrywork.com
==============
Message: 12
Date: Tue, 10 Jan 2017 16:39:08 -0700
From: A.
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Refrigerator Advice
Message-ID:
Content-Type: text/plain; charset="utf-8"
tgeiger wrote on Tue, 10 January 2017 16:19
> I see there was a lot of good information pertaining to the electrical setup. I did not see anyone discuss the propane setup. I don't know if
> that is because it just does not perform well or if the original preference was leaning to electric? I too have been debating this issue and would
> like to boondock at times so I was leaning towards a 3-way fridge for most flexibility. Any thoughts pertaining to that?
>
> Thanks,
> Tom
> 76 Eleganza II with electrical fridge now
There is no discussion of the propane fridge because it would unquestionably do the job. We are all trying to convey the potential difficulties of
going with an electric fridge.
Personally, my gut tells me to use propane to produce heat, and electricity to remove it. That's why the roof AC has a compressor instead of an
absorption refrigeration unit. But electricity is hard to store. By unit of energy, a propane tank stores hundreds of times as much energy as a lead
acid battery. So an incredibly inefficient absorption fridge can run way longer on a tank of propane than an incredibly efficient swing motor
compressor can run on the same size/weight of lead-acid battery bank. Just a little bit of electricity appropriately applied (like a couple of solar
panels and the right charge controller) can swing the equation in favor of the electric fridge. The Onan and a conventional converter/charger is NOT
the correct way to get that little bit of electricity back into the house battery bank. It won't get the voltage high enough to charge the battery in
an hour or three.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality.”
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Jerry & Sharon Work
78 Royale
Kerby, OR
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