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Old 02-24-2016, 01:35 PM   #41
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Originally Posted by pgandw View Post
The small fridges in PUPs and A-frames are continuous run, and are not thermostatically controlled. Therefore there is no auto-start, no solenoid valve, and no DC control board.
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Thanks Fred, I learn something new every day,
What model is that? Who makes it?

I was looking at the Dometic REFRIGERATOR MODEL RM 2191 & RM 2193 and it looks like what you described.

So as long as the gas is turned on at the bottle, you can turn off the DC and AC switches and the fridge will still run; is that correct?

It says there is a "flame sensing unit" to monitor that the flame is lit. What is not clear is how it does that and what shuts off the gas when the flame goes (or is blown) out?
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Old 02-24-2016, 02:20 PM   #42
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Great response Fred, like I have said before its fun to learn something on here
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Old 02-24-2016, 03:43 PM   #43
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What model is that? Who makes it?

I was looking at the Dometic REFRIGERATOR MODEL RM 2191 & RM 2193 and it looks like what you described.

So as long as the gas is turned on at the bottle, you can turn off the DC and AC switches and the fridge will still run; is that correct?

It says there is a "flame sensing unit" to monitor that the flame is lit. What is not clear is how it does that and what shuts off the gas when the flame goes (or is blown) out?
I've had 2 Dometic fridges of this type (model numbers unknown) - the first in a 2000 Coleman Westlake PUP (looked identical to your photo), and the second in my 2014 Rockwood A122 A-frame.

You do not want to have more than one source turned on at a time. The
Coleman installation had a mechanical interlock to prevent propane and electric operation simultaneously. The propane shut-off valve handle had to be in closed position or it interfered with depressing the AC and DC switches. Fridge runs just fine on propane alone (AC and DC switches off), once you light the burner.

I don't know of any flame sense device besides the view port flap - rotate the flap and see if you can see the flame. Nor do I see how one could work. It would be impossible to light the burner if there was an interlock to shut the gas off with no sensed flame. At a minimum, there would have to be a logic board with a timer, which would also likely result in electronic ignition. As it stands, you press the metering valve for extra gas, and light the burner by pushing the igniter button to create a spark (or I have used a flame stick or even matches when I was having problems). As far as I know, the gas is shut off manually. Given the location of the fridge burner (outside the living area with vents to outside only) and the very small amount of propane used by the fridge, I could live with flame-out and gas flowing (and I think I have).

I verify the burner is lit by feeling the chimney heat up, or after a few hours by putting my hand across the upper vent/access and feeling the warm air.

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Old 02-24-2016, 04:06 PM   #44
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I agree Fred, but this is from the manual. Look at the NOTE at the bottom; it had me scratching my head.
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Old 02-24-2016, 04:15 PM   #45
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The flame sense device would be a thermocouple.
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Old 02-24-2016, 05:18 PM   #46
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I agree Fred, but this is from the manual. Look at the NOTE at the bottom; it had me scratching my head.
The note makes total sense to me. The disabling of the flame sense is done by pushing in the gas metering valve knob (part of the start procedure). I always understood pushing in the knob gave a little extra gas (primer) to aid in lighting off. But disabling the flame sense is needed to prevent shutting off the gas while trying to light the burner.

Based on that, there probably is a very small parasitic 12V DC to operate the fridge on propane - power the thermocouple and a solenoid to cut off propane without a flame. Intelligent design to save power would be the solenoid valve is sprung open, DC powered closed. Safety would say the other way around.

My older PUP didn't have the flame sense and had a manual shut-off. Today's standards probably require the auto shut-off.

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Old 02-24-2016, 06:37 PM   #47
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The thermocouple does not need power to operate, just heat. If the heat is removed from the thermocouple it shuts down the gas flow to the pilot light.
That fridge heating unit would operate basically the same as a household water heater.
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Old 02-24-2016, 07:37 PM   #48
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The thermocouple does not need power to operate, just heat. If the heat is removed from the thermocouple it shuts down the gas flow to the pilot light.
That fridge heating unit would operate basically the same as a household water heater.
Ah, the thermocouple generates the power to keep the valve open. I did not think such a tiny potential could work against a spring loaded valve.

https://en.wikipedia.org/wiki/Thermocouple "quote"

Many gas-fed heating appliances such as ovens and water heaters make use of a pilot flame to ignite the main gas burner when required. If the pilot flame goes out, unburned gas may be released, which is an explosion risk and a health hazard. To prevent this, some appliances use a thermocouple in a fail-safe circuit to sense when the pilot light is burning. The tip of the thermocouple is placed in the pilot flame, generating a voltage which operates the supply valve which feeds gas to the pilot. So long as the pilot flame remains lit, the thermocouple remains hot, and the pilot gas valve is held open. If the pilot light goes out, the thermocouple temperature falls, causing the voltage across the thermocouple to drop and the valve to close.

Some combined main burner and pilot gas valves (mainly by Honeywell) reduce the power demand to within the range of a single universal thermocouple heated by a pilot (25 mV open circuit falling by half with the coil connected to a 1012 mV, 0.20.25 A source, typically) by sizing the coil to be able to hold the valve open against a light spring, but only after the initial turning-on force is provided by the user pressing and holding a knob to compress the spring during lighting of the pilot. These systems are identifiable by the "press and hold for x minutes" in the pilot lighting instructions. (The holding current requirement of such a valve is much less than a bigger solenoid designed for pulling the valve in from a closed position would require.) Special test sets are made to confirm the valve let-go and holding currents, because an ordinary milli-ammeter cannot be used as it introduces more resistance than the gas valve coil. Apart from testing the open circuit voltage of the thermocouple, and the near short-circuit DC continuity through the thermocouple gas valve coil, the easiest non-specialist test is substitution of a known good gas valve.
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Old 02-24-2016, 08:40 PM   #49
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Many years ago I had an old tent trailer with a small fridge like that. I used to have to light the pilot light manually the same as you do for a household water heater.
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Old 02-24-2016, 10:00 PM   #50
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It sounds like the general opinion is 6 volt is the way to go but I can't get two 6 volts in my rack, too long and I've got 3 perfectly good 12 volts I plan in connecting in parallel and just sit on the ground while camping. Any problem with doing this?
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Old 02-25-2016, 12:54 AM   #51
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It sounds like the general opinion is 6 volt is the way to go but I can't get two 6 volts in my rack, too long and I've got 3 perfectly good 12 volts I plan in connecting in parallel and just sit on the ground while camping. Any problem with doing this?
Not really, just make sure to attach the positive cable to battery one, then parallel battery two, then three, then attach the negative cable to battery three.

You'll likely catch a lot of grief about putting batteries on the ground unprotected, but that's outdated info. Modern cases prevent the grounding out issue batteries used to have. But, you can always get a board to put under the batteries if it's a concern.
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Old 02-25-2016, 01:21 AM   #52
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Not really, just make sure to attach the positive cable to battery one, then parallel battery two, then three, then attach the negative cable to battery three.

You'll likely catch a lot of grief about putting batteries on the ground unprotected, but that's outdated info. Modern cases prevent the grounding out issue batteries used to have. But, you can always get a board to put under the batteries if it's a concern.
Thanks, was thinking about build a rack that would mount them, just while on location, above the present batteries.

Regarding two six volts, I looked at some 6 volts that were 230 am/hrs. does that mean two fo them will provide 230 amps at 12 volts?

thanks in advance
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Old 02-25-2016, 02:22 AM   #53
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Thanks, was thinking about build a rack that would mount them, just while on location, above the present batteries.

Regarding two six volts, I looked at some 6 volts that were 230 am/hrs. does that mean two fo them will provide 230 amps at 12 volts?

thanks in advance
Exactly right, when you connect two 6V batteries in series you double the voltage, but not the amp hours.

But when you parallel two 12V batteries you stay at 12V but double the amp hours.

I like my 6V batteries, I've got four in a series/parallel arrangement. 12V at 460ah.
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Old 02-25-2016, 06:34 AM   #54
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I wonder what would the cost difference would be between four six volt T-145 and six T-105. I know the difference in amps, I would get more amps


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Old 02-25-2016, 10:41 AM   #55
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Will the stock WFCO converter handle 6 volts (in series) exactly like a 12 volt. Is that resting voltage for the 2 6 volts about 12.7 volts like the 12'?
thanks in advance.
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Old 02-25-2016, 11:54 AM   #56
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Will the stock WFCO converter handle 6 volts (in series) exactly like a 12 volt. Is that resting voltage for the 2 6 volts about 12.7 volts like the 12'?
thanks in advance.
2 6 volt batteries is series is exactly the same number of cells as a 12 volt battery. No difference except more capacity per cell.
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Old 02-25-2016, 08:15 PM   #57
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So I've determined that I can fit the Century battery box and 2 - 6 volt batteries in it on the tong of my TT in the usual position. Trojan seems to offer 4 different terminals. Which one do you guys recommend?

http://www.trojanbattery.com/pdf/dat...ata_Sheets.pdf
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Old 02-25-2016, 08:20 PM   #58
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The easiest way is to get the same terminals that your current batterys have.
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Old 02-25-2016, 09:41 PM   #59
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Great thread. Learning alot. IMO regarding 6v vs 12v, you can get approx. 35% more amp/hrs in the same footprint with 6v batteries. Since my batteries are on the trailer tongue, space is paramount. If i'm missing something, tell me.
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Old 02-25-2016, 10:01 PM   #60
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I have the same setup.....are you sure you don't want 2 T145 30% more capacity for just a few more dollars.
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