Using Dometic refrigerator on 12 volts - Page 7 - Fiberglass RV


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Old 01-11-2018, 03:45 PM   #85
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If you DO run your own heavier trailer charge wire, I would add an isolation relay to it, triggered by the same circuit as the current charge relay in the tug, I'd probably use a 50A relay for safe margins here (if your trailer battery is seriously discharged, and you've run 10 gauge, the dead battery could easily pull 30A down that wire.

the relay's function is to disconnect the trailer when the tug engine is off.
This is a very good plan. A common way to do it is with a Ford type, continuous duty relay, but I'm sure there are other good ones too.
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Old 01-11-2018, 04:52 PM   #86
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This is a very good plan. A common way to do it is with a Ford type, continuous duty relay, but I'm sure there are other good ones too.
I use something like this:
https://www.princessauto.com/en/deta...or/A-p8511875e

A 140A, voltage sensing relay. At 13.3 volts, it closes, (turns on). At 12.8 volts it opens, (turns off). This prevents the trailer from draining the vehicle battery. Not cheep, but everything at Princess Auto eventually goes on sale.
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Old 01-11-2018, 06:40 PM   #87
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Since the factory charge line is typically included in the tow package why didnt the manufacturer use 10 ga wire to begin with? I doubt it's cost.
Yes, it's the cost. Copper is expensive nowdays. Few cents saved on thousands of vehicles bring sizable profit to shareholders.
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Old 01-11-2018, 07:04 PM   #88
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I use something like this:
https://www.princessauto.com/en/deta...or/A-p8511875e

A 140A, voltage sensing relay. At 13.3 volts, it closes, (turns on). At 12.8 volts it opens, (turns off). This prevents the trailer from draining the vehicle battery. Not cheep, but everything at Princess Auto eventually goes on sale.
That looks interesting. Invisible to the user, which makes it more foolproof and easy to use.

Does it measure the trailer battery voltage for it's reference? If it measured the TV battery it might have a continuous battery draw even when off.

Thanks for that link. Very useful.
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Old 01-12-2018, 03:57 PM   #89
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Never know what the risk is for sure! I was coming south on I 75 in Lake City Florida and there was a contractors wheelbarrow in my lane in heavy traffic! Just missed it.
Always get fuel in a station with a canopy over the pumps. You never know when space junk is going to fall from the sky!
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Old 01-12-2018, 04:19 PM   #90
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Never know what the risk is for sure! I was coming south on I 75 in Lake City Florida and there was a contractors wheelbarrow in my lane in heavy traffic! Just missed it.
Always get fuel in a station with a canopy over the pumps. You never know when space junk is going to fall from the sky!
not sure that tin canopy would be much help... just sayin'
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Old 01-12-2018, 04:23 PM   #91
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Maybe someone can give us the specs on what is actually needed to do the job.
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Old 01-12-2018, 04:52 PM   #92
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I don't run my fridge on propane while driving down the road because it's a risk I prefer not to take. It's my understanding the flow restrictor on a twenty pound tank limits to 5 psi. The output of the regulator on my trailer I believe is 1/2 psi. If true, a ruptured line will continue to supply gas despite the safety device. But what concerns me more is the use of hydrogen gas as a component in the refrigerant. With no moving parts these fridges often fail through metal fatigue, most likely caused by vibration. The smell of ammonia is the tip off. But if the hydrogen encounters an open flame, an explosion occurs. Do a search for "RV refrigerator explosion", lots of stories, law suits etc. Interesting that Norcold is producing absorption refrigerators that use helium in place of the hydrogen.


When I encounter a guy smoking a cigarette while he's pumping gas, I drive away. He's been doing it that way for years. So what? Been driving for years with the fridge running on propane. I have the same reaction. I really don't care what others do, I just don't what them to take me with them. Raz

I looked at a number of RV and propane associations and they all said not to drive with the propane on. The FMCA (Family Motor Coach Association) looked at the safety devices and concluded that, while a small risk, and despite the cut-off, there would still be enough propane out there to cause a catastrophe, and they recommended driving with the propane off. I saw on a forum where certain propane associations gave the same recommendation, but do not know if it was this forum. Another organization noted that the number of ppm's of propane needed to cause a catastrophe was tiny and they also recommended not driving with the propane on.

While it may be very unlikely to have something happen, that is not the same as it cannot happen. Many prefer to take the risk. Many claim that there is no risk. That is not, however, what a number of organizations very familiar with this say. Now I am sure that many people who drive with their propane on will want to bash any organization or any persons who do not, and who used facts such as the above to make their decision. That is always the way it will be on many issues.

It is not impossible that I saw old information but I don't think so. If those organizations did not recommend not driving with propane on, we would not be doing it. Also saw the report of the average 5000 fires per year at gas stations in the U.S. You all can do what you want and we will do what we want. We use ice packs that we freeze overnight while stopped and switch them with others in a cooler in the car. May be interested in trying 12v with solar some time as some have had success and others not.
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Old 01-12-2018, 05:06 PM   #93
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That looks interesting. Invisible to the user, which makes it more foolproof and easy to use.

Does it measure the trailer battery voltage for it's reference? If it measured the TV battery it might have a continuous battery draw even when off.

Thanks for that link. Very useful.
I found the manufactures web site for this product:
AOPEC Automotive Electronics - Products

They only give this spec for the 100A, (not 140A) version, but I suspect they would be the same:
Standby current:<3mA@12V;<6mA@24V
As for which battery they reference, it would have to be the tow vehicle battery. Otherwise, the unit would never see when the alternator is producing voltage. Though in the wiring diagram, and instructions, it says to wire the negative reference to the accessory battery, (not possible on a trailer). This implies that it is measuring the accessory battery. Since both batteries are shown with the negative terminals connected, it would make no difference.

On the Princess Auto web site they link the user manual:
https://images11.palcdn.com/hlr-syst...875_manual.pdf
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Old 01-12-2018, 05:18 PM   #94
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Cathi, this is one of those hot button issues. It typically provokes arguement. "I've done it for years and never had a problem. " is a common response. Or "there's no law against it" is common too. Since this is a forum, all points of view are valid and should be tolerated. That said, one of my favorite sayings is " We all dig our our holes." But " let's take all the warning labels off and see how things sugar off" might be more appropriate. Stay safe, Raz
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Old 01-13-2018, 01:31 AM   #95
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I found the manufactures web site for this product:
AOPEC Automotive Electronics - Products

They only give this spec for the 100A, (not 140A) version, but I suspect they would be the same:
Standby current:<3mA@12V;<6mA@24V
As for which battery they reference, it would have to be the tow vehicle battery. Otherwise, the unit would never see when the alternator is producing voltage. Though in the wiring diagram, and instructions, it says to wire the negative reference to the accessory battery, (not possible on a trailer). This implies that it is measuring the accessory battery. Since both batteries are shown with the negative terminals connected, it would make no difference.

On the Princess Auto web site they link the user manual:
https://images11.palcdn.com/hlr-syst...875_manual.pdf
David,
You're right. It has to measure the primary battery or it can't work, but then there is a continuous draw on that battery. I know it's small, but still. Might be better to energize it with the ignition key. Have you noticed your primary battery getting discharged?
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Old 01-13-2018, 05:11 AM   #96
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David,
You're right. It has to measure the primary battery or it can't work, but then there is a continuous draw on that battery. I know it's small, but still. Might be better to energize it with the ignition key. Have you noticed your primary battery getting discharged?
There is a parasitic drain on your battery already. It maintains the radio settings, the engine settings, the alarm, etc. It's easy to measure. I doubt 3 mA more will matter. Raz
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Old 01-13-2018, 05:25 AM   #97
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There is a parasitic drain on your battery already. It maintains the radio settings, the engine settings, the alarm, etc. It's easy to measure. I doubt 3 mA more will matter. Raz
Good point. I wonder how often a new car has to be started to maintain itself?
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Old 01-13-2018, 05:36 AM   #98
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Good point. I wonder how often a new car has to be started to maintain itself?
Good question. I just bought a new pickup that sat on the lot for over a year. Battery is still good. They must have done something. I don't run my pickups in the winter to avoid road salt. I disconnect and put the charger on occasionally. I should measure the parasitic current next time.
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