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Old 09-07-2011, 03:33 PM   #11
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I'm new to all this but I think here's what my plan is.

I have an A126 Rockwood popup hardside. 3-way Dometic fridge (no freezer).

I plan on precooling on 120vac day before heading out, stock the fridge before leaving.

Then while on the road I'll use 12vdc to power the fridge. The trailer gets 12vdc supply form the Jeep through the 7-way.

Shore power at the CG will be back over to 120vac.

I can only see using LP when no shore power is available (boondocking).

From what I can tell my Rockwood A126 has a battery isolator so I won't drain my TV battery while stopped for short periods of time when traveling.

I've read a number of places (including the fridge owners manual) that you should never run the Gas on the fridge while at a fueling station. I can certainly see why - nobody wants to go boom before reaching the CG form an accidental ignition of gasoline vapors. 12vdc while on the road avoids the need to remember to kill the LP before refueling and relighting after leaving gas station.

If you don't foresee the need to stop for refueling I guess LP would be a fine traveling option with the exception of loss of flame by winds while traveling. I've heard that can be an issue with some fridges.

I however drive a Jeep Wranger and will be stopping for fuel regularly

I may learn better of my above plan but that's what I've gleaned from these forums.
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Old 09-07-2011, 04:36 PM   #12
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I had a previous trailer with a 3 way power fridge.
I found that it actually partially drained my trailer battery while on the
road. It really is a HUGE amp draw on 12v dc power.
This was not an issue if I was going to a CG with electric hook ups but it
was an issue if we were boon docking.
IF you find that your trailer battery is still full when you get to your
camp ground, your plan sounds fine.

IF not, many of us run with the LP on. Some of us even leave it on while
fueling. Typically my trailer is hanging out in the parking lot
while my truck sits at the gas pump. I'll risk it.

Good luck and happy camping!!
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Old 09-07-2011, 09:28 PM   #13
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Absolutely... What voltage should I be looking for on the battery when I get to the cg? I'll bring my dmm along for then ride and see how it goes. As always I'm here to learn.
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Old 09-07-2011, 11:01 PM   #14
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i'm thinking the tv disconects the 12 volt when the ignition is off. have never tested it though. i have an electric freezer that runs while we go for lunch and the tv battery doesn't go down. again, i haven't actually tested to see if the 12 volt is live or not.
i run with propane on on the frig. i'll admit that i refuel with it on. i'm sure there is a risk but gasoline vapors hug the ground. if i had a gasoline vehicle, i would be more concerned with vapor and a hot catalytic converter. on ur trailer, i believe the frig is closer to the ground than mine. i can see that being a little more of a concern.
sounds like u have a good plan.
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Old 09-07-2011, 11:06 PM   #15
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Hi

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Originally Posted by Jeep4Two View Post
Absolutely... What voltage should I be looking for on the battery when I get to the cg? I'll bring my dmm along for then ride and see how it goes. As always I'm here to learn.
I have only been on this forum for 5 minutes. Maybe we are cautious over this side of the Pond but it is for a good reason. We don't tow our vans with the gas supply running. That means no fridge on gas and no supply to any other LP appliances in van. That means no gas can build up in the van whilst travelling and no possible explosion if a leak develops in any appliance or appliance supply. This sounds like a good practice to me. Have you wondered why that going through certain tunnels over there you are required to have LP equipment turned off and gas supply turned off? It is for a good reason. I would advise to not have gas turned on whilst travelling. What is you were in an auto accident and in the process the flame for the fridge went out of a gas line or appliance (Any of the LP in your van) ruptured? Outcome could be dissasterous.

The 12V power supply through your plug and socket connection (Vehicle and van/trailer) is NOT sufficient to run 12v Fridge or achieve the 12V charging of you van battery unless you use that supply to run a DC to DC battery charger for the van battery and run that power from the van battery direct to the fridge for it to have sufficient voltage to run it on 12 volts.
The other alternative is what I have done and it is to run 12 volts in a heavy fused cable from vehicle battery(or Auxillery battery if fitted) to Anderson plug at rear of vehicle and then have that same cable size with anderson plug going straight to your van battery. Cable size minimum of 16mm2. I used 25mm2 cable to achieve even less voltage drop. 175 amp Anderson plug required for this large cable connection. Fuse cable at both ends with minimum 50 amp mega fuse or breaker.
This is the only way a 12v supply to fridge will be sufficient to run the fridge. If you use the vehicle power through the standard auto to van plug and socket connection voltage drop will cause the 12V supply to your fridge to be insufficient for fridge to operate as required. This same voltage will also be insufficient to charge your van Deep cycle battery unless you drive for 8 hours or more a day, every day.
If you want to see what I am talking about re voltage drop start your vehicle. Measure the voltage at your start battery terminals. Measure the voltage at your 2nd under hood battery (Aux battery). This should be very close as same as start battery. 14 or so volts. Then if you have power supply in trailer socket measure the voltage there? You will notice a voltage drop due to cable size supply. By the time the voltage goes from vehicle socket to plug to van battery the voltage drop will be further due to cable size. Then even further as the cable supplies the fridge its 12 V. The total voltage drop will cause a fridge running on 12V to not have sufficient voltage to function as designed. This is what I have learnt and seen first hand. The cable size of supply to fridge requires it to be upsized as well.
This is my opinion and the opinion of more experienced in 12V electrical in a forum here www.myswag.org. I have a 0.01 voltage drop from my auxillery battery to my Anderson plug on rear of tow vehicle using 25mm2 cable or 3AWG for you. You could use down to 5AWG at a minimum size for suppply.
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Old 09-07-2011, 11:29 PM   #16
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@All:

Good points. I'll check some voltages once hooked up and see what I get across the full loop of electrical with the TV idling.

The TV has a factory harness that supplies 12V back to the trailer plug (fused). I'll compare voltages between the TV battery and the trailer plug. I do know that in my case I show voltage on the +12 and ground on the TV trailer plug when the vehicle is off (key removed, ignition off). This of course is due to the power supply going all the way up to the battery. There is a relay on the harness but I think that relay is related to turn signals, not power off of the 12v accessory post on the trailer plug (isolation).

I'm assuming that the trailer includes isolation (I may be mistaken) so avoiding drain in cases of the TV being parked and off with 12v fridge should be covered. I'll have to watch this particular point.

I'll also measure my trailer's battery before I leave out and when I arrive to get a gauge of whether or not the trailers battery is being maintained with the fridge on 12v or not. I'd prefer to have 12v for the fridge during transit (and that's how it was 'advertised' by the sales folks and service staff at my dealer - but I know to take that with a grain of salt).

Ahh - the details. I enjoy the details - they make it fun

Thanks again - great community here.
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Old 09-07-2011, 11:45 PM   #17
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Hi

Quote:
Originally Posted by Jeep4Two View Post
@All:

Good points. I'll check some voltages once hooked up and see what I get across the full loop of electrical with the TV idling.

The TV has a factory harness that supplies 12V back to the trailer plug (fused). I'll compare voltages between the TV battery and the trailer plug. I do know that in my case I show voltage on the +12 and ground on the TV trailer plug when the vehicle is off (key removed, ignition off). This of course is due to the power supply going all the way up to the battery. There is a relay on the harness but I think that relay is related to turn signals, not power off of the 12v accessory post on the trailer plug (isolation).

I'm assuming that the trailer includes isolation (I may be mistaken) so avoiding drain in cases of the TV being parked and off with 12v fridge should be covered. I'll have to watch this particular point.

I'll also measure my trailer's battery before I leave out and when I arrive to get a gauge of whether or not the trailers battery is being maintained with the fridge on 12v or not. I'd prefer to have 12v for the fridge during transit (and that's how it was 'advertised' by the sales folks and service staff at my dealer - but I know to take that with a grain of salt).

Ahh - the details. I enjoy the details - they make it fun

Thanks again - great community here.
I think you are doing what needs to be done for you to be satisfied that it is operating how it suits you. Salesmen will tell you anything for a sale.
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Old 09-08-2011, 12:42 AM   #18
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what frig are u trying to run? i looked at a dometic that required 11 amp to run on DC. that's an RM8555 6.7 cubic ft. requires 130 watts on DC for short version and 170 watts on DC for tall version.
the electric ref/freezer that i run in Freeze takes just under 5 amps DC.
i'm missing something because that doesn't translate into more than #12.

the reason that i would think they would want u to turn off the propane while going thru a tunnel is that propane will tend to collect in the low areas. u have to assume that it will find a source of ignition.
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Old 09-08-2011, 09:50 AM   #19
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I'm pretty sure it's a 2193 compact 3-way model (looking at their website, I'm not near my owners manual right now). It's a fridge only, no freezer and quite small.

Looking at that manual for the 2193 model on Dometic's website, that unit uses a 125 watt (10.5 amps, 12v) element for the 12vdc operation. Minimum wire size for the wiring is 14awg. The positive and negative on my trailer harness is 12awg running direct from the battery approximately 6ft of length to the 7pin socket on the TV. I'm assuming Forest River has followed those recommendations and is using at least 12awg (versus the minimum recommended 14awg) to go from the power supply on the trailer to the fridge.

I haven't had a chance to measure any voltages yet but the DMM is on the list for this afternoon after some shopping and packing
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Old 09-08-2011, 10:40 AM   #20
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i know DC is less forgiving than AC on line length (continuous vs average). just didn't think it required #6 or larger. was trying to figure out what else they had that i wasn't seeing.
i would think forest river would have wired correctly between the battery and frig. with amperage that close, i would hope they used 12.
at least a voltmeter will tell the tale.
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