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Old 08-14-2014, 06:50 AM   #1
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Refrigerator, DC ops in general

Being of the "learn by doing" nature, I've been all over and under the A127TH since purchasing it at the end of May. I've read and re-read most of the manuals. Due to many other factors, we've only been out in it one time, and that was at a full-hookup CG for only 2 nights. As a result, I'm just now getting a handle on the onboard freshwater system and how it relates to shore water and the DC system and how it relates to shore power.

Last weekend, I powered up the fridge on shore power. Works great, but of course takes a couple of hours to get seriously cool inside. I don't envision getting entirely away from coolers, but I want to use the fridge on a long weekend trip set to begin tomorrow morning. I'll power it up this evening and load it with cold groceries in the morning before setting sail. I'm seeing some varying opinions about on-the-road operation of the fridge on propane vs DC. I'm much more comfortable with DC. It seems, however, that the DC fridge operations are likely to discharge the battery where the drain from the fridge will exceed the 7-pole's recharging capacity. Is this generally correct? I'll have shore power for Friday and Saturday nights but will be boondocking Sunday night, so I'll need battery power for onboard water pumping, fridge, and lights Sunday evening/Monday morning. I have a 2000 watt Honda gennie and all appropriate connections to power up through shore power connections and can readily do so. I understand I can't run the A/C on the gennie, but I assume I can run the lights and charge the battery. Should I assume I'll need to run the gennie for a while Sunday/Monday morning in order to top up the battery for shower water pumping Monday morning and DC fridge operation on the road for the 6 hour drive home?

It seems that, generally, whenever shore power is connected, the inverter powers up, its fan running, and AC "takes over", excepting the manual toggles to shut down the DC to the fridge and power up the AC for it. Also, the inverter system apparently, according to my read of its manual, automatically toggles between full charge and maintenance charge on the on-board battery while shore power is connected. I'm not seeing any switches to manually start/change over the charging, and not reading anything other than automatic operations as to the charging system. Does this sound correct?

Really looking forward to the trip to WV and far western VA tomorrow! Thanks for any inputs/advice!
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Old 08-14-2014, 07:17 AM   #2
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On my pop-up I did not have a battery permanently hooked up so when we traveled the DC power for the fridge came from the TV. What are you towing with and have you verified that the DC charge line is functioning, on some TV's you need to install a fuse to activate the charge line. You should be able to go one night without having to charge the batteries just don't have the lights running all night. Most new campers change between AC and DC operation by them selves and the charging of the battery is automatic.
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Old 08-14-2014, 07:23 AM   #3
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Sounds like you're a little confused. You are saying "inverter" when you mean "converter".

When you are 'boobdocking', remember to use the fridge on LP. It does require 12v for the electronics and ignition. 12v operation is used while towing and just to maintain temp.
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Old 08-14-2014, 08:02 AM   #4
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Some of the camping experience is "learn by doing" so you'll have to
see what works for you.

Here is a link to a pole we took regarding the LP on or off while on the
road discussions- Do you run with your LP on or off
77% of folks who took the pole do travel with the fridge on LP mode.

If you use DC mode on the refer while on the road going to your campground it -might- discharge your trailer battery somewhat.
My 1st trailer would do that and I am sure the trailer plug did have
pass thru engine charge voltage when it was plugged in.
It's just so far down stream from the engine alternator that voltage drop
over the distance resulted in the DC fridge sucking juice out of the trailer
battery.

Since you are camping with shore power your first 2 days any loss will
be replaced by your onboard power center Converter. It converts
120v ac to 12v DC and is specifically designed to charge your trailer
battery(s)

On day 3 just be sure the fridge is on LP mode and not DC mode and
you should be just fine. I doubt you'll need the genny at all but that's
where your learning from experience comes in to play. Try it and see.

Enjoy your camping trip!!
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Old 08-14-2014, 10:20 AM   #5
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Yes, the fridge running on 12V while towing can run down or even deplete the battery. If you are uncomfortable running on propane you should install a power cut off switch on the battery. But that must be done in a way that does not interfere with your breakaway switch operation. There is an old thread on that, but post a new question if you cannot find it or it does not address your concerns.

I run on propane when traveling. Some people shut off the fridge when pulling into a gas station. Something that is a good idea for the unlikely but possible set of circumstances where an open flame could ignite fumes.

My fridge/cooler use works something like this. In the fridge goes white wine, condiments, yogurt, preserved lunch meats and the like. Stuff that won't go bad if the temps rise into the 40s. I also put in a half gallon bottle of ice, or two. It helps moderate temperature swings from opening the door and provides cold water to drink. In the cooler goes cold drinks and stuff that has to stay very cold like uncooked fish or meats. Start with the meats frozen except for that nights dinner. YMMV

The comment above is incorrect, the fridge does not need 12V to run, as there are no electronics or auto ignition. He was referring to the larger fridges on bigger campers, not the small ones on our folding trailers.
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Old 08-14-2014, 10:43 AM   #6
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Here is an idea to see how your rig works. With the camper unplugged from the AC mains, disconnect the battery, connect to the running TV and turn on the fridge. Measure the DC voltage at the fridge. When I did this on a prior camper, it was about 8 volts, so I about 1/3 of the TV electrical supply went to line losses. The fridge is on a 20 amp circuit for a reason, it draws a lot of current.

Reconnect the battery and connect to the TV and measure your fridge voltage again. In my testing the voltage was higher. So I was draining power from the battery.
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Old 08-14-2014, 10:50 AM   #7
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Quote:
Originally Posted by Pooneil View Post
...The comment above is incorrect, the fridge does not need 12V to run. He was referring to the larger fridges on bigger campers, not the small ones on our folding trailers.

I'll admit I don't have one of the smaller fridges, but I don't see how that's possible. A control system requires electricity from somewhere. Without it, the fridge couldn't run. Same with the furnace, hot water, etc... They may use LP for the heating/cooling, which is the majority of their energy usage, but they still need 12v to run the controls that operate them.

To the OP: I assume your concern with running the fridge on LP is during transit? Or do you not want to use LP at all? If it's just during transit, I wouldn't worry too much about it. I've known some people who swear they can pack their fridge full of cold foods, and then drive 8 hours with the food perfectly fine. The key I hear is to pack the space so there's very little airspace. The fuller the fridge, the longer it supposedly stays cold.

If you're concerned it won't keep, then you could always use the DC, knowing that it'll take a chunk out of your battery. If your fridge has any kind of temperature control, then the more you turn it up, the less often the DC will be used to call for cooling.

Lastly, if you're really concerned, you could install a solar panel or two to the top of your camper that's exposed during transit. With a good set of panels and the right controller, you might be able to get just enough juice between them and the alternator on your TV to offset what's used by the fridge.

The solar route will also help down the line to minimize the need for a generator if your planing on doing a lot of boondocking.




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Old 08-14-2014, 11:19 AM   #8
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I'll admit I don't have one of the smaller fridges, but I don't see how that's possible. A control system requires electricity from somewhere. Without it, the fridge couldn't run...
There is a substantial difference in the small 3-way fridges used in pop-ups and A-frames, and the fridges in larger trailers.

The small 3-way fridges draw 6-7 amps on DC - continuously. There is no adjustment on DC - it's a fixed resistance coil, and no thermostat in the circuit. If the hitch wiring is reasonable, the tow vehicle will power the fridge without draining the camper battery(ies).

As was suggested, test the voltage with the fridge on DC will prove very enlightening. I would test the voltage at the camper battery with tow vehicle connected and on (and the fridge on). If less than 13 volts, the hitch wiring is not keeping up with the load and the fridge is draining the camper battery. Ideally, the voltage at the battery should be the same at tow vehicle and camper batteries.

On propane, the small fridges run continuously with the size of flame set by a knob on a gas valve. The fridge burner is lit manually by a piezio spark igniter when starting the unit on propane. There is no thermostat or ignition to draw DC power.

On AC, the resistance element is more powerful than the DC element. Again, there is no thermostat, just an SCR controller similar to a dimmer switch for incandescent lights in your home (only the more recent models have these, older versions had a fixed AC element).

Very simple - when using AC or propane, temp control is performed manually by dialing back the cooling when the fridge gets too cold (or turning the cooling up if it starts to warm).

Bottom line - there is no DC drain from the fridge when running on LP.

For the OP: I run on DC while towing. I switch to AC or LP as soon as I disconnect the tow vehicle. DC will only hold my fridge, it does not get colder. I usually reconnect the batteries (to charge them), plug the camper in, and run the fridge on AC (max cool) for 12-36 hours before a trip to pre-cool. That seems to work pretty well.

just my experiences with PUPs and A-frames
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Old 08-14-2014, 11:43 AM   #9
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There is a substantial difference in the small 3-way fridges used in pop-ups and A-frames, and the fridges in larger trailers.

The small 3-way fridges draw 6-7 amps on DC - continuously. There is no adjustment on DC - it's a fixed resistance coil, and no thermostat in the circuit. If the hitch wiring is reasonable, the tow vehicle will power the fridge without draining the camper battery(ies).

As was suggested, test the voltage with the fridge on DC will prove very enlightening. I would test the voltage at the camper battery with tow vehicle connected and on (and the fridge on). If less than 13 volts, the hitch wiring is not keeping up with the load and the fridge is draining the camper battery. Ideally, the voltage at the battery should be the same at tow vehicle and camper batteries.

On propane, the small fridges run continuously with the size of flame set by a knob on a gas valve. The fridge burner is lit manually by a piezio spark igniter when starting the unit on propane. There is no thermostat or ignition to draw DC power.

On AC, the resistance element is more powerful than the DC element. Again, there is no thermostat, just an SCR controller similar to a dimmer switch for incandescent lights in your home (only the more recent models have these, older versions had a fixed AC element).

Very simple - when using AC or propane, temp control is performed manually by dialing back the cooling when the fridge gets too cold (or turning the cooling up if it starts to warm).

Bottom line - there is no DC drain from the fridge when running on LP.

For the OP: I run on DC while towing. I switch to AC or LP as soon as I disconnect the tow vehicle. DC will only hold my fridge, it does not get colder. I usually reconnect the batteries (to charge them), plug the camper in, and run the fridge on AC (max cool) for 12-36 hours before a trip to pre-cool. That seems to work pretty well.

just my experiences with PUPs and A-frames
Fred W
2014 Rockwood A122
2008 Hyundai Entourage (minivan)
camped 3 weekends so far this year, Labor Day weekend at Ridgway

Ah, ok. So it is like I thought for the only way it could run on LP with no DC. It constantly runs. That's gotta be a real bugger to control. Do you have to constantly adjust it throughout the weekend? Like turning it down at night when the fridge remains closed and the ambient air is cooler, but turn it up during the day when it's hot out and the kids are constantly in and out?




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Old 08-14-2014, 12:51 PM   #10
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Ah, ok. So it is like I thought for the only way it could run on LP with no DC. It constantly runs. That's gotta be a real bugger to control. Do you have to constantly adjust it throughout the weekend? Like turning it down at night when the fridge remains closed and the ambient air is cooler, but turn it up during the day when it's hot out and the kids are constantly in and out?
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I donno what you're saying....
MY old 3 way power fridge manual said DC mode was ONLY FOR WHEN
THE TOW VEHICLE ENGINE WAS RUNNING as it was a power drain and
would deplete the trailer battery pretty quickly.
It also said DC mode would not cool as well as AC and LP.

When a fridge is on LP gas mode it still requires a small amount
of 12v power because the control board needs it to function.
It does NOT run (cool) all the time. Once the interior temp is cold enough
the LP will shut off.
If it's running (cooling) on AC 120v the board still needs 12v DC to operate.
Same as LP- it will shut off the AC heater once the inside temp is cold
enough to satisfy the "thermister" that sends signal to the control board
that it's cold enough.
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