3-Way Fridge vs AC DC Fridge? - Page 3 - Fiberglass RV


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Old 04-13-2016, 06:36 PM   #29
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My Norcold DE-704 with the swing compressor has an input of 12 vdc or 120vac.
The 12 volts runs an oscillator ar 60 hz. and has a transformer shared with the 120 vac with an output from the DC oscillator or the 120VAC of about 24 VAC at 60Hz.
The swing compressor is very sensitive to the frequency of the power going to it.
Many of these fridges don't work correctly because the oscillator has drifted off that 60 hz.
Some of these wont work on 12 vdc or don't work on 120vac.
The advantage of these units is that they don't have a current surge on starting.
The dorm fridges will work on an inverter, but it has to be a fairly large on to start.
I had a 300 watt inverter that would not start a 40 watt dorm fridge.
A cigarette plug in inverter about maybe 100 watt or less will run the Norcold on 12 volt easily, but the the thing will run on 12 VDC all by itself.
My long term test on power showed that it averaged about 17 watts over several weeks.
Also the fridge runs fine on power from the tow car and when stopped the trailer battery will also keep up easily.
Personally I prefer this to the propane/12/120 unit I had in a 1980 VW Westfalia camper years ago.
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Old 04-14-2016, 10:43 AM   #30
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One thing about battery driven fridges (or any other type), is that in the long run the watt/hours required to keep the fridge cool is exactly equal to the loss of heat from opening the door, leakage through the seals and leakage through the body of the fridge plus the heat discharged from the pipe containing the heating element. It's the law of conservation of energy. So, anything you can do to reduce heat loss will extend battery run time. When I remounted the fridge in our Trillium, I realized there was room surrounding the fridge, so I surrounded the fridge in 1" rigid foam insulation and sealed it well with tape. Also the better you can vent the top outlet of the pipe that contains the heater, away from the body of the fridge, the better.


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Old 04-14-2016, 10:48 AM   #31
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Quote:
Originally Posted by Raz View Post
Much of this discussion revolves around camping without hook ups. If one camps where AC is available most of the time, then a "dorm" fridge provides an inexpensive solution with a ice chest back up for the occasional off grid adventure.
Very valid point Raz and as the OP is located in BC where few Provincial Campgrounds have AC its something that needs to be given serious considered.
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Old 04-14-2016, 11:05 AM   #32
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I forget who it was that posted the fridge modification of hanging clear plastic or vinyl curtains in front of each fridge shelf. Sort of what like what might be in the doorway of a walk in freezer. It allowed owner to see where item was located and retrieve it without allowing all the cold air to spill out of the refrigerator. One approach to conservation of energy.

There have also been pictures of adding the extra insulation around the ice box. I'm pretty sure it was ice box but no reason it could not be done with a fridge too.
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Old 04-14-2016, 11:39 AM   #33
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There have also been pictures of adding the extra insulation around the ice box. I'm pretty sure it was ice box but no reason it could not be done with a fridge too.
I added the foil bubble wrap around the fridge in my Scamp and sealed off all the gaps in the rear compartment with tape and it did help somewhat its old fridge in warm weather.... but I suspect adding the fan to the rear compartment returned the biggest bang for the buck.
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Old 04-14-2016, 11:46 AM   #34
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I forget who it was that posted the fridge modification of hanging clear plastic or vinyl curtains in front of each fridge shelf. Sort of what like what might be in the doorway of a walk in freezer.
Several members on Escape Forum thought that was a good idea too, until they bought the product, installed it, and used it in practice. Ended up holding the door open longer, struggling to get some item off the shelf at the back, etc.
I'd save my money and just not open the door as often.
I still haven't convinced my wife to close the door while trying to remember why she opened it in the first place.
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Old 04-14-2016, 12:26 PM   #35
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On my Norcold Swing compressor fridge I added insulation in the form of 1/4" cork top, bottom and sides and styro-foam along the back against the outside wall.
The back of the fridge has an air channel for removing heat from the coils and I provided the "chimney" below and above with plenty of clearance.
I also added a small quiet computed 12 volt fan that is operated from the switched power to DC oscillator. This powers the fan to improve the heat transfer when running on 12 v DC. The fan only runs when the compressor is actually running on 12 V.
I can't speak for all of the swing compressors, but the fridge in my Scamp is the noisiest thing in the thing camper (TV possibly excepted or my wife's snoring) Shhh don't say a word!
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Old 04-14-2016, 03:21 PM   #36
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I installed a Norcold sawafuji swing motor fridge in my Scamp 16 and I agree. The mounting points for the compressor are hardened and the vibration transfers to the shell.
Sitting alone outside of the camper (mine is a freestanding marine variant) it is literally the quietest fridge I have NEVER heard. xD That all changed when it was pressed against the wheel arch. The very worst is when the AC and the fridge are both running. The two 60hz wave forms clash within the fiberglass shell. It's kind of like when two trucks or buses are idling next to each other. You get a loud sound that comes and goes. Sometimes it goes quiet as they cancel themselves out, other times it gets 5 times louder as they amplify the other. WHOOooooooooWHHOOOooooWHOOOoooo over and over. I have since fixed this by mounting both compressors in oil filled silicone bushings. The type used to mount optical drives.

I took the fridge apart and foam filled it, and I am also filling the entire cavity in the scamp around it with polyiso foam board insulation. I have one layer so-far.

Even with the noise as it was, I loved the DC compressor fridge compared to my 3 way propane one. That thing was just so picky it was almost never cold.
We had an awesome full size propane 2 way fridge in our class A RV that worked amazing though. It depends on a lot of factors.
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Old 04-14-2016, 03:30 PM   #37
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Oh I forgot to mention, my 55 amp tiny alternator keeps up with all of the loads I put it under while driving. If your trailer isn't charging off of your tow vehicle I HIGHLY doubt it is the alternators capacity that's the issue. Even my dinky 55amp alternator can run a 3 way fridge on DC. That's a LOT of power. Mine took some 200 watts. The actual reason that it won't keep up with the fridge, or won't charge the battery is voltage drop.
You can take care of that by using a boost regulator in the battery box as close to the batts as possible. Set it at 14.4 (or wherever you want) and feed that with the connection to your tow. Even if the voltage drops to 9v through the wires to get there, it will charge your battery. Just make sure that this is only happening when the key is on and engine running. Otherwise it WILL drain your vehicles starting battery at all times. Not good.

I use two more buck regulators (those drop the voltage) between my trailer brakes to reduce their power, and the other combined with a small microprocessor to reduce my furnace power consumption and noise by over half. I also have a custom pwm speed regulator for the furnace. Some folks have asked to buy them from me, which sent me down the path of my more recent and simplified approach with the buck regulators. The custom one was profiled for my exact furnace and sail switch etc. so I couldn't sell it and expect it to work for other furnaces.
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Old 04-14-2016, 04:18 PM   #38
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I know when I saw the gauge wire supplied in my brake controller wiring kit that it wasn't going to do much charging of my coach battery. It's a pretty long run from the truck alternator to the trailer battery, and the wire can't be more than 14 gauge...

I know when I was wiring my motorhome, I was looking at nothing smaller than 8 gauge wire for any charging needs.
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Old 04-14-2016, 04:23 PM   #39
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My stock trailer aux power wire included with my Geo/Suzuki Tracker drops voltage so badly that the 14.4 measured at my battery when running becomes 12.1 at the 7 pin connection. No load. Without the booster it's useless.
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Old 04-14-2016, 05:15 PM   #40
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When I installed the 12 power to the trailer in my 2013 VW Sprotwagen I used a 20 amp breaker ans a 30 amp relay to disconnect if the car was not running.
The wire I ran to the rear was #10 as was the wire from the brake controller.
(I had the wire already so why not a little overkill?)
On the Swing compressor I replaced the old hard rubber mounts with Sorbothane ones, but it didn't help a lot.
Sometimes the noise is louder than others I suppose the pressures are different with different temps.
You are correct in that the resonances between the fridge and the other thins are the most irritating.
My wife doesn't notice it, but knowing what is running etc I assume I am more attune.
The Norcold will keep stuff cold though not like the small 3 way in the old VW van camper. I think you could set the thermostat and freeze the whole box.
when I have checked the voltage (and current) at the trailer with various loads there is very little drop with my setup.
I installed some inexpensive power monitors so that I could tell what was going on with those pesky electrons.

These cost than $20 each. This is how I know that the fridge averages about 17 watt per hour in use.
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Old 04-14-2016, 05:24 PM   #41
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I have both of those monitors myself, great to keep an eye on what's going on.
I also have a Kill-a-watt for spot readings, and my pure sine inverter has an LCD readout too.

I am currently working on running 4/0 gauge cable from my batteries to a distribution bar behind said equipment. Every other 12v wire that will run anything more than my LED lights will be 8 gauge or better. I can't stand for any voltage drop with my solar and generator setup. Gotta be as close to zero drop as I can get.
I don't mind necking it down once it gets where it is going, as it isn't about raw amps for me. Just the resistance of the wire and subsequent voltage drop in distance.
It ends up being important when your charger thinks the voltage is one thing, but it's actually not.

Since you have the power from your vehicle going through a relay you may do well with a booster installed by the batter(y)ies on your trailer. Even 10 gauge wire will drop enough voltage to cut the charging way down from the alternator. Depending on the distance you drive at a time in hours, you could set the booster up to 15v and get a nice equalization charge from it. This will increase the life of your batteries dramatically. Just check the water level. If it's AGM 15.5 volts is better yet.
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Old 04-14-2016, 05:35 PM   #42
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I have the PD-4045 power unit that should take care of the battery when it is on charge.
I have a hankering for a solar system on the roof that would take care of the battery plugged in, driving, or free standing.
Most of my power distribution at 12 volts higher current is #6 with #6 for ground.
Many times people forget that the ground (-) is as important as the + side.
I have a good ground buss fabricated and each circuit has its own supply and return wires.

I put in two sets of terminal srtips and used most of the available fused outputs for individual circuits for pumps, lights, fridge,etc.
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