DC Fridge

[Over59]

Is anyone running on DC for the fridge while on the road.
I am about to get a fridge for "The Bat Cave Express". I like the idea of a three way but I don't see on the dometic site how much they draw (RM2663). They have a 30amps inline fuse and call for #8 wire for 25 feet from the battery. However, how much can I expect my truck (2005 2500 Duramax) to put back into the battery while going down the road give the truck wiring which I think may be #12 or #10. Will I be drawing down the battery. Would an inverter to the AC side of the fridge be a better option?

[scottanlily]

Hello Over59,

Lew will probably have your correct answer ,but it does depend on ,as you say ,the draw .from the fridge .Im sure a good rv store with a dometic catalog could tell you. now I am looking at some norcold fridges in my rv catalog from biils rv .It shows a n300 3 way ,draws 11.7amps @12v dc. its a 1.7 cu.ft. The largern510 5.5 cu. ft draws.14 amps at 12v dc, the big n400 3 way draws 14.2 amps.It appears that depending on your fridge size ,you will can draw 11 amps to 14 .Sorry no dometics are listed.Run the fridge on lp if it allows .My 60 trdwnd has a dometic not new,stays on ,always has.I have had no trouble and no 12v troubles.I would believe that it would work just fine with you chevys charging system .Your 10 gauge charge wire is fine. they want the power line from the fridge to the batteries to be 8 gauge ,but then it wont be 25ft away from the batteries will it?Now if you do the inverter the a/c draw is only about 2 amps ,even there big rv fridge is 2 amps seems that idea is a better one . 14 amp dc draw is decent size,youll note that most auto and truck fuses are 15, 20, and 30 amps (power windows or a/c on the 30 amp)tail ,stop signals interior lamps ,dash lamps etc. are on 15 or 20 amp fuses This is all for your comparison of what the fridge can draw. 14 amps is at the limit within 1 amp of blowing a 15 amp fuse but fine with a 20 amp fuse.I say that it will work , after all when driving at night your lights are all on, headlights on, wipers in the rain and the charging system handles all of that including charging the rv batteries and all the lights on your coach.The batteries should be fine and stay in a good state of charge. Now if you have the tow vehical umbilical unplugged and have the fridge going ,there will be power loses of course .you could and should install a 12volt amp gauge in the wireing to monitor your battery loads when power devices are on , Only then will you be able to see how much each appliance draws ,you can turn each device or appliance on 1 at a time and see.Long post Im sorry ,I hope this can help you.

Scott

[nickcrowhurst]

My Dometic takes 22 amps on 12 volt, which is too much for the charging system on my Dodge 3/4 ton truck. You will find several discussions on this by using the search facility. One is at http://www.airforums.com/forum...t=nick+dometic
These refrigerators rely on a heat source to boil the internal fluid. The same amount of heat, and hence, energy, will be required if you use an inverter for 12v/120v conversion or 12v direct. In fact, because of the % efficiency of the inverter, you would use slightly more.
Nick

[lewster]

Originally Posted by Over59

Is anyone running on DC for the fridge while on the road.
I am about to get a fridge for "The Bat Cave Express". I like the idea of a three way but I don't see on the dometic site how much they draw (RM2663). They have a 30amps inline fuse and call for #8 wire for 25 feet from the battery. However, how much can I expect my truck (2005 2500 Duramax) to put back into the battery while going down the road give the truck wiring which I think may be #12 or #10. Will I be drawing down the battery. Would an inverter to the AC side of the fridge be a better option?

Over59,

I think that the DC fridge was a bad idea from the start....way too much amp draw for most applications and you have to have a really big cable to get those little amps back to the DC heating element. As far as your Dodge powering it.....depends on the size of your alternator and the associated demands of your TV. I think that your idea of an inverter is a much better way to go. Use the +12VDC charge line that runs through your 7-way plug to keep your batteries up and the inverter will put out enough to power the fridge on AC. If you go this way, I would add a second battery (if you don't already have 2) and size the inverter to have twice the capacity you need to power the fridge. I personally like the Xantrex line of inverters. They have a huge selection of models and the prices have come way down for the lower wattage units. The spec on the fridge should tell you the wattage requirements of the AC heating element.

The other benefit to going 2-way is you have a much bigger selection of units. There are very few 3-ways made any more .

[jcanavera]

Originally Posted by Over59

However, how much can I expect my truck (2005 2500 Duramax) to put back into the battery while going down the road give the truck wiring which I think may be #12 or #10. Will I be drawing down the battery. Would an inverter to the AC side of the fridge be a better option?

I remember running the fridge on battery on my old Hi-Lo while towing. On our first long trip out we drove from STL to just west of Nashville Tn. It was close to 95 degrees so I'm sure the fridge was pulling a goodly amount of amperage. Well, we get to our site, I unhitched and pushed the button on the Hi-Lo to raise the top up. All I heard was a groan with little lift. I quickly diagnosed that the battery is dead. To make matters worse, even though I plugged into the electrical outlet at the campsite, the charger in the trailer wasn't putting enough voltage back into the battery fast enough, to run the sizable motor that was used to power the hydraulic ram which was connected to the lift cables. It ended up I turned the car around and used my jumper cables to jump the trailer battery and get enough voltage to raise the top.

When I went to diagnose the original problem I found that the 12 volt feed contact in the trailer plug was somewhat corroded and therefore not providing a good clean connection. From that point on I learned to make sure the outlet on the TV and the plug on the trailer were clean before going on a trip. Bottom line you have to have a good amperage flow from the TV to the trailer battery to keep enough charge in the battery to support that DC refrigerator. A dead battery is not the end of the world, unless you are boon docking, but obviously it will put a damper on the life of a deep cycle if you continue to discharge it fully.

Jack

[markdoane]

I believe that most TV charging systems cannot push enough power to the house batteries to run a Dometic.

If you look at the voltage drops from the alternator, through an isolator, through 20 to 40 feet of #10 wire, and a corroded umbilical cord plug, I think you would be lucky to have 12.5 volts at the house battery. That's not enough to charge the battery. You'd need to put a lot of thought into design and wire sizes to make it work efficiently.

If you want a regular compressor refrigerator that runs on 12V and uses very little (6 amps) juice, you need to buy a NovaKool. Bring your checkbook!

[overlander64]

The first RV that I purchased new came with a 3-Way refrigerator in 1980. Since then, I have always insisted upon the 3-Way refrigerators in my RVs -- it was something of a relief when it came time to replace the 2-Way refrigerator in my '64 Overlander with a modern 3-Way Dometic. In the 25+ years that I have utilized these 3-Way refrigerators, I have never had a problem when traveling -- I always remind the dealer about the 3-Way refrigerator when a "new" tow vehicle is prepared for towing -- and as Jack mentioned, I also keep close tabs on all of my 12-volt connections. Most of my travel is limited to the hot, Midwestern summers, and often I am on the road for seven or eight hours with no problems. I very rarely boondock as air conditioning is a requirement during Midwestern summers so the coach battery is replenished each night by the power converter. My Overlander also has solar panels, but even with my prior coaches that relied only on the house battery I didn't experience any problems with battery capacity.

With certain tow vehicles, particularly my pre-1980 Chrysler product, it was necessary to adjust the voltage regulator output. I haven't encountered any problems with my GM tow vehicles (1975-1999) once they have been properly wired.

I know based upon my past experiences, the 2-Way Dometic in my Minuet is history the first time it gives me any trouble; and its replacement will be a new 3-Way Dometic.

Good luck with your research and refrigerator selection!

Kevin

[scottanlily]

Hello everyone,
22amps is quite a draw , the new norcolds I posted about didnt come close to that ,at least their claim in the specifications. Jcanavaras problem was absolutly the corroded 12v feed wire . the batteries most likely were not getting much of any charge ,how old and how fully charged were they to begin with? I would also recommend a colehersey (brand name) solenoid instead of an isolator (those blue units) They are used in many heavy duty applications to isolate batteries and keep them charged up. I use one on the travelall to provide charging power to the trailer house battery , i have 14volts present the battery ,charging from the travelall.Turn off the ignition and the solenoid shuts off conection is terminated, the house battery cannot draw or drain the tv battery.The isolator terminates the connection also ,but those isolators take 1volt of current to operate ,Just put a voltmeter on your outlet terminals ,there will only be about 13.00 to 13.50 volts present easy to test and its a problem. that extra volt is lost to your tv battery also .The solenoid is used all the time with dual battery installations .It is enough loss to cause poorly charged batteries . the best rate of charge you need is about 14.00 to 14.50 and no more Go higher and overcharging is a result .Bad for the batteries .We have all heard about dead rv batteries ,blue isolators ,you need that lost volt!

Scott of scottanlily

[lewster]

The best company I have found for isolators and separators (depends on your alternator and the application) is Sure Power in Oregon. They are direct manufacturers and their tech dep't. is excellent. Give them a call or check them out at www.surepower.com.

[uwe]

Originally Posted by jcanavera

When I went to diagnose the original problem I found that the 12 volt feed contact in the trailer plug was somewhat corroded and therefore not providing a good clean connection. From that point on I learned to make sure the outlet on the TV and the plug on the trailer were clean before going on a trip.

There-in lies the heart of the problem. The 7-way flat trailer connectors are rated at only 20A continuous. Add to that a little dirt, corrosion, and undersized factory wiring, and it's bound to fail.
A much better ( unfortunately non-RV standard) solution are the 7-way round connectors, rated at 30A continuous, and 80A peak.
I use them in my rig, as my hydraulic brake requires 30A capacity to conform to factory specs. I also beefed up the factory charge wire, by running a second, 10ga parallel to the 12ga in the loom. I have excellent, and trouble free charging and energy transfer now, surely able to supply 20or so amps to a 12V fridge element. My burb has a 140A alternator with teh factory tow package, if I'm not mistaken.
I think the problem lies not in the 3-way fridge, but rather in the lack of proper preparation for it by the RV owners that had bad experiences with them. After all, 22A is not that much, certainly not more than running headlights and foglights at the same time.

[Chaplain Kent]

We have a three way in Chummy and use it all the time. My understanding from Dometic is that it will not cool the unit on DC but will help maintain the cold during the driving times. I was also told that Dometic will no longer be making a three way.

[scottanlily]

Hello uwe,

The 22amp is is a fair load ,most of your fuses are 15 or 20 amp. You have main fuses to handle your headlights ,alternator ,high load items ,they are 30 ,50,or 80 amp .Your correct about the trailer connector rating,not surprising as 22 amps is a decent load and your 20 amp fuses blow when they are exceeding the rated amps.The ecm is on a 20 amp fuse in the fuse center under the hood ,most power draws in the vehical dont exceed 20 amps,except the a/c compressor and your brake system . what kind of master cylinder setup operates those hydralic brakes?Your fuse for that 30 amp brake load has to be a 40 0r 50 amp .

scott

[uwe]

Originally Posted by scottanlily

Hello uwe,

The 22amp is is a fair load ,most of your fuses are 15 or 20 amp. You have main fuses to handle your headlights ,alternator ,high load items ,they are 30 ,50,or 80 amp .Your correct about the trailer connector rating,not surprising as 22 amps is a decent load and your 20 amp fuses blow when they are exceeding the rated amps.The ecm is on a 20 amp fuse in the fuse center under the hood ,most power draws in the vehical dont exceed 20 amps,except the a/c compressor and your brake system . what kind of master cylinder setup operates those hydralic brakes?Your fuse for that 30 amp brake load has to be a 40 0r 50 amp .

scott

The hydraulic brakes are operated by an electric/hydraulic actuator. Basically, an electric motor and a hydraulic pump, coupled to a small control unit inside the motor part. It is conected to the trailer batteries and charge line via a 30A fuse as per Dexter's instructions.

[Over59]

Have a new Norcold N600 3 way. I'll see what the trimetric says is draws once it's in the trailer. Figure I'll run a dedicated fused #6 charge line back from the alternator or other those big labeled lugs with a switch and a separate plug hookup to the trailer. Have to find a plug/Socket set that will work. Think I'll put a relay on the trailer side so the fridge cann't draw battery juice if the alternator isn't putting out. Not sure how to do that but seems like the right approach.

Thanks for the input.

[uwe]

Originally Posted by Over59

Have a new Norcold N600 3 way. I'll see what the trimetric says is draws once it's in the trailer. Figure I'll run a dedicated fused #6 charge line back from the alternator or other those big labeled lugs with a switch and a separate plug hookup to the trailer. Have to find a plug/Socket set that will work. Think I'll put a relay on the trailer side so the fridge cann't draw battery juice if the alternator isn't putting out. Not sure how to do that but seems like the right approach.

Thanks for the input.

No need for the separate plug hookup, if you use the old Airstream style 7-round connector at the TV and trailer's umbilical cord. They have a high enough rating for your refrigerator's 12 V needs.
Running a 6 or 8 ga from the battery Truck's battery back to the charge connector might be a good idea.
You can use a diode and a 30A relay to disable the 12V to the fridge when the tow vehicle is unplugged. I have a diagram for this somewhere, need to look for it and post it for you.
The fridge's 12V draws only little more than a pair of powerful offroad lights, 150W or so. It is not really a major draw.

[Over59]

Diodes is one of those things I never want to meet in a dark alley. They are oneway do dahs? "The Bat Cave Express" design is optimized for being "on the road". That's why the 12volt fridge. I didn't want gas on while making an 8 to 10 hour run. The schematic would be helpful.
I'm thinking I want to come off the alternator so I don't run the risk of draining the truck batteries while stopped over night without disconnecting. That's probably one of those diode issues again?

[uwe]

Originally Posted by Over59

Diodes is one of those things I never want to meet in a dark alley. They are oneway do dahs? "The Bat Cave Express" design is optimized for being "on the road". That's why the 12volt fridge. I didn't want gas on while making an 8 to 10 hour run. The schematic would be helpful.
I'm thinking I want to come off the alternator so I don't run the risk of draining the truck batteries while stopped over night without disconnecting. That's probably one of those diode issues again?

Diodes are nothing more than electrical check valves. Current flows one way only. Properly dimensioned, they are rarely a cause of trouble.
The Alternator is typically parallel to the battery, meaning that if you hook up to the alternator, it will still draw down your battery if you forget to disconnect with the fridge on 12V. Maybe some sort of battery isolator coul dbe amployed?
Another way to disconnect the 12V as soon as the engin is turned off, is to use a fuel pump safety relay. Those relays read engine dwell ( or ignition rpm) and turn off as soon as the motor stops. But then you might as well wire a relay in the ignition circuit, which turns off when you turn the key off.
I can't see how you can provide an automated 12V management for your fridge without some sort of electronic device. You will have to somehow modify your tow vehicle's wiring to accomodate this.

I agree with your concern that each and every system that is added to the trailer/tow vehicle at some point can fail and cause you grief.

[scottanlily]

Hello Over59,

I recommend a cole hersey (brand name) solenoid to isolate your draw issues on the truck batteries.Large cable off alt stud to isolator one side large stud,then large cable from isolator other large stud back to airstream or your feed to fridge.Small terminal is key on power only from a fused 20 amp circuit .Key on ,solenoid on power flows to fridge ,key off alternator is isolated as are the batteries in the truck .I use this same solenoid for my 12volt needs and my travelall battery never can be drained by the trailer or its 12volt sources.I do not use any blue isolator as sold by rv outlets. they require 1 full volt of power to operate so you can not get more than 13.50 volts to your truck or rv batteries. they work excellent in dual battery installations as well.uwe has the same idea of thinking as well.
Scottof scottanlily

[bhayden]

Originally Posted by Chaplain Kent

We have a three way in Chummy and use it all the time. My understanding from Dometic is that it will not cool the unit on DC but will help maintain the cold during the driving times. I was also told that Dometic will no longer be making a three way.

Ah, so maybe my Dometic is actually working as intended. On AC it seems to cool pretty well. On DC it sort of maintains the cool (I think, kinda sorta . Haven't yet been able to test out LP gas operation. The controls are less than intuitive (i.e. a button that says "manual" or "auto" but no sign of a switch that controls operation when it's on "manual).

Seems like moving a frozen water bottle from the freezer to the fridge is a must while traveling. I'll have to try running it on 12V in the driveway for a while and monitor battery voltage. If it's attempting to maintain a constant power draw then amperage is going to go up as the battery voltage drops. If it's constant amperage then the already limited cooling will be almost non-existant in short order unless the battery is on a charging circuit.

-Bernie