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I have a 2004 National  Tropi-Cal T396 the refrigerator works on AC power or propane brand Dometic when going down the road I do not use the propane an the fridge is not connected to the inverter I have used the generator to power the fridge .Can the fridge be wired to the inverter safely ? Or does the heater on the fridge when turned on to ac draw to much power ? I am not sure of the size of alternator , do not have solar ,do have 4 interstate deep cycle 6 volt batteries . Your thoughts .thanks Rick

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Lots of people run the motorhome  generator running down the road since the roof air cools better than the dash air and you should run your generator under load monthly for 2 hours if you can.  Your inverter needs to be a pure sinewave one for many fridges to run properly, otherwise they could burn out.  If you have a standard built-in inverter (or inverter/charger) it is probably modified sinewave, so you would need to replace it with a pure sinewave one or add a pure sinewave one just for the fridge for $200 or more. 

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Some of the mechanical compressor refrigerators will require PS, some will run on MSW.  The heater on an RV fridge does not matter.

Ken

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4 minutes ago, Rick i Carter said:

Thanks for the input I will get a hold of xantrex an see if my inverter/charger is a pure sinewave .Rick

I've been running our chest freezer and dorm refrigerator on a Xantrex modifided sinewave inverter for years without any problems, not all modifided inverters are created the same. The cheap ones are a square wave and the higher end ones like Xantrex a step wave. I also run out TV, sat dish and reciever off the same inverter.

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Rick, there are a few issues that need to be ironed out ...................

1) If your fridge is a combination LP Gas or Electric RV Absorption unit, NOT a 120 VAC Compressor, as I infer from your post;

     Many run them on LP gas while driving, while others don't for various safety concerns, but that's YOUR choice, it can work

     Some run them on 120 VAC using the onboard Genset while driving, AGAIN that's YOUR choice, it can work but its NOT my preferred method................

     NOTE if its an Absorption type, NOT a 120 VAC compressor power, a cheaper Modified Sine Wave MSW (or sure a  Pure Sine Wave PSW) Inverter can supply the pure resistive heater NO PROBLEM. The heater will work and supply heat regardless if MSW or PSW 120 VAC is applied. IE you can get by with a cheaper MSW Inverter if its only job is to power the fridges resistive heating element 

    HOWEVER if its a 120 VAC Compressor fridge I recommend PSW over MSW, even if MSW may work

    If starting from scratch I would definitely use a PSW Inverter to avoid worries in the future.

2) If its an Absorption unit and you choose electric over LP gas using your battery power and an Inverter while driving, the Inverter and your house batteries can power it PROVIDED your alternator has the capacity PLUS you have a system so your alternator is furnishing charge to the house batteries while driving. I prefer a DC to DC charger in that situation which protects the alternator plus provides a decent quality charge to the house batteries. 

 Are you set up so the Alternator (if it has sufficient capacity) provides charge to the house batteries when driving???? If so and its done properly to protect the alternator and furnish adequate charging to the house batteries while driving, sure you could use the house batteries and Inverter to run the fridge on electric when driving to avoid using LP Gas...  

FWIW My preferences if its a combination LP Gas or Electric Absorption fridge would be LP gas while driving, although sure its safer if you run it on Electric using your house batteries and Inverter PROVIDED THAT you have a system so the alternator is charging the house batteries while driving.  

PS some people just shut the fridge OFF when driving if not too long and turn it back on once they're plugged in at the campground. LOTS OF WAYS TO DO THIS. Or let the house batteries run the inverter and fridge without any alternator charging so long as they dont drop below 50% SOC 

Got it??

John T

Edited by oldjohnt
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1 hour ago, Rick i Carter said:

Thanks for the input I will get a hold of xantrex an see if my inverter/charger is a pure sinewave .Rick

You can do that by looking up the model number, you don't need to contact  them.  Although you clearly said your refer is NOT a residential, I think there's still some confusion here.

Edited by hemsteadc
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20 hours ago, hemsteadc said:

Although you clearly said your refer is NOT a residential, I think there's still some confusion here.

He said  "works on AC power or propane"...  I'm not familiar with "Residential" fridges that can run on propane, but hey I haven't seen them all and its never too late to learn if any exist ???? of course, such a fridge (if ran on propane) would need appropriate venting. I agree the model number is a good way to find the answer. 

Take care n stay safe yall

John T

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7 hours ago, hemsteadc said:

Yes, most Dometics are like that.

Indeed when he posted "works on AC power or propane" PLUS also mentioned "Dometic" (Like you ones I've seen are like that) and since I haven't seen any "Residential" fridges that ran on Electric plus Propane, I didn't think there was some confusion (I figured it was a typical RV Gas or Electric fridge instead of a residential) but hey a person never knows and I'm never too old to learn lol.... 

Pleasure chatting with you, keep safe now

John T

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Whatever the 120VAC amp-draw of the refrigerator is, the inverter will draw 10X that much DC amperage from the battery bank.

 

2000 Winnebago Ultimate Freedom USQ40JD, ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG retired;Good Sam Life member,FMCA ." And so, my fellow Americans: ask not what your country can do for you--ask what you can do for your country.  John F. Kennedy 20 Jan 1961

 

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On 5/11/2020 at 11:05 AM, oldjohnt said:

Rick, there are a few issues that need to be ironed out ...................

1) If your fridge is a combination LP Gas or Electric RV Absorption unit, NOT a 120 VAC Compressor, as I infer from your post;

     Many run them on LP gas while driving, while others don't for various safety concerns, but that's YOUR choice, it can work

     Some run them on 120 VAC using the onboard Genset while driving, AGAIN that's YOUR choice, it can work but its NOT my preferred method................

     NOTE if its an Absorption type, NOT a 120 VAC compressor power, a cheaper Modified Sine Wave MSW (or sure a  Pure Sine Wave PSW) Inverter can supply the pure resistive heater NO PROBLEM. The heater will work and supply heat regardless if MSW or PSW 120 VAC is applied. IE you can get by with a cheaper MSW Inverter if its only job is to power the fridges resistive heating element 

    HOWEVER if its a 120 VAC Compressor fridge I recommend PSW over MSW, even if MSW may work

    If starting from scratch I would definitely use a PSW Inverter to avoid worries in the future.

2) If its an Absorption unit and you choose electric over LP gas using your battery power and an Inverter while driving, the Inverter and your house batteries can power it PROVIDED your alternator has the capacity PLUS you have a system so your alternator is furnishing charge to the house batteries while driving. I prefer a DC to DC charger in that situation which protects the alternator plus provides a decent quality charge to the house batteries. 

 Are you set up so the Alternator (if it has sufficient capacity) provides charge to the house batteries when driving???? If so and its done properly to protect the alternator and furnish adequate charging to the house batteries while driving, sure you could use the house batteries and Inverter to run the fridge on electric when driving to avoid using LP Gas...  

FWIW My preferences if its a combination LP Gas or Electric Absorption fridge would be LP gas while driving, although sure its safer if you run it on Electric using your house batteries and Inverter PROVIDED THAT you have a system so the alternator is charging the house batteries while driving.  

PS some people just shut the fridge OFF when driving if not too long and turn it back on once they're plugged in at the campground. LOTS OF WAYS TO DO THIS. Or let the house batteries run the inverter and fridge without any alternator charging so long as they dont drop below 50% SOC 

Got it??

John T

 

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Great input team thanks,I have found out my xantrex is a modified sinewave an to run the refrigerator safely it should be a pure sinewave .So on long trips I will turn on generator an then turn on fridge. I have been going to California desert for approx 34 years an have always cooled fridge down at home an then relight once to the desert an this has worked .We have recently retired an have bought a DP which had a inverter none of my other rigs had a inverter .And to clarify the fridge is not a residential style it is a Dometic runs on propane or ac power.I did just notice late last night the cooling unit on fridge was changed out in 2012 an my motorhome is a 2004.thanks Rick

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Thanks for the update. Hey whatever works best for you sounds like a good plan. While there are certain appliances that may not fare well using a MSW inverter, most any appliances do fine using a PSW, so why take a chance if there's any room for reasonable doubt.

John T  Self quarantined and getting bored grrrrrrrrrrrrrrrr

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I was holding off responding to this thread because the other responses were giving the information needed, but I can’t let it go anymore.

The 120 volt heating element of a gas absorption refrigerator is a high energy draw (like all electric heating elements).  When I install inverters, I never hook high draws like that to the inverter (electric side of RV fridge, electric side of RV water heater, etc.) unless there is a specific need and the battery bank and charging system (typically solar) are scaled large enough to handle such high loads.

I would be surprised if your inverter is wired to actually run the electric side of the refrigerator in your RV as this is not typical (even in a whole house inverter system) in most inverter installs.

You haven’t described what supporting components you have to go along with the inverter; like how large a battery bank you have, whether you have solar to augment the charge in the batteries, what size Xantrex inverter you have, what type of battery monitoring you have, or if you are going to rely on your vehicles alternator to charge the batteries alone.

Based on the information provided so far, I am assuming you do not have solar (as it has not been mentioned).  I’m also assuming you have a fairly standard house battery bank (because nothing has been said about it) which is usually a couple of six volt deep cycle batteries.  I don’t know if you have battery monitoring or not, but if your system was a factory install it is a crap shoot whether it was installed or not.  If these assumptions are the case (or even close), I would not recommend running your refer on the inverter (assuming it is even wired to power the refer).  I think you will find a small battery bank with only the alternator to recharge it will have a hard time keeping up with the power needs of running an RV refrigerator from an inverter over long periods (like an all day drive).  You would definitely need a battery monitor at the very minimum to make sure you do not draw down your batteries too much (something like a Trimetric or Victron BMV).

I would much rather run the refrigerator on propane than try running it on AC through an inverter (again assuming a standard battery bank with no augmented charging like solar).  The propane will be much more power efficient and ensure you have sufficient battery power when you arrive at your destination.

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9 hours ago, Chad Heiser said:

I would much rather run the refrigerator on propane than try running it on AC through an inverter

Chad, MAJOR DITTO 

As an electrical engineer and 49 year RV owner I also prefer and have ran my RV fridges on LP Gas for yearssssssssssss when dry camping or driving..........To power using batteries and Inverter SURE it can work (I've done it, but I have plenty of batteries and Inverter and re charge capacity) if he has enough battery capacity and enough re charging capacity. If not, then I wouldn't go that route. 

There are people who don't like to run on LP Gas when driving (so must use electric) and I understand and respect their opinion and choice. If they have enough Battery and Battery re charging capability and sufficient Inverter HEY THEY CAN GO FOR IT if they like, their choice sure not mine lol.

Of course,  what power the fridges heating element requires when running on 120 VAC MAKES A HUGE DIFFERENCE AND IS MOST RELEVANT !!!!!!!!!!!!!!!!!   

FWIW I don't consider the resistive heating element in an RV fridge as any HIGH POWER device like a heater or microwave or coffee maker etc which may be 1000 or 1500 watts. I don't have the specs but believe it may be less then 500 watts, is it 300 ? is it 400 ?    THEREFORE, if a person has enough battery and battery charging capacity and if indeed ????????? the heating element isn't a 1000 or 1500 watts like a heater ENOUGH BATTERY AND RECHARGING CAPACITY CAN ENABLE IT TO BE INVERTER POWERED...  But I still use and prefer LP Gas when dry camping. But if it were 1000 or 1500 watts THEN ITS MUCH HARDER TO RUN USING BATTERY AND INVERTER POWER albeit still certainly possible given adequate batteries and charging capacity...  

I Wonder how may watts his fridges heater requires ??????????????????? Anyone have that spec????  (Talking LP and Electric here NOT any compressor powered fridge) Is it 300 or 400 or more Watts ???? 

 NOTE Ricki

PS if the 120 VAC is ONLY to provide power to heat up a pure resistive heating element THEN EITHER A MSW OR PWS INVERTER CAN WORK FINE. HOWEVER IF YOU HAD A 120 VAC COMPRESSOR TYPE RESIDENTIAL FRIDGE THEN ID WANT A PSW 

Its a pleasure sparky chatting with you  

John T   Quarantined n bored grrrrrrrrrrrrrrrrrrrr

Edited by oldjohnt
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6 hours ago, Rick i Carter said:

Great input team thanks,I have found out my xantrex is a modified sinewave an to run the refrigerator safely it should be a pure sinewave .So on long trips I will turn on generator an then turn on fridge. I have been going to California desert for approx 34 years an have always cooled fridge down at home an then relight once to the desert an this has worked .We have recently retired an have bought a DP which had a inverter none of my other rigs had a inverter .And to clarify the fridge is not a residential style it is a Dometic runs on propane or ac power.I did just notice late last night the cooling unit on fridge was changed out in 2012 an my motorhome is a 2004.thanks Rick

An RV absorption fridge works perfectly fine on an MSW inverter. The electric resistance heater is not fussy...

Dutch
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1 hour ago, Dutch_12078 said:

An RV absorption fridge works perfectly fine on an MSW inverter. The electric resistance heater is not fussy..

AMEN DUTCH FWIW I agree 100% The heater is PURE RESISTIVE there's no inductance or capacitance involved so MSW or PSW will cause it to produce heat regardless.  

 

John T

Edited by oldjohnt
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oldjohnt, my Norcold 1200 two 120VAC resistance heaters draw 380W each. Discounting the efficiency rate of his Xantrex the draw on the battery bank is approx. 10X that. Am I right?

Edited by Ray,IN

 

2000 Winnebago Ultimate Freedom USQ40JD, ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG retired;Good Sam Life member,FMCA ." And so, my fellow Americans: ask not what your country can do for you--ask what you can do for your country.  John F. Kennedy 20 Jan 1961

 

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9 hours ago, Ray,IN said:

oldjohnt, my Norcold 1200 two 120VAC resistance heaters draw 380W each. Discounting the efficiency rate of his Xantrex the draw on the battery bank is approx. 10X that. Am I right?

Hey Neighbor Ray, how are things in your neighborhood ?? You know I sold the farm and moved out on Whitehall Pike ?

1) That figure of 380 Watts per heating element in a LP/Electric fridge sounds reasonable. Many fridges I've used over 49 years have only one such element (Yours is much bigger then mine lol) . Seems like they may be the 300 + or so watt range, BUT I HAVE NO SPECS OR DATA   no warranty !!! yet still don't consider them high energy 1000 or more watts like a heater etc. which aren't good or very feasible/reasonable for use with battery and inverter.

2) YES you are about right in your computation that every amp at 120 VAC would require 10X (120/12)  or 10 battery amps HOWEVER due to inefficiency and heat losses I always use a conservative rule of thumb approximation that for every amp at 120 VAC it takes 11 Amps at 12 VDC................... Since 120/12 = 10, sure 10X is a reasonable rule of thumb

NOTE As far as using battery and whatever re charge capacity (Solar or engines alternator) you have to power a fridge using an Inverter I ONLY SEE THAT AS FEASIBLE/POSSIBLE  WHEN DRIVING (alternator can keep up the 300+ watts charging) OR IF YOU'RE USING SOLAR TO CHARGE .

If you're NOT driving (alternator can safely deliver the necessary fridge power)  or you're NOT parked in the sun (Solar can deliver sufficient charging) I RECOMMEND USING LP GAS PERIOD...... Even if the fridge heater was as low as 300 watts and especially if it was 500+,  RUNNING ON BATTERY AND INVERTER  WHEN THERE'S  NO SOLAR OR ALTERNATOR CHARGING ISN'T A GOOD IDEA !!!!    

Keep safe neighbor

John T

 

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14 hours ago, Ray,IN said:

, my Norcold 1200 two 120VAC resistance heaters draw 380W each. Discounting the efficiency rate of his Xantrex the draw on the battery bank is approx. 10X that. Am I right?

I think I know what you meant, but, no, it's not 10x 380w.  The wattage doesn't change.

Edited by hemsteadc
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