Run 12v/propane refrig on inverter while driving?

[chriscowles]

Please do not turn this topic into a debate about using propane while driving. I have done that but am exploring alternate approaches.

Our near-future 2507S will have a propane/AC refrigerator. I'm contemplating the wisdom (or stupidity) of using an inverter to power it on AC while driving. Yes, it would kill the trailer batteries in short order if used as wired at the factory. I'm exploring whether I could run wire of sufficient capacity from the front of the truck back to the trailer, to prevent that.

I'd probably replace the Aux 12V aux wire on pin 4 of the trailer connector with a larger gauge. Yes, I know it would have to be very large to mitigate voltage drop. I'd create a circuit in the trailer specifically for that purpose and use the inverter only when actually driving. When stopped, I'd switch to gas. The wire from the truck would incorporate a relay to avoid inadvertently draining the truck battery.

Is this a numbskull idea? If not totally stupid, what capacity would the inverter have to be to power only the refrigerator? What gauge would the wire from the front of the truck to the inverter have to be?

Would it be more efficient to have the inverter at the front of the truck and run AC to the back? I could install an AC outlet at the refrigerator used solely for that purpose and just move the plug when traveling. I'd put it back into the standard plug for normal use. That avoids having to adapt existing wiring in any way. Alternatively, a DPDT switch of some kind could make that easier but I'd have to be certain it would not cause electrical damage to me or anything in the trailer.

[67L48]

Sounds like an interesting project. PUPs have 3-way fridges that can select 12 VDC. I'm not sure why TTs only have 2-way fridges. Speaking in 100% ignorance, I'm wondering if you could borrow from the circuitry design (and maybe even actual components) of how those smaller 3-way fridges work to draw off the 12 VDC side.

The other thought is the necessity of the project. How far are you driving?

I start by cooling down the fridge the night before, so everything is ice cold.

From there, I have found the fridge is a pretty darn good cooler. Within our normal drive (2-4 hours), I can't tell that we've lost any significant temperature.

If we're driving longer distance (6-8 hrs), I'll put any raw chicken in the freezer and I may add a couple of 1 gallon bags of ice inside. Works like a charm.

Maybe this isn't as effective in the larger refrigerators, though.

Good luck and let us know how the project goes.

[Mountndream]

not sure your purpose in doing this but...


would one of the newer 12v only refrigerators better serve your purposes


Think they are Everchill brand

[tomkatb]

Typically they install a 1000 watt inverter for a fridge.

Check the specs of the fridge. They are online.

Inverters come in quality levels. You would be better off with the higher efficiency models. 10 % loss rather than 20%.

Installing an inverter remember that 12 line loss is ridiculous compared to 110. I.E. you want the absolute minimum 12 volt wire lengths. Also bigger wire is better! Less loss. 2/0.

Get the biggest capacity batteries you can. 6 volts have smaller footprints and are more durable. A couple of Costco sixes are over 200 amps. 100+ usable. Might be enough most of the time. Lithium is better but pricey.

Trucks typically have big alternators. Running a big wire to the trailer would work. Lots of work but not a lot of money.

Inverter plus wire and fuse, .$200.

Costco batteries $210.

New power lead $100 (big guess). Wire plus fuse.

[chriscowles]

Originally Posted by Mountndream

not sure your purpose in doing this but...


would one of the newer 12v only refrigerators better serve your purposes


Think they are Everchill brand

Thanks, but that wouldn't be an efficient choice for my purpose.Those refrigerators draw a lot of power. Yes, I realize I'd be drawing similar power levels while driving but that would be supported by the generation power of the truck.

I want to use propane whenever I don't have shore power. Otherwise I'd chew through my batteries every night. If I were somewhere cold and wanted to run the furnace, I doubt I'd even get through the night.

[chriscowles]

Originally Posted by tomkatb

Typically they install a 1000 watt inverter for a fridge.

Is that inverter spec'd for a 'residential' refrigerator that doesn't use propane? Or to power a heating element that substitutes for a propane flame?

[chriscowles]

Originally Posted by 67L48

Sounds like an interesting project. PUPs have 3-way fridges that can select 12 VDC. I'm not sure why TTs only have 2-way fridges. Speaking in 100% ignorance, I'm wondering if you could borrow from the circuitry design (and maybe even actual components) of how those smaller 3-way fridges work to draw off the 12 VDC side.

The other thought is the necessity of the project. How far are you driving?

I start by cooling down the fridge the night before, so everything is ice cold.

From there, I have found the fridge is a pretty darn good cooler. Within our normal drive (2-4 hours), I can't tell that we've lost any significant temperature.

If we're driving longer distance (6-8 hrs), I'll put any raw chicken in the freezer and I may add a couple of 1 gallon bags of ice inside. Works like a charm.

Maybe this isn't as effective in the larger refrigerators, though.

Good luck and let us know how the project goes.

I'm aware of 3-way refrigerators from my PUP days and was surprised to learn they weren't available for TTs when we bought a hybrid 5 years ago. Perhaps it's a capacity issue? The heat needed to run a refrigerator that size may surpass what a battery can reasonably do.

This is a future project. We'll be taking long distance trips over several weeks, possibly a few months. Some days may be long hauls.

[dahagen]

I don't understand the question here. If the fridge is 110/propane (like most RV refers) why not run on propane when no AC is available instead of going to all the work to install a 110 volt inverter system?

[chriscowles]

Can anyone tell me what model of refrigerator is in late model Mini-/Micro-Lite trailers? I'll look up the power specs online, as suggested.

[Larry-NC]

Originally Posted by chriscowles

Please do not turn this topic into a debate about using propane while driving. I have done that but am exploring alternate approaches.

Our near-future 2507S will have a propane/AC refrigerator. I'm contemplating the wisdom (or stupidity) of using an inverter to power it on AC while driving. Yes, it would kill the trailer batteries in short order if used as wired at the factory. I'm exploring whether I could run wire of sufficient capacity from the front of the truck back to the trailer, to prevent that.

I'd probably replace the Aux 12V aux wire on pin 4 of the trailer connector with a larger gauge. Yes, I know it would have to be very large to mitigate voltage drop. I'd create a circuit in the trailer specifically for that purpose and use the inverter only when actually driving. When stopped, I'd switch to gas. The wire from the truck would incorporate a relay to avoid inadvertently draining the truck battery.

Is this a numbskull idea? If not totally stupid, what capacity would the inverter have to be to power only the refrigerator? What gauge would the wire from the front of the truck to the inverter have to be?

Would it be more efficient to have the inverter at the front of the truck and run AC to the back? I could install an AC outlet at the refrigerator used solely for that purpose and just move the plug when traveling. I'd put it back into the standard plug for normal use. That avoids having to adapt existing wiring in any way. Alternatively, a DPDT switch of some kind could make that easier but I'd have to be certain it would not cause electrical damage to me or anything in the trailer.

No, no! Don't do it this way!

Put the inverter under the hood of the tow vehicle, connected by a very short stub of heavy wire to the battery (or relay). Run simple AWG 12 SJO wire (like a heavy extension cord) to the rear of the tow vehicle. Put a female receptacle at the rear of the tow vehicle, possibly on a bracket at the rear bumper.

Put a plug on another segment of SJO. Run that from the tow hitch to the refrigerator, perhaps along the towing frame and underneath. The plug-and-socket at the rear of the tow vehicle serves as a safe breakaway.

By transferring power at 120 volts instead of 12 volts, you are carrying a manageable amount of current.

[formerFR]

it sounds like it would be simpler, and safer, to just add an additional dedicated 12v battery for the fridge, and a small power inverter, at the wattage sized for the fridge's compressor needs, and turn it on while traveling.

Even if it wasn't able to handle the whole travel day, it would put you a long way toward the fridge already being cooled when you arrive and plug in.

Also, you'd need to find a way to plug in the fridge to this power inverter, rather than it's regular outlet behind the fridge, to make use of the inverter's power, though I suppose there may be space behind the fridge already to place it easily, especially if the battery could be in a storage bay just beneath the fridge, etc.
Some small inverters come with only a 12v round plug, while others come with both a 12v plug AND alligator clips, for attaching directly to the battery.
Since the power inverter already has it's own 120v outlet, it's easy to make use of it rather than feeling you have to 'wire' a dedicated outlet to it.

[formerFR]

also, a small 12v charger placed next to the battery would be an easy way to provide for recharging it when you've arrived - just plug it into the additional outlet at the campground power pedestal with an extension cord, if needed, or even into one of your RV's outlets.

[TitanMike]

Originally Posted by chriscowles

Please do not turn this topic into a debate about using propane while driving. I have done that but am exploring alternate approaches.

Our near-future 2507S will have a propane/AC refrigerator. I'm contemplating the wisdom (or stupidity) of using an inverter to power it on AC while driving. Yes, it would kill the trailer batteries in short order if used as wired at the factory. I'm exploring whether I could run wire of sufficient capacity from the front of the truck back to the trailer, to prevent that.

I'd probably replace the Aux 12V aux wire on pin 4 of the trailer connector with a larger gauge. Yes, I know it would have to be very large to mitigate voltage drop. I'd create a circuit in the trailer specifically for that purpose and use the inverter only when actually driving. When stopped, I'd switch to gas. The wire from the truck would incorporate a relay to avoid inadvertently draining the truck battery.

Is this a numbskull idea? If not totally stupid, what capacity would the inverter have to be to power only the refrigerator? What gauge would the wire from the front of the truck to the inverter have to be?

Would it be more efficient to have the inverter at the front of the truck and run AC to the back? I could install an AC outlet at the refrigerator used solely for that purpose and just move the plug when traveling. I'd put it back into the standard plug for normal use. That avoids having to adapt existing wiring in any way. Alternatively, a DPDT switch of some kind could make that easier but I'd have to be certain it would not cause electrical damage to me or anything in the trailer.

An accurate answer as to practicality would require knowing how much the refrigerator draws when operating on AC. Chances are if it runs on Propane the AC side only powers a heater element.

Depending on Refrigerator I've seen heating elements that are rated from the low 100 watt range up to over 300 watts (just the ones I found quickly).

With this "rating" now divide by 12.5 volts and you'll know how much current draw for the inverter. For example, a 300 watt heater element will draw 300 watts from an inverter and the inverter will draw 25 amp from the batteries WHEN COOLING.

FWIW, my 12 v power lead on my Tow Vehicle is fused for 30 amp. Most pigtails have #14 wire for lights, #12 for brakes, and #10 for the Charge/ground wires.

Truck has similar sized wire and I find I can get just under 20 amp from my truck (based on Victron Monitor) so taking into consideration that a refrigerator only runs when cooling is necessary, the average tow vehicle should be able to keep up with the drain on the batteries. Start with a cold refrigerator and the draw will be intermittent and charging will be continuous (while engine is running).

I don't think it's a screwball idea, but I just use Propane. I use the output from my TV to charge batteries (LiFePo and Renogy DC-DC Charger) replacing what I used while boondocking.

[chriscowles]

Originally Posted by dahagen

I don't understand the question here. If the fridge is 110/propane (like most RV refers) why not run on propane when no AC is available instead of going to all the work to install a 110 volt inverter system?

I do and I will, when parked. I also have done so while driving but I'm exploring if there's a practical way to run it on 110, through some arrangement using an inverter, instead. My question revolves around the wattage required to do that, and how to provide power to the heating element in the refrigerator, without killing the battery.

Since the refrigerator can run solely on AC when available, I assume the heating element is AC. Is that a correct assumption?

[bikendan]

Originally Posted by 67L48

Sounds like an interesting project. PUPs have 3-way fridges that can select 12 VDC. I'm not sure why TTs only have 2-way fridges. Speaking in 100% ignorance, I'm wondering if you could borrow from the circuitry design (and maybe even actual components) of how those smaller 3-way fridges work to draw off the 12 VDC side.

PUPs have dorm size fridges and no true freezer section.
So the 12v DC setting simply keeps an already cool fridge cool during the trip.
I owned two Popups and the fridges never got cold enough while driving, unless I pre-cooled them the previous night.
A larger RV fridge with a separate freezer would require much more juice to keep the much bigger spaces cold.

[JLeising]

I also do not think it's a "screwball idea". Been discussed previously in a Motorhome forum:

http://www.forestriverforums.com/for...ml#post1579020

From my comments at that time, about 320 watts resistive load for a typical Dometic two way RV fridge. A simple 400 watt modified sine wave inverter should suffice.

Voltage drop would be least with the inverter in the tow vehicle and running 120 volt line back, but safety with that 120 volt line would be a concern. The inverter should draw around 30 amps when the fridge is running. Recommend oversizing the wires from the tow vehicle battery.

If you go ahead with this mod, let us know how it works out -

Jim

[chriscowles]

Originally Posted by TitanMike

An accurate answer as to practicality would require knowing how much the refrigerator draws when operating on AC. Chances are if it runs on Propane the AC side only powers a heater element.

Depending on Refrigerator I've seen heating elements that are rated from the low 100 watt range up to over 300 watts (just the ones I found quickly). ...

Thanks for that information. It's useful and encouraging. I already own a 300W inverter purchased to power our (former) college students' laptops while on long trips. That being the upper end of the cited range, I can start with a very simple arrangement routing AC to the trailer rather than DC.

My initial attempt will be with the inverter in the back seat of the truck and a 16ga extension cord run back to the trailer hitch. I'll use the shortest one I have that meets the need. I'll probably do something simple like run it out the rear sliding window using duct tape to seal the open crack temporarily.

From the trailer hitch I'll run another 16ga extension cord, attaching it to the underside of the trailer and routing it to the 110v cord of the refrigerator. I won't do any wiring at all. Just unplug it from the normal outlet and plug it into the extension cord.

As I'll be running AC to the back, power loss should be nominal. The inverter I have should be able to handle it. It has an internal fan and will be in the air conditioned cab of the truck, if heat dissipation is a consideration.

If all of this works I'll figure out a practical and durable permanent solution. It may still involve moving the AC plug from one receptacle to another.

[chriscowles]

Originally Posted by JLeising

... From my comments at that time, about 320 watts resistive load for a typical Dometic two way RV fridge. A simple 400 watt modified sine wave inverter should suffice. ...

Whenever we buy the trailer I'll get a larger inverter if the demand is higher than my current 300W inverter can handle.

Thanks for the support.

[TitanMike]

Originally Posted by chriscowles

Thanks for that information. It's useful and encouraging. I already own a 300W inverter purchased to power our (former) college students' laptops while on long trips. That being the upper end of the cited range, I can start with a very simple arrangement routing AC to the trailer rather than DC.

My initial attempt will be with the inverter in the back seat of the truck and a 16ga extension cord run back to the trailer hitch. I'll use the shortest one I have that meets the need. I'll probably do something simple like run it out the rear sliding window using duct tape to seal the open crack temporarily.

From the trailer hitch I'll run another 16ga extension cord, attaching it to the underside of the trailer and routing it to the 110v cord of the refrigerator. I won't do any wiring at all. Just unplug it from the normal outlet and plug it into the extension cord.

As I'll be running AC to the back, power loss should be nominal. The inverter I have should be able to handle it. It has an internal fan and will be in the air conditioned cab of the truck, if heat dissipation is a consideration.

If all of this works I'll figure out a practical and durable permanent solution. It may still involve moving the AC plug from one receptacle to another.

Just be aware that most power outlets in vehicles are fused for 15 amp so they max out at about 180 watts. You may have to install a heavy duty outlet similar to this which runs direct to the battery and has it's own fuse and is rated for 30 amp (375 w max)

https://www.amazon.com/YCIND-Female-...gateway&sr=8-4

[rlh1957]

Just some thoughts. Rigs that have Residential Fridge units usually only run on AC120v power anyway, which they have a 1500Watt Inverter to pull 12vDC out of the battery and change to 120V. When on shore power or gen power the 120v comes from there.
The residential fridge getting AC voltage from the inverter, it runs while driving or in camp. When the batteries are depleted to about 50% or whatever level is selected by system it shuts off.
While driving the TV charging system will supply charging voltage to the batteries.
It is a slow steady charge to keep them up and not a bulk charge.
If a refrigerator/freezer is already at temperature and then all shut off and door not opened, the unit will maintain at cold temperatures for a day of driving, not opening or closing the door.
Best way to prove out 'your' system is to get it down to temp in the driveway.
Put ice cube trays in the freezer and frozen hot dogs, put bottles of water or beer in fridge that are cold. When fridge temps are what you usually run at, shut it all off. Turn off the Inverter. Leave it all day 6 or 8 hours and then check to see what you end up with. I talked to a guy that used a wireless thermometer and could know temps all day. At the end of a driveway drive day... check your water and beer, check the ice cubes and how thawed the hot dogs are. That will give you a good indication of what to expect in insulation performance of your fridge.