Shore power while towing

[coasttocoast]

Originally Posted by GeeSag

Has anyone found a good way to run the fridge on long drive days without the propane?

I am wondering about a small inverter for just the fridge. Run only the fridge on 120 volt while driving and leave propane off at the tanks.

If the fridge is about 400 watts on AC, then a 500 watt or even a 1000 watt inverter might do the trick.
500 watt inverter is probably too small for peak amps, but a 1000 watt should draw only the 400 watts plus inefficiencies as steady state assuming the fridge is really about 400 watts.

Has anyone run thru all the numbers?

Would 400 watts steady state kill the truck alternator?

Goal Zero will set you free. Everyone is trying to come up with a solution. I can lead you to water...

[TouringDan]

I believe your fridge is a compressor type and operates on 12v. I would think that the normal 12v umbilical cord would provide enough power to operate the fridge. If not you could install a 9 amp Victron dc/dc converter to provide the necessary current. This would also be useful for charging your lithium batteries when you switch to lithium. The third option would be to run a #14 line from your TV inverter to your Airstream using a 15 amp connector. Your Airstream may be 50 amp but all you need is enough current to power your converter to keep your batteries charged. 15 amps will be adequate. This solution also will allow you to charge lithium batteries while driving down the road. I did this on my 66 Tradewind.



Dan

[Bill M.]

If it is a 12 Volt fridge then I would install a DC to DC converter in in the trailer to provide power from the tow vehicle. If it is a 110 fridge then I would not try to run it from the truck 110 inverter.

[GeeSag]

Has anyone ever done a 12 volt normally closed relay in series with the 12 volt supply to the fridge?

Then run the control of the relay to an upfitter switch in the tow vehicle.

This would allow flipping the upfitter switch to "On" as approaching the fuel station. causing the relay to "Open" and shutting off the fridge.

Then after leaving the fuel pumps, turn off the upfitter, and the normally closed relay returns the trailer fridge to normal behavior.


This would solve one problem: Turning off the flame at fuel pumps.


It still does not solve the turning off the propane at the tanks problem.


Does the 7-pin connector normally have one un-used pin still left available that could be used for this control circuit?

[SSquared]

Originally Posted by GeeSag

Has anyone ever done a 12 volt normally closed relay in series with the 12 volt supply to the fridge?

Then run the control of the relay to an upfitter switch in the tow vehicle.

This would allow flipping the upfitter switch to "On" as approaching the fuel station. causing the relay to "Open" and shutting off the fridge.

Then after leaving the fuel pumps, turn off the upfitter, and the normally closed relay returns the trailer fridge to normal behavior.


This would solve one problem: Turning off the flame at fuel pumps.


It still does not solve the turning off the propane at the tanks problem.


Does the 7-pin connector normally have one un-used pin still left available that could be used for this control circuit?

The 7-pin cable has all pins used, except that one is for back up lights which many trailers lack.


The manual for the Dometic RM3762 fridge in our 2013 25FB has an explanation of a control circuit that can be wired to the ignition switch. When the ignition switches off, the fridge shuts down. When the ignition comes back on, it waits 15 minutes and then restarts the fridge. We've thought about wiring something up to implement this, but have not done so.


We often run our fridge on propane when on the road. We do in fact make a practice of stopping short of the pumps and turning it off manually, and turning it back on only when we have pulled away. Other times we run on electric via our inverter, counting on our 435 watts of solar.

[Bill M.]

Our 1987 trailer came with a 9 pin connector and it did cut the fridge off when the TV ignition was off. But... I am not sure why starting a gas refrigerator when you pull out from the pumps would be that much safer than just leaving it on. I run with the gas fridge on. I try to think about it when refueling. With the diesel I do not refuel more than 1 time per day.

[GeeSag]

Thanks for reminding me of the Dometic already having the ignition off feature. I had read about that years ago and forgotten. This forum proves to share so much.

The problem I see with Ignition shutoff is the intent is to cut of the fridge flame before getting to the pump and re-igniting after well clear of the fuel station area.

I suspect the wiring for the ignition control could fairly easily be run to an up-fitter switch instead.
The up-fitter switch problem is remembering to do turn it off, and very important: remember to tun is back on again! But it is better than flame at pump.

I still think the best solution might be to have a DC-DC converter + 2-pin connector (High amp + weather proof) plus an inverter mounted in the fridge area. Keep the live 120 volt just within the fridge control area. Problem with this solution is to have an easy conversion back to shore power based 120 Volt operation. I guess an A/B type switch for 120 volt could be "Drive/Park" and have it be a transfer switch type operation. I guess a brute force method would work. Inside the fridge control area, have two 120v AC plugs: one for shore power feed, and one for inverter feed. Then just make it part to the campsite set up and tear down to remember to move the plug. Maybe a relay with ignition control to flip to inverter only when the ignition is on and back to shore 120 volt feed when ignition is off.

I have not seen good 2-pin weatherized connectors for quick disconnect/re-connect. I suspect they are out there, but compiling the list of all material is part of the challenge.

The Victron DC-DC and the Victron inverter probably are good choices for that part of the puzzle.

I suspect 8 guage wire might be enough for the long DC runs. But by the time running 8 ga, might as well consider 6 ga.


I still question if the standard 100+/- amp alternator would live through a continuous 35 amps in addition to all the other existing loads.
I have seen some youtube videos on converting to a 370 amp alternator. Not sure if that is just a good idea, or required.

The ultimate goal is to get the propane off when driving. (Not to say having a 35 amp fused pigtail is a good idea! But probably still better in the event of an accident having 35 amps of 12 volts rather than a propane leak)
Keeping the 120 volt to as short a distance as possible also seems safer that having live 120 volt wiring throughout the whole trailer.

I am hoping someone else has already mastered this and has experience to learn from.

[Bill M.]

I think the new 12 volt compressor fridges make a lot of sense for towing. Might work boondocking with lithium batteries and a generator.

[GeeSag]

Thanks XCountry for making me rethink this whole topic.

Thanks Wazbro for pointing out the Compressor based fridge in the newer models.

Thanks to this thread, I took action and installed a remote cutoff switch for my old fashioned LP based fridge. (Posted as a new thread since this thread is really for Compressor based newer models)

[AbbyA]

We just make sure everything in the freezer is frozen solid. You could put some ice packs in the frig too. Then we just turn it off and don’t open it. If your days are really long, which sounds unpleasant, get an Otterbox or Yeti cooler and just use that.

[GeeSag]

This thread asks a very interesting question:

Can a compressor Fridge run off the 7-pin connector?

XCountry: Please clarify: Your Fridge is a Compressor style, Correct?
Is it a Norcold? Is it 7 cu. ft.?
See attached photo showing Norcold 7 cu.ft. drawing 3.2 amps on DC. That is amazing!

Does anyone have the specs on how many amps is the 12 volt DC rated on the 7-pin connector? Seems like well above the 3.2 amps shown in the Norcold specs.

I admit going down the wrong path like so many others on this thread thinking absorption type fridge. If this is really a compressor fridge, it opens a whole new simplicity to running down the highway with the Propane off.

For all those 3-way fridges, the ability to shut off propane and run on DC is a great feature. The 20 amps for the 3-way raises a good question if the 7-pin can handle that. Separate wiring from the tow vehicle for the 20 amps gets complicated. I am talking 20 amps based on the Norcold 19.93 amps shown below. I think my old fashion Dometic would be closer to 35 -40 amps required on 12volt.

Thanks XCountry for starting this thread.

[Wazbro]

Originally Posted by GeeSag

This thread asks a very interesting question:

Can a compressor Fridge run off the 7-pin connector?

XCountry: Please clarify: Your Fridge is a Compressor style, Correct?
Is it a Norcold? Is it 7 cu. ft.?
See attached photo showing Norcold 7 cu.ft. drawing 3.2 amps on DC. That is amazing!

Does anyone have the specs on how many amps is the 12 volt DC rated on the 7-pin connector? Seems like well above the 3.2 amps shown in the Norcold specs.

Well I believe the standard is 30 amp fuse on a 10 gauge wire for the 12volt power. Some manufacturers don't necessarily follow that, someone said theirs only had a 15 amp fuse. Now that doesn't translate to what you can expect to get through that wire with a trailer battery in the line.

Frankly with the TV battery charged 3 amps would be optimistic with keeping the trailer batteries fully charged.

Still only 3.2 amp draw would only be 32 amp hours in ten hours if the fridge was running 100% of the time, not a problem without any charge from the TV if heading somewhere with hookups.

A 9amp DC/DC converter would work well to keep the batteries charged and run that small of a load.