Can I run the refrig on AC from an inverter in the tow vehicle?

Thanks for all the quick and helpful comments on my 12V battery contention question. Texas Camper hit the nail on the head with his question. Why would I want to do this? Here are my thoughts. First, I saw at least a rumor that the new TM can have shore power connected while closed down. Second, I am a DRY camper and am interested in multiple days without recharging (2*T106 batteries). Third, I have read most of the posts regarding driving with refrigerator on (12V) and arriving with a LESS THAN FULLY CHARGED TM battery (due to voltage (12A refrigerator) drop between the TV alternator and the TM battery I am convinced).

So my next request is for comments on the following:
Starting my trip with a fully charged TM battery.
(a) I pull the fuse in the TV which supplies 12V to the 7 pin trailer connector.
(b) I install a 110VAC inverter in TV (say 500w)
(c) While travelling, I connect output of inverter to TM (as in shore power)
(d) I Run the TM refrigerator on 110VAC (I'm guessing 200 watts)
(e) The TM battery will be charged by the TM converter.

Seems this would allow me to arrive with FULLY charged TM battery. Must be a big flaw in this scheme somewhere. (I know the TM battery must be fully charged to start else the 500W inverter will choke)
Thanks for all your great comments.

[Bill]

Originally Posted by hingarfi

I have read most of the posts regarding driving with refrigerator on (12V) and arriving with a LESS THAN FULLY CHARGED TM battery (due to voltage (12A refrigerator) drop between the TV alternator and the TM battery I am convinced).

So my next request is for comments on the following:
Starting my trip with a fully charged TM battery.
(a) I pull the fuse in the TV which supplies 12V to the 7 pin trailer connector.
(b) I install a 110VAC inverter in TV (say 500w)
(c) While travelling, I connect output of inverter to TM (as in shore power)
(d) I Run the TM refrigerator on 110VAC (I'm guessing 200 watts)
(e) The TM battery will be charged by the TM converter.

Seems this would allow me to arrive with fully charged TM battery.

This should work. In fact, Bob Rederick and I have discussed it at some length, since we are among those afflicted with ARRIVE WITH LOW BATTERY syndrome. I have been getting ready to try it myself. Please post your results as soon as you have some.

Since your very first step was "a) pull the fuse in the tow vehicle", you undoubtedly understand the potential problem if you don't do it. Let me emphasize for anyone else, though, that this step is vitally important. It is not optional! If you power up the TM's converter from an inverter in the tow vehicle, you MUST interrupt the 12-volt line from the tow vehicle to the TM.

Another way to approach the problem is simply to bring 110VAC from the inverter directly to the refrig compartment. Unplug the refrig from the TM's AC power system, and plug it (and nothing else) into inverter power. This means that
a) you don't need to remove the fuse in the tow vehicle
b) with the refrig running from AC power, the 12-volt load in the TM is nearly zero, which means that the tow vehicle will, in fact, charge the TM battery. As Ray points out, it is not a very hefty charge rate, but if you start with a fully charged battery, it is more than enough.

By the way, you are right about the fact that the large load (the refrig) causes a voltage drop. I made (and posted) some measurements a while back.

Using an inverter to power the refrig is really a pretty crappy band-aid fix. Although I will do this temporarily, no one should have to do it for long. The problem is NOT in the TM, by the way, which is properly wired. In my case, part of the problem was due to a damaged Bargman 7-pin connector on the tow vehicle, and part was due to the fact that Ford used some lightweight wire in the 12VDC line from the tow vehicle alternator to the Bargman connector. I have replaced the Bargman, but haven't had a chance to assess the difference, if any. If necessary, I will run a new wire directly from the alternator to the Bargman.

Bill

Originally Posted by Bill

Another way to approach the problem is simply to bring 110VAC from the inverter directly to the refrig compartment. Unplug the refrig from the TM's AC power system, and plug it (and nothing else) into inverter power. This means that
a) you don't need to remove the fuse in the tow vehicle
b) with the refrig running from AC power, the 12-volt load in the TM is nearly zero, which means that the tow vehicle will, in fact, charge the TM battery. As Ray points out, it is not a very hefty charge rate, but if you start with a fully charged battery, it is more than enough.

I like your approach which is much simpler. Also the inverter output waveform issue should be minimal. MODIFIED SINE WAVE should be fine for refrigerator. I am not so sure the TM Converter would enjoy MODIFIED SINE WAVE. There are PURE SINE WAVE inverters for $300-400. What do you think about installing the inverter right in the TM? Maybe behind the refrigerator.

Posted by hingarfi

What do you think about installing the inverter right in the TM? Maybe behind the refrigerator.

Folks: Please ignore this idiotic idea. Obviously the 12V voltage drop would still be there. Inverter needs to be in TV.

[Bill]

What do you think about installing the inverter right in the TM?

I presume you mean "put the inverter in the TM and use it to power the refrig and only the refrig". I don't believe it will work.

Regardless of where it is located, the inverter must get its power from the tow vehicle. The original problem was low voltage in the TM, caused by the heavy current running back to the TM. Because the voltage is so low back there, the TM battery actually tries to "help" power the refrig, and in doing so, discharges itself. If you put the inverter in the TM, it further increases the load back there, since the inverter is not 100% efficient. This creates an even lower voltage in the TM. The TM battery will try even harder to "help" power this load, and will discharge even faster. Does this make sense?

And don't even think about disconnecting the TM battery to isolate it from this problem while on the road. If you disconnect it, the breakaway switch won't work.

Even without other problems, the voltage in the TM will likely get so low that the inverter's undervoltage protection (set at about 11 volts) will shut down the inverter.

Sorry, but the inverter has to be in the tow vehicle, right up near the alternator. And you have to run an AC cord back to the TM. Like I said, this is not an ideal solution.

Good thought process, though. Fun, ain't it?

Bill

[RockyMtnRay]

GUYS!!! All of these elaborate plans to use inverters, 110 Volt power lines running from the interior of the TV back to the TM, under the TM and then eventually to power the TM's converter would make Rube Goldberg very proud of you!

But come on now, if you're going to go to all this effort to safely transmit rather dangerous 110 Volt power to the trailer, why not simply run an 8 or 10 gauge conductor directly from the TV's battery (or alternator) to the Bargman connector on the TV?????? The only protection you will need is a simple 30 amp self-resetting circuit breaker in the engine compartment. If you run the wire along the bottom of the TV, it should not take you more than 20 or 30 minutes total...and that's allowing time to properly secure the wire so it won't fray or be caught by road hazards.

As Bill notes, some of the manufacturer's engineers designed so many plugs/connectors into the trailer harness that significant voltage drop is entirely likely. If that's the case, simply bypass all that and do it right with your own heavy duty wire.

Never lose sight of the K.I.S.S. principle!

This thread has been great to read.

This problem seems like it may be common, but then I have to question is this an issue with older vehicles or certain TV makes/models?

I would have to believe some the Automakers have taken this in consideration for some vehicles that are common to towing trailers.

Ray said:

But come on now, if you're going to go to all this effort to safely transmit rather dangerous 110 Volt power to the trailer, why not simply run an 8 or 10 gauge conductor directly from the TV's battery (or alternator) to the Bargman connector on the TV?????? The only protection you will need is a simple 30 amp self-resetting circuit breaker in the engine compartment. If you run the wire along the bottom of the TV, it should not take you more than 20 or 30 minutes total...and that's allowing time to properly secure the wire so it won't fray or be caught by road hazards.

Ray I surely agree it sure sounds Rube Golberg. However, even if you had a dedicated separate #8 wire from the TV battery to the TM battery, with NO CONNECTORS, the 12A feeding the refrigerator would cause about 0.5 Volt drop (assuming 60 feet of wire round trip) If TV battery fully charged is 12.7 V, this would put the TM battery voltage at 12.2 V which is about 60% charged battery. I agree running separate 110VAC is bad idea. A separate 12V #12 gauge circuit from TV battery to run the refrigerator would solve the problem since the TM battery would then see the full 12.7V of the TV battery. The refrigerator would see about 12.5 V which should be OK. Again, this is a kluge. There seems to be no easy answer. Fun to discuss though.

[Bill]

Ray -

I fully agree that this solution is worthy of Rube Goldberg (and I'm wondering how many people on this board are too young to know who Rube Goldberg was!) Thanks for the link - I'm enjoying it. But entertainment value aside, we all agree that running 110VAC around is, as Bert said, a bad idea.

Running a separate wire from the tow vehicle battery to the Bargman connector is clearly the right idea - except that I am unwilling to cut open the weather seal on the back of the molded Bargman. Once open to the weather, these things cannot be resealed (in my experience, and I have tried), so the connections inside corrode like mad. I would do myself a disservice to open it. So that means finding someplace upstream, in a weathertight location, to make the connection. Although it would be better, part of the advantage is immediately lost. Incidentally, that is the next step in my MASTER PLAN.

Bert - I have also considered your approach of running a separate wire from the tow vehicle battery to the refrig. It would work great, and solve all the problems - except that it would require a new one-wire connector located at the trailer hitch. Again, a kluge.

The interesting thing is that (in my case at least), I don't recall having this problem when my TM and tow vehicle were new. Something has changed, or perhaps I have become more aware of what is going on. If I ever get my TM back from its new home at the repair shop/aka dealer, I will make some new measurements and post them. Should be interesting.

Bill

[RockyMtnRay]

Originally Posted by hingarfi

Ray said:


Ray I surely agree it sure sounds Rube Golberg. However, even if you had a dedicated separate #8 wire from the TV battery to the TM battery, with NO CONNECTORS, the 12A feeding the refrigerator would cause about 0.5 Volt drop (assuming 60 feet of wire round trip) If TV battery fully charged is 12.7 V, this would put the TM battery voltage at 12.2 V which is about 60% charged battery. I agree running separate 110VAC is bad idea. A separate 12V #12 gauge circuit from TV battery to run the refrigerator would solve the problem since the TM battery would then see the full 12.7V of the TV battery. The refrigerator would see about 12.5 V which should be OK. Again, this is a kluge. There seems to be no easy answer. Fun to discuss though.

Concur that there will be roughly a .5 volt drop from the connection under the TV hood to the TM battery (will vary a bit depending on whether the TM battery is on hitch or in the rear). And your values for the TV battery are correct when the TV engine/charging circuit are not operating.

However, really BIG however, the voltage at the TV battery is NOT 12.7 volts if the TV engine is running and the alternator is spinning. It will in fact be around 14 volts (probably anywhere from about 13.5 to nearly 15 volts, possibly as high as 16 volts). Most TV charge regulators are voltage/current sensing and increase the charging voltage anytime they sense high drain...which is exactly what will be happening with the trailer hooked up and its refer running on DC. Using a nominal voltage of 14 volts at the TV battery, that means the TM battery will be seeing at least 13.5 volts which is at least .8 volts higher than a fully charged battery...and more than enough excess voltage to provide a good rate of charge.

Ergo there is any easy answer and no kluge is required...just run a heavy gauge conductor from the TV charging point back to at least the bargmann connector.