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Old 11-25-2017, 10:16 PM   #1
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7 way plug charge line amp requirement

Question for the forum. For the new 5.0TA's, with the 3 way, 6 ft^3 fridge, what is the amperage requirement when operating at 12 volts? We're on our way up to pick ours up and the owners manual for our 2018 Chevrolet Colorado, with the HD trailer package, discusses a charge line for the 7 way connection that (para) "assists battery charging". And it is only active with the lights or the tow haul mode turned on. I'm guessing that the fridge requires ~25 amps, which is much more than the 5-6 amps required for max battery charging. So, if my charge line is lacking, I need to let Trademasters know the day before our 5.0TA pickup, when we're getting our Anderson hitch and pickup bed plug installed.
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Old 12-04-2017, 02:56 AM   #2
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I found a manual for the Dometic 2663, which I think is the correct model, and it mentions a 30A fuse on the 12v DC heater. So, that's an upper bound anyways. Your 25A guess is probably about dead on. So, 10AWG is good enough for safety anyways.
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Old 12-04-2017, 08:43 AM   #3
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For the new 5.0TA's, with the 3 way, 6 ft^3 fridge, what is the amperage requirement when operating at 12 volts?
I'm very interested as well in actual measurements people have done. I'm guessing with a 30 Amp fuse it is not as high as 25 Amps. That seems too close to the limit. I did a quick search and found a couple of people mentioning 15 Amps. But I did not know if these were actual measurements or not. FYI...

Battery Charging While Running Fridge on 12V
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Old 12-04-2017, 03:21 PM   #4
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The service manual says 18.0 amps for an RM 2663 (and presumably any Americana 6 cubic foot)... but that's at 12 volts.

If you give it more voltage (battery voltage is usually higher than that, and charging voltage even higher), it will take more current. The element resistance is listed as 0.67 ohms, so - for instance - if it is hit with 14 volts it will take 21 amps. If - for another example - your battery or charging system is struggling to maintain 11 volts at the refrigerator (after voltage loss due to resistance in the wires) the DC heater would take 16.4 amps.
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Old 12-04-2017, 04:45 PM   #5
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The service manual says 18.0 amps for a 2663 (and presumably any Americana 6 cubic foot)... but that's at 12 volts.

If you give it more voltage (battery voltage is usually higher than that, and charging voltage even higher), it will take more current. The element resistance is listed as 0.67 ohms, so - for instance - if it is hit with 14 volts it will take 21 amps. If - for another example - your battery or charging system is struggling to maintain 11 volts at the refrigerator (after voltage loss due to resistance in the wires) the DC heater would take 16.4 amps.
Took possession last week. My nameplate (near hinge, with door open), says 23 amps, at 12 volts. I.e., 276 watts, which jives with 2.7 amps at 110 volts (also on nameplate), Actually nameplate MIGHT be at 120 volts, but it's all part of the same required wattage "fact family". FYI, my problem is now with my Colorado diesel charge line. It won't keep the Escape battery up with the fridge on. NO good reason for this, except for Chevy minimizing charge line capacity. The alternator can put out ~1.7kw, so it's just a matter of getting fusing, switching, and line sizing right. That's what I need to investigate when we return home, just B4 Christmas..
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Old 12-04-2017, 04:56 PM   #6
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Maybe this would work better:

Purpose of 6ga hot wire from converter/charger to hitch

See Post #10
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Old 12-04-2017, 05:13 PM   #7
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Took possession last week. My nameplate (near hinge, with door open), says 23 amps, at 12 volts. I.e., 276 watts, which jives with 2.7 amps at 110 volts (also on nameplate)...
Great info - what specific model of refrigerator is this?

Nameplate info is usually a maximum, so that may mean 23 amps at the highest actual voltage expected from a (nominally) "12-volt" power source.

Also, the 12 volt DC and 120 (or 110) volt AC power don't need to correspond at all, since they are separate heaters (two separate elements installed in the same housing). The DC heater is routinely lower-powered than the AC heater, which is one of the reasons that DC operation is recommended only when AC power and propane are not available.
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Old 12-04-2017, 07:37 PM   #8
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Maybe this would work better:

Purpose of 6ga hot wire from converter/charger to hitch

See Post #10
Post 10 didn't help me much, but the use of the 6 gauge wire by Escape validated what we already knew. That (in spite of them telling folks falsely that most TV's can't keep a 12 volt fridge going), they EXPECT that kind of amperage from the TV. In fact, it's required, and the TV charge line needs to be just as burly. This helps me....
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Old 12-04-2017, 07:45 PM   #9
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Quote:
Originally Posted by phalaney View Post
Post 10 didn't help me much, but the use of the 6 gauge wire by Escape validated what we already knew. That (in spite of them telling folks falsely that most TV's can't keep a 12 volt fridge going), they EXPECT that kind of amperage from the TV. In fact, it's required, and the TV charge line needs to be just as burly. This helps me....
What I was told is that if you are boondocking and running the furnace and fridge etc., and you leave that campsite with a depleted battery, driving while running the fridge on 12V, you will arrive at your next campsite with a depleted battery.
They did not say that the tow vehicle won't keep the 12V fridge running.
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Old 12-16-2017, 02:14 AM   #10
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Got a battery meter installed, so now I can give an actual answer to this. The 6cu ft 3-way Dometic fridge in my 2017 19' (presumably the same model as the 6cu ft 3-way in the 21') draws 23.4A at 13.11V.
A duty cycle under 100% will bring that average down, of course, but based on other threads about the effectiveness (or lack thereof) of the fridge on 12V power, I'm guessing it's not far off 100% if the weather's warm.
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Old 12-21-2017, 09:23 PM   #11
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Got a battery meter installed, so now I can give an actual answer to this. The 6cu ft 3-way Dometic fridge in my 2017 19' (presumably the same model as the 6cu ft 3-way in the 21') draws 23.4A at 13.11V.
A duty cycle under 100% will bring that average down, of course, but based on other threads about the effectiveness (or lack thereof) of the fridge on 12V power, I'm guessing it's not far off 100% if the weather's warm.
Thx D. Validates the number on the inside door jamb.

Just got home from our extended 5.0TA pickup trip and need to investigate why my Colorado power line won't provide that much. Should be easily work aroundable.

But I can attest to the fact that, even while partially discharging our golf cart batteries if the fridge was kept on while driving all day, they kept the fridge just as cold as the 120. Is their any admonition in the book that the fridge can't get and stay cold enough on 12 volt? Hasn't been our experience, with 2 previous 3 ways and this one, but I'll check....
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Old 12-21-2017, 09:33 PM   #12
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What I was told is that if you are boondocking and running the furnace and fridge etc., and you leave that campsite with a depleted battery, driving while running the fridge on 12V, you will arrive at your next campsite with a depleted battery.
They did not say that the tow vehicle won't keep the 12V fridge running.
Agree, if your charge line can't keep up. But it should. Most alternators put out 5-7* the amps required for fridge power, and even huge deep cycle installs (like the dual 6 volt packs that Escape offers) can only accept ~100 watts (~8 amps) max. So, I "expect" to be able to both charge my battery bank AND keep my fridge on while driving. I.e., less than 400 watts total, plus a little for lights and vehicle power, from a ~1.7 kilowatt alternator.
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Old 12-21-2017, 09:36 PM   #13
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I believe the key here is the ambient temperatures when you are running the refrigerator on 12 volt. Now, in late December, we are unlikely to encounter the same daytime highs that will occur in July, Yes, the refrigerator will perform fine at this time of year, but once we change seasons the 12 volt will not be adequate to keep things cold enough.

I have monitored interior refrigerator temperatures very carefully in 80 degree temperatures. Driving just for a half an hour on 12 volt will show the start of a gradual decline in interior temps. By three hours of driving the interior temps will be approaching unsafe temps for certain foods. After six hours the temps inside the refrigerator will be in the 50's. I have not tried 12 volt with 90 degree temps, and most of these units cannot handle 100 degree temps running on gas, much less 12 volt.

As Brian pointed out in an earlier post, the 12 volt cooling is being done with a substantially smaller heating element and will not come close to the cooling capability of propane.
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Old 12-21-2017, 09:50 PM   #14
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The way it was explained to me was that the charge line in your tow vehicle is designed and sized to charge your trailer battery .
It is not designed to charge your trailer battery , run the refrigerator, run your furnace , run your roof top fan and run all the trailer lights while traveling.

So far what I was told is extremely accurate and from what I see, is based in fact
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Old 12-22-2017, 03:02 PM   #15
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The way it was explained to me was that the charge line in your tow vehicle is designed and sized to charge your trailer battery .
It is not designed to charge your trailer battery , run the refrigerator, run your furnace , run your roof top fan and run all the trailer lights while traveling.

So far what I was told is extremely accurate and from what I see, is based in fact
Agree on the furnace, roof top fan, and trailer lights. The furnace and roof top fan is not used while driving. The trailer lights have their own lines. And as for the rest of your described duties, I'm sure that many charge lines are insufficient.

But I have made sure that ALL of my tow vehicles had charge lines plenty big, and that they were properly fused/breakered. In fact, ALL of the factory breakers/fuse boxes on vehicles I owned, that were equipped with "trailer towing packages", already included a dedicated breaker/fuse plenty big enough for every duty I wanted. The vehicle manufacturers understood that this is about the ONLY reason folks buy 3 way fridges.

So, it was just a matter of running the big line. On my truck, ran it myself. On the Volvo XC90, hired it done to make sure it was safe and properly routed. Not sure what Chevy did on my Colorado, but it is intentionally limited - even though it is equipped with a high amp (50) external power breaker. I have all winter and half of spring to figure it out.

And to repeat, the alternators on the kinds of vehicles we are discussing don't know the difference. ...
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Old 12-22-2017, 04:01 PM   #16
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Agree on the furnace, roof top fan, and trailer lights. The furnace and roof top fan is not used while driving. The trailer lights have their own lines. And as for the rest of your described duties, I'm sure that many charge lines are insufficient.

But I have made sure that ALL of my tow vehicles had charge lines plenty big, and that they were properly fused/breakered. In fact, ALL of the factory breakers/fuse boxes on vehicles I owned, that were equipped with "trailer towing packages", already included a dedicated breaker/fuse plenty big enough for every duty I wanted. The vehicle manufacturers understood that this is about the ONLY reason folks buy 3 way fridges.

So, it was just a matter of running the big line. On my truck, ran it myself. On the Volvo XC90, hired it done to make sure it was safe and properly routed. Not sure what Chevy did on my Colorado, but it is intentionally limited - even though it is equipped with a high amp (50) external power breaker. I have all winter and half of spring to figure it out.

And to repeat, the alternators on the kinds of vehicles we are discussing don't know the difference. ...
I have acquaintances who travel in the Fall with their refrigerator set on 12VDC , their furnace turned on to keep the trailer warm and several interior lights turned on so when they get to their destination they have light. When they arrive at their destination , their trailer battery is badly depleted / dead. . Their tow vehicle was never designed for that kind of load. (3/4 ton diesel truck )

We have a 2014 truck with the tow package and a 180 amp alternator. My factory charge wire is a #12 fused at 40 amps .
If I travel with my refrigerator on 12 VDC, I will arrive at my destination with a depleted trailer battery.
Again , from what I was told the TV charge system is designed to charge the trailer battery only .If I want to run my refrigerator while traveling and arrive at my destination with a charged trailer battery then I set the refrigerator to propane.
This method has never failed me !!

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Old 01-08-2018, 10:39 PM   #17
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#12 wire is no where near big enough. This is easy to check, just measure the voltage over your rv battery posts with the tug engine running and the fridge and whatever else you want supplied turned on. If the charge voltage at the rv battery is less than 14.2 volts minimum with the battery 50% or so discharged, you need bigger wire.

If you are interested in the details, read on.

If, for the sake of illustration, the entire charge circuit of, say 40 feet one way, was #12awg wire, and you pushed 30 amps through it (20 for the fridge, and 10 for battery charging), the expected voltage drop to the battery would be between 3 and 4 volts. Your alternator voltage (assuming it is not down regulated to save fuel) will be about 14.2 or or more volts. A drop of even 2 volts, much less 3-4, would result in trying to charge the battery at about 12.2 volts - ain't gonna happen. With this scenario, battery depletion, not charging will result.

Assume for further illustration that the fridge is turned off, and only 10 amps is needed for battery charging. Keep in mind here that at 10 amps, it will take 5 hours of driving to put just 50 amp hours into a depleted battery. Put another way, if your dual 6 volters are down to the half mark, you will need to drive for ten hours straight to top them up. But actually, the current will taper off as they charge, so full charging will take much longer than those 5 and 10 hour estimates.

Anyway back to our second illustration - 10 amps over a 40 foot #12 circuit (battery charging only, no fridge or other load). Voltage drop here would still be about 1.3 volts, taking the battery charge voltage down to about 13 volts - still FAR too low to accomplish significant charging on a partially depleted deep cycle battery.

For another scenario, lets assume that the battery is not much depleted, and we need only, say, three amps to top up a bit. Even at only 3 amps, the voltage drop in #12 wire will still be around 0.4 volts, taking battery charging down to, maybe 13.8 or so. This is only just barely able to keep a fully charged battery topped up. It will not accomplish significant charging.

Bottom line, unless wire size is larger, battery depletion, not charging will occur if the fridge is run, and if the fridge is not run, the only thing you might just barely accomplish is keeping a fully charged battery topped up.

Ok, I'm almost done. If you are still with me, you might consider a nice movie, or some couch time with the other half...

Final illustration - fridge on plus 10 amp charging for a total of 30 amps, but this time with #4awg battery cable for the entire circuit. (Price that out for further entertainment, and make sure that it is pure copper, not coated aluminum). Voltage drop for this setup will still be almost 0.6 volts, taking battery charging down to maybe 13.6v or so. Again, this is nowhere near enough voltage to effectively charge deep cycle batteries. Without fridge load, and charging at 10 amps, charge voltage will be ~14 volts. Finally, we have voltage that will charge a depleted battery, but likely very slowly. At this voltage, in fact, the dual six volters will only accept a fraction of the 10 amps we are assuming here, so charging would be horribly slow.

Bottom line - even with #4 cable, you are not going to charge depleted rv batteries with the fridge turned on, at least not with the 21 with the batteries at the rear of the trailer (nice idea that - NOT). Some charging will occur without the fridge load, but it will not be fast or efficient. Other trailers which allow shorter runs will be less of a problem, but I expect that stock charging circuits are bloody unlikely to be anywhere near heavy enough.

I have puzzled over this for some time now, and the only way I have found that MAY accomplish proper rv battery charging by the tug alternator is to use #4 wire (mostly, will have to downsize to get through the 7way plug) to feed a battery to battery charger near the rv battery. Bottom line here is that even with #4 wire, the tug alternator will often not supply high enough voltage at the rv battery to do the job. Further, even if voltage drop were not an issue, the regulators on most if not all tug alternators do not supply a properly patterned multi stage charge, which is the only way to accomplish much with depleted deep cycle batteries.

Sorry about the bad news, but there is no cheap cure for this issue. For what it is worth, I will be installing #4 charge wire, plus a 20 amp battery to battery charger in our 21 next year, and I will report on results. I will initially try to run the return current through the trailer frame rather than cable to see if that works, but if it doesn't, the entire circuit will be #4 copper. The saving feature of this setup is that as long as I manage to deliver 13volts to the charger, it will step the voltage up to the levels needed for a proper multi stage charge. With #4 cable, I think I can do that, even at the back end of the 21. We shall see.
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Old 01-08-2018, 11:00 PM   #18
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Good post. I have an answer. Run the fridge on propane instead, and get solar. We arrive at our destination fully charged.
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Old 01-08-2018, 11:49 PM   #19
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Another alternative for the electrically adventurous is a DC-DC boost converter. I'll not go into details for various reasons, mostly due to the complexity of the design. It won't come from a book...

Robert's solution is a whole lot easier, and it is the one I use.

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Old 01-09-2018, 01:18 AM   #20
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I have 2/0 welding cable to my rear bumper to run my winch. I should be able to pump some amps through this 1/2 in dia cable.
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