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Old 12-14-2013, 01:09 AM   #21
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Originally Posted by jamie beers View Post
I read a blog I found on google, this person mentioned from their tv's 130 amp alternator...
The alternator capacity isn't likely important, because even 30 amps to the trailer (three times what the 'fridge needs, and enough that most people would be happy with the battery getting this charge rate) is no problem for any modern auto electrical system.

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Originally Posted by jamie beers View Post
... they were getting 5 amps of battery charging. They installed #2 wire and then got 25 amps battery charging.

Is this what people mean when they say you need to install a heavy wire from your tv if you want to run your fridge on 12v? So it gives your batteries a better chance of handling the fridge draw? j
Sort of. The problem is that the tow vehicle is regulating the alternator's output to a suitable voltage level in the tow vehicle. If any significant current is flowing to the trailer (whether it is going to the refrigerator or battery), voltage is lost to resistance in the wiring. Since any loss will bring the voltage lower than ideal for battery charging, this is a problem.

The original wire gauge is not given, but if it were 12 ga, 40 feet of that (from the front of the tug to the trailer and back, but not allowing for connectors or the wire in the trailer) would have about 0.064 ohms of resistance. That doesn't sound like much but at 5 amps that would be about 1/3 of a volt, enough to make a significant difference to charging when the trailer battery is close to charged... and if 10 amps is going to the refrigerator at the same time that's another 0.64 volts lost, a substantial difference.

2 ga is huge (starter cable size), with one-tenth the resistance of 12 ga... probably not a good value for the cost and weight of the cable. I ran 10 ga - the largest that would go into the same crimp splice as the wire from the socket for the trailer - but if I were to do it again I would use something substantially larger... maybe 6 ga.
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Old 12-14-2013, 08:21 AM   #22
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I assume if you have solar it will provide enough current to run the frig on 12v while traveling. Am I assuming correct?
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Old 12-14-2013, 08:47 AM   #23
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Jamman's link to the Dometic specs shows the 855x as being 130W @ 12v or 10.1 ah. No idea how much time in a day the fridge is actually running though, does anyone have know or have any guesses? I'd think it would depend a lot on how long your "traveling".
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Old 12-14-2013, 09:11 AM   #24
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And, it may have a lot to do about the weather you're towing in as how effective the solar would be recharging the battery.
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Old 12-14-2013, 09:49 AM   #25
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I assume if you have solar it will provide enough current to run the frig on 12v while traveling. Am I assuming correct?
I have the solar and even in direct sunlight it will not allow the fridge to run on 12V without draining the batteries. I drive with the fridge running on propane.
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Old 12-14-2013, 09:57 AM   #26
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We tow with the frig on 12V.
Our tow vehicle is a 2012 Tundra work truck with the tow package. The maximum alternator output is 170A. The 12V charging supply wire is 10 gauge. The 12V voltage supply from the TV is turned off when the ignition switch is in the off position.
The 2013 Escape 19 has 2 photovoltaic panels factory installed on the roof and two 6V batteries.
When we tow for 7 hours on a clear day and stopping aprox. 1.5 hours to refuel the vehicle and ourselves the battery level reads 85% after we set up and convert to LP gas. So, it seems that the output from the truck alternator and the solar panels is adequate but the batteries are somewhat depleted. This is the longest that we have towed with the frig on 12V power. We usually plan smaller, more realistic, and comfortable trips between campgrounds. We tow aprox. 55 mph and take the time to enjoy the ride and plan accordingly.
Pre-cooling the frig before the trip with 120V, putting cold items in the frig, and removing the freezer compartment make a big difference.
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Old 12-14-2013, 10:24 AM   #27
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I think the key here is a proper tow vehicle set up where the charge wire and alternator output is sufficient to allow the voltage back to the trailer battery, combined with the solar to add back enough charge. Most factory wiring is not adequate and a separate charge line is sometimes needed.
At 50% run time of 10 amps over 8 hour towing would require 40 a/h discharge. Without any allowance for solar and alternator, a 128 a/h group 29 or dual 6 volts 230 a/h should be sufficient. The input from solar and alternator would mitigate longer run times and higher outdoor temperatures. Towing at night would probably only allow minimal charge from the tow vehicle due to use of head and other lights and the additional use of trailer lights. Of course no solar at night either.
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Old 12-14-2013, 12:52 PM   #28
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Thanks everyone for the input. I have to study everyone's responses again to let it all sink in, it's all new to me.

I suppose ideally I'd know the alternator's output, what amps the tv requires to function, how many amps are going to the trailer battery, how many amps the fridge is using, how many amps are left for charging the tv battery (it seems like tv battery is last to receive amps?), plus the amps provided by solar? I suppose a person could spend a few hun for a high output alternator (190+ amps?) too.
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Old 12-14-2013, 01:00 PM   #29
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This was something we had no experience with before we got our 19' (6.7 ft3 fridge, single 12v battery, solar option).

We're still figuring out our preferences, but have concluded that it's not really that big a deal.

Yes, you can run on 12v while driving. Don't forget to switch back to automatic when you pull over -- it doesn't take long running the fridge on 12v to suck the battery down, even with the solar panels on the roof.

Yes, you can run on propane while driving. You should switch the fridge off, or over to 12v, when you pull into a gas station to fill up. A minor hassle, and some times we forget.

Yes, you can pre-cool everything and run with the fridge off for a couple of hours and everything will be fine.

It's all good, don't sweat it.
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Old 12-14-2013, 02:28 PM   #30
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Quote:
Originally Posted by floorpanel View Post
I assume if you have solar it will provide enough current to run the frig on 12v while traveling. Am I assuming correct?
As others have mentioned, the refrigerator is going to use about 10 amps when it is running (which is not all the time, just enough to stay cold). That's 120 watts... do you have panels which put out 120 watts in any weather, or at least the average power used by the refrigerator (e.g. 60 watts if it runs half the time)? If not, you cannot assume that the solar system will keep up... but it would certainly help!

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Originally Posted by jamie beers View Post
I suppose ideally I'd know the alternator's output, what amps the tv requires to function, how many amps are going to the trailer battery, how many amps the fridge is using, how many amps are left for charging the tv battery (it seems like tv battery is last to receive amps?), plus the amps provided by solar? I suppose a person could spend a few hun for a high output alternator (190+ amps?) too.
I wouldn't bother with a high-output alternator, or even worry about the capacity of the one you've got... that's not likely a problem.

No, there is no order of priority in flow of current. Everything gets what it takes dependent on the supply voltage. If the alternator can't keep up, everything (including the tow vehicle's own parts) will get less power... and I think that's unlikely. The challenge for the trailer battery is that it is at the end of a long wire, so it gets less voltage (if current is flowing in the wire), and thus less ability to take charge current; it is affected more by low voltage that the tug's parts.

Yes, I would look at how much current is flowing to stuff in the trailer, so you can see how much has to come down that tug-to-trailer wire after accounting what solar provides... but there's not likely anything of significance other than the refrigerator running in the trailer. The current in that wire, and the size of the wire, determines how much voltage is lost, and thus how much battery charging is limited.
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