Scamp 12v Charging on Road Question - Fiberglass RV


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Old 08-13-2014, 04:39 PM   #1
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Scamp 12v Charging on Road Question

Quick question before we leave on extended trip. Our tow vehicle has the 7 pin connector and I believe that has a live 12v output. Am I correct in thinking that this live 12v will run my refrigerator and charge the battery as I go down the road? Or will the refrigerator draw too much and drain the battery.

Sorry if it's been asked before but I don't have time to check any other threads.
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Old 08-13-2014, 04:52 PM   #2
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Don't know your specifics, but I opted not to get a 3-way fridge when I was told that the fridge on 12V would use all the power that could be delivered by the tow vehicle, leaving none to charge the battery. So, if you left camp with a depleted battery, you would arrive with a depleted battery.
On top of that, you would require a #10 ground in the tow wiring or it wouldn't deliver enough power to run the fridge, never mind charge the battery.
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Old 08-13-2014, 05:05 PM   #3
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We have found that in general it's not necessary to run the fridge when driving. It stays relatively cold. If you're concerned put some ice into a sealed container and it will keep the fridge cold enough.
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Old 08-13-2014, 05:48 PM   #4
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We are driving and on the road 14-16 hours the first and last day and it's hot out! So the fridge draws that much?
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Old 08-13-2014, 06:00 PM   #5
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Chill your fridge a couple of days before you leave. Fill it with cold stuff at least a day before you leave,

In the mean time fill a couple of small containers with water and freeze them solid. Put them in your fridge it will easily keep the fridge cold for your drive. Before you leave to return home buy yourself some ice and put it in a container in the fridge, it will keep the fridge cold for the ride home.
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Old 08-13-2014, 06:36 PM   #6
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Why not just run it on LP and forget about 12 volt problems (Which you will have if you try to run the refrigerator off of the charging line) It's safe and legal.....

I run mine n LP all of the time while underway and most of the time when camped.

If it's a regular 2/3 way RV refrigerator it will draw about 9-10 amps on DC. and you will be lucky to get 6 of those out of the charging line, the rest will come out of your coach battery

BTW: towing for 14-16 hours straight is a recipe for bad things to happen.



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Old 08-13-2014, 09:40 PM   #7
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So the fridge draws that much?
A lot will depend on how big it is, but yes, you can recharge your trailer battery OR run the refrigerator, but not both at the same time.
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Old 08-13-2014, 09:48 PM   #8
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Why not just run it on LP and forget about 12 volt problems (Which you will have if you try to run the refrigerator off of the charging line) It's safe and legal...
A lot will depend on how old the fridge is, and how vigilant you are about inspecting the burner in the back. I had a 40 year old fridge, and just assumed that it was OK without really knowing if it was...

http://www.fiberglassrv.com/forums/f...ire-37702.html
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Old 08-14-2014, 03:42 AM   #9
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We have found that in general it's not necessary to run the fridge when driving. It stays relatively cold. If you're concerned put some ice into a sealed container and it will keep the fridge cold enough.
+1. We freeze a gallon water jug. It works well. Raz
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Old 08-14-2014, 05:11 AM   #10
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The Dometic 3 way w/o freezer pulls about 10 ADC. When I run it on DC I almost always arrive with a dead trailer battery. I've checked and my tow vehicle is putting out about 4 amps to the trailer so it's a net loss for me with the refrig on DC. A longer tow time is just a worse situation.
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Old 08-14-2014, 06:08 AM   #11
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Don't know your specifics, but I opted not to get a 3-way fridge when I was told that the fridge on 12V would use all the power that could be delivered by the tow vehicle, leaving none to charge the battery. So, if you left camp with a depleted battery, you would arrive with a depleted battery.
On top of that, you would require a #10 ground in the tow wiring or it wouldn't deliver enough power to run the fridge, never mind charge the battery.


Hi Glenn,

I learned something new here today. Always thought driving to or from site how cool it was to keep my fridge cold on 12v while charging my battery too! Guess that's not happening as I thought!

So basically, the fridge gets some amperage from the tug and the rest from the battery while towing? Why does all the power go automatically from the tug to the fridge if it's on then? In my pea brain somehow thought it would split or share between batt and fridge.

Glenn, my mechanic installed my wiring and 7 pin for me. Is there any way I could tell if I got under vehicle if I have that #10 ground wire you mentioned?

Finally, When I'm plugged in to shore power, isn't the battery getting a charge?


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Old 08-14-2014, 06:26 AM   #12
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I'm not Glenn, but my 2 cents worth is that all the current from the tow goes to the trailer battery. The refrig is getting its power from the battery. For many/most, less is going into the battery (from the tow vehicle) than is being drained by the refrig on 12v.

Assuming your trailer has a converter it probably has a charging funtion as well so plugging in to shore power will charge your trailer battery.
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Old 08-14-2014, 06:33 AM   #13
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Steve,

Thanks for replying. Yes trailer has a converter. When I'm driving and fridge is on 12v, should I have converter main switch turned to on? I have had it turned off, with 12v switch turned on at fridge. Maybe this is why my fridge wasn't as cold on last long trip I took? Had battery tested and is pushing 500 amps, still good for this year. Tester said battery was good but at 50%. Didn't get that...he used Snap On tester. Said most batteries when good will often push more amps than stated.

Prior owner left trailer plugged in all winter with batt on trailer. Next year I'll get new one, maybe that group 27 once I learn more about it. I keep it on batt tender in basement all winter on a wood block and in garage in summer on same.


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Old 08-14-2014, 08:58 AM   #14
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You probably know this but what might not be understood by some novices is that the charging function of the converter only applies to when it is connected to AC power. While towing it’s inert, just a jumble of electronic parts. It doesn’t charge when the trailer is on DC only and has no effect on drain or recharging. You can have the main switch pretty much on or off as you please. On is probably better since it’s one less thing to remember when you hook up to shore power.
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Old 08-14-2014, 09:02 AM   #15
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Steve,

Thanks for replying. Yes trailer has a converter. When I'm driving and fridge is on 12v, should I have converter main switch turned to on? I have had it turned off, with 12v switch turned on at fridge. Maybe this is why my fridge wasn't as cold on last long trip I took? Had battery tested and is pushing 500 amps, still good for this year. Tester said battery was good but at 50%. Didn't get that...he used Snap On tester. Said most batteries when good will often push more amps than stated.

Prior owner left trailer plugged in all winter with batt on trailer. Next year I'll get new one, maybe that group 27 once I learn more about it. I keep it on batt tender in basement all winter on a wood block and in garage in summer on same.


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All converters are not created equal.... tell us the year and make of the converter you have in your SCAMP. There are some early converters that should be replaced before they burn up your battery, there are some converters Scamp used that just burn themselves up, and there are the latest ones that finally get a decent converter/charger, the Progressive Dynamics PD-4045.

Because you mentioned a converter ON/OFF switch I suspect that you have one of the earlier versions which, if left ON all winter as mentioned, was sure to have done some damage to the battery

The comments from the person who tested the battery are somewhat confusing. First a battery doesn't "Push" amps, they are drawn by what ever load is seen.. Second, a brief test showing a 500 amp surge gives little clue about the batteries ability to deliver a much lower current flow for a period of time and third, a battery at "50%" is about kaput and is in need of replacing unless all you want to run are very basic needs, such as a few lights. My initial suspicion is that the existing battery, if left on it's charger all winter as claimed, was boiled and is now on it's last legs and yes, a new battery is in your near future.

And... if you have the older style of converter, this winter is also a good time to update that converter to current Scamp specs with a Progressive Dynamics PD-4045 power center/converter/smart charger. You and you battery will be much happier as a result.



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Old 08-14-2014, 09:17 AM   #16
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Mine works, but is properly sized & wired:
The fridge draws 10A on 12V.
The 12V coach wire through the 7 pin connector is wired with 12ga wire, which can carry a max of 20A. It comes straight from the alternator terminal.
The white ground wire is 10ga because it has to carry ground for running lights, trailer brakes, and fridge.
The trailer has a newer, but smallish, automotive battery from a junk vehicle, and the TV has an oversize alt & an oversize batt.
While going down the road, it has no problem providing 10A for the frig and 5A to charge the coach batt.
Parking the rig for a couple hours for sightseeing & lunch discharges the batteries some, but not enough to be concerned about (~150AH of total cap, drawn down by 20AH). When running down the road the 110A alternator easily recharges both batteries.

In summary, it is possible to run the fridge, charge the batteries and keep the radio on while driving. BUT, the equipment has to be sized right and well-constructed.
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Old 08-14-2014, 09:38 AM   #17
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I think that your junque yard battery is your best friend in this case.

As it is small and not a deep cell class of battery, it reaches a fully charged state fairly quickly (as automotive type batteries are designed to do) leaving the alternator current available for the refrigerators operation. . If you were trying to charge a deep cell Group 24 or 27 battery that had been run down more than a few percentage points the night before I think your results would be somewhat different.

A higher output alternator just doesn't make that much difference. When you are driving down the road with the a/c and boom box blasting away and all your lights on, you might be drawing a total of 20-30 amps, that leaves a lot of capacity left over for the charging line if needed from even the smallest of automotive alternators. Put a DC amp clamp on the lines and see what you are drawing.

So far, in over ten years of working on (and discussing) this problem in mini-motorhomes as well as in towed RV's, there has now been exactly 3 peeps that have found a combination that actually works and. in all of those examples, excluding the deep cell battery in one manner or another was included.



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Old 08-14-2014, 10:01 AM   #18
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Yes but take that same charge rate coming from your alternator at idling in traffic on a rainy day with your lights on, windshield wipers going and the defroster and see if you will get enough charge to the trailer and battery. Most modern cars have large enough alternators these days when tooling down the highway at 3500 rpm and light demand but significant running at low speed and extreme conditions and you are likely to come up short.
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Old 08-14-2014, 10:36 AM   #19
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Ooops.... I hope that none of us are "tooling down the road at 3500 RPM". That would be about 75 or more in most TV's and over 90 in 5th gear in my Blazer.

Others may be different, but a 4 cylinder GMC Sonoma and a Honda CRV would never see 3500 RPM.



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Old 08-14-2014, 10:49 AM   #20
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Think of your battery as a reservoir being filled by your TV charging system, your fridge is drawing from the reservoir as it is being filled. If you draw more from the reservoir (battery) than flows in (from TV charging) the level in reservoir drops.

If you want the battery to last you don't want it to draw down below 50% charge.

Wire size matters due to voltage drop, longer and thinner the wire the more the voltage will drop between the alternator and the battery end. You can only "push" charge into a battery if the charging voltage is greater than the battery voltage. More voltage differential between charge wire and battery then it charges battery faster than less differential.

This is not the same aspect as what Jim is describing in the ability of the TV to supply the amps to run the fridge. Related in some ways but not the same issue being addressed.

The heating element on the fridge does not care as much about the voltage as long as it can get the amps. Fridge would probably run fine on 11.9 volts where battery with only 11.9 volts of charging voltage would not really get charged much over ~40% charge. Once the battery gets charged to 11.9 volts the "pressure" is equal between the battery and 11.9 volts on charging line. Not much current would flow to battery to increase the charge.

All numbers are examples not actual voltages for given wire of given length. Just trying to clarify the difference.
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