Scamp 12v Charging on Road Question - Page 2 - Fiberglass RV


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Old 08-14-2014, 10:02 AM   #15
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Originally Posted by CampyTime View Post
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, 10:17 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, 10:38 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, 11:01 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, 11:36 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, 11:49 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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Old 08-14-2014, 11:56 AM   #21
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It is unlikely that you have a #10 ground unless you specified it. My installer charged me an extra $25 because he had to buy #10 wire, which is not normally used.
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Old 08-14-2014, 01:05 PM   #22
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It is unlikely that you have a #10 ground unless you specified it. My installer charged me an extra $25 because he had to buy #10 wire, which is not normally used.
Same with my installer of my 7 pin plug on the TV except that they did not want to go and purchase the #10 and went with #12.

Going to scrap yard you can often get good #10 or #8 wire cheaper than you can buying it new.
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Old 08-14-2014, 01:34 PM   #23
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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.
Not so much when you are traveling across Nevada in the summer! With the outside being OVER 100F and the refrigerator side of the Scamp in the sunlight the 'fridge struggled to stay cooler than 40F even when set to "MAX". We do, though, always "cold soak" the refrigerator for a couple of days before heading out.
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Old 08-14-2014, 01:51 PM   #24
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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...
Or think of this fine gentleman, think of your alternator as filling the cup (the battery charge). If he's drinking faster than.... Oh never mind.
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Old 08-14-2014, 03:32 PM   #25
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Dear Bob,

No doubt I explained everything incorrectly, and would be hard pressed to correct. My knowledge does not even approximate any replies I read, and so I am just a learner. A lot to soak in, if you will.

My Scamp is a 2012. 13er. I will ask my mechanic to change out ground wire to #10 when I speak to him next. I will probably wait to buy new battery as it will just sit all winter anyway.

Thank you for teaching me some. I understand things theoretically, but not deeply as you gentlemen can.

What is the difference between group 24 and 27 batts? Everyone calls the 27 an upgrade, so when I buy I should get that?


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Old 08-14-2014, 04:20 PM   #26
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Paying your mechanic to install a larger ground wire is no assurance of, and has almost no chance of, fixing what is a much larger problem that has yet to be easily resolved in the RV community as a whole.

But it sounds like you may have the newer type of converter, but I am confused about the mention of an ON/OFF switch of some sort. Can you tell us the name on the front of the converter, it could be either 'American" brand or "Progressive Dynamics". The American brand will have about 5-6 fuses positions, the Progressive about 10-12 fuse positions.

Bottom line, running the refrigerator on 12 volts while under way is not a viable option for at least 98% of RV'ers. To that end, many RV refrigerators are 2 way, 120VAC and LP only and almost none are offered as 12VDC and LP except for large truck applications.

Is there some concern with using LP while under way? If so. voice your concerns.

BTW: A Group 27 battery is the next size larger from a group 24 and has about 50% more reserve capacity, meaning it's sorta like having an extra 1/2 of a battery. BUT, as it has a higher capacity, it can draw more from you alternator to recharge while towing.
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Old 08-14-2014, 04:24 PM   #27
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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.

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
It's true that the fridge wants to see amps but amps come from volts and power is amps times amps.

As to wire size, the nice thing about small trailers is that wires are short and it's the combination of length and diameter that counts. The difference between these wire sizes #8, #10, #12 over 20 feet is about 0.1 volts between sizes.

I might use a larger wire if wiring from scratch but I doubt that I would spend time replacing a #12 with a #10 for a tenth of a volt improvement.
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Old 08-14-2014, 06:03 PM   #28
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Amps times Amps = ???
Power Formula sez: Amp times Volts = Watts
Voltage drop over a distance is relative to current flow and is not a fixed value.
I (current) x R (resistance) = E (voltage drop)
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