Charging Battery from TV - Fiberglass RV


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Old 09-23-2008, 11:07 AM   #1
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Hi All,

Forgive me if this has be discussed to death already, but I've exhausted the search function and the Scamp Wiring Diagram in the Doc Centre just isn't speaking to me...

I'll be installing a new PD Intelli-Charge converter in my Trillium in the next few months, which will take care of battery charging requirements while connected to mains power. What about when underway?

From what I see in the Scamp wiring diagram, the tow vehicle's incoming 12V positive, the battery's 12V positive, and the converter's 12V positive are all connected to the same black 12V wire, which would then (theoretically) be connected to the positive on the trailer's fuse block. If this is the case, does that mean the trailer's battery will be charged from the tow vehicle? At (I assume) approximately 13.6V constant? Does this present any long-term danger to a typical deep cycle battery (or twin 6V batteries)?

I ask because I'd like to install a DC-only fridge and ideally have it running full-time, even while underway. This drain will likely be too much for long-term operation on the house batteries without power input from either the converter or the TV.

Any words of wisdom are appreciated!
~Tim
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Old 09-23-2008, 11:17 AM   #2
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I tested just this question on my trailer hooked up to my Ford with the trailer tow package that had 12v to the appropriate pins on the 7 pin connector over about a 5 hour trip.

It did nothing more than replace the current being drawn out. Drain incurred during the stopped periods when the reefer ran off of the trailer's battery was never replaced.
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Old 09-23-2008, 11:31 AM   #3
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I tested just this question on my trailer hooked up to my Ford with the trailer tow package that had 12v to the appropriate pins on the 7 pin connector over about a 5 hour trip.

It did nothing more than replace the current being drawn out. Drain incurred during the stopped periods when the reefer ran off of the trailer's battery was never replaced.
Similar result here. We've towed for many hours with no problem. If you consider the voltage drop in the wire to the trailer (even #8 or so) plus the power it's taking to run your fridge, you're just not going to over-cook your battery. If you're lucky, you'll just about maintain an almost full charge.

Parker
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Old 09-23-2008, 11:36 AM   #4
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Interesting... and a bit of a disappointment, too! I was hoping that there would be enough juice flowing into the battery to charge it back up after an overnight draw-down. Since my wife and I are typically on the move from one unserviced site to the next, I was hoping the TV would act as a generator during the long driving days.

This is going take more thinking!

~Tim
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Old 09-23-2008, 11:44 AM   #5
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Interesting... and a bit of a disappointment, too! I was hoping that there would be enough juice flowing into the battery to charge it back up after an overnight draw-down. Since my wife and I are typically on the move from one unserviced site to the next, I was hoping the TV would act as a generator during the long driving days.
Tim,

Give it a try before being too disappointed. With a depleted battery from overnight use without recharging, the voltage will be low enough that it will certainly receive a charge and be ready to go again. By overnight use, I'm talking about lights and small current draws. As you indicated, the battery won't run the fridge all night. If you really want to operate that way, I suggest getting a 3-way fridge that can run on propane when you're not towing or connected to mains power.

Parker



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Old 09-23-2008, 11:45 AM   #6
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In my case, the charge line from the TV is more than enough to recharge my (small) trailer battery as well as run the fridge on 12V. However my fridge isn't very efficient on 12V mode so I'd assume that this only works because it has a lower power draw than more modern units. I'd also assume that bigger wiring from the TV battery would help a great deal.
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Old 09-23-2008, 11:48 AM   #7
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Hi Parker,

Will test before lamenting! As to the suggestion of getting a 3-way, however, that's not really an option in my Trillium. It's currently equipped with only an icebox, and retrofitting in a sealed combustion area (along with installing the venting needed to supply that area!) isn't something I'm willing to take on at this point in time.

An aside for anyone else out there with an icebox, those 'freezer paks' are fantastic! 5 of those kept the box cold all through last weekend, though we did have torrential downpours and ~10C ambient temperatures.

~Tim
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Old 09-23-2008, 11:15 PM   #8
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it will vary between rigs and batteries and charging systems, but for the most part, if running your fridge on 12v you will not get much of a recharge at all.

I think you will find with your iceboz.. that a good days drive will recharge enough for basic needs, and sometimes beyond.

With the 12 connection between tow and trailer, you can also use the car battery in emergency situations for short periods. I ran a few days like that, starting the car when I wanted to take a shower and was drawing a ton for the water pump.

The other stuff.. have a back up system or two.

I have never been stranded without the basics using these tools and methods. I may not have gotten to watch all of the Final season of the Sopranos on my 12v tv when I wanted, but I have always been warm dry and well lit..

oh, and I had good lights too! :-P
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Old 09-23-2008, 11:20 PM   #9
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Tim,
Another option to consider would be an alternator for your tow vehicle with much larger capacity. Auto parts stores should have some higher amperage units available. Think ambulances, and police/fire vehicles. Larger gauge wire for the charge and ground conductors will also help to reduce line loss. Cleaning all ground connections, particularly at frame contact points may make a significant improvement. In fact, that should be a regular maintenance item as ground problems are by far the most frequent electrical problems with RV's.
Contemplating solutions to RV challenges can be a lot of fun, ultimately rewarding but during the process quite frustrating.
Welcome to the educational process,
Kurt & Ann K.
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Old 09-24-2008, 06:32 AM   #10
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My sense of the problem is that the tow's alternator is seeing some kluged together voltage of both batteries together. More likely, it's just seeing the tow's battery. It doesn't know that the trailer's battery is down.

I expect that when hooked up to the trailer, the tow's battery will try to equalize with the trailer battery and the tow's alternator will try to keep the one battery it sees topped up. All in all, pretty slow way of recharging the trailer battery.

Another, but vastly more expensive option, is a second alternator tied through the 7 pin connector to the trailer battery. We sell trucks with a second alternator option. Chassis cabs, etc. destined for ambulances and such with heavy electrical loads and multiple batteries.
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Old 09-24-2008, 11:30 PM   #11
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Dual output alternators are also available from the marine world.
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Old 09-25-2008, 07:57 AM   #12
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Dual output alternators are also available from the marine world.
This is a good observation. Especially since marine alternators tend to be more robust for providing high current for long periods of time. They are usually paired with an external voltage regular.

BALMAR is a well know brand of marine alternators and regulators.

I wonder if those people with a high efficiency solar panel on the roof don't do as well with on-the-road charging. Although I wonder how the electronics of the charge controller handles the constant flickering of current that a moving solar cell might see.

(I'm trying mightily to resist the urge to hijack the tread into one of my silly "get rich quick" diversions about mounting an alternator on the roof with a little propeller...must.....stay.....on.....topic.....arg h!)
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Old 09-25-2008, 10:54 AM   #13
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Hijack away! That's how we all learn... and I've already had many answers to my questions. Thanks, all!

I'll do some testing first, once I rewire the Trillium this winter and save up enough $$ for the twin 6V system I'm pining after.

I'm not too keen on changing out the alternator on my tug, though, so here's hoping this wind-powered generator concept is more than a pipe dream! Our tow vehicle is an '05 BMW X3 that's still under warranty; my buds at the dealership have politely suggested that I'd void the warranty, should I start mucking about with the electrical system that deeply.

~Tim
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Old 09-25-2008, 11:36 AM   #14
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Tim,
They use wind generators on sailboats all the time, but not sure if it would stand up to going down the highway. Plus there a little noisy for in a camp ground.

Bill K


I'm not too keen on changing out the alternator on my tug, though, so here's hoping this wind-powered generator concept is more than a pipe dream!
~Tim
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