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Old 10-22-2014, 05:17 PM   #1
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Converter basics

I've devoured every thread I can find on every nuance of battery and converter best practice, but the basics still elude me, and some of the info seems contradictory.
Clearly the 120v system needs to be supplied by shore or generator power. But how does the converter (OEM Parallax or upgraded with Progressive DC charger) handle the 12v circuit? Is there a charging circuit parallel to the coach circuit or does the charger pass the coach 12v power through the battery circuit? If batteries are absent or physically disconnected, does the converter directly power the 12v circuit? Sorry this is so dumb, but the whole power system constantly stymies me.
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Old 10-22-2014, 05:38 PM   #2
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The converter is wired to the battery circuit which is also the main circuit for the 12 volt "stuff". That main circuit also goes to the fuse panel where several smaller circuits deliver the power to the various items which need 12 volts in the trailer. The converter/charger simply keeps the battery charged at all times. If the battery is not there, the converter/charger directly supplies the needed power which the 12 volt "stuff" uses. With the battery in place, it not only keeps the battery charged, but supplies all the power for the "stuff". When disconnected from 120 volts, the battery supplies the "stuff" alone.
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Old 10-22-2014, 06:48 PM   #3
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Even more confusion; there are three 12 volt systems in the trailer.

The exterior vehicular lights (running lights, turn signals, brake lights, reverse lights) are powered by the tow vehicle only.

The trailer brake system is powered by the tow vehicle during normal towing conditions, but is powered by the trailer battery if the trailer becomes accidentally disconnected from the tow vehicle.

The lighting inside the trailer, entertainment systems, water heater igniter, range hood, refrigerator ignition, tongue jack, etc.... are powered by the converter/battery system.

Think of the converter as a battery charger and/or power supply. While connected to shore power, the newer converters will provide ~12-14 volts dc to charge the battery and/or provide 12 volt dc power if there is no battery present. The older converters charge the battery, but can be damaged if there is no battery in place while the converter is energized.
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Old 10-22-2014, 10:52 PM   #4
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Hi Al,
There should be no contradiction with a modern converter or power center that you have. Its either the 7355 power center that has a converter mounted below the breaker and fuse panel (all in one unit) or a stand alone deck mount 7455 that is a metal box about the size of a shoe box and your breakers and fuse panel are on the wall separate from it.
Regardless the converter works the same.
Its job is to receive AC input and convert it to DC output for your DC loads and also charge the battery. It is a shared load between those two. You have 55 DC amps to work with and the distribution is totally dependent on what you are running at a given time. In other words, if you are running your furnace fan, some lights, etc and it equals 10 amps, you have reduced your converter capacity to charge your battery down to 45 amps. That is just a general example.
With modern switch mode converters, it does not matter if you have a battery. It did and does with older Univolts. Modern units have their own internal filtering and will work fine with or without a battery.
The reason so many people upgrade to multi stage units however is because of the better/faster battery charging and maintenance features they provide.
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Old 11-06-2014, 07:07 AM   #5
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I want replace the Univolt in my '73 Argosy 22. I see many different choices for new converters. How do I figure out the necessary amperage for the new converter? It's a relatively small trailer with one battery.
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Old 11-06-2014, 07:53 AM   #6
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Converter basics

45 amps is plenty for your coach.
I installed a Progressive Dynamics 9245 in our '74 Argosy 26' 4 years ago. Along with a new blade type fuse block.
It has worked flawlessly.


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Old 11-06-2014, 10:52 AM   #7
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Quote:
Originally Posted by Sdbraverman View Post
I want replace the Univolt in my '73 Argosy 22. I see many different choices for new converters. How do I figure out the necessary amperage for the new converter? It's a relatively small trailer with one battery.
I agree 45 amp would be adequate. In that 70s era, your univolt may or may not have an integrated DC fuse board. If so, you would need to separate it from the univolt and reuse it or you can replace it with a nodern DC fuse board that uses common blade style fuses.
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Old 11-06-2014, 11:08 AM   #8
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Battery charging from TV?

A follow on newbie question...

It is not clear to me whether or not the batteries are charged from the TV when underway through the "umbilical." Is this standard or a mod made by the owner?
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Old 11-06-2014, 11:14 AM   #9
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The TV alternator will charge your batteries when connected to your Airstream.
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Old 11-06-2014, 11:33 AM   #10
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Thank you
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Old 11-06-2014, 11:54 AM   #11
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The truck umbilical is capable of charging coach batteries under the following conditions:

1) wired correctly to connector on truck.

2). Trailer umbilical wired to batteries correctly and appropriately fused.

3) good ground connection between truck and coach when plugged in. 7-way connectors MUST be clean and tight fit this to work at all.

4) most critical: truck charging system is up to the task. A low output alternator in the truck will not provide much of a charge current. A high output alternator is usually part of a towing package.

I get some charging hooked up to my Tacoma, but not near as much as the converter on shore power....and when I am running at night with all the headlights and other lights on, it's a lot less available to charge the coach batteries. It's a YMMV thing, unfortunately.

When I'm towing in daylight the solar system on the coach also contributes some. I've never run out of power on the road, knock on wood.


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Old 11-06-2014, 12:12 PM   #12
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Thanks 68 Overlander and rmkrum
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Old 11-07-2014, 03:40 PM   #13
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i just pulled out original Univolt convertor from 1972 Sovereign, the 12volt system was working but wasn't charging the battery ... in fact it overloaded the battery, the cables went super hot into the battery. bear in mind this AS had been sitting for years ... ok, so tried wiring in new power converter & panel.. now there's no 12v working..
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Old 11-07-2014, 04:49 PM   #14
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Converter basics

It sounds like the battery was bad if the cables were getting hot.
When you pulled the Univolt. Did you remove the fuse panel and use it with the new converter?
If so. How did you wire the new converter to the old fuse panel? Pics would be nice.
Do you have a white wire going to the negative post on the fuse panel? Is it connected to the skin/frame of the coach?
Have you read the output voltage of the converter?
Most converters have reverse polarity protection. Usually 2 fuses. Are they still good?
If you don't read voltage from the converter. Disconnect the + and - wires at the converter. Make sure the converter has AC power. Then check for voltage at the + and - terminals. Most converters will "crowbar" shutdown if the output is overloaded.
There are basic steps to trouble shooting your problem.
First disconnect the battery leads and tape off the positive lead.
Check the reverse polarity fuses.
Make sure you have the positive from the converter to the positive of the fuse panel. And the negative to the negative.
Before you power up the converter. Pull all of the fuses from the fuse panel. Check for voltage on the buss that feeds all of the fuses. Your coach may have a fuse in the negative wire going to the battery. Mounted alone on the skin.
If you have voltage. Install the larger fuses first. Checking the voltage after each fuse.
If things are wired correctly. I would guess when you disconnect the battery. You will have 12 volt power.
If not, we will take it one step at a time.


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