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Old 08-12-2009, 05:30 PM   #1
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2005 30' Classic
Burlington , Ontario
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Charging voltage?

We've just been away with the trailer for a short one week trip.

Before we went, I plugged a digital battery condition meter into a 12v socket in the bedroom and kept an eye on it all week while we were plugged in to 110v.

Every time I looked at the meter it registered either 13.8 or 13.9v.

I'm just wondering if this is normal?

Should I not at some times be reading a voltage somewhat lower as the charger cycles on and off, or am I in fact seeing the voltage that the converter is putting into the trailer's wiring system which may not be the same as what it is delivering to my coach batteries?

Just don't want to ruin the new agm batts I just put into the trailer!


Brian & Connie Mitchell

2005 Classic 30'
Hensley Arrow / Centramatics
2008 GMC Sierra SLT 2500HD,4x4,Crew Cab, Diesel, Leer cap.
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Old 08-12-2009, 05:35 PM   #2
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Common Sense , Texas
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13.8 Volts is the normal charging voltage, and the converter does not cycle on and off charging the battery in its factory configuration.

If however, you disconnect from AC power, the battery voltage should then slowly go down to 12.6, or so, with no load.

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Old 08-12-2009, 05:37 PM   #3
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2002 22' International
Austin , Texas
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I'm not an expert, but when I check voltage it varies with what is turned on and operating at the time. Since you raised the question, I would have to do a test to see if the internal trailer charger drops voltage as the the batteries approach full charge. I hope someone else has this all researched.
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Old 08-19-2009, 05:03 AM   #4
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1984 31' Excella
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Go on line for the type of converter you have. Each manufacturer will have information (at least mine did) concerning charge rates/current/voltage.
All your questions should be answered there.
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Old 08-23-2009, 10:51 PM   #5
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13.9 is fine if you are using the Airstream on a regular basis and drawing from the battery but in time, especially if you don't draw it down much, it will start to gas the water out. I like 13.6 as a nominal everyday voltage output. Those tenths do make a difference in a few weeks or months.
I really think the higher voltage during bulk is best, even up to maybe 14.8 is safe but the float needs to be 13.5 or even lower in hotter climates if you store your unit in the summer.
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Old 08-23-2009, 11:16 PM   #6
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13.8 volts is normal...but it depends on what kind of charger you have. The new high end chargers are three stage, and go in to trickle mode when the batts are charged. And actually a 12 volt batt isn't a 12 volt batt. 12 volts is actually considered dead.
You have to give batts more voltage than they are rated at to get them charged.
Kind of like when you have to pay a mandolin player more than they are really worth.
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Old 08-24-2009, 06:30 AM   #7
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If the voltage is too high, the battery will get hot and give off noxious gases. If you pay the mandolin player too much, will he exhibit a similar physiological condition?

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