Thread Tools Search this Thread Display Modes
Old 01-10-2010, 06:38 PM   #15
Rivet Master
Lumatic's Avatar

1971 25' Tradewind
1993 34' Excella
Currently Looking...
Estancia , New Mexico
Join Date: Feb 2005
Posts: 5,880
Images: 16
Perhaps my ignorance is my bliss, but I have never felt charging the tt battery while towing was a problem.

Sail on silver girl. Sail on by. Your time has come to shine.
Lumatic is offline   Reply With Quote
Old 01-10-2010, 07:00 PM   #16
Wise Elder
Jammer's Avatar
2010 30' Classic
Vintage Kin Owner
South of the river , Minnesota
Join Date: Dec 2009
Posts: 4,023
Originally Posted by Inland RV Center, In View Post
All modern tow vehicles, can easily charge the trailer batteries. Thousands of owners, do it everyday, without any problems.

However, there are some "must haves" in order to do so.

The charge line wiring within the TV, must be 10 gauge or larger.

The trailer/TV connectors must be in excellent condition.

If charging from 12 volts is inadequate, wow, we then have hundreds of thousand of RV owners that have dead batteries. NOT.
There is a general sentiment in the broader RVing community that the power from the TV cannot be relied upon to provide any meaningful amount of charging. Let's take a closer look. As you note, a typical tow vehicle has 10 gauge wire to the trailer, typically protected by a 30 to 40 amp fuse or circuit breaker, depending on the TV. Often this circuit also feeds the clearance lights on the trailer, through a relay.

Under optimal conditions -- clean, tight connections and relatively new batteries in the Airstream -- the math in my initial post tells us that we're going to max out somewhere below 30 amps, because at 30 amps the voltage at the batteries in the Airstream is going to be 12.7, and at 12.7 volts the batteries won't take 30 amps. What will happen, more typically, is that the batteries will charge at around 15 amps, and if there's a 12 volt fridge or another electrical load in the trailer, the charging rate will be reduced by something like half the amount of the load. As the batteries in the Airstream get older and their internal resistance increases, this rate will drop. It will also drop as the batteries approach full charge.

At this rate, with two group 31 deep cycle batteries, it will take around 8 hours of towing to get from 40% to 90% charge. So yes, the batteries will charge, after a fashion. But they will not charge enough that in a typical move from one boondocking site to another any substantial charging will take place, and they will not charge enough that it makes sense to idle the tow vehicle engine for a period of time just to charge the batteries. Hence, there are people who carry a generator, for no other reason than to charge the batteries.

Originally Posted by ROBERT CROSS
Hassle to you....convenience to me. [...] idling at the campsite, waste of time & gas. A modern genset is much quicker and more efficient.
Gensets have their advantages, among them the possibility of running air conditioning. They also have cost and weight associated with them and in many setups require their own fuel source and require that the generator be physically moved from a storage to operating location. While there exist well-integrated generator installations in Airstreams, that draw fuel from the propane tanks on the tongue and deliver power through a transfer switch, they are rare due to the various difficulties they pose. While it is true that there are efficiency tradeoffs, they are not as great as one might think, because modern pickup truck engines are more efficient at idle than the small gasoline engines in gensets. If we were willing to pay for a water-cooled genset engine with sequential multipoint fuel injection, oxygen sensor, computer, etc., the tradeoffs would be more considerable.

A well designed dual alternator setup on a tow vehicle could easily deliver 75 A to the batteries, at idle, more than any but the more sophisticated generator/converter combinations.


To go through the trouble of supplying 120 AC to the converter that's in the trailer, is to me, a waste of time trying, and a waste of money.

First off all, the TV alternator would "NOT" run at constant speed, therefore it cannot continuously provide 120 volts AC, at 60 cycles, which is required. Any frequency for the 120 volts AC much different than that, will more than likely, burn up the 12 volt DC converter.

Or, did I miss something in the original post?

Andy, I think we're in vehement agreement on that. ;-) That wasn't the suggestion in my initial post. I believe you're replying to a comment by barts.

Jammer is offline   Reply With Quote
Old 01-10-2010, 09:15 PM   #17

2003 25' Classic
Zanadude Nebula , WNY
Join Date: Jun 2007
Posts: 10,802
Images: 1


So....... when your finished looking, do it your way.

I'll do it mine, and we'll both be happy.

Stream Safe...
AF #1

"Sticks & stones can break your bones...and hail will dent your Airstream"

So when is this..."old enough to know better" supposed to kick in?
ROBERT CROSS is offline   Reply With Quote
Old 01-10-2010, 10:22 PM   #18
Maniacal Engineer
barts's Avatar
1971 25' Tradewind
Menlo Park , California
Join Date: Jan 2010
Posts: 1,210
Images: 1
Blog Entries: 4
What I was trying to say was that the problem of reduced charging rate due to voltage drop has several solutions, some of them commercially available:

Newmar DC-DC Converters

These units will allow your towing vehicle to charge the batteries correctly if configured as a charger. The isolated units take 10-16V in and deliver 13.6V out.

- Bart
Bart Smaalders
Menlo Park, CA
barts is offline   Reply With Quote
Old 10-09-2011, 09:28 AM   #19
Rivet Master
Dwight's Avatar
1999 34' Excella
Joshua , Texas
Join Date: Apr 2002
Posts: 548
Images: 2
Good info...

History doesn't repeat itself, people do!
Dwight is offline   Reply With Quote

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Tow vehicle charging batteries safari 28 Batteries, Univolts, Converters & Inverters 25 11-15-2009 10:28 PM
Battery charging from tow vehicle ? rwnash Batteries, Univolts, Converters & Inverters 3 07-29-2008 08:17 AM
Charging the batteries using tow vehicle bci 2006 - 2010 Classic (all lengths) 22 06-09-2008 09:57 PM
Charging AGM trailer batteries from vehicle mswartz Batteries, Univolts, Converters & Inverters 5 05-15-2004 02:34 PM
tow vehicle isolated from A/S batteries?? BOBHASTINGS Electrical - Systems, Generators, Batteries & Solar 13 02-05-2004 12:50 PM

Virginia Campgrounds

Reviews provided by

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002-2015 Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 02:11 PM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.