Go Back   iRV2 Forums > MOTORHOME FORUMS > Class A Motorhome Discussions
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on iRV2
Thread Tools Search this Thread Display Modes
Old 05-31-2014, 09:33 AM   #15
Moderator Emeritus
Gary RVRoamer's Avatar

Fleetwood Owners Club
Freightliner Owners Club
Join Date: Jan 2000
Location: Silver Springs, FL. USA
Posts: 16,418
The amp-hour size of your battery bank is a limit on how much power the inverter can draw, but need not be a limit on the size of inverter you purchase. On the other hand, there is no point in buying extra inverter capacity you can't use, unless perhaps you plan to upgrade the battery bank in the future, or move the inverter to another RV.

You really need to come at the problem from the other direction. Figure out the wattage you feel you need, then spec the inverter that can deliver it PLUS a battery bank that can deliver the necessary amps for the desired number of hours. If you are unable to meet the battery amp-hour demands, then you need to reset your power usage expectations and that will in turn reduce the size of the inverter and the battery demand. It's a matter of matching wants and needs to a budget, something most all of us grapple with every day.

A common mistake in assessing battery capacity is to overlook voltage. An inverter requires a minimum voltage, often 10.0-10.5dcv, in order to produce usable 120v power. A high amp rate reduces the battery voltage, which generally means you cannot expect to get a full 235 AH from your 2 x 6v batteries and still have adequate voltage for inverting. Even a brief moment of high amp draw might force the battery voltage below the inverter's minimum, resulting in an inverter shut-down. The 5-hour rate is typically much more representative of actual battery capacity when using an inverter, but it depends on how much amps you expect to draw.

Gary Brinck
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL
Gary RVRoamer is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 05-31-2014, 12:05 PM   #16
Senior Member
tropical36's Avatar
Join Date: Jul 2007
Location: SW Florida
Posts: 1,163
Originally Posted by ardbark View Post
I'm finally getting around to adding an inverter and want to make sure I match the Inverter size to the house battery pack.

I've got my eye on the Xantrex PROWatt SW series, it seems to be the favorite of lots of veteran RV'ers. It's a pure sine wave model which my computer will enjoy, and comes in several sizes which I have to pick from. Hence my question.

I have two 6v house batteries each rated at 225 amp hours @ 20 hours and 185 AH @ 5 hours. The most load the inverter will see at one time will likely be no more than house lights (all 12v) and a laptop and monitor, or a flat screen TV and DVD player if we're watching TV, maybe a small 110v sound system, awning lights (110v) when we're on the patio, those sort of things. No hair dryers, no residential fridge (although I wouldn't mind keeping that in mind if/when the Norcold finally dies). So no really big loads. If I need AC or the microwave I'll fire up the genny.

I get adding up watts from all the toys and picking an inverter size to match, but is there a formula for matching Inverter watts to rated Amp Hours for the batteries?

With just the two batteries, you'd want no more than a 1KW, even though you don't even need that much with a 400 watt, capable of doing the job. Just so you know, the lights have nothing to do with the inverter, except to rob some battery power from it. If your puter is a laptop or otherwise running off of it's own battery, it won't care about the wave form and most other things you mentioned won't either, unless maybe you install a residential fridge with an ice maker and it's funny electronics. If I ever replace the fridge, I expect to pay about $400 for a small one that will hold more than the OEM and an ice maker will be the furthest thing from my mind. I don't even like them, with all the different water supplies, entering the coach. There's convenience stores all over that sell the stuff, when needed. I don't want to be chopping on the woodwork either with enlarging the opening and removing well needed storage drawers and such. I've found that it's hard to go very far without passing a grocery store and could probably get by with less than that, even.
Just so you know, we have a 1KW mod sine wave inverter and run our OEM fridge on it, when going down the road and for short periods in between. I installed a relay as well, so that it switches over when a 120vac external source is present and whether it be from the shore or genset. You can shut the electric off at the fridge and when on propane for now.

07 Fleetwood Revolution LE 40E_Spartan MM_C9 Clatterpillar_ Allison 3000
1998 36ft. National Tropi-Cal Chevy Model 6350 (SOLD)
Dinghy_2010 Jeep Wrangler JKU ISLANDER
tropical36 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
Inverter for whole coach question jdwky RV Systems & Appliances 51 02-25-2016 10:25 AM
Magnum Inverter Question. gemini5362 5th Wheel Discussion 28 05-19-2014 10:28 PM
Dimensions 2000 Watt inverter, no battery charging, need help ASAP! FIRE UP Winnebago Industries Owner's Forum 29 02-23-2014 11:36 PM
Dimensions 2000Watt Inverter LJowdy Winnebago Industries Owner's Forum 8 02-10-2014 05:23 AM
Full Time TV on Inverter max49 Technology: Internet, TV, Satellite, Cell Phones, etc. 18 12-23-2013 08:37 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 01:27 AM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.