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Old 11-27-2021, 12:27 PM   #1
fishmaine's Avatar
Newmar Owners Club
Workhorse Chassis Owner
Join Date: Jul 2018
Location: Maine/Arizona
Posts: 80
Inverter Selection Help Please For 400 Watt Inverter

I am replacing the inverter in my 2004 Newmar Scottsdale motorhome which is putting out voltage readings between 7 volts and 108 volts and never worked properly. It originally had a Dimensions brand 300 Watt quasi-sine wave inverter (OEM). Later that was replaced with a 400 Watt Xantrex sine wave inverter which never worked properly (XS400 model). Apparently (per Newmar) this inverter is just intended to power my "entertainment equipment" only: TV, blue ray, etc. It may also power laptops, printers, etc. On the Newmar's web site they recommend the Magnum MM612 600W as a replacement for my OEM unit but that recommendation is (I'm sure) probably several years old, and that unit is quite pricy on Amazon at $306.00**. I am thinking there is probably a newer, better (& probably less pricy) option. In terms of selection here are the criteria:

1) My motorhome has 2, 12 volt batteries (lead acid).
2) I do definately need the "pass through" power option (passes house power through inverter when rig attached to shore power).
3) Preferably pure sine wave, but quasi sine wave would probably work also.

Don't necessarily need remote on/off switch but would be nice.
Any help would be appreciated.

2004 Newmar Scottsdale on 2003 W-22 Workhorse Chassis, 8.1 Vortec, super short 30.5', AZ in winter & ME in summer. Half Of Life Is Just Showing Up
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Old 11-27-2021, 03:53 PM   #2
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Join Date: Sep 2018
Posts: 187
I would follow the Newmar recommendation, but install the current model MM612.

There is a big "however," of which you should be aware.
These pass-through inverters frequently fail to maintain the proper voltage when there are voltage sags and surges as is common in older RV parks. They also become erratic when the house batteries start to sulfate. Ambient temperature in the installed space/cabinet also impacts their performance, too hot and they shut down until they cool off enough to restart. In hot climates the capacitors dry out and start to fail after only a season or two if the unit is stored in the heat.
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