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.
Reply
  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 10-10-2016, 01:08 PM   #1
Member
 
Krash's Avatar
 
Join Date: Nov 2014
Posts: 71
MSW Inverter and Kill A Watt

Can anyone tell me if a Kill A Watt meter will work the same on a modified sine wave inverter as on shore power?

I am asking because I am testing our new residential refrigerator, and I am reading .5 amps when plugged in to electric, and 1.7 amps when on the inverter.

The rest of the readings are the same on both. 120v, 60 Hz.
I already know that some refrigerators do not play well with MSW inverters.
__________________

__________________
2002 Diplomat pulling:
23' Enclosed Tilt Trailer with:
Car, Boat, Harley, 660 w solar,and 2 bikes
Krash 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 10-10-2016, 01:39 PM   #2
Senior Member
 
Pigman1's Avatar
 
Join Date: Sep 2011
Posts: 1,680
Wow, better than 3 times the current? That's a lot and sounds like something isn't reading right somewhere. Is there any way to get an actual bench meter or even a clamp-on to check and see what your actual current being used is. I've been using a TrippLite dedicated MSW on my KitchenAid household refer since I got the Bus (61,000 miles ago), but haven't done an actual current draw measurement. Just know we boondock a lot and I have not been having battery problems or excessive draw down's overnight. Can't tell daytime as we have 840W of solar on the roof.
__________________

__________________
Pigman
2013 Tiffin Allegro Bus 43QGP
2011 Chevy Silverado 1500 Toad
Pigman1 is offline   Reply With Quote
Old 10-10-2016, 05:00 PM   #3
Member
 
Krash's Avatar
 
Join Date: Nov 2014
Posts: 71
Has anyone ever measured with a Kill A Watt meter on a MSW vs shore power? It is just hard to believe that it would be this far off, but like Pigman1 said, it's more than three time the power being used??

The only thing I can think of is the Kill A Watt can not accurately measure a modified sine wave. But this is really hard to believe!

Does anyone notice extremely heavy draw when using a MSW inverter with anything? Mine is a MSW Xantrex 1500 watt, and has always worked fine. Other than the overhead for the inverter itself, the amp draw of any 120 volt appliance should be the same on shore power or inverter, right?
__________________
2002 Diplomat pulling:
23' Enclosed Tilt Trailer with:
Car, Boat, Harley, 660 w solar,and 2 bikes
Krash is offline   Reply With Quote
Old 10-10-2016, 05:08 PM   #4
Senior Member
 
powercat_ras's Avatar


 
Winnebago Owners Club
Solo Rvers Club
Join Date: May 2015
Posts: 602
Quote:
Originally Posted by Krash View Post
Can anyone tell me if a Kill A Watt meter will work the same on a modified sine wave inverter as on shore power?

I am asking because I am testing our new residential refrigerator, and I am reading .5 amps when plugged in to electric, and 1.7 amps when on the inverter.

The rest of the readings are the same on both. 120v, 60 Hz.
I already know that some refrigerators do not play well with MSW inverters.
I think the important question is what is the DC power being used being used by the refrigerator. If you can read DC amps being used then you can determine the refrigerator use by looking at DC Amps with refrigerator on and with it off, and the difference is what the fridge uses. Multiply this by 12.5 to get watts. Then you can compare that to power used on normal AC ( 60 Watts ). This is the best way to see what the "real" power use when running from the inverter is.

If you do see 2 - 3 times the power being used when the fridge is being driven by the modified sine wave inverter, then this bad - most likely the non 60 HZ power components of the modified sine wave output are turning into heat somewhere most likely inside the refrigerator compressor and may lead to premature failure of it.
__________________
Randy - Manhattan, Kansas
2015 Vista 27N
2016 Honda HR-V
powercat_ras is online now   Reply With Quote
Old 10-10-2016, 05:16 PM   #5
Senior Member
 
Join Date: Jul 2014
Posts: 5,929
My 7.4 c.f. residential refrigerator draws .9 amps when running.

.5 amps seems real low, unless it's a dorm room size unit.

I understand that some new fridges use varable speed compressors. That could effect the amp draw.
__________________
twinboat is online now   Reply With Quote
Old 10-10-2016, 05:17 PM   #6
Member
 
Krash's Avatar
 
Join Date: Nov 2014
Posts: 71
Quote:
Originally Posted by powercat_ras View Post
I think the important question is what is the DC power being used being used by the refrigerator. Then you can compare that to power used on normal AC ( 60 Watts ). It is a pretty sure bet that the 1.7 is not accurate.
That is a great idea! I have a Tri-Metric wired in, so I will measure the difference between the refrigerator on and off while using the inverter. Why didn't I think of that??
__________________
2002 Diplomat pulling:
23' Enclosed Tilt Trailer with:
Car, Boat, Harley, 660 w solar,and 2 bikes
Krash is offline   Reply With Quote
Old 10-10-2016, 05:21 PM   #7
Senior Member
 
Join Date: Jul 2014
Posts: 5,929
My 7.4 c.f. residential refrigerator draws .9 amps when running.

.5 amps seems real low, unless it's a dorm room size unit.

I understand that some new fridges use varable speed compressors. That could effect the amp draw.
__________________
twinboat is online now   Reply With Quote
Old 10-10-2016, 05:26 PM   #8
Moderator Emeritus
 
Gary RVRoamer's Avatar


 
Fleetwood Owners Club
Freightliner Owners Club
Join Date: Jan 2000
Location: Silver Springs, FL. USA
Posts: 16,621
I can readily see a 3x difference IF the Kill-O-Watt algorithm doesn't take MSW in account. There are a dozen ways to calculate power usage and MSW can mess up several of them. Just like digital clocks typically run at the wrong time (speed) with MSW, a KOW can make mistakes too. As a low cost, consumer grade, device, they probably aren't designed to handle anything but standard utility electric power.
__________________
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
Old 10-10-2016, 05:34 PM   #9
Senior Member
 
Join Date: Sep 2012
Posts: 4,253
That is well within the current capacity of most of the True RMS DMM's on the market. Tap the line and put in a DMM that measures true RMS and compare that to the reading the Kill a Watt gives.

The basic issue is that a true RMS meter actually slices the current wave form in many slices, calculates the power in each one and add that up to give you a loaded average for the wave form applied. Before the integrated circuits that do that were developed the choice was a device that measured the heat generated in a sampling resistor. Other meter types read the peak of the power applied and scale it as if it was a sine wave.
__________________
nothermark is offline   Reply With Quote
Old 10-10-2016, 05:59 PM   #10
Senior Member
 
Tiffin Owners Club
Appalachian Campers
Mid Atlantic Campers
Coastal Campers
Freightliner Owners Club
Join Date: Jan 2015
Posts: 414
I don't have a MSW, or I'd measure it for you.

The MSW is a square wave, with typically higher voltage spikes on the leading edge of each wave as the transistors are switching. You obviously know that the PSW is a nice smooth sine wave curve. When I was a brandy new EE 40+ years ago I worked at company that made precision DC to DC converters and timers for missiles. Same process as the MSW, we just rectified it and made it DC at the final step. That just tells you how old the MSW technology is..................

You have two unknowns here. You don't know how well the kill-o-watt measures correctly a square wave, and you don't know how much the refrigerator is consuming on a square wave.

Personally, I'd upgrade to a higher wattage PSW.
__________________
DaveB, Raleigh, NC
2015 Tiffin RED 33AA
2014 Honda CRV
Kiawah is online now   Reply With Quote
Old 10-10-2016, 06:11 PM   #11
Member
 
Krash's Avatar
 
Join Date: Nov 2014
Posts: 71
Yep, I certainly am thinking of installing a PSW dedicated to the Refrigerator, but I am now very puzzled by the Kill A Watt readings.

I designed my whole solar set up using the Kill A Watt and my Tri-Metric. Both have been great tools for my purposes. I just never came across a situation where I measured on the inverter vs commercial power. So now, I am very curious.

I think I will try it with my toaster, on and off the MSW, and see if I get different readings. Then, maybe some other appliances too.
__________________
2002 Diplomat pulling:
23' Enclosed Tilt Trailer with:
Car, Boat, Harley, 660 w solar,and 2 bikes
Krash is offline   Reply With Quote
Old 10-10-2016, 06:38 PM   #12
Senior Member
 
powercat_ras's Avatar


 
Winnebago Owners Club
Solo Rvers Club
Join Date: May 2015
Posts: 602
Quote:
Originally Posted by Krash View Post
Yep, I certainly am thinking of installing a PSW dedicated to the Refrigerator, but I am now very puzzled by the Kill A Watt readings.

I designed my whole solar set up using the Kill A Watt and my Tri-Metric. Both have been great tools for my purposes. I just never came across a situation where I measured on the inverter vs commercial power. So now, I am very curious.

I think I will try it with my toaster, on and off the MSW, and see if I get different readings. Then, maybe some other appliances too.
The toaster is a simple resistive load vs. the refrigerator compressor which is a AC induction motor with a complex inductive load so do not be surprised if the difference in Kill A Watt readings comparing the toaster between sine wave shore power and the MSW inverter power is totally different ratio than what you see with the residential refrigerator. The toaster won't care what the frequency content of the power is because its just making pure heat. The induction motor is tuned to work best with a pure 60 Hz power source and was not designed to work with something else like MSW that is not pure 60 Hz power. Does not mean it won't work with MSW but it is not a sure thing.
__________________
Randy - Manhattan, Kansas
2015 Vista 27N
2016 Honda HR-V
powercat_ras is online now   Reply With Quote
Old 10-10-2016, 06:45 PM   #13
Member
 
Krash's Avatar
 
Join Date: Nov 2014
Posts: 71
Powercat, can you recommend an appliance that might provide a good simulation of the refrigerator?
__________________
2002 Diplomat pulling:
23' Enclosed Tilt Trailer with:
Car, Boat, Harley, 660 w solar,and 2 bikes
Krash is offline   Reply With Quote
Old 10-10-2016, 06:54 PM   #14
Senior Member
 
Join Date: Jul 2014
Posts: 5,929
An electric mixer
__________________

__________________
twinboat is online now   Reply With Quote
Reply

Tags
inverter


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
Upgrading from Magnum ME-2000 MSW inverter to Magnum ME-2800 PSW inverter. Stan&Jacquie MH-General Discussions & Problems 7 11-12-2015 08:54 PM
Keurig 2.0 and MSW Inverter? nodine Technology: Internet, TV, Satellite, Cell Phones, etc. 1 11-30-2014 06:29 AM
Kill-a-watt reading over voltage? monkey Just Conversation 28 09-22-2014 10:28 PM
Residential Refrigerator / MSW Inverter Compatibility Mahlon RV Systems & Appliances 16 09-14-2013 05:33 PM
Kill-A-Watt Meter ??? Bilito Vintage RV's 6 10-24-2012 11:58 AM

» 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- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 09:05 PM.


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