Sine waves, square waves, and a fridge.

[Trebor English]

Sine wave inverters cost more than modified square wave inverters.  The cheaper modified square wave inverters must be bad.  Here are two posts from this forum:

the modified square wave dosen't run the compressor at full power, greatly reducing efficiency, ie has to run longer for the same cooling power

He knows he will have early 110v refrigerator failure at five years, given the motor will run hot. Inverters that are not pure sign wave will do that. 


On August 8th and August 11th I ran a pair of tests using my 120 volt Haier dorm fridge, Florida Power and Light sine waves, and my Harbor Freight 400/800 modified square wave inverter.


My fridge setup is described on this forum at:  
https://vanlivingforum.com/showthread.php?tid=27624  

The way it works is that there's 8 pounds of ice in the freezer compartment.  Each day it runs an hour or two.  At night and when there are rainy days with no solar charging the ice keeps it cool up to 3 days with no battery use.  

For the testing I started at 8:30 AM with the ice all melted and 81 degrees.  I let it run until it got to -0.7 degrees Celsius and the thermostat turned it off.  On the first day the compressor got FPL sine waves.  On the second day the compressor got modified square waves.

According to the infrared thermometer the hotter output side of the compressor was 138 degrees.  The cooler side was 130 degrees.  The temperatures were the same both days.  The higher temperature with square waves was not observed.  

The run time from all melted to all frozen took 520 minutes, 8 hours 40 minutes, with sine waves and 525 minutes with the inverter.  Five minutes difference in 500 minutes is 1%.  That's not a significant difference.  

My inverter actually runs about 59 Hertz, about 1.6% slow.  That could account for the 1% longer run time.  

The induction motor that turns the compressor depends on the frequency of the alternating current.  

Since I don't have a sine wave inverter I don't have a measurement of 12 volt dc amp hours for both tests to compare.  I have not seen a claim that generally sine wave inverters use less dc energy.  I have not seen a comparison of a specific pair of inverters.  The efficiency comparison is yet to be done.  

Bottom line, the increased temperature and increased run time with a modified square wave inverter were not observed.

 

[John61CT]

The results will vary depending on the specific inverter and what fridge.

Those who get a decent result

defined as anywhere near AH per day efficiency comparable to a 112V compressor fridge

should simply post a detailed HowTo with purchase links to the inverter/fridge pair that they used.

The need to use a 12V thermostat to turn the inverter on and off will be the challenging bit for those with little electrickery experience.

Note that in better regulated 240V markets, very efficient home fridges are sold that are actually **more** energy efficient than 12V portable units, even with inverter overhead.

So if you know someone being moved from overseas by their employer covering shipping costs on a container. . .

 

[Moxadox]

John, when I moved from America to Israel years ago, there were companies in the U.S. that made 240v appliances that shipped worldwide. Amana was one, but there were several. I looked at the advantages of doing that vs taking pot luck with Israeli/Mediterranean "native" models and the math worked out toward buying local yonder, but according to the veteran emigrants I polled, aside from the difficulties of warrantee service, well, they never needed it anyway esp with Amana. So if you want a really good 240 fridge, buy American [emoji8]. Seriously, they're better made.

The Dire Wolfess

 

[John61CT]

That must have been a long time ago.

I'm talking energy efficiency here, not some other measure of "quality".

For a 12V compressor fridge designed for mobile living off grid, 40AH per day is considered a **lot** of power.

Find me one 120V fridge that comes close to that, I don't care where it's made (but pretty sure it won't be American).

The U.S. "energy star" requirements used to be relevant, but years of industry lobbying has caused them to stagnate, not even a challenge for manufacturers, and "free market demand" does not provide enough incentive to use the new tech to drive greater efficiencies in the U.S. S&B home market.

However in Australia, N.Z, Europe etc all the more developed world, the regulators have kept pushing for ever higher energy efficiencies, and consumers in those markets care a lot more about their carbon footprint.

So an inverter fridge marketed as "very energy efficient" for normal homes in those markets completely blow away anything available in the U.S.

To the point that just sticking one on a good inverter will use less energy than a portable Engel, one of the most efficient portable brands.

They also run from 240V, so generally not imported to NA.

I'm not saying the internals are **made** in those countries, it's a global industry, and the leading asian firms can locate their factories or outsource anywhere without losing control over quality.

Of course these factors make such units more expensive here, but being powered off 240 makes no difference when you're mobile.

 

[Trebor English]

The thread title and original post are about square waves and sine waves.  If someone needs an inverter they have to decide between a $25 square wave  unit and a 150$ sine wave unit.  I was attempting to debunk the claims that square wave inverters will cause longer run times and higher motor temperatures.  These claims are given with no data.  I performed a test looking for this.

That must have been a long time ago.

I'm talking energy efficiency here, not some other measure of "quality".

For a 12V compressor fridge designed for mobile living off grid, 40AH per day is considered a **lot** of power.

Find me one 120V fridge that comes close to that, I don't care where it's made (but pretty sure it won't be American).

First, this thread is about square waves causing longer run times and higher temperature vs sine waves, not efficiency.  In the original post I said "The efficiency comparison is yet to be done."  

Second, where did you get the 40 amp hour figure?  My fridge, what I used for this square wave/sine wave test, uses 6 amp hours per day when the temperature in the van is in the 80s and up to 13 amp hours per day when the temperature in the van is in the 90s.  Again, my post was not about energy consumption.  

Do you have anything to add about square waves?  Why don't you start a new thread about your own ill will towards inverter/fridge combinations.  You could provide a description of your own favorite "12 volt fridge." Does it have a circuit board and a hermetically sealed induction motor compressor unit?  Maybe you could explain why this circuit board is not an inverter.  It takes 12 or 24 volts dc and makes alternating current for the induction motor differently.  What would be different?

 

[tx2sturgis]

Trebor this reminds me of the time when an experiment I suggested here was rebuffed. 

I had done similar things in the past so I knew more or less the results that others would see....but my suggestion for an experiment was ridiculed as dangerous. 

So I did it, again, and this time, I posted the actual pictures and results. I never heard from the nay-sayer.

It takes time and effort to do these things, so my hat is off to you.

I do know that in our class 8 tractors, we had 2200 watt modified, and 300 watt pure, and the microwave oven running on the 2200 watt MSW inverters were pretty noisy, buzzing a lot, and they heated food much slower, but seemed to run hotter, than when plugged into a normal home wall socket. I chalk this up to efficiency loss on modified square wave input. 

But I never did a laboratory-style A/B side-by-side test....and you know, someone else might get different results. 

And so it goes....

 

[John61CT]

Second, where did you get the 40 amp hour figure?  My fridge, what I used for this square wave/sine wave test, uses 6 amp hours per day when the temperature in the van is in the 80s and up to 13 amp hours per day when the temperature in the van is in the 90s.

I have no "ill will" toward the idea at all.

Leaving the rest for now, yes my focus is on energy efficiency.

If the "mains fridge on inverter" came close to the efficiency of any 12V compressor fridge apples to apples, in fact I'd be very happy.

I'm pretty sure your consumption figures of 6 and 13AH per day are at 120V mains power after the inverter.

300 kilowatt-hours per year is normal for small supposedly efficient US fridges, so that would check out.

The 40AH per day, which is **very** inefficient relative to an Engel, is at 12V DC, so equivalent to 4AH per day on mains.

If you still feel all this is OT for you as the OP, feel free to just ignore this post and I'll bow out, and if someone else wants to continue, start a new thread?

BTW a good quality inverter like Magnum puts out a much closer-to-sine shape than the Chinese cheapos, so would likely give a better result. But they can cost more than an Engel too, so there's that.

 

[captndiet]

Trebor

Good timing.

I have been S+B off-grid for going on 9 years.

I have two 24v forklift batteries (1840 ah total)

My 120v needs are fairly low all things considered so I originally started with a 1000w pure sine wave inverter (Ebay special)

It would not run the HP LaserJet printer I had. (not big enough for the heater in it)

I already had a used 2400 watt Trace Modified Sine Wave inverter, so hooked it up. The printer did not like it either. (acted weird and would not print)

So I ponied up and bought an Outback FX2524T 2500 watt pure sine wave inverter. 

Runs everything and all is happy!!

Fast forward to yesterday.

My go-to generator needed work so I hooked up a 3500 watt Briggs & Stratton Brute generator and let it charge the batteries.

Sue started a load of laundry and you could hear the generator pitch change with the washing machine agitator.

Then Sue noticed the cycles were not working correctly.

So I put the system back on inverter mode and all ran fine again.

We had replaced the washing machine about two months ago and it ran fine on the same generator.

Moral of my story is some appliances don't like the square wave and some appliances don't like generator power.

If you can afford it, buy a pure sine inverter or inverter generator to avoid potential issues.

But my new printer works with the square wave inverter. (just tried it)

Jeff

 

[Trebor English]

I'm pretty sure your consumption figures of 6 and 13AH per day are at 120V mains power after the inverter.

No, it is dc into the inverter.  Actually it is between 13 and 14 volts dc.

 

[John61CT]

That is **very** efficient.

Before I say suspiciously so 8-D

what was the temp differential?

extra insulation?

 

[TerraNova]

... we had 2200 watt modified, and 300 watt pure, and the microwave oven running on the 2200 watt MSW inverters were pretty noisy, buzzing a lot, and they heated food much slower

For such cases better to look reviews with pros and cons. New models are coming every year, I have found this one interesting for me 
3000 Watt Pure(Modified) Sine Inverters

 

[bigskybob]

I have one of each.The only thing I can see different is the MW growls and heats slower.Everything else works just fine.I run my 2 ACs off the modified and they work fine.