Trebor English
Well-known member
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.
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.