When looking a building your remote power system, the selection of your DC to AC inverter is very important. There are two styles of inverter. The difference between the two is how closley they reproduce the standard mains power. The diagram below illustrates the situation:
The modified sine wave output is the mose economical and commonly used inverter for most home power systems. The true sine wave inverter technology is more complex and expensive, but does have its own set of applications.
I’ve had a modified sine wave type of inverter now for ten years, and it has served well. We use two Trace DR 2400 inverters that can be synced together and provide 240AC output. (Trace Engineering changed names and is now Xantrex)
There are rarely any appliances that ever give us trouble with the modified sine wave. All our computers, routers, and switches work well. There are two cautions to be aware of before taking the modified sine wave inverter route.
First, we have rarely had issues with the bulky ‘wall wart’ style of power supply for our electronic appliances. You know, the bulky transformer on the plug type power for small items. These transformers can get very warm if it is one of the problem types. I was never able to determine what made one wall wart different from the other that had problems. Be assured that this is rare. Last time I saw it was for the charger for my old Motorola flip phone about eight years ago. Whenever using a new wall wart power supply, I watch it for the first 30 minutes before ‘blessing’ it for use in my system.
Second, is the 60Hz hum that it will introduce to AM broadcast radios, or in my case HF Amateur radio. I wish I had a true sine wave inverter to test with, but I suspect the noise is minimal. I have toyed around with the idea of purchasing a small true sine wave inverter to run my ham radios with, but they don’t seem to offer any of these complex units for power less than a thousand watts.
If you have experience with the true sine wave inverters, please post a comment. Does the AM band work or do they generate the same noise?
Related posts:
Hi there. I was referred your site by a friend of mine and read this post. I have to point out that with about $15-$20 in parts, you could get a cleaner sine wave than your modified sine wave. Also, as long as you’re not using multi-phase systems, this should work perfectly. There will be a minor phase shift, but since you’d be installing a resistor in series to the output of your inverter, all electricity would be disconnected and nothing would be risked.
Look up Low Pass Filtering or RC circuits. Here’s a good source (if you have java) to play around with parameters before you commit:
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/experiment/lowpass/lpf.html
An RC filter will smooth out the impulses of each step, making the output look a little more like a sine wave, and decreasing the noise output of all of your analog parts that are converting this to digital. The external noise is coming from the fact that your modified sine wave has on each step a tiny fraction of the real signal you want, and a LOT of noise. Each wall wart has to filter this noise out, and you’re taking a significant power loss there. It’s power that’s going to be lost anyway if you have an RC filter, but at least you’ll know that your wall warts won’t be generating as much heat as they used to.
Another source of the wall wart heat could be that there’s a DC offset in your sine wave. This would usually cause all of the AC/DC converters to heat up, so I’m thinking this can be ruled out. The DC offset of the wave should be 0V compared with ground. This is, of course, if all of your outlets are tied to the same ground (i.e. Earth).
So, once you figure out the resistor and capacitor values you need to make your sine wave more sine-y, go to Digikey or the like and find components that are rated for the voltage and amperage your inverter can output + 20% or so, and you will have a cleaner, less noisy, less lossy system for your generator!
I have a degree in Electrical Engineering, but I’m not an expert since I’ve switched career paths since then. However, if you have any questions, please feel free to email me.
Ben Henry
.-= Ben Henry´s last blog ..11/21/09 – Gardening Party! =-.
Thanks Ben!
Ditto on the EE degree. You solution would help in a smaller situation than my readers would face. Think of dozens of different loads, many resistive and some inductive in a constantly changing home/office power environment of 500 – 2000 Watts. Now some of the “constants” we might assume in the RC filter design would be changing. For a small inverter and a fixed, known, load your RC filter is very helpful!
Thanks for your input
This story is evolving… looking forward to reading updates.
.-= Dave Doolin | Website In A Weekend´s last blog ..How NOT to Comment on Blogs (Dude, you’re busted) =-.
First I must declare my interest and background
I worked for Xantrex back when it was Statpower and we bought up Trace and then Heart Interface company. I worked there as their marine applications engineer. This is back in 2000 and the debate raged over pure sine versus MSW. While doing the Miami boat show I got talking to an air conditioner company that was attempting to drive their product using our inverters. Yes I said drive air conditioning with an inverter. Turns out they had only tested our MSW Prowatt 1800 model so I gave them the Pure sine inverter from our booth and asked for a lab test report. To everyone’s amazement they realized a 20% improvements in run time on a full charge of the same battery. The company subsequently sent me a couple of their air conditioner models and I did some more experiments of my own. In addition I demonstrated how you could run the air conditioner using a smaller inverter. 800 watt prowatt to be exact. By sequencing blower and compressor we reduced the start surge.
The reason this worked so well has to do with something called power factor. The company had done extensive research looking for the most efficient compressor. MSW is not as good as utility power because of the harmonics and loss of power associated with non sine wave.
In Europe it is law that appliances must be power factor corrected but this is not law in the US. What it means in the real world is you end up wasting energy with MSW especially oif the load is not power factor corrected. Fridges and inductive loads tend to run hotter due to the harmonics generated when running on MSW. Now you have to run your genset longer to charge up the battery again. The problem is exacerbated if the charger itself is not power factor corrected. This wastes fuel.
Xantrex made a corporate decision to withdraw from the European market because the MSW products would require extensive design changes to meet this more stringent European standard. Further testing also showed that whereas I could power an apartment fridge with approximately 600 watt pure sine inverter it required an 1000 watt inverter of the MSW output to start the same fridge.
since leaving Xantrex I have been working as a system designer for boats which is a specialized kind of off-grid application. A 50 – 60 foot boat can be run on a 2000 – 3000 watt inverter even when equipped with all the normal amenities found in a luxury condo. I learned that sensitive satellite TV recievers, surround Sound home theater and many other electronic equipment including some lap top computers do not like MSW power. The price of pure sine wave inverters has come down quite a bit. Enough so that it is no longer justified to buy the cheaper MSW because what you save up front is eaten up by the increased fuel burn and shortened life of inductive loads like fridges and fan motors.
If you are purely solar consider you need to charge more to power inductive loads with an MSW inverter.
I realized this may not find favor with the minimalist mindset so many off-grid people prefer.
I recall one instance where our MSW product actually burned out a laptop to be used in a trans Atlantic race entrant boat. The computer company was donating a new laptop for use in navigation but before the boat even left the dock they lost a couple of computers. Not wishing to ruin a third laptop they called me since it was our MSW inverter product being used. The lap top was fitted with a universal power cube to supplement the battery power and to charge up the laptop battery. I changed them over to using a pure sine inverter and no further problems occurred.
My one sucess story with MSW is for use with lights and mainly resistive cooking appliances. A friend who drives long haul extra wide loads spends most of his time living in the sleeper of his rig. After he had burned out several brand X inverters and the alternator on his rig he asked me to install a system that would not fail him. He had a fridge, a kettle, a frying pan and a coffee maker, all 120V. Six years later when he changed trucks he asked me to move over the original system to his new rig. Not once did he end up with a flat battery even though he used the start battery for powering the inverter. He did however have to replace his fridge as predicted due to the compressor running hotter on MSW
power. I make my money designing, not selling product so it doesn’t matter to me if the client uses MSW or sine wave but I have seen enough proofs that in the long run pure sine wave inverters are worth it and justify the higher cost in longer service life and better appliance performance.
Arilid, Thanks for your comment. On a similar note, do you know anything about the radiated RF noise differences between MSW and SW inverters and power systems? Is my assumption that true Sine Wave is probably quieter??
Hi,
Liked your comparison of MSW & Pure Sinewave Inverters. Have to say it is 100% fact.
Found out the hard way.
Live in a remote area of North Donegal, Ireland and during building a house there was no grid power available.
Started off with a generator & then installed a wind turbine.
Initially used MSW’s to power lighting, TV system, Laptop etc. These MSW’s were guaranteed for use with the above items.
Not the case.
Fridge would not start & two Satellite TV Receivers and one Wireless Telephone System were blown up before I realised where the problem was.
Replaced MSW’s with a Sinewave unit & everything was okay since – cost quite a bit more though.
Can tell you I felt pretty stupid about it.
My background is Industrial Control System Design – (Hardware & Software) and I am now looking at putting together a combined Solar/Wind System which is domestic friendly
Regards
Michael
While I worked for an inverter manufacture I encountered this situation quite often. Look back to an early post here from Ben who suggest a simple RC filter circuit will solve the problem. Not true!
Harmonics and power factor come into play. When the European Union revised their electrical specificatons for consumer products we realized it would required extensive design revision to meet the new specifications and we decided to withdraw our MSW products from the European market. The loss in sales was outweighed by the cost of compliance. Resistive loads like heater elements do not care but virtually all others do. Now that many countries are also banning tungsten filament bulbs in favour of the CCF the situation gets even more complicated. Good LED lights have a current regulator and may also have problems with MSW. Everybody looks at initial price when purchasing but sometimes the cheaper MSW inverters are not worth it in the long run.
Arild Jensen´s last [type] ..Why Doesnt My Solar Panel Deliver Rated Output
Yes, when using MSW, your mileage may vary. Its a little harder on motors and some electronics. You will never have to discover this if you build your power system around a True Sine Wave inverter.
You mentioned wanting a smaller pure sine wave inverter. Several companies including Xantrex and Victron now offer 500 watt pure sine wave inverters. No doubt this is due to popular demands for powering home entertainment systems surround sound home theater and satellite signal recievers.