# Inverter/AC motor noise



## greg273 (Aug 5, 2003)

Anyone know the hows and whys of what makes certain AC motors 'dislike' the modified sine wave of cheap inverters?
I'm using a small, cheap 600watt 'Harbor Freight' inverter to power lights, radio, tv, etc until I get my Trace/Xantrax DR2424 hooked up. I have noticed using this inverter that some cheap box fans are very noisy, and some are not. I am wondering what is it that makes one brand of fan hum loudly, while the others do their job in relative quiet? 
I am wondering if I should expect the same level of noise when I switch to the higher quality inverter... ( although it, too, is modified sine wave)


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## WayneR (Mar 26, 2007)

Have you considered using a larger computer style fan instead of the box fan.
Lower current consumption, 12 or 24 VDC operation, inverter not needed :dance: 

Your suppostion on the Horror Fright inverter is probably right. You could try reversing the plug on your fan if it's two pronged. An interference filter (radio shack) in the line could also help.

I tried one of their inverters, was supposed to be 1200W with peak higher than that. Would only produce about 375W measured with a Sencore AC watt meter. Took it back :grump:


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## Jim-mi (May 15, 2002)

A one line answer is not possible.

Theres several different types of AC motors.
Most all will react differently to that mod sign wave (mod square wave really)
They were designed for a sign wave.......slooping up to its peak . . .rather than the vertical rise of that mod square wave. 
The windings are "protesting"--with that noise.

I'll stop.

Check any "loud" motor to make shure it doesn't get dangerously hot . . . . .motor life will be shortened with mod sign.

The DR might be better.....................A inverter that has been used by an awfull lot of folks.

I would not at all be suprised if some of those cheapie junk *inverters* were a square wave.

Ya get what ya pay fer.


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## greg273 (Aug 5, 2003)

Well, in defense of the el-cheapo inverter, although I bought it years ago from harbor freight, it does have the 'Xantrax' name-brand on it, the 'Porta-Wattz', probably a made-in china import, but it has given 3 years of reliable service, even after I clipped its fan wires. Yeah, I know, you get what you pay for, but it was an interim solution until I get the 24volt setup going.... (ha, 3 years later, the DR2424 is still in its box...)

I will definitely try reversing the plug on that box fan. The fans dont seem to be getting hot, they just have an annoying hum to them. But it is only the newer fans, not the older box fan I've had for years.


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## Ed_Stanton (Dec 28, 2004)

Some appliances just may not like modified sine waves. I had a Trace DR 3624 modified sine wave inverter and one of my high end computer monitors buzzed like crazy when in use. Sometimes the performance was even worse, with buzzing, flickering, weird color. The only way that I was able to use the monitor with the DR 3624 was by having a 60 or 100 watt tungsten light bulb on at the same time. It still buzzed a little, but it was much better. Also the microwave buzzed a bit and the TV had a moving horizontal line that I could not get rid of. I was also told that not all high end rechargeable batteries for tools and toys like a modified sine wave inverter.

Eventually I bought a used Trace SW 4024 to replace the DR 3624 and I have never looked back. The pure sine wave works perfectly with everything that I've thrown at it and I would not go back to a modified sine wave inverter unless the use was for just the electrical basics. I was also told that it was hit and miss which appliances would accept the modified sine waves, but I don't know if they'd be damaged by them.


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## Jim-mi (May 15, 2002)

A good point there Ed. There is a track record of mod sign wave inverter's smoking Makita and Dewalt battery chargers.
With out digging into the files I'm quite certain those are the two . . . . . . .AND there is others that will smoke(burn out) on mod sign wave.

Also the point about the high end monitor. It is a function of the internal power supply to what ever the unit is. They just don't get along with mod sign---period.
I've also heard that Lazer printers will not work with mod sign.
Greg, Yes the PortaWatt units are a reasonable low end inverter. 
When you said cheapie I just assumed that you ment one of those truck stop $49.95 pieces of crap.

Not trying to discourage anyone from setting up a system with a mod sign-----But you should know ahead of time that mod has its limitations.

My first inverter was\is a good ole 2012SB from Trace(zantrax) . . . .its a "good ole unit" . . . . .
I'm still using it with a seperate (12vdc) batt bank to power a couple saws while I'm building on to my barn.


Yup . . . .as to inverters, there ain't no free lunch.


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## greg273 (Aug 5, 2003)

So far so good on the DeWalt charger, I've got a 14volt DeWalt drill I've been using for a couple of years on the Porta-Wattz, never gets overly hot, and so far the batteries seem to be holding up well. I am actually pretty careful about leaving it on, though, I dont let it charge unattended, because of the horror stories I've heard. My cell phone, and Nicad charger seem to work OK with it also.
Hey, by the time I am ready to install the DR2424, I may be ready to upgrade to a pure sinewave!


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## Ed_Stanton (Dec 28, 2004)

I forgot to mention that an industrial electrician friend of mine explained to me that some motors and appliances (and deep cycle batteries in our off grid homes) do best when running on "peak voltage" which is around 170 volts, or at the top of the pure sine wave, vs. 110 volts, which is the middle of an AC current. 

Modified sine wave inverters have their peak voltage squared off and compromised at least (with the better ones). Cheaper modified sine waves can actually have a really squared off and stepped wave form, vs. the nice horizontal S curve of a pure sine wave that the grid produces and that motors and appliances are generally manufactured to run on. 

So you might want to do some research on peak voltage and also on the two different types of modified sine waves compared to a pure sine wave and see if that helps to answer your question? Perhaps your cheaper inverter is putting out a really squared off wave and the motor that is protesting over it and is looking for a higher peak voltage from a smoother sine wave that is more continuous? 

Also, I wonder if any motor or electrical appliance manufacturer ever states what the optimum peak voltage that their product runs best with, so finding what motor works fine with your Harbor Freight vs. DR 2424 vs. a pure sine wave inverter/the grid and at what peak voltage the motor requires, is still going to be trial and error.


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