Author Topic: Pure sine? . . . Modified sine? . . . Generators  (Read 6077 times)

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Offline bayview

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Pure sine? . . . Modified sine? . . . Generators
« on: August 03, 2011, 10:53:51 AM »

   I periodically run our RVs 13500 BTU air conditioner off an older 5000 wt generator . . .   

   Am I damaging the compressor and fan motor?   Should I be using a generator with a pure sine inverter?

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    . . . said the focus was safety, not filling town coffers with permit money . . .

Offline peternap

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Re: Pure sine? . . . Modified sine? . . . Generators
« Reply #1 on: August 03, 2011, 12:22:32 PM »
No, modified is fine for that. You start to run into trouble with computerized equipment.
Chargers are especially prone to problems.
These here is God's finest scupturings! And there ain't no laws for the brave ones! And there ain't no asylums for the crazy ones! And there ain't no churches, except for this right here!

Offline bayview

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Re: Pure sine? . . . Modified sine? . . . Generators
« Reply #2 on: August 03, 2011, 03:12:10 PM »


Thanks!

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    . . . said the focus was safety, not filling town coffers with permit money . . .

Offline NM_Shooter

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Re: Pure sine? . . . Modified sine? . . . Generators
« Reply #3 on: August 04, 2011, 07:40:20 AM »
Bayview, your question confuses me a little.

Modified sine is a term that is related to inverters, not generators.  What makes you think that your old generator is outputting a unit step type AC waveform?  I'm curious, as I have not heard of such a generator. 

Or are you asking about using an inverter to drive your AC unit? 

Most of the newer _laptop_ computer chargers won't care.  The first thing that they do is rectify the incoming voltage and go straight to DC.  Note on your charger if the voltage range is large... if it says 120V to 240V (or similar range) you are good to go.  Older computers and larger power supplies for big desktops are going to like clean sine signals. 

Here is a good site for reference : http://www.donrowe.com/inverters/puresine.html

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Offline bayview

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Re: Pure sine? . . . Modified sine? . . . Generators
« Reply #4 on: August 04, 2011, 09:06:39 AM »

  I’m confused too!   That’s why I had asked the question. . .   

   Supposedly a “conventional” generator has a square-modified wave . . .      An inverter generator will produce cleaner pure sine wave 120 volts.



   I want to get a new generator (with electric start) and saw some inverter generators on e-Bay.   There are over 200 of them for sale if you search “inverter generator”.   I didn’t know if they are worth the extra expense 

   I need to run some tools and occasionally the RV’s A/C unit.   I’m thinking about another 5000 wt generator.   Some of my tools are battery operated and will need the chargers attached to the generator.

/.
    . . . said the focus was safety, not filling town coffers with permit money . . .

Offline MountainDon

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Re: Pure sine? . . . Modified sine? . . . Generators
« Reply #5 on: August 07, 2011, 08:20:34 PM »
My old RV (1983) came from the factory with a Dometic branded generator. The usual kind that runs at 3600 rpm's all the time to output whatever kind of current it made. It had 953 hours on the clock when we bought it. We used it for a year and 75 hours or so, mainly to run the A/C. I have no idea how much the A/C was used by the previous owner. The A/C unit was original and still worked when we bought the RV. So, it does not seem to have been bothered by whatever waveform the generator produced.

I replaced the old genset with an inverter generator only because I could not stand the noise from the 3600 rpm, old generator. I don't know if the A/C liked the new power source any more or less. It still produced "cold" on my demand.

Just because something has been done and has not failed, doesn’t mean it is good design.

Offline NM_Shooter

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Re: Pure sine? . . . Modified sine? . . . Generators
« Reply #6 on: August 08, 2011, 09:25:54 AM »

I'm still confused by that modified sine wave... was that a marketing graphic from and inverter generator manufacturer?

Here is a link to an overview of generators.  Note that the "standard" type generator is more of a sine wave.  Granted it has a significant amount of distortion, but it is much closer to a sine than to the modified sine. 

http://www.electricgeneratorsdirect.com/stories/28-How-Inverter-Generators-Reduce-Unwanted-Noise.html

Seems like a lot of information about power is FUD, designed to get folks to spend more $$$  here is another link :

http://answers.google.com/answers/threadview?id=458939

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Offline MountainDon

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Re: Pure sine? . . . Modified sine? . . . Generators
« Reply #7 on: August 08, 2011, 01:06:14 PM »
 
   Supposedly a “conventional” generator has a square-modified wave . . . 

Where does that come from?   I don't understand that statement.   The generator in any conventional generator operates on the same principle as a huge hydro electric generator, as far I know. My understanding of AC power generation is that as the generator armature spins the electrical field rises and falls in that sine wave pattern.

Spinning at 3600 RPM's is what produces our 60 Hz cycle. That's why engine driven generators run at a screaming 3600 RPM, except for those with geared up systems which will run at lower speeds, like 1800 RPM. If the generator has a lousy governor system, that is it can not control engine speed properly, then the frequency can wander and that may not be good for certain types of equipment.

Square wave "modified sine" patterns come from electronic switching that tries to emulate the sine wave. I could be all wrong on all that, it is just my understanding.
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline peternap

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Re: Pure sine? . . . Modified sine? . . . Generators
« Reply #8 on: August 08, 2011, 03:47:14 PM »

Spinning at 3600 RPM's is what produces our 60 Hz cycle. That's why engine driven generators run at a screaming 3600 RPM, except for those with geared up systems which will run at lower speeds, like 1800 RPM. If the generator has a lousy governor system, that is it can not control engine speed properly, then the frequency can wander and that may not be good for certain types of equipment.

 

I think that's where it is coming from Don. I'm guessing that since there is such a large variation in China Engines the speed is inconsistent.
The inverter models supposedly compensate for that.
These here is God's finest scupturings! And there ain't no laws for the brave ones! And there ain't no asylums for the crazy ones! And there ain't no churches, except for this right here!

Offline NM_Shooter

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Re: Pure sine? . . . Modified sine? . . . Generators
« Reply #9 on: August 09, 2011, 09:00:15 AM »
Where does that come from?   I don't understand that statement.   The generator in any conventional generator operates on the same principle as a huge hydro electric generator, as far I know. My understanding of AC power generation is that as the generator armature spins the electrical field rises and falls in that sine wave pattern.

Spinning at 3600 RPM's is what produces our 60 Hz cycle. That's why engine driven generators run at a screaming 3600 RPM, except for those with geared up systems which will run at lower speeds, like 1800 RPM. If the generator has a lousy governor system, that is it can not control engine speed properly, then the frequency can wander and that may not be good for certain types of equipment.

Square wave "modified sine" patterns come from electronic switching that tries to emulate the sine wave. I could be all wrong on all that, it is just my understanding.

That's what I was confused about too.  The modified sine wave is generated by semiconductors such as a large MOSFET or similar turning on and off like a switch.  It is either on or off..... if it is in the linear region it gets really, really hot and does not work well.  For a generator which spins a coil in a magnet to put out a square wave sort of signal would require brushes, which would not work well at all.  The EMI from something like this would be huge, and you could hear it with an am radio a mile away.  I thought that generators that do not have pure sine inverter technology still put out sine patterns due to the way the armatures are wound.  They may have harmonic problems, and be distorted, but they are still sine waves.  Most of our AC power on the grid goes through so many transformers and long transmission lines that by the time we get it to our houses all the high frequency components are out of it, and the sine is fairly clean (disregarding lighting strikes and solar flares  ;D). 

I still think that any type of spinning coil generator is going to put out a clean enough power source to use with all new electronics and power tools.  Actually, inductive loads like drills and saws and probably don't care.  It could be a problem if you had multiple phases, but for single phase power even a crappy sine (not the modified sine) is plenty good. 

The issue might come from things that use stepper motors... such as new washing machines, AC units with variable speed fans and the such.  Maybe also microwave ovens. 

But for most electronics, as mentioned before, the power is immediately rectified and then filtered and go straight to a switching power supply.  Those are VERY robust for cleaning up noise.  However, those supplies can be damaged by transient voltages, so use a good surge protector.

Still curious as to where that graphic of the sine vs. modified came from.  I betcha a burger it is from a pure sine generator marketing presentation.
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