Pure Sine Wave Inverter

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Old 06-06-11, 05:54 AM
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Question Pure Sine Wave Inverter

I am looking for some advice as to how to go about purchasing and installed a pure sine wave inverter to assist in cleaning up the power coming from my generator when needed. Thanks!
 
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Old 06-06-11, 06:03 AM
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How were you planning on wiring this? A generator already puts out a true sine wave.
 
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Old 06-06-11, 06:31 AM
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Are we talking about a gas generator? They produce power just like the big boys, spinning a magnetic field through a coil. Voltage can change due to load but the wave should be fairly stable.
 
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Old 06-06-11, 06:47 AM
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Most cheaper portable generators put out very dirty power. Fine for motors and incandescent lights, but can wreak havoc on sensitive electronics and make fluorescents flicker and hum.

Don't remember the specifics..but I think most are called modified sine wave?

Some excellent (but pretty deep!) reading here...ScreenLight & Grip E-Mail Newsletter - Use of Portable Generators in Motion Picture Production

Go down to "anatomy of a generator" and then a little further look at the different waveforms...
 
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Old 06-06-11, 09:24 AM
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Have you thought about just buying a generator that already has a sine wave inverter like the Honda i-series? They are designed for maximum efficiency and power quality. Honda Inverter Generators

An alternative would be to buy a computer UPS unit that has automatic voltage regulation and run any loads on the generator through that. Although with this option I'm not sure how well and AVR UPS cleans up frequency. In most small generators the voltage and frequency are both a factor of the engine speed which is hard to precisely regulate on a small engine.

My final suggestion is to get a generator with an AVR feature. They produce power that's pretty good. It's not pure sine wave, but it is much better quality than your typical generator.
 
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Old 06-07-11, 04:29 AM
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Originally Posted by Tolyn Ironhand View Post
Are we talking about a gas generator? They produce power just like the big boys, spinning a magnetic field through a coil. Voltage can change due to load but the wave should be fairly stable.
The frequency of the wave is directly tied to the RPMs of the engine. Things like an improperly adjusted governor, a dirty or out of adjustment carb, dirty air filter, etc can all make the engine run faster or slower than the normal 3600 RPM. This in turn will make the wave frequency go higher or lower than 60Hz. Mains frequency is not like voltage, where most devices can tolerate a 15-20 volt swing in either direction. Electronics for use in the US require 60Hz, period. They may be able to tolerate 59-61Hz, but beyond that you risk burnout (the exception would be world power supplies which are designed for 50-60Hz). The main thing that can cause a frequency swing is a large load turning on. If the engine is undersized, it can bog down under the strain and cause the frequency to dip out of spec. This is the most common cause of damage from a 'cheap' generator - more that it was undersized to save money rather than its brand status.

Originally Posted by Gunguy45 View Post
Most cheaper portable generators put out very dirty power. Fine for motors and incandescent lights, but can wreak havoc on sensitive electronics and make fluorescents flicker and hum.

Don't remember the specifics..but I think most are called modified sine wave?

Some excellent (but pretty deep!) reading here...ScreenLight & Grip E-Mail Newsletter - Use of Portable Generators in Motion Picture Production

Go down to "anatomy of a generator" and then a little further look at the different waveforms...
FYI this only applies to inverter generators like the Hondas. These generators engines run an automotive style alternator which in turn powers an inverter. These gennys are popular because they can reduce their engine speed under partial load, which saves gas and reduces noise. Their downside is high price and varying degrees of 'cleanliness' of the wave (which is directly proportional to the price).

Your standard worksite genny does not use an inverter. There is a generating coil attached to the engine which generates 120/240v directly by turning a magnet inside coils of wire. This is exactly how generating stations make power, and as such only makes a true sine wave - it is impossible to create a square (modified sine) wave like this. As I explained above though, maintaining the 3600RPM engine speed is critical to ensuring quality of the power. If properly sized for the application and properly adjusted, there is nothing wrong with using a standard generator for sensitive electronics.

I run a 10kW (12kW surge) generator for my backup, even though the running demand would never exceed 7500kW. But it allows me to run my central AC, fridge, and a chest freezer without fearing for the life of the furnace control board or my electronics.
 
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Old 06-09-11, 07:52 AM
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All the advertising hype makes it sound like ALL inverter generators have a clean safe-for-sensitive-electronics output but this is certainly not true. Same goes for regular inverters that make AC by chopping DC into square waves, then filtering the output to resemble a sine wave. The inexpensive ones have a modified square wave output that can harm your TV, furnace electronics board, etc. Be careful when sorting through the marketing hype trying to find a clean-output genny or inverter.

This excellent article is referenced in the "Lighting" article and really illustrates the problem with many inverters and inverter-generators:
"The “Hows” and “Whys” of Inverters and Inverter Generators"

Technology does exist to assemble a clean sine wave in an inverter but it's expensive and not found in budget devices.
 
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Old 06-09-11, 09:10 AM
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Very true. It's also not exactly true that all generators put out a pure sine wave. It would be true if the generator had large mass, good speed regulation and tight control over the excitation current in the field coils like power plant generators do. However as small generators don't have that level of inertia or control, the frequency and amplitude vary significantly. This produces a smooth wave but one that lacks the characteristic regularity in period and amplitude of a "pure sine wave".
 
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Old 06-09-11, 10:59 AM
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hi guys –

I’m not an electrical guy at all – so you all can justifiably just tell me to “SHUUUTTT UUUUPPPP” (LOL). But shouldn’t there be some kind of a more precise mathematical definition of a “pure sine wave”? After all, like Plato said, a circle is just a mathematical abstraction. No circle ever measured will be perfect. That must also be true of a sine wave? (No I haven’t been drinking. LOL). So what’s a pure sine wave?

I came across a definition somewhere that said a pure sine wave inverter produces a sine wave with less than 3% total harmonic distortion. Is that a good definition?

The very good article (“Hows and Whys…”) referenced in post #7 below uses the term true sine wave, but I don’t think he really expands on what true means. But maybe I missed it. How do I know if a sine wave is true?

(Ok – yes I have too much time on my hands.)
 
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Old 06-09-11, 11:56 AM
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Like a perfect circle, a "true" sine wave is a theoretical construct based in the Euclidean geometry we are all familiar with. Harmonic distortion is one way of estimating how far away from the mathematical model a particular device is. Whether that's "good enough" depends on the task -- running household electronics, certainly; running physics experiments, probably not.
 
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Old 06-09-11, 06:22 PM
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The other thing you want to watch out on the inverter generators is the surge wattage rating they don't really have much leeway with surges { when the motours start up that useally bog them }

I have two diesel generators and they are not a inverter duty at all they are standard generators but very clean power due very low RPM engines one run at 900 T/min { RPM } and other one at 450 or 600 depending on the slection switch I hit and I did ran a octscope to read the sine wave it is very clean for my useage. { the larger one will able parallel without issue and have done that quite few time I will not get into the details on this for safety reason }

Merci,
Marc
 
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Old 06-09-11, 08:19 PM
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While on the subject of inverters another thing in their literature defies logic (for me at least). It's that "dirty" generators can damage sensitive electronics like TV's, computers, furnace controls, etc. Am I mistaken that nearly everything anymore has a power supply in it that converts the AC mains juice into DC? If true then these "sensitive electronics" can't be harmed as the dirty mains power is rectified and regulated into smooth DC.
Some may argue that the harmonic distortion in these cheap generators leaks through the power supply (which by design is normally intended to only filter clean 60Hz power) and is similar to the static, whistles and buzzes generated by noisy light dimmers & easily heard on AM radio stations. I've never seen a warning that a nearby lamp dimmer can harm my computer so I don't know why the distortion from a generator will. Just sounds to me like scare tactics intended to get you to trash your old reliable genny and buy the newest tekkie trend. But maybe that's just my skeptical side...
 
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Old 06-09-11, 09:11 PM
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Originally Posted by ibpooks View Post
Very true. It's also not exactly true that all generators put out a pure sine wave. It would be true if the generator had large mass, good speed regulation and tight control over the excitation current in the field coils like power plant generators do. However as small generators don't have that level of inertia or control, the frequency and amplitude vary significantly. This produces a smooth wave but one that lacks the characteristic regularity in period and amplitude of a "pure sine wave".
I think for the purposes of this discussion, it's true enough. Any magnetic generator is going to put out a "real" sine wave. It may be dirty, but it's still a real sine wave. This compared to an inverter generator which puts out something that closely resembles a sine wave, but isn't by definition.

Originally Posted by ibpooks View Post
Like a perfect circle, a "true" sine wave is a theoretical construct based in the Euclidean geometry we are all familiar with. Harmonic distortion is one way of estimating how far away from the mathematical model a particular device is. Whether that's "good enough" depends on the task -- running household electronics, certainly; running physics experiments, probably not.

Electronics are a lot more tolerant of a moderately distorted sine wave than they are of a square or stepped square (modified sine) wave. But as I said the damage caused by non-inverter generators has a lot more to do with the frequency of the wave than its quality.
 
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Old 06-09-11, 09:52 PM
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Originally Posted by guy48065 View Post
While on the subject of inverters another thing in their literature defies logic (for me at least). It's that "dirty" generators can damage sensitive electronics like TV's, computers, furnace controls, etc. Am I mistaken that nearly everything anymore has a power supply in it that converts the AC mains juice into DC? If true then these "sensitive electronics" can't be harmed as the dirty mains power is rectified and regulated into smooth DC.
Some may argue that the harmonic distortion in these cheap generators leaks through the power supply (which by design is normally intended to only filter clean 60Hz power) and is similar to the static, whistles and buzzes generated by noisy light dimmers & easily heard on AM radio stations. I've never seen a warning that a nearby lamp dimmer can harm my computer so I don't know why the distortion from a generator will. Just sounds to me like scare tactics intended to get you to trash your old reliable genny and buy the newest tekkie trend. But maybe that's just my skeptical side...
From what I understand it's actually a multifaceted issue. First, 120v is an RMS (average) voltage. The 'peak to peak' on a 120v RMS sine wave is approximately 170 volts. On a square wave it's only 140v. This means on the square wave the device is going to draw more current which means more heat.

Second, even though it is happening 60 times per second, a sine wave is constantly ramping gently up and down. This is what components like capacitors and resistors need to operate properly. A square wave is different - it instantly jumps from low to high. Trying to 'force feed' a capacitor like this basically turns it into a short circuit, which can domino into the rest of the circuit causing major damage - especially if it contains any silicon (including chips, transistors, diodes, and power rectifiers).

Third, the square wave has sharp edges where it goes way out of line with proper sine. This is what causes noise and hum in everything from ballasts and motors to TVs and radios.
 
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Old 06-10-11, 03:58 AM
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To add to Matt's post: An analog DC power supply (rectifier/regulator/filter) may be somewhat forgiving of modified-sine or square-wave power, but many electronic devices use digital switching supplies that depend on the graceful "ramp" of a pure sine wave.

Also, in reality a pure sine wave is almost never "pure". It always has harmonics riding on the fundamental. But as long as the fundamental is not clipped, squared or otherwise modified the load device will operate -- provided the device's power supply (or outboard conditioner) has adequate filtering to minimize the harmonics.
 
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Old 06-10-11, 09:31 AM
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Originally Posted by JerseyMatt View Post
This is what components like capacitors and resistors need to operate properly. A square wave is different - it instantly jumps from low to high. Trying to 'force feed' a capacitor like this basically turns it into a short circuit
This is my understanding too. The failure mode is usually overheating of the electrolytic capacitors in the power supply and all the nasty smelling oil leaks out.
 
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Old 06-10-11, 09:49 AM
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Originally Posted by JerseyMatt View Post
Second, even though it is happening 60 times per second, a sine wave is constantly ramping gently up and down. This is what components like capacitors and resistors need to operate properly. A square wave is different - it instantly jumps from low to high. Trying to 'force feed' a capacitor like this basically turns it into a short circuit...
I never thought of that. Unless there's a current-limiting device between the transformer (if it has one) and capacitors the fast rise time of the square(ish) wave will cook the capacitors or overload the diodes ahead of them.

Another example of how the theory of inverters is good but the cost-cutting reality of what is being made can be drastically different.
 
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