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WHAT makes an Inverter Gererator so special. ???

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Reloadron

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This link does a good job of illustrating poles in an AC generator.

Inverter type generators are relatively new to the scene and have their advantages as well as disadvantages. Long before the inverting types came along millions of RVs used and were fine with the older more conventional AC generators.

Just as a reference and as was pointed out in the links KISS posted the formula for frequency in an AC generator is Freq = Engine_RPM * Number_Of_Poles / 120. I have an old Coleman 60 Hz 2 pole gasoline powered 4.0 KW (5.0 KW Surge) generator driven by an 8 HP engine. .It runs at 3600 RPM for 60 Hz. Similar units using diesel fuel are 4 pole running at 1800 RPM. The 8 HP engine consumes fuel based on generator load while maintaining 3600 RPM. That old generator saved my butt last fall. A storm moved through and it was pouring. All of my downspouts sump into my basement. Power went out and my sump was filling fast. The whole house generator started automatically just as it should and did a transfer as it should but no voltage. Sump is filling fast. I dragged that old Coleman out added gas (I stored it totally empty) and two pulls it was running. Plugged in my sump and away things went.

My whole house unit was a 13 KW unit which ran on natural gas or LPG and we have natural gas service. Rather than mess with it I replaced it with another whole house unit and went with 16 KW. Come Spring I'll look at the old 13 KW unit which is now in the garage.

Anyway, long before the inverter design units were around the old conventional units worked just fine and still do. My old Coleman unit regulated fine at 243 VAC out and before inverter units were around the old conventional units served well in RV as well as boats.

Ron
 

gary350

Well-Known Member
OK your calling the magnet coils poles. I know from working with electric motors for 45 years, a 120 volt, 60 Hz, single phase synchronous motor that has 4 RUN winding inside will run at 1800 rpms. If it is not synchronous the motor runs about 1725 rpms. A 2 pole motor runs at 3600 rpm.

3 phase motors are different they are designed to run at many speeds, low speed motors, 900, 1000, 1100 rpms are used to run hydraulic pumps. Faster motors of other things, fans, belt drive, air compressors, etc. 3 phase come in many voltages 240 to 7200 volts, 1/2hp to 800hp.
 

Reloadron

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OK your calling the magnet coils poles. I know from working with electric motors for 45 years, a 120 volt, 60 Hz, single phase synchronous motor that has 4 RUN winding inside will run at 1800 rpms. If it is not synchronous the motor runs about 1725 rpms. A 2 pole motor runs at 3600 rpm.
The same formula I posted above pertains to synchronous AC motors. Here is where your 1725 RPM is derived from and it is an approximate number. A synchronous AC motor having 4 poles running at 60 Hz. will run at 1800 RPM. Freq = Engine_RPM * Number_Of_Poles / 120 or 60 = 1800 * 4 = 7200 / 120. However, that is the unloaded motor speed. Under its rated load that same motor will run about 1600 to 1750 RPM and that is where the popular 1750 is derived from. Under a load the motor rotating (rotor) will experience what is known as "pole slips" so that 1800 RPM synchronous motor will not run at 1800 RPM but a slower speed. A two-pole motor will operate at 3,600 RPM unloaded and between 3,000 and 3,450 RPM under load.

So while not exactly generator related that is where the numbers come from and how they work out. The same formula can be expressed as RPM = (120 * Frequency) / # of poles in the motor.

Back to generators all of this reminds me the reason I was not aware my old whole house unit had no output voltage was because every Sunday at 9:00 AM it ran doing an "exercise" routine for 15 min. During that period it would start and run but never transferred for a load. Now, while I still have an exercise routine I also just go downstairs and turn off my 200 Amp mains breaker and let the generator actually handle the load. Wife gets annoyed because she needs to reset clocks and stuff but I do not plan on that nightmare happening again. The high temperature today was around 15 degrees and I don't plan to be without power. :)

Ron
 

Reloadron

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Hey Ron, buddy, I have a very long extension cord .......
Wouldn't be the first time. During prolonged outages we have supported our neighbors. During extended outages some stand to lose several hundred dollars in meats in a freezer. During winters as you know, it gets cold up here so we keep their furnaces running. Today we are without water as a line broke down the street so they are out there working on it. Hell, this morning a 36" main ruptured across town creating a frozen river mess, we just had what I call a small leak. :) We put up water for the dogs and toilets before they shut it off. :)

Ron
 
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