# 7kw generator not properly running 1200w microwave oven.



## Soya (Jan 24, 2020)

My 7kw coleman generator can run my well pump, freezer, refrigerator and hi efficiency gas furnace just fine.

But when I start my 1200w microwave oven the light in the oven kind of dims and yellows and the turn table seems very slow and the sound of the magnetron does not seem normal. When I try running it every other circuit on the gentran panel is off. The microwave and maybe 160w of lighting is all that the generator is powering.
The generator doesn't hesitate like it does when I plug in the freezer compressor but for some reason the microwave is not being powered correctly. It is on a 20A circuit. I'm powering the gentran panel from the 240v output of the generator.

Is it a case of "dirty power" from a non inverter generator?


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## Browse Deweb (Jan 16, 2021)

Microwaves are probably very sensitive to frequency variations and dirty power. An inverter generator would most likely solve this problem.


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## BobS (Aug 26, 2020)

Before you can even guess what the problem is you need to get a "kill a watt" - cost approx. $25 or a good meter and test the voltage and hertz. The voltage should be between 110 and 125 volts. The hertz will vary and should be between 59 and 62.5 Hz. If you are in the above ranges, then the quality of the power is probably too poor. There is no cheap method to correct this. I have 18 year old coleman powermate 6500 watt. The engine is a honda gx390 (excellent) but the generator head was junk. I got the generator on a special sale (cheaper than the engine). My UPS's would not accept the power from this generator (my others generators of much better quality had no issues). At approx. 150 hours, the generator head's AVR could not be adjusted (voltage over 135 volts) so I replaced it with a mecca generator head. It runs great and now has no problem even running a 4 ton AC (** inverter type).


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## speedy2019 (Jan 29, 2019)

Very few UPS will accept a non inverter generator and for this reason you can buy "generator friendly UPS's"


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## BobS (Aug 26, 2020)

You don't need an inverter generator for good power, but it needs to be put in proper perspective. A good 6,500 watt non inverter generator will cost you $1,500+. You need a good generator head (alternator) on the generator which is expensive. My 4 current generators are all non inverters and work with all of the UPS's that I have which range from $75 to $700. When my clients pick up cheap generators, they have many problems with computers, lights and ups. Almost all if not all of the cheap generators have generator heads with aluminum wiring and cheap voltage regulation systems. The whole generator is cheaper than a good generator head. You need to determine your power requirements, amount of money your are willing to spend and the dependability that you require.


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## Soya (Jan 24, 2020)

BobS said:


> Before you can even guess what the problem is you need to get a "kill a watt" - cost approx. $25 or a good meter and test the voltage and hertz. The voltage should be between 110 and 125 volts. The hertz will vary and should be between 59 and 62.5 Hz. If you are in the above ranges, then the quality of the power is probably too poor. There is no cheap method to correct this. I have 18 year old coleman powermate 6500 watt. The engine is a honda gx390 (excellent) but the generator head was junk. I got the generator on a special sale (cheaper than the engine). My UPS's would not accept the power from this generator (my others generators of much better quality had no issues). At approx. 150 hours, the generator head's AVR could not be adjusted (voltage over 135 volts) so I replaced it with a mecca generator head. It runs great and now has no problem even running a 4 ton AC (** inverter type).


I used a killawatt meter last fall to test the gen under load from a heater. It was within those specs. So the quality must be suspect. It runs my 90+ efficiency gas furnace with all kinds of circuit boards and interlocks fine, so far. The MW must just be more sensitive.

To make sure I'm testing correctly; I plugged the killawatt into the 120v outlet on the gen, then plugged the load (heater) into the killawatt. I then started and ran the gen to get the reading. Would this be the correct procedure?

How to test power quality? Do you need an oscillascope?


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## Old man here (Nov 5, 2020)

Soya said:


> I used a killawatt meter last fall to test the gen under load from a heater. It was within those specs. So the quality must be suspect. It runs my 90+ efficiency gas furnace with all kinds of circuit boards and interlocks fine, so far. The MW must just be more sensitive.
> How to test power quality. Do you need an oscillascope?


An oscilloscope will only show what the sine wave looks like, voltage and frequency.
To look at the THD (power quality) you would need a power analyzer. A very expensive tool.
Something like this:








PA1000 Single-Phase Power Analyzer (Discontinued)


This product has been discontinued, but information is still available



www.tek.com


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## BobS (Aug 26, 2020)

There are meters that can test TDH (total harmonic distortion) but good ones are normally expensive. Certain oscilloscopes can be used but I haven't used one in over 40 years. There are many others on this forum that are experience in testing TDH. Based on your results, I would assume that the power quality is insufficient for the microwave. There ways to clean up the power but they are very expensive. I would be probably better (cheaper) to not use that microwave with the given generator, try a different microwave or replace the generator.


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## speedy2019 (Jan 29, 2019)

This is my 2800watt gen I have, I haven't really used it yet(only monthly exercise, with low load) even though I have had it for 2yrs now........ Electric Key Start Generator | Bohmer-AG - 6500W-e Portable Generator


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## Soya (Jan 24, 2020)

BobS said:


> There are meters that can test TDH (total harmonic distortion) but good ones are normally expensive. Certain oscilloscopes can be used but I haven't used one in over 40 years. There are many others on this forum that are experience in testing TDH. Based on your results, I would assume that the power quality is insufficient for the microwave. There ways to clean up the power but they are very expensive. I would be probably better (cheaper) to not use that microwave with the given generator, try a different microwave or replace the generator.


Yup. Seems like good advice.
What are the benefits of inverter gens over standard ones for the large price difference? I'm referring to the Honda gens. I believe the EU line is inverter and the EM is standard, is that correct?

I've been to several Honda gen pages but none of them list THD for the EU and EM gens. Maybe I'm not looking in the right place but you'd think they'd emphasize that if it was superior to the competition.


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## speedy2019 (Jan 29, 2019)

Surely its mainly down to how smoothly and continuously the engine can keep the 3600rpm and thats down to you, how well you maintain and look after the generator?


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## BobS (Aug 26, 2020)

An inverter generator takes the power produced from the generator and converts it to 120V (in your case 230V) at either 50 or 60 Hz electronically usually producing a good sine wave with very low TDH. All of the Honda generators (real Honda's) have a very low TDH with the Honda inverters having excellent power quality with lower noise, higher price and better fuel usage compared to non inverter Honda's that have to run at 3,000 (50 Hz) or 3,600 (60 Hz) to produce very good power. Either one will be good. I also noticed that the generator you posted is a UK version. I assume that you are using a 50Hz generator. What was the hertz that was being produced?


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## Soya (Jan 24, 2020)

The price difference between the inverter and non-inverter models of Honda is substantial. I guess if the standard Honda will power everything ok then the fuel savings would take forever to pay back the difference when the gen is used on an occasional emergency power basis.


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## BobS (Aug 26, 2020)

Speedy - the engine speed will affect the Hz and possibility the voltage (depending on the method used to regulate the voltage). The THD is dependent on the quality of the generator head. Taking care of the generator will help it reach it max. life span. Many of the cheaper generators (not all) only last 20 to 200 hours. The people that can give a better answer to the longevity are construction personnel (not quality of power but longevity) and food trucks that use the generator almost every day.


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## BobS (Aug 26, 2020)

If you have the money, Honda inverter generators are the gold standard for gasoline generators. The Honda non inverter generators are also excellent. They always run at 3,000 or 3,600 rpm (louder) and can use more fuel at lower loads.


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## speedy2019 (Jan 29, 2019)

My gen is 50hz, 230v and Id say its done 10-15hrs in exercise runs now.


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## Soya (Jan 24, 2020)

BobS said:


> If you have the money, Honda inverter generators are the gold standard for gasoline generators. The Honda non inverter generators are also excellent. They always run at 3,000 or 3,600 rpm (louder) and can use more fuel at lower loads.


They can be converted to run on propane or NG correct?


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## PLX (Nov 22, 2020)

If you have access to another microwave, swap it out & see if you get the same results. Also check all the connections on the microwave circuit (grounds, white, black or red) at the outlet & at the breaker box. I would start here 1st before I ran out & got another genset. JMO


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## Soya (Jan 24, 2020)

PLX said:


> If you have access to another microwave, swap it out & see if you get the same results. Also check all the connections on the microwave circuit (grounds, white, black or red) at the outlet & at the breaker box. I would start here 1st before I ran out & got another genset. JMO


Sounds good. I know that the electrician that wired my house was fond of backstabbing outlets and switches.


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## BobS (Aug 26, 2020)

Soya said:


> They can be converted to run on propane or NG correct?


Yes, but Honda does not support it. Many people on this forum have converted them. I would ask the question on the forum for a good company to purchase it from.


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