What is "dirty electric"?

[John White]

I have seen this term used term used when talking about generators. I have a few questions? What is the minium and max. range a gen should operate at? Should your speed be set so that it shows 60 cyles? What do you do if your voltage is too high or too low at that setting. Will one of those gauges you see advertised on e-bay for $20 that is supposed to show voltage and cycles work in setting your gen? My old gen always showed 120 volts under load or on load. I never checked the fequency of it. I purchased a Kubota diesel light plant (like the ones on the highway for night lights) I noticed my lights a little briter than my other gen. so I checked it and it was putting out 130 volts. I reduced the engine speed a little, back down to 120, but when a load was applied,(1500 watt heater) it didnt appear to speed up and pick up the load. Does the Kubota D850 have a governor? I ordered one of those voltage frequincey meters off e-bay last night to try and montor my generators a little better. My older generator (De velbiss) always seemed to work ok and I even watched tv with using it, and even ran a older computer (which I hear is a no, no) that seemed to work ok. Noticed I said my old one, not my new one. I hear tv's and computer and microwave ovens are pretty sensitive to voltage. Any help appreciated.

 

[3930dave]

It sounds like your governor control on the Kub is not working properly. I don't know that generator at all, so can't suggest how to diagnose it - best to get a service manual, if you are hands-on inclined, remembering that lethal voltages are involved ! Any doubts, tow it to a qualified generator repair shop.

With that wide a voltage swing, I wouldn't run that Kub on anything more valuable than a light bulb, and not indoors (meaning the bulb).

Homepower.com is usually a good goto source for general alternative power information. "Dirty" can refer to the grade (electrical quality) of the output power, or to the fact that you are burning fossil fuel to run it - depends on the context of the statement as to which applies.

Rgds, D.

 

[joshuabardwell]

With regard to a generator, "dirty electricity" usually refers to the quality of the AC power coming out of the generator. When I first heard the term, I thought you were referring to "dirty" vs "clean" electricity in the environmental sense, but now I don't.

AC energy should be a perfect sine wave. The AC energy coming out of a conventional generator is usually not a perfect sine wave, for various reasons, including the quality of the stator/rotor (consistency of the windings, for example) and the quality of the governor on the engine (can it run at a perfect 3600 RPMs, or does it vary slightly). This is because conventional generators simply consist of a motor that drives a rotor that spins in a stator. So there is basically no fancy cleaning or regulation of the AC output. The engine is tuned at the factory to spin at 3600 RPMs, which causes it to output 120-volt / 60 Hz power, which is then sent out to the breakers and receptacles.

An alternative to conventional generators is "inverter" generators. These generators output three-phase AC from the stator/rotor, which is then rectified to DC, which is then converted back to AC by an inverter. They put out near-perfect waveforms and are much more fuel-efficient and quiet than conventional generators, but they're also much more expensive.

For perspective, here is the output of two different conventional generators:



Notice that one is cleaner than the other, but neither is perfect. Here is the output of an inverter generator, for comparison. This is also comparable to what you would see coming out of your wall, from the utility:



Now, you will hear people talk all day long about how "dirty power" from conventional generators damages "sensitive electronics" like computers. I think these claims deserve some skepticism. For one thing, modern computers all have switching power supplies, and have for the last ten years or so. This means that the first thing the power supply does is convert the incoming electricity to DC, then convert it to high-frequency AC, then convert it to whatever form the appliance needs. This means that these devices are very tolerant of incoming signal that is not quite in spec. Devices with analog PSUs might have more problems with out-of-spec power, and might be more likely to be damaged.

But wait! I have done a substantial amount of research on this topic (although I'm just some guy) and anecdotally speaking, here is what I have found. In nearly every case I have found where a person claims that a generator damaged their equipment, they were overloading their generator. If you're overloading your generator, then the voltage is going to drop, and consistent low-voltage conditions WILL damage all electronic equipment that is attached to them.

This is why I'm very skeptical of the "sensitive electronics / dirty power" claim. You never hear the people making this claim tell you that modern "sensitive electronics" have switching PSUs that probably aren't going to be damaged by "dirty power". So it just makes me wonder what else they don't know or aren't telling me. And then you do some research and find out that all these people who are blaming their generators' "dirty power" on destroying their equipment were overloading their generator. Guess what? It doesn't matter if you're using an inverter generator or a conventional one, if you overload the genny, you're going to get low voltage conditions.

 

[k0ua]

Joshua, good explanation, and I liked you O' scope screen shots.

James K0UA

 

[General Lee]

Dirty electric is is basically less than pure clean voltage so to speak. The power you get from the grid is a clean sine wave but some genny's depending on how their tuned or condition can put out dirty power. My genny puts out about 130 volts w/ no load but drop close to normal under load. I have never tested it while I was running several items in the house. I know my ceiling fans don't like the genny, they hum and last power outage our microwave was damaged. It worked but sounded like it lost a lot of its power. So maybe I have an issue with my genny as well. Using my TV, computer and everything I saw no issues.

 

[joshuabardwell]

Joshua, good explanation, and I liked you O' scope screen shots.

Thanks, James. Credit where credit is due, I just pulled those off the web somewhere.

I think the bottom line is that if your genny is putting out 120/60, or thereabouts, you are probably fine. I shouldn't have said "in nearly every case, the person was overloading their generator." In some cases, the generator was operating out of spec. But my point is that I can't find a single case where a conventional generator destroyed some equipment AND was basically operating in spec (putting out 120/60). Either it was overloaded, and was undervoltage, or it was running out of spec and was putting out 50 Hz instead of 60, or 130 volts instead of 120, or what-have-you.

 

[dex3361]

With most generators the Hz, frequency, cycles (all the same) should be Hz. If you speed up the engine then the Hz will rise, slow the engine down then the Hz will drop. The acceptable range is 59Hz-61Hz and ideally 60Hz. The voltage in most newer generators are controlled be an AVR(Automatic Voltage Regulator). So the governor is to make sure that the frequency does not vary to much under load.

 

[RickB]

Thanks, James. Credit where credit is due, I just pulled those off the web somewhere.

I think the bottom line is that if your genny is putting out 120/60, or thereabouts, you are probably fine. I shouldn't have said "in nearly every case, the person was overloading their generator." In some cases, the generator was operating out of spec. But my point is that I can't find a single case where a conventional generator destroyed some equipment AND was basically operating in spec (putting out 120/60). Either it was overloaded, and was undervoltage, or it was running out of spec and was putting out 50 Hz instead of 60, or 130 volts instead of 120, or what-have-you.

I totally agree with your thoughts and message. To provide further response to the OP, an inexpensive frequency/voltage meter such as a found on eBay and other places is a great tool for setting generator speed/output. It is entirely possible that the 1500 watt 'load' was not enough to cause voltage drop, a decrease in engine/generator speed, or a noticeable reaction from the engine's governor.

 

[RobertBrown]

Thanks, James. Credit where credit is due, I just pulled those off the web somewhere.

I think the bottom line is that if your genny is putting out 120/60, or thereabouts, you are probably fine. I shouldn't have said "in nearly every case, the person was overloading their generator." In some cases, the generator was operating out of spec. But my point is that I can't find a single case where a conventional generator destroyed some equipment AND was basically operating in spec (putting out 120/60). Either it was overloaded, and was undervoltage, or it was running out of spec and was putting out 50 Hz instead of 60, or 130 volts instead of 120, or what-have-you.

Thanks from me too. I've always wanted to know more about those things.
Can you tell me how one determines when a generator is overloaded or how much of the rated watt output you can use before it becomes questionable? Furthermore, how would one go about sizing a generator?

 

[joshuabardwell]

Thanks from me too. I've always wanted to know more about those things.
Can you tell me how one determines when a generator is overloaded or how much of the rated watt output you can use before it becomes questionable? Furthermore, how would one go about sizing a generator?

In general, I think it's safe to assume you can use 100% of your generator's rated capacity. But it's certainly true that a generator running at 100% capacity is going to wear out sooner than one running at a lower capacity. That's true of any engine. Keep in mind that appliances with motors (including the compressor in your fridge or chest freezer, or your AC unit) have a surge draw when the motor starts up that is 3x or more the normal running draw. That's why generators have surge rating as well as continuous rating. However, if two or more appliances kick on at the same time, the amount of draw can increase a surprising amount, and overload your generator.

IMO, the simplest way to be sure you're not taxing your generator is to check the quality of the AC it's putting out. If it's 120 volts at 60 Hz, then you're probably okay. What will happen when the motor in the genny can't keep up with the draw is, it will begin to bog down, and the voltage that's put out will start to drop. If your generator has a volt meter built in, you can see this there, or you can buy a Kill-A-Watt for $25 or so and leave it plugged in to an outlet being fed by the generator. I highly recommend owning a Kill-A-Watt anyway, if you're going to be using a generator.

Regarding sizing a generator, what you do is add up all the wattage of all the things you want to run at the same time, and buy a generator at least that big, but IMO, I would buy one maybe 25-50% bigger than that, or maybe even up to 2x as big, because like I said, you don't want to be running at 100% all the time, and you will probably end up finding more things to run once you get started. When you add up the wattage, you also have to take into account surge watts. It can be hard to know how many watts things draw, so once again, the Kill-A-Watt comes in handy, because it can show you in real time how much any 120-volt appliance is pulling. For example, my chest freezer pulls a few hundred watts when the compressor kicks in, but only for a few seconds, and then it immediately drops down to something much lower (don't remember what).

If you seriously believe that you will be working your generator at close to its rated load a significant portion of the time, I would recommend either sizing up significantly, or look into one of the 1800 rpm diesel generators. Since they are running at a much lower RPM and are diesel, my intuition is that they are much more tolerant of heavy, long runtime. If you buy a bargain-basement generator that just barely meets your needs, and then run it hard for days at a time, don't be surprised if it needs repair after only a few hundred hours, or maybe less.