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Hammer

Portable generator question...

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Hammer

I don't know that much about portable generators, so I thought that maybe someone here might know the answer to this question.

 

If a generator puts out "dirty" volts ac, which means that it has a total harmonic distortion percentage that is too high to be able to run sensitive electronic equipment on, as opposed to a generator that has an inverter that has a low harmonic distortion that you can run sensitive electronic equipment on, if you connect an uniterruptible power supply (UPS) plugged into the generator that outputs "dirty" power, then plug your sensitive electronic equipment into the UPS, will the UPS clean up the "dirty" voltage so that your sensitive electronic equipment can be safely run, or will the "dirty" ac damage the UPS unit?

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Kit

Funny enough, I had exactly this situation at my previous job.

 

The office had a generator, since power outages weren't as infrequent as they should have been.  but it was really a residential unit.  if power went out, I would have to turn off the entire breaker box, flip a switch to disconnect from street power and switch to generator power.  Go pull the generator outside, get it hooked up, started, flip the main switch, then turn on those breakers which were required.  Powering the entire place was more than the generator could handle.  And, when the power came back on, we basically did the entire thing again.  Wheee.

 

Our servers were connected to high end UPS units.  When I needed to switch to the generator, I would have to shut down all of the servers before I could do anything else.

 

So I contacted APC and asked them if I really needed to shut everything down or if the UPS would cushion out anything caused by the return of power.  I requested information three times.  Never received an answer.

 

But, back to your question.  Yes I have run sensitive equipment off a generator going through a UPS.  However, I was not the person who had set the system up, so I honestly don't know if there was anything about the setup I was unaware that may be a factor.

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OneEye

When PG&E said they were going to turn off electricity grids here in California for what could be "days" at a time ...I wasn't going to go to the rescue center and sit around all day chatting it up with people complaining about their lot in life. I decided to buy a generator and make my own electricity and stay home.

 

I bought a Champion Dual Fuel 3950 Watt generator that I run on propane. I have four 30# propane cylinders that last 11 hours each with the generator running at 50% power. I chose a dual fuel because the last thing I want is three or four 5-gallon plastic jugs of gas sitting around my trailer when it's 100 degrees out.

 

I, like you, was concerned about my computer, my modem, my WiFi and my TVs. I talked to a few guys in my motorcycle forum and all of them said don't worry about it...they've run things off their generators with no problems. So...Wednesday at 3 in the morning PG&E shut off the power. Around 10 o'clock I fired up the generator, let it run for a few minutes then plugged my trailer into it. Ran it until 4 o'clock that afternoon when PG&E turned back on the electricity. No problems. The generator put out 119 volts at 60 Hz...steady.

 

Any device that "cleans up" the "dirty voltage" should say that's one of its features. I had no problems.

 

 

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Hammer

Well, it's my understanding that a UPS (uniterruptible power supply), runs your sensitive electronic components off of it's battery backup, while the electricity that the UPS is plugged into, keeps the UPS's battery charged.  What I wasn't sure of is whether the "dirty" voltage coming out of the generator would damage the UPS unit?  I have searched this and can't find an answer to it.

 

The reason I'm asking is because, a generator that outputs "dirty" voltage, is a lot cheaper than a generator that has an inverter that outputs clean voltage.  If you bought a generator that outputs "dirty" voltage, then added a UPS unit to it, it would be a lot cheaper than buying a generator that has an inverter and outputs clean voltage.

 

What I have been doing, is to look for a generator/s for my radio club to use in the field.  Since our radios, as well as the computers that we use, will be needed for field use, need to have clean voltage, I need to find a low cost solution to this.  The club has discussed buying four 2200 watt Honda generators that output clean ac, for about $4500, and to parallel two generators to give us 4400 watts for two of the generators combined, but we can buy two 7,000 watt generators that output dirty voltage, so we'd have 7,000 watt generators, meaning that we would have one generator for our two emergency radio stations, but we'd need to clean up that dirty voltage so that we could run our radios and computers off of it.  The lights, coffee maker, and any other, non -sensitive equipment, wouldn't need clean voltage, so other than the radios and computers, dirty power would be fine, but I don't know if the "dirty" power would damage the UPS units.

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OneEye

Any device that turns AC into DC as its power source...I wouldn't be concerned about. I've found that the warning about "dirty voltage" is just that, a warning. More or less like a "best by" date.

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Hammer

OneEye, a UPS doesn't convert AC to DC, it uses a battery that is contained in the UPS unit, and converts it to AC.  Dirty AC is a slang term that means that, the AC that you get out of your wall outlet is pure AC, meaning the the sine wave of the AC voltage is a perfect sine wave, but "dirty" AC, is AC voltage that isn't a perfect sine wave.  A sine wave looks like this....https://legacy.earlham.edu/~tobeyfo/musictechnology/2_SineWaveMath_edit.html   A dirty sine wave looks like this....https://electronics.stackexchange.com/questions/314022/trying-to-determine-the-snr-of-a-dirty-signal  See how the dirty sine wave isn't as pure as the clean sine wave is?  The dirty sine wave has many fluctuations along the sine wave, which makes it unusable for sensitive electronic equipment, as those fluctuations would damage the equipment.

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TX_Clint

In my experience dirty power is not much of an issue. It may be an issue of you run very sensitive equipment but the major issue is a power spike. A power spike is likely to occur if you have a momentary dip in power. This is often caused by other equipment coming on, such as a compressor, causing a sudden increase in load on the generator. I would recommend you run your equipment on an independent generator to prevent this. Don't run your AC or refrigerator on the same generator as sensitive electronics. Battery chargers are not an issue. I run my fridge, a small AC, and phone charger on a generator. I simply don't run anything else. As long as the cell towers are running I can use an ipad networked through my phone for connectivity. Most often though I just get out my Kindle, read and relax.

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OneEye

So then, what changes in a "dirty" sine wave...the volt-ampere, the Wattage or the Hz or all of them? And what's the variance...enough to fry a circuit? When I had my generator running I had my A/C on at the same time. The A/C pulses between compressor/fan and fan as it runs. I could hear the momentary drop in the generator rpm as the load would increase...but it never affected my computer, my monitor, my TVs, my WiFi or my modem.

 

I also run a gadget inline so I can see what's going on with the electricity. It's call a Kill A Watt meter. Handy little device. With my A/C off, the draw on my generator is about 330 Watts. When the A/C kicks on it jumps to 1310 Watts. Doesn't seem to affect anything. Maybe all this stuff I'm running isn't "very" sensitive! 

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TX_Clint

 I say it's more likely for a power surge to cause damage. Not that it will.

The only time I've ever had issues along these lines was when my power provider started playing with the power distribution by kicking one leg out then back in repeatedly. Blew my microwave control panel. I wanted a new one anyway.

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Hammer

If you look at the clean sine wave, the wave starts at the zero reference point on the left.  It rises up to a peak, then drops back down to the zero reference point.  If we say that the peak is +120 volts, then the sine wave starts at 0 volts, and slowly rises up to +120 volts.  All along that rising slope is a voltage.  It starts at 0 volts, then increases to +1 volt, then +2 volts, etc. all the way up to +120 volts.

 

If you look at the dirty sine wave, it should also start at 0 volts, then rise to +1 volt, then jump to maybe +50 volts, then drop down to maybe +3 volts, then shoot up again to maybe +100 volts, then drop down to some lower voltage.  It's not a steady increase from 0 volts to +120 volts, like the clean sine wave it.  The dirty sine wave will still get to +120 volts, but it's not a smooth rise from 0 to +120.  For most electrical appliances, a dirty sine wave is fine, but for sensitive electronics, a dirty sine wave can destroy the electronic circuits. (that picture of the dirty sine wave isn't from a 120 volt source, but it does show you how a sine wave looks when it's dirty.)

 

If you ever look at ads for generators, those generators that have inverters on them, cost more, and they also state that the generator is safe for sensitive electronic equipment.  If the generator doesn't have an inverter, the ads usually state that the generator is good for running appliances (like refrigerators, coffee makers, window a/c units, power tools, etc.)  They never say that it is good for sensitive electronics.  If the generator outputs clean voltage, the ad will usually state the total harmonic distortion (THD).  The distortion is what you see happening to the dirty sine wave, and if the THD exceeds a certain percentage, it's considered to be dirty voltage.

 

Keep in mind that the clean sine wave you see in the picture, starts at 0 volts, rise to a peak of +120 volts, then drops back down to 0 volts, and continues dropping until it hits a peak of -120 volts, then rise back up to 0 volts.  That is one complete cycle.  Here is the states, the electricity coming out of the wall outlet is repeating this cycle 60 times a second, so appliances aren't that affected by dirty voltage, since they are usually running some type of motor, heating up something like a coffee maker, powering lights, etc., things that are resistant to fluctuations of the voltage like this. 

Edited by Hammer

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Hammer
3 hours ago, TX_Clint said:

FYI the peak for 120 vac line voltage is 170 volts peak.

Yes, that's true, but what I was referring to was the peak that the voltage reached in the sine wave.  Yes, peak voltage is 1.414 of the RMS voltage, the RMS voltage (the Root Mean Square) is .707 of the peak voltage.  The RMS voltage is the amount of AC voltage, that will do the same amount of work as the same amount of DC voltage.  That means that 120 volts of DC voltage, will do the same amount of work as 170 volts of AC voltage.

 

DC voltage is more efficient than AC voltage, but it can't be transmitted over long power lines, whereas AC can, which is why we all get AC voltage out of our house's power outlets.  Most of today's electronic equipment requires DC voltage, but since the wall outlets provide AC voltage, that AC voltage needs to be converted to DC voltage before the electronic equipment can use it.

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TX_Clint

Food for thought... a sine wave has 70.7% of the area of a square wave with the same peak. A saw tooth or triangular wave has 50% of the area of a square wave. And I've gone way too far off topic again.

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