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capt2 10-13-2007 08:23 PM

Computer on Generator
 
I keep hearing about generator power output as "dirty."I'm curious if my Gaurdian 13 kw gas powered genset output is too "dirty" to run our computer????? I was hoping not.Thanks

sestivers 10-13-2007 10:15 PM

Yes, the electrical output from your generator is subject to a lot of different things. Depending on the quality of the generator, you are probably starting out with a much less than perfect sine wave. On top of that, any large changes in load on the generator will cause surges which make the frequency vary. Hiccups in the fuel supply to the engine or any problems with the governor will cause the same surges. All of these things are undesirable for electronic equipment. Or if you simply let the engine run out of fuel, you'd suddenly lose power to your computer and potentially lose data or worse.

If you connected a UPS between your generator and computer, you would be safe against power loss, and I think it would also work as a filter for the "dirty" generator output. Hopefully, someone else could confirm that for you.

If you are using a laptop or notebook computer, you would be fine. These types of computers use DC and the transformer inside the charger/power cord will essentially filter out any problems from the generator.

Mike Swearingen 10-13-2007 10:51 PM

I'm not an expert on this subject, but Steve appears to be one, and I agree with what he has to say, from what I do know. I've never had a problem with my comuter on my 5500w portable generator, but I have a UPS 650.
Mike

jwhite 10-14-2007 06:38 AM

Some inexpensive UPSs back up power only. Some will clean power as well and even provide surge protection.

You can get a medium quality UPS for under 100 dollars that will clean, surge and provide a minute or two of backup. I personally like the APC brand. http://www.apcc.com/products/family/index.cfm?id=21

I would stay away from running a computer, expensive TV or sterio, or battery charger on generator power.

joed 10-14-2007 06:32 PM

Not all UPSs put out clean power either. I have one UPS that if I plug another UPS into it, the second UPS will not go to line power. It detects the first UPS output as bad power.

elkangorito 10-15-2007 03:06 AM

Quote:

Originally Posted by sestivers (Post 67941)
Yes, the electrical output from your generator is subject to a lot of different things. Depending on the quality of the generator, you are probably starting out with a much less than perfect sine wave. On top of that, any large changes in load on the generator will cause surges which make the voltage vary. Hiccups in the fuel supply to the engine or any problems with the governor will cause the same surges. All of these things are undesirable for electronic equipment. Or if you simply let the engine run out of fuel, you'd suddenly lose power to your computer and potentially lose data or worse.

If you connected a UPS between your generator and computer, you would be safe against power loss, and I think it would also work as a filter for the "dirty" generator output. Hopefully, someone else could confirm that for you.

If you are using a laptop or notebook computer, you would be fine. These types of computers use DC and the transformer inside the charger/power cord will essentially filter out any problems from the generator.

I don't entirely agree with some of the above comments.

Any generator of reasonable quality will produce a much better sine wave than many inverters/UPS's, particularly if the UPS/inverter uses PWM (Pulse Width Modulation) in its manufacture of the output waveform. Also, many UPS units have a modified Crest Factor (should be 1.4 for true sine wave), thus providing a slightly distorted sine wave. The only UPS that produces a good sine wave is a Dual Conversion or Online unit. Computer power supplies (switch mode power supplies) are not too sensitive to the modified sine waves produced by many UPS/inverters.
Also, AC generators "naturally" produce sine waves. As mentioned above, any changes in load & Power Factor can vary the output voltage & distort the waveform but this generally happens with generators that have poor voltage regulation & are cheaply designed. Generators are susceptible to harmonics, which have the effect of reducing the capacity of the generator.

HVAC_NW 10-15-2007 07:00 AM

If you want clean sinewave output, get a Honda Eu1000i or the larger EU2000i. There is no small generator with a cleaner output.


Using a UPS with the average generator isn't a good idea. The UPS might think the power is too dirty and might not switch over to line operation or hunt back and forth between battery and generator power.

Computers are tough on a generator, because the current waveform is highly harmonic, so you'll have to oversize the gennie. You'll reduce the burden on the gen-set if you use an active PFC power supply in the computer.

sestivers 10-15-2007 10:02 PM

Quote:

Originally Posted by elkangorito (Post 68140)
I don't entirely agree with some of the above comments.

You caught me, I am guilty of talking out of my ass at least a little bit. You're certainly right that a generator, which is rotating machinery, would naturally produce a true sine wave more easily than an UPS, which creates an electronic replication of a sine wave. I am not sure why I didn't think of that.

HVAC_NW 10-16-2007 12:27 AM

Quote:

Originally Posted by elkangorito (Post 68140)
I don't entirely agree with some of the above comments.

Any generator of reasonable quality will produce a much better sine wave than many inverters/UPS's, particularly if the UPS/inverter uses PWM (Pulse Width Modulation) in its manufacture of the output waveform. Also, many UPS units have a modified Crest Factor (should be 1.4 for true sine wave), thus providing a slightly distorted sine wave. The only UPS that produces a good sine wave is a Dual Conversion or Online unit.

Not true.
Most, if not all double conversion UPS's are sinewave as the load is continuously running from the inverter, but there are plenty of standy by UPSs with sinewave output.

Double conversion means that input power is rectified and AC output is regenerated with the inverter

APC Smart-UPS series are a very common type of UPS, but they're standby. When there's an outage, the transfer switch puts the load on its sinewave inverter.

Quote:

Computer power supplies (switch mode power supplies) are not too sensitive to the modified sine waves produced by many UPS/inverters.
Also, AC generators "naturally" produce sine waves. As mentioned above, any changes in load & Power Factor can vary the output voltage & distort the waveform but this generally happens with generators that have poor voltage regulation & are cheaply designed. Generators are susceptible to harmonics, which have the effect of reducing the capacity of the generator.
Portable generators' power is plenty dirty. The RPM must remain exactly 3600 or 1800 to maintain 60 Hz, but with a small generator this is very hard to do when the load is fluctuating. Even when driving a benign load, the output is far from sinusoidal.

Electronic sinewave inverters makes far cleaner power and they don't suffer from frequency drift with changing load.

Some guy ran a test comparing the Honda inverter generator (gas engine turns a high frequency alternator which then powers the 60Hz 120V electronic inverter) and an ordinary generator and the crappiness of the regular generator is very clear.

http://www.jkovach.net/projects/powerquality/


Since the inverter generator doesn't require tight regulation of rotor speed to maintain steady output, it doesn't need a heavy inertial flywheel. If it's only lightly loaded, the engine will actually run at a reduced speed, something an ordinary generator can't do w/o losing the frequency regulation.

elkangorito 10-16-2007 09:53 AM

Quote:

Originally Posted by capt2 (Post 67936)
I keep hearing about generator power output as "dirty."I'm curious if my Gaurdian 13 kw gas powered genset output is too "dirty" to run our computer????? I was hoping not.Thanks

If the model of your Guardian generator is 5242, then its output is NOT dirty & the generator has been designed for use with "home" electronic equipment. Also, your 13kW generator does not use an inverter to modify the output waveform. It does use solid-state technology in its automatic voltage regulation. The "clean" sine wave is mechanically manufactured by the rotating machinery.

Here is the link to the specifications for the Guardian 13kW Model 5242 generator.

http://www.guardiangenerators.com/pu...0174520SBY.pdf


Quote:

Originally Posted by HVAC_NW (Post 68304)
Not true.
Portable generators' power is plenty dirty. The RPM must remain exactly 3600 or 1800 to maintain 60 Hz, but with a small generator this is very hard to do when the load is fluctuating. Even when driving a benign load, the output is far from sinusoidal.

Electronic sinewave inverters makes far cleaner power and they don't suffer from frequency drift with changing load.

Some guy ran a test comparing the Honda inverter generator (gas engine turns a high frequency alternator which then powers the 60Hz 120V electronic inverter) and an ordinary generator and the crappiness of the regular generator is very clear.

http://www.jkovach.net/projects/powerquality/


Since the inverter generator doesn't require tight regulation of rotor speed to maintain steady output, it doesn't need a heavy inertial flywheel. If it's only lightly loaded, the engine will actually run at a reduced speed, something an ordinary generator can't do w/o losing the frequency regulation.

I'm sorry but I must further disagree.

The OP mentioned that he was using a 13kW generator (standby) & not a portable generator, which is a significantly different machine.

I agree with you that "portable" generators may not supply a clean waveform. This is primarily because they are "brushless" & as you say, crappy. The OPs generator is not brushless as is the case with most good quality generators that do mechanically supply a good sine wave.


In any case, the use of electronic equipment loads like computers etc with any generator, will cause sine wave distortion (harmonic distortion). If you placed a cathode ray oscilloscope on your "normal" home power, it's quite possible that you would not see a clean sine wave due to all the harmonics being passed back into the power grid by computers etc. While this harmonically distorted waveform will not harm equipment (providing the Total Harmonic Distortion is not too high), it can cause a generator to be "derated" somewhat. That is, it will no longer be able to deliver its rated power output.

I also found this on the Guardian website:

"Why should I buy an automatic standby generator instead of a portable generator?
While portable generators do supply power, an automatic standby generator produces a higher quality of electricity. It operates automatically and runs a weekly self-test to ensure proper response to your needs. There are no extension cords to plug in and no gas tanks to fill. It operates automatically so it protects your home even when you’re away. When utility power returns, the standby generator shuts itself off."

Stubbie 10-16-2007 10:48 AM

I can't add much to what has already been said about clean vs. bad power. I think we could argue the physics till we are all blue in the face. However, this is a home standy unit and is designed as already mentioned by kangaroo to be specified for electronic equipment. So the anwser to Captains question is ...yes...you can operate your computer.

One thing I would like to mention is that if you havent installed yet give some consideration to the noise level of the guardian while it's operating. I believe it states 90 db. Pretty loud...so maybe locate it appropriately and some sound management construction around it. I don't mean box it in but maybe a barrier to help deaden noise from entering the home.

stubbie

renet123 10-18-2007 10:23 AM

i need to buy a generator for a computer that is sitting out in the middle of nowhere taking some environmental readings. I was thinking about putting a generator on it so that it can stay on 24/7 with a ups or line conditioner. Any recommendation on the type of generator to use? I imagine it would be something like a standby generator, or maybe some type of solar source - but i am unfamiliar with this - any recommendations? maybe someone can point me in the right direction.

Wildie 10-22-2008 09:13 PM

I have a Coleman 1850 generator that I use for camping in a 5th wheel trailer.
It never occurred to me that 'dirty' power could be a problem.
I have used it to power my laptop computer and the satelite TV box, and the TV as well, with nary a problem.
Once, after an ice storm the power was off for 6 days and I used this generator to run the kitchen frig. My desktop computer and the TV. And a kitchen light!
Not altogether though!

ScottR 10-22-2008 11:07 PM

Major manufacturers (Dell, Sony, etc) will usually put the same PSU in a desktop regardless of where in the world it's being sold, and they buy PSUs designed for a wide range of voltages and cycles. And they know that not all the world's power is as clean as ours. :whistling2:

Even cheap BYOPC/replacement power supplies nowadays have ratings for 110/220V, 50/60Hz. They can handle variations around those numbers, too. I've seen midrange ($50) PSUs that are spec'd to handle 47-63Hz @ 100-240V, in any combination.

A couple of the guys up there nailed it -- there once was an accepted definition that an SPS (Standby Power Supply) provides a "pass through" for mains power when it's on, and battery power through an inverter when mains are off. UPSes (Uninterruptible Power Supply) provide mains power to an inverter (via a DC transformer), and the inverter continues to be powered during a mains outage by the battery. On a high quality UPS, you would not even see the sine wave miss a beat on an oscilloscope during transfer to/from battery (quite untrue for those $100 units).

Nowadays everyone calls everything with a battery a UPS. So the difference is online vs. offline (whether the inverter is online or offline during normal operation). The inverters in SPSes are usually cheap and not intended to run for extended periods. UPSes have higher quality inverters rated for continuous use. If you're looking at two units that both carry the same VA rating, but one is three times more expensive than the other, the more expensive one is probably a true UPS.

Inverters in either SPSes or UPSes can be sqare-wave, sine-wave, or somewhere in between. The best (and by far most expensive) protection for your equipment will be a full-sine-wave, online UPS. (Almost all SPSes/UPSes on the market will have spike/surge protection as well).

I think someone said it above, but you can get dirtier power from a cheap SPS (when it's on battery) than from a fancy generator.

I guess my point here is that you'd have to feed a (newish) computer some _really_ dirty power to have it effect the output. (<-- May not hold true for really crap computers). They do a pretty good job of smoothing that "messy" AC to nice, even DC. If they didn't, your computer would fry everytime you ran the vacuum off the same outlet as the computer.

So to the OP and whomever else: Buy the cheapest (name brand!) SPS with the highest VA rating you want to afford.. you'll be fine.

Last thing: Ever had a momentary blackout (lights turn off for just the blink of an eye) and see that your computer hasn't rebooted? Yup, they'll work on 0VAC too, but only for a half second or so (and that's 30 missing cycles!) So that's my 2c.

rgsgww 10-23-2008 07:21 AM

You could get an isolation transformer and then connect a good quality ups to that...


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