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  #1  
Old 05-17-2018, 11:28 AM
scsmith scsmith is offline
 
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Default OT portable generator waveform?

I'm sorry this is a stretch to call it RV-related, except that people may use portable generators for power in their hangars where their RVs are kept. But I wanted to try to tap into the expertise here.

I am shopping for a 8000W class portable generator for home use during power outage, as well as portable power for the barn. There are several products in the $1000 range, and a desirable feature of some of them is dual-fuel (LPG and gasoline).

A friend suggested I pay attention to the output waveform of these generators. But the vendors supply no specs or data.

For most things, I'm not sure if I care. The main power draw will be my well pump. I suppose motors run better, cooler, with cleaner power waveforms, but I don't know that it will effect pump performance or life for the limited time it will run off the generator. We would probably want to run the computer. Nowadays, they have pretty sophisticated power supplies, and my suspicion is that it would clean up any dirty power signal to keep the rest of the computer happy.

By comparison, a Honda gas-only 7000W generator is about $4000.
Other than the great reputation and brand loyalty for Honda, why so much? Does it produce a cleaner output waveform? How would I know?

Any insights appreciated.
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  #2  
Old 05-17-2018, 11:56 AM
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Mike S Mike S is offline
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Steve, many so called portable generators are actually alternators-----not sure if that makes much of a difference, but this might help.

https://yamahaef2000is.com/conventio...ter-generator/
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Old 05-17-2018, 12:01 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by scsmith View Post
By comparison, a Honda gas-only 7000W generator is about $4000.
Other than the great reputation and brand loyalty for Honda, why so much? Does it produce a cleaner output waveform? How would I know?
I can't comment on wave forms of the output, but in my experience the most evident difference between a Honda and some of the lesser expensive brands is operating noise level. Most of the Honda's are relatively quite. Most of the cheaper brands, not so much.
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Old 05-17-2018, 01:04 PM
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Raymo Raymo is offline
 
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If concerned about smaller electronics and power fluctuations, consider using a UPS or isolation transformer to keep things happy.

I have a medical grade Isolation Transformer/UPS inline for my computer and network equipment to ensure there are no spikes or under-currents.

When you decide on a generator, I would be interested in your pick as I need one for the same reasons. Horses go through a LOT of water.
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Old 05-17-2018, 01:21 PM
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Lenny Iszak Lenny Iszak is offline
 
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I took apart one of those portable generators a few months ago (courtesy of hurricane Irma), and to my surprise there wasn't any electronics in it. Basically it's just two spinning coils connected straight to the output. Computers will not run on that, because the waveform is all over the place as it depends heavily on engine speed and load.
If you want to run any sensitive electronics on it you would probably get away with using a UPS made for PCs. The UPS itself won't be happy (mine kept beeping occasionally), but the electronics/computers will run fine on it.
Those Honda generator use an inverter to convert the power back to a proper waveform and voltage. They are expensive, but they are way better built, a whole lot quieter and last much longer than the $1000 spinning coils.
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Old 05-17-2018, 01:26 PM
scsmith scsmith is offline
 
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Quote:
Originally Posted by Mike S View Post
Steve, many so called portable generators are actually alternators-----not sure if that makes much of a difference, but this might help.

https://yamahaef2000is.com/conventio...ter-generator/
That is a big help Mike. Now I understand why the Honda is so much more money. It is an inverter generator, true sine wave output. They can also be paralleled.

Thanks to Raymo and Lenny too. Yes, the cheap ones are just an alternator. So the choice is to run the alternator type, with a UPS, or get the Honda or similar.
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Last edited by scsmith : 05-17-2018 at 01:29 PM.
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  #7  
Old 05-17-2018, 01:32 PM
rv7charlie rv7charlie is offline
 
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All the 'traditional' AC line current generators are alternators: they must make alternating current.

Their wave forms will be pretty close to what you'd see on regular line voltage. Their *frequency stability* (how close they stay to 60 Hz in the USA or 50 Hz in Europe, etc) might vary a bit between brands, and certainly with loads that vary quickly between minimum and near max rated. Smaller and intermittent duty models typically run at 3600 rpm; larger and continuous duty models sometimes run at 1800 rpm. Note that both are divisible by 60 (Hz).

The relatively new inverter generators might be DC generators, or multi-phase AC alternators rectified to DC (similar to our aircraft alternators), with the DC voltage being fed to an inverter to create AC voltage. This is where quality of product could make a big difference. Poorly designed/built models might have both poor frequency control, and poor synthesis of a clean sine wave to mimic AC line power. The reason is that it's a lot easier (read: cheaper) to make an inverter that generates a square wave than a sine wave. The 'corners' of a square wave is where the noise is. Frequency stability will likely be good on any of them, but waveform cleanliness could vary a lot between brands/models.

No one else can make the call for you, but you can find lots of accounts of people using traditional portable generators to run their households during power outages. I've run my freezer, fridge, computers, and fans numerous times over the years on an ancient 3.5 KW pull-start 'portable' (probably weighs 150 lbs). That includes almost a week of intermittent use to keep the food from spoiling and fans running at night, in the aftermath of Katrina.

Charlie
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  #8  
Old 05-17-2018, 01:57 PM
krhea krhea is offline
 
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Default http://www.vansairforce.com/community/showthread.php?p=1260657#post1260657

Buy a Honda and ask for Japanese rectifier. If they don't know have them find out.
From experience i can tell you that some equipment will not like a dirty sine wave. Some gas fired furnaces and mini-split AC and heat pumps won't run on them.

Keith Rhea
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  #9  
Old 05-17-2018, 03:22 PM
cczarnik cczarnik is online now
 
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+1 for an inverter-style generator. If you're looking for lots of KVA check into a pair of Champion 3100's or the new Harbor Freight Predator models in a parallel setup. You can get two of them for less than the cost of one Honda. I have the Champion. 100's of hours so far not a hiccup. 120v only though.

FYI a normal consumer grade UPS will NOT clean up the line noise from an open frame non-inverter generator. It may trim voltage and spikes, but will not correct frequency (varies with rpm) or the harmonics. It takes a serious UPS (costing way more than a good genset) to do that.
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  #10  
Old 05-17-2018, 03:59 PM
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F1Boss F1Boss is offline
 
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Default OPtion:

If you have a tractor, you can use a trailer mounted gen that uses the tractor output shaft. Of course, you can't use the tractor while this is in operation...

This one looks like a good unit @10KW output/42A - made in USA! Less than 5% THD.

https://www.absolutegenerators.com/w...-10-kw-515-rpm
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