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  #11  
Old 05-17-2018, 06:31 PM
scsmith scsmith is offline
 
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Location: Ashland, OR
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Quote:
Originally Posted by F1Boss View Post
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
An interesting concept. My old tractor would go through diesel pretty fast doing this. I guess the output frequency depends on tractor PTO rpm? I doubt I could set rpm to within a couple of percent to maintain 60 hz.
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  #12  
Old 05-17-2018, 06:33 PM
scsmith scsmith is offline
 
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Quote:
Originally Posted by cczarnik View Post
+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.
Good to know. I do need 240V. Too bad the parallel setups can't be run 180 degrees out of phase to produce 240V.
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  #13  
Old 05-17-2018, 10:36 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Lenny Iszak View Post
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.
These spinning magnets are pretty much what you will find at your local electrical power plant, albeit on a larger scale. Lots of sophisticated electronics there for control, but not for the raw production of AC; It's just spinning magnets. The key is maintaining a constant RPM of the magnets under varying load conditions. As charlie mentioned, the frequency is controlled by the RPM of the spinning magnets, but fluctuating Hz is not a problem, even for computers, if kept between 50-70. Most well maintained and adjusted generators will hold 55-65 pretty well. No wave form anomolies from spinning magnets; Just a perfect sine wave if the RPM is stable.

Its the DC->AC Inverter rigs that create havoc with sensitive electronics. This is because all but the most expensive inverters use a modified sine wave and not a true sine wave. Motors and resistive devices have no problem with this, but electronic power supplies often choke on it. The move to inverters is not done because it is electronically better. It is because the frequency is no longer set by RPM and the engines can run at much lower RPMs and therefore produce less noise and lose the need for a sensitive governor and its need for frequent adjustment.
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Last edited by lr172 : 05-17-2018 at 10:50 PM.
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  #14  
Old 05-17-2018, 10:55 PM
lr172 lr172 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/
An alternator, by definition, is a device, typically automotive, that produces AC current and internally converts the final output to DC (usually via a rectifier bridge). Most mechanical devices that produce a power output, AC or DC, are called generators. The Inverter rigs you referenced use DC generators and an adjunct inverter to convert the DC to AC.

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Last edited by lr172 : 05-17-2018 at 10:58 PM.
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  #15  
Old 05-18-2018, 01:01 AM
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Plummit Plummit is offline
 
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I just had to use a generator a couple of weeks ago when our power was out for upgrade. I have a Champion duel fuel generator from Costco that puts out around 8500 watts. I run it on propane so the max power output is somewhat less than gas, but it serves our needs and powers our whole house (except our AC unit).

I don't have a transfer switch so I back-feed my power from a heavy duty sub-panel in my garage. It works very well aside from the noise. There are ways to quiet the engine but I don't bother.

I have 2 propane bottles so I can run the generator while re-filling one of the bottles.

I power everything in my house including my cable modem, router, computers, microwave, tankless water heater etc. Everything works fine and I bought the unit used for $400. New they run around $800.

-Marc
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  #16  
Old 05-18-2018, 04:24 AM
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rzbill rzbill is offline
 
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Quote:
Originally Posted by krhea View Post
Some gas fired furnaces and mini-split AC and heat pumps won't run on them.
Had that experience. Tried to run a Triad gas boiler from an ancient 2KW generator but the frequency instability prevented it. A few years later I bought a 7.5KW unit. First try the boiler did not like it. I put an oscilloscope on the output and adjusted the run speed on the carburetor until I got 60Hz. Boiler quit complaining and the generator has worked for us for a number of winter seasons so far, even with varying load from other items in the house.
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  #17  
Old 05-18-2018, 06:51 AM
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humptybump humptybump is offline
 
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Default Generators and typical UPS do not play well

(Indeed my post is not RV related and I won't be offended if it is removed)

Most typical UPS are not compatible with generators. If you plan to use a UPS off of a generator you may consider what is called an "on-line" or "double conversion" generator.
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  #18  
Old 05-18-2018, 09:27 AM
rv7charlie rv7charlie is offline
 
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In the interest of more precise technical language, here's the definition of an alternator:

https://www.google.com/search?q=alte...hrome&ie=UTF-8

The things used in cars (and planes, etc) have been called alternators because, unlike their DC generator predecessors, they produce alternating current. The internal diode block that rectifies AC to pulsing DC is effectively an accessory; not the alternator itself. Alternators are a subset of a much larger constellation of 'generators'.
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