generators and clean ac power

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Old 02-14-10, 11:55 AM
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generators and clean ac power

OK--I have been beating this to death over the last few months. I know that the smaller "inverter" generators produce clean ac power. It would seem that the larger home standby generators must also produce clean ac power or they would not be as reliable as they are.

By clean ac power I mean a steady 60 HZ cycle and voltage regulation as the newer electrnically controlled furnaces need to operate correctly.

I was trying to get a portable generator between $1k and $2k to accomplish this and I have found no concrete answer. I tried posting in the HVAC section to see if anyone had any experience that was GOOD in using a portable with a newer microprocessor controlled furnace. I got no response with any experiences in doing so.

I found that the Honeywell and Honda's are supposed to be clean, but they act they they are withholding information as to how clean and how they get the clean power. I did find this Briggs and Stratton model that has both automatic voltage regulation and electronic idle control. I would think that this model would be ok to power a newer furnace. Generac sells a few models that have "AVR", but the idle is not electronically controlled.

Elite Series- Engines & Outdoor Power Equipment - Briggs & Stratton
 
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Old 02-14-10, 01:53 PM
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Originally Posted by signalnc View Post
...I found that the Honeywell and Honda's are supposed to be clean, but they act they they are withholding information as to how clean and how they get the clean power. I did find this Briggs and Stratton model that has both automatic voltage regulation and electronic idle control. I would think that this model would be ok to power a newer furnace. Generac sells a few models that have "AVR", but the idle is not electronically controlled...
You remind me of me!

Good detective work. That is the way to do it, read the fine print and ask questions.

And it does not surprise me that the sales people would not tell you everything you need to know.
 
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Old 02-14-10, 02:28 PM
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I am not aware that Honeywell makes generators, could you provide a website?

All inverter generators work the same way, the engine turns a high frequency alternator (probably a three-phase but it might even be a six-phase) and the AC output of this alternator is then rectified to a DC voltage. The DC voltage is then run to a crystal-controlled inverter which changes the DC to 60 Hz AC. Obviously the addition of the inverter raises the cost substantially over a more conventional generator set. The power quality is directly affected by the design and quality of the components used in the inverter.

A high quality inverter will hold a fairly constant voltage (+/- one or two volts from no load to full load) and frequency of +/- one Hz. I ran some tests on my Yamaha early last summer and I found that at no load it put out 121 volts and at full load it was 119.5 volts. The frequency was almost rock steady at 60 Hz. Going from no load directly to full load would cause the voltage to momentarily dip to maybe 115 for considerably less than a second, almost too fast for my meter to see and the frequency would dip for about the same amount of time to maybe 58 Hz but recovered just as fast as the voltage. I no longer have an oscilloscope so I couldn't run any waveform tests.

Idle control...Idle control is mostly a sales gimmick although it can be used with the inverter generator under some specific conditions. Contrary to what many people believe (and many sales people will tell you) idle control will save little fuel. In a non-inverter generator using idle control WILL cause the frequency output to drop significantly when idling, in fact, most non-inverter generators will have quite a range in their "normal" frequency output. A range of 54 to 66 Hz would not be uncommon and this is because the frequency output is directly related to the rotational speed of the generator and small generators simply do not have governors that can closely control the speed of the engine. Even with an inverter generator if you are going to have heavy starting loads (such as electric motors) the manufacturer will recommend that the idle control NOT be used. It is because the idle control cannot react fast enough when a heavy load is imposed, such as a well pump, and using the idle control could mean the difference between starting the motor and killing the generator.

I'd be very much surprised if you could find a generator that has a decent output, low electrical noise and close frequency control for much less than $2,000, my Yamaha EF3000ise sells for about $1800. and the 6kw model sells for about $3,000.
 
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Old 02-14-10, 03:06 PM
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Old 02-14-10, 03:10 PM
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These claim to be "Electronics Friendly"...

Honeywell Home Standby Generators
 
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Old 02-14-10, 03:30 PM
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Thanks, Bill, I'll read these later.
 
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Old 02-14-10, 06:14 PM
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I know that rpm and HZ are related. I wonder if you get a big enough generator that has a built in auto voltage control and when it powers up the blower fan on the furnace if it doesn't really tax the motor maybe the HZ won't fluctuate so much.
 
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Old 02-14-10, 06:42 PM
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Well, if you get a big enough generator you can do most anything but I kind of doubt that you would want this generator.




Non-inverter generators with single-cylinder engines will always have more problems with electrical noise and speed (and frequency) variations than will engines with multiple cylinders due to the fact the single-cylinder engines have less rotational mass and are therefore more easily affected by load changes on the generator.

I don't remember the exact figures but as I recall my furnace draws around 800 to 900 watts when the hot surface ignitor is energized and somewhere around 450 watts when running in the first stage heating position. The variable speed motor does NOT place a sudden large load on the generator because it is electronically controlled to "ramp up" in speed from a stopped position. Quite honestly, my 3000watt gennie has absolutely no trouble at all when the furnace kicks in while also supplying the refrigerator, television, DVD player and several lights.
 
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Old 02-14-10, 08:35 PM
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Originally Posted by signalnc View Post
I know that rpm and HZ are related. I wonder if you get a big enough generator that has a built in auto voltage control and when it powers up the blower fan on the furnace if it doesn't really tax the motor maybe the HZ won't fluctuate so much.
The whole way a ICM motor that we use in HVAC-R (variable speed) work is it rectifies AC into DC and then inverts it back into AC there for cleaning up dirty power

What I would be more concerned about is the micro-controller circuit boards in modern high efficiency gas and high efficiency oil furnaces, but unless your generator is off the china express and running on a 100 foot extension cord you should be just fine

Ben HVACR TECH
 
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Old 02-15-10, 03:37 AM
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thanks for the input Ben

I have a 6 year old gas furnace regulated by a Honeywell mini zone--looks like a circuit board controller to me. I also have central a/c. I would think that the controller has something to do with both heat and ac because of the electronic dampers.
 

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Old 02-15-10, 11:12 AM
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yes that sounds like it probably does. I was just referring to the variable speed blower motors used in modern furnaces and heat pumps

best thing is to call the the company and ask if generator use will harm the furnace and if its still under warranty if such warranty would become void
 
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Old 02-15-10, 04:45 PM
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thanks again Ben.

If anyone is interested I looked up the specs on a generac 10kw and 14kw standby generator. I figured they must be good. They claim + or - 2% for voltage regulation and they have an electronic governor that maintains a constant 60 HZ. It also says they use a revolving field generator with a skewed rotor for a smooth output waveform--10kw model---and a skewed stator for the 14kw model.

I am going to research the portables and see if I can find any that have what these standby gen. do.
 
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