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Very good point about fuel consumption. We were without commercial power for 12 days after Sandy. I had a Coleman 5kw generator that kept us going. I needed to power a well pump, furnace (it got cold here), refrigerators and freezers, plus convenience stuff (lights, TVs, microwave, router, modem, etc.). I didn't run the generator at night and we went through about 5 gal. every 10 hours. I had to drive an 50 miles into PA every two days to get refilled.

After that experience, I now keep 6 five gal containers filled with gas, use Stabil, and replace two containers every month so no gas is older than 3 months. The generator was straining sometimes because of the motors running or starting at the same time. It dropped 10VAC and 7Hz between no load and about 70% load. That's why I will be going to a 10kw with electronic AVR (but I'll keep the 5kw as backup). I'd prefer a 15kw generator but the gas consumption is too high. The "killawatt" is what alerted me to the Hz drop. That worried me a lot more than the voltage drop.

Originally Posted by Casper99

Thanks - that was very clear!
Do you happen to know if a high efficiency furnace like the Carrier Infinity uses a SMPS (switched mode) power supply? From what I can tell in the schematics, it drops the voltage to 24VAC but it doesn't show how it gets the DC needed for the CPU. With a SMPS, I wouldn't worry about the generator harmonics and regulation.

I do commercial HVAC, but as I said previously, I doubt if your home made power would be any dirtier than what comes off the grid nowadays.

Something to consider.. fuel consumption. I have 4 generators; most of them run. From 8kw to 2kw. The 8kw unit will burn through 6.5 gallons of gas in around 10 hours under half load. The 2kw I've run for 12 hours drawing about 150w on less than a gallon of gas. The Onan 4kw in the motor home will average about 0.5 gallons of gas an hour, and it's hooked to a 35 gallon tank.

How long do you expect power to be out? My sister has one of the larger portable generators (10kw 'ish) and a transfer switch. I've told her to keep 4 empty 5 gallon gas cans in the shed. When something's coming, go out and fill up the gas cans. Don't wait for the storm to arrive. 25 gallons of gas will get her about 50 hours of run time, depending on load.

That 25 gallons of gas will get me around 300 run hours on low load with this generator

http://www.ruralking.com/champion-po...FSbNOgodJQUAxw

It's the one I use most. When the power went out for half a day earlier this year, I ran the TV and video game console with it.. filled it up with gas before I went to bed and ran the box fan, alarm clock and cell phone chargers all night. The big generator will pump water, heat water and allow us to use the electric stove, but it drinks gas like a fiend. When all you need to run is some lighting.. that big generator still sucks down a considerable amount of fuel.

You can pick up a 'killawatt' watt meter for measuring plug loads for around $20.. use it and you'll find the fridge only uses around 150w, or how much your TV uses, etc. Also helpful for troubleshooting stuff.

hope this helps.

Originally Posted by timebuilder

The neutral and equipment grounding conductor are NEVER (repeat that as many times as you need to) EVER tied together at the equipment.

A modern furnace needs an independent grounding conductor (the bare wire) and the neutral conductor to be at the same electrical potential, from the panel, no matter how the panel is being powered. Whether or not the two conductors are tied together at the gen itself is determined by whether or not you are using a transfer switch that breaks the neutral, because you want to avoid "objectionable current" (that means non-fault current) on the grounding conductor.

Consult an electrician for the NEC code requirements in your area.

How the panel is being powered has nothing to do with flame rectification.

Thanks - that was very clear!
Do you happen to know if a high efficiency furnace like the Carrier Infinity uses a SMPS (switched mode) power supply? From what I can tell in the schematics, it drops the voltage to 24VAC but it doesn't show how it gets the DC needed for the CPU. With a SMPS, I wouldn't worry about the generator harmonics and regulation.

The neutral and equipment grounding conductor are NEVER (repeat that as many times as you need to) EVER tied together at the equipment.

A modern furnace needs an independent grounding conductor (the bare wire) and the neutral conductor to be at the same electrical potential, from the panel, no matter how the panel is being powered. Whether or not the two conductors are tied together at the gen itself is determined by whether or not you are using a transfer switch that breaks the neutral, because you want to avoid "objectionable current" (that means non-fault current) on the grounding conductor.

Consult an electrician for the NEC code requirements in your area.

How the panel is being powered has nothing to do with flame rectification.

Great info in this thread! I also want to know if it is safe to power my Carrier Infinity furnace with a portable generator through a manual transfer switch. I have asked Generac and Carrier customer support sites and only got CYA liability responses. I am torn between a Generac XG10000E and the XP10000E. They both have AVR. I like the XP because it has an electronic governor, and "True Power Technology" which they say brings THD < 5%. Cons: it costs about $1,000 more and has full GFCI on all outlets. This causes the GFCI to trip because the generator ground is bonded to neutral in the generator. Generac says the dealer can break the bond and keep the unit under warranty. However, in this thread, "danielthechskid" says: "flame rectification microamp sensing furnaces require that the neutral and ground be bonded". I guess my question is whether a generator like the XG with >5% THD, and a mechanical governor would keep the Carrier Infinity electronic controls and that very expensive software controlled blower motor happy?

Thanks for any insight!

Originally Posted by danielthechskid

A couple thoughts, PCs aren't nearly as sensitive to bad power as many think, the first thing most non or passive power factor corrected switched mode power supplies do with the power is run it through a bridge rectifier and into a large filter capacitor, or in the case of 115/230 switchable PC power supplies, when set to 115 it is 2 capacitors in series, 1 is charged by the positive peak of the wave, the other is charged by the negative peak. Active PFC is a different animal. Some active PFC controller ICs are just picky and won't even run on a modified sine inverter.

What is more important for SMPS is a proper wave peak voltage as that determines what the capacitors get charged up to, see what timebuilder posted. A non PFC unit only draws current when the instantaneous input voltage is higher than the DC rail voltage, hence why the current is drawn in pulses. The peak voltage of a pure sine is 1.414x the RMS so the SMPS expects the DC rail to be at 160-170 or 320-340v

These current pulses on a cheap generator with too high of a winding resistance cause the sine wave to become flat topped, thus reducing the peak voltage.

Also flame rectification microamp sensing furnaces require that the neutral and ground be bonded. My POS True Blue 90 runs just fine on my cheap Chinese 2 stroke ~1kw generator (the same one that is sold all over the place under various names and labeled from ~800-1200 watts).

Good to know, Thx.

A couple thoughts, PCs aren't nearly as sensitive to bad power as many think, the first thing most non or passive power factor corrected switched mode power supplies do with the power is run it through a bridge rectifier and into a large filter capacitor, or in the case of 115/230 switchable PC power supplies, when set to 115 it is 2 capacitors in series, 1 is charged by the positive peak of the wave, the other is charged by the negative peak. Active PFC is a different animal. Some active PFC controller ICs are just picky and won't even run on a modified sine inverter.

What is more important for SMPS is a proper wave peak voltage as that determines what the capacitors get charged up to, see what timebuilder posted. A non PFC unit only draws current when the instantaneous input voltage is higher than the DC rail voltage, hence why the current is drawn in pulses. The peak voltage of a pure sine is 1.414x the RMS so the SMPS expects the DC rail to be at 160-170 or 320-340v

These current pulses on a cheap generator with too high of a winding resistance cause the sine wave to become flat topped, thus reducing the peak voltage.

Also flame rectification microamp sensing furnaces require that the neutral and ground be bonded. My POS True Blue 90 runs just fine on my cheap Chinese 2 stroke ~1kw generator (the same one that is sold all over the place under various names and labeled from ~800-1200 watts).

Originally Posted by madhat

Hondas have low oil shutdown, not sure if the other engines have this.

Everyone I have looked at has this safety shutdown. Pretty sure any known brand has it.

Originally Posted by catmanacman

call your carrier dealer they have a line of standby generators that hook to the natural gas line or propane tank , carrier generators are rebadged generac

Is there any benefit to this? I would be connecting the generator to my intire panel. The generator and panel will still have an earth ground.

Originally Posted by timebuilder

So, if you are using a modern gen set, the chances are good that the power you are producing for use in your home is more than capable of meeting the quality that you are normally receiving from your utility.

By the way, many power utilities have quietly allowed the line frequency to vary from the sacrosanct 60 Hz that was almost a laboratory standard. Apparently, the tightly controlled frequency costs money to maintain, and allowing it to vary slightly brings a cost saving to the power industry.

So, a true sinusoidal output from a Gen means you are likely good to go for any residential load.

Thanks timebuilder. It seems that I should be safe with any of the newer higher end units. I am thinking if it has an idle control and some type of AVR I will be good. My brother inlaw has picked up a Generac XG8000E. I think I may try his out.

Originally Posted by Zoltrix

The new inverter Gensets seems to produce very clean power. Have run several pieces of very sensitive electronics with Honda's EM5000iS. Also used the EU2000 for electronics. Both produce clean sine waves.

Iv run the EM5000 with sensitives electronics and large inductive loads starting and you dont even notice it. That think purs no matter whats connected.

The EU series does not produce enough wattage. I am looking for at least 7-8K watts. Would prefer more. I really do not wan't to get two. Just one to power my whole panel and select loads by breakers. The EM5000s and EM5000is seem like very good generators. Nice that the is has the inverter. But they cost so much. I cant believe there technology and engines are just that much better. They are the only generator in the 5K watt range that I have seen with an inverter though. But it is not eneough wattage for me. At the cost of Hondas I would start to think about a whole house generator. But I will be moving so not a option.

call your carrier dealer they have a line of standby generators that hook to the natural gas line or propane tank , carrier generators are rebadged generac

Hondas have low oil shutdown, not sure if the other engines have this.

The bottom line for Gen power is whether or not you are producing a true sinusoidal waveform. Many modern gen sets will do this.

Consider the load spectrum on your normal power company service. It starts as a three phase rotating sinusoidal field at the power station. For residential, one of those phase legs is fed to a transformer, where the two ends of the secondary become your two ungrounded service conductors, with a secondary center tap that is grounded at the transformer and which becomes your service neutral, tied to an earth ground of some type at your service entrance.

Everyone on the local area fed by that phase leg from your substation has a variety of loads. Many of these loads are both inductive AND non-linear. So, the power coming into your home often has transients and harmonic distortion, and voltage is not as steady as we would like to see. This is due to the increased use of non-linear devices like compact fluorescent lighting and the many motor loads that change the power factor of the grid. As this increases, utilities will have to take more steps to improve power factor for residential grids.

Look at the waveform of a typical CFL bulb:

Attachment 324251

So, if you are using a modern gen set, the chances are good that the power you are producing for use in your home is more than capable of meeting the quality that you are normally receiving from your utility.

By the way, many power utilities have quietly allowed the line frequency to vary from the sacrosanct 60 Hz that was almost a laboratory standard. Apparently, the tightly controlled frequency costs money to maintain, and allowing it to vary slightly brings a cost saving to the power industry.

So, a true sinusoidal output from a Gen means you are likely good to go for any residential load.

The new inverter Gensets seems to produce very clean power. Have run several pieces of very sensitive electronics with Honda's EM5000iS. Also used the EU2000 for electronics. Both produce clean sine waves.

Iv run the EM5000 with sensitives electronics and large inductive loads starting and you dont even notice it. That think purs no matter whats connected.

I wonder the same things even with a less sophisticated HVAC system. I've used our generator for PCs with a surge type protective strip but never an entertainment center or our new furnace using flame rectification. I was thinking, in a pinch in heating season, that I would just wire around the board and send 24 volts to the gas valve, 120 to the blower and start it manually and stop it with a separate stat. A royal pain, but it would provide some heat.

I'm really hoping I never have to find out, but I might just do a test next time I start the generator and stabilize the gas.

Also heard there maybe a filter of sorts to clean up the dirty juice from the generator???

Generator question related to TDH and AVR

So I have been looking into buying a gas powered generator. It has come down to one or two things. Hoping to get some info here:

AVR: Automatic Voltage Regulator
TDH: Total Harmonic Distortion

Will a generator having AVR technology give you low/low enough TDH to run sensitive electronics.

It has come to my attention that a low TDH, 5% or lower is needed to run flat screens, laptops, etc safely. If a generator was to have a higher TDH could a quality surge protector such as Monsters filter this for electronics?

My other concern is with my HVAC. I have a Carrier Infinity furnace w/ 2 stage coiling down stairs and a Performance series HP upstairs. I am concerned that if the power is not clean enough it will damage the circuit boards, ECM's, gas valve, etc. Or cause a problem with the ignition control. Does anyone with knowledge of this have an opinion?

I had a guy call me the other day and said his gas furnace worked fine until he needed to use his Generac GP800E generator. I believe he said it will lite but not stay lit, could be wrong. I am guessing the generator is effecting the flame sensing.

The only generator's I have found so far that claims it can safely run electonics are the Generac XP series which has True Power Technology and runs below 5% THD and and the Briggs & Straton Pro Series which states it's AVR can hold a 3%-6% THD.

In my research I have found that all Generac's have an AVR. But not Briggs & Straton.

In closing I am leaning towards the Generac XP10000E. I have left out Honda because they seem so freaking expensive for the same technology. If you can make the case for the Honda have at it and provide a M# that seems like it compares in technology.

Thanks all