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-   -   Portable generator and Lennox furnace (http://www.diychatroom.com/f18/portable-generator-lennox-furnace-64090/)

joshbloomberg 02-10-2010 03:53 PM

Portable generator and Lennox furnace
 
I'm an HVAC technician (but not an electrician). I installed a Lennox gas furnace at my mother's house, where the power goes out frequently. I installed a double pole switch first (from the breaker) and then a tandem box with a single pole switch (wired to the hot lead of the furnace) and a receptacle (wired together so that the receptacle remains hot, except when the double pole switch is depressed). When the power did go out, I turned off the double pole switch (to prevent backfeed if the power went back on), and I used a Briggs and Stratton 3500 watt portable generator (outside) with a male-to-male extension cord. One end of the cord was plugged into the generator and the other end to the receptacle, thus energizing the switch to the furnace.
The furnace was energized (and running, the furnace only draws about 5 amps peak), and my fluke true RMS meter read 130 v. The problem was this: The circuit board on the furnace read an error message. When the power came back on, all returned to normal operation. What happened and why? Is the voltage from the generator too unsteady to power sensitive circuit boards? Everything else that I powered up with the generator (including a gas hot water heater wired similarly to the furnace) worked fine. Any suggestions?

wirenut1110 02-10-2010 04:14 PM

Your generator's output frequency is not within the specifications of the furnace control.

There was the same issue with another Lennox system last June.

Billy_Bob 02-10-2010 05:40 PM

I've heard quite a bit about newer furnaces with electronic controls not working with generators.

I was hoping while reading your message (that you're a HVAC technician) that you could tell us why these don't work with generators! :(

Anyway here are some pictures of "dirty" electricity. If you learn more, please let us know what you found out...
http://www.jkovach.net/projects/powerquality/

Also they are now selling "electronics friendly" generators. Here is info on those...
http://www.google.com/#hl=en&source=...a94940edcea411

And you can get a "true sine" "online" UPS which will clean up the electricity. (These always make their own electricity)...
http://www.google.com/products?hl=en...-8&sa=N&tab=wf

HouseHelper 02-10-2010 06:13 PM

Quote:

...I turned off the double pole switch (to prevent backfeed if the power went back on), and I used a Briggs and Stratton 3500 watt portable generator (outside) with a male-to-male extension cord. One end of the cord was plugged into the generator and the other end to the receptacle, thus energizing the switch to the furnace.
PLEASE, PLEASE, PLEASE get rid of this cord... they call them suicide cords for a reason.

kerry42 02-10-2010 07:00 PM

THIS QUESTION HAS CAME UP BEFORE ,WHAT YOU ARE DEALING WITH IS dirty power IT WILL DAMAGE YOUR BOARD IN THE FURNACE. PERIOD !!!!!!!!!!. SOMETIMES RIGHT AWAY OTHER TIMES AFTER A COUPLE OF TIMES BELIEVE ME I HAVE SEEN AND DEALT WITH IT BEFORE . Yes you can get a line conditioner to prevent this action or the Honda genie is more consistent (power and cycles)..,And like the other post states PLEASE PLEASE get rid of that DEATH cord do the right thing .. Also any electronic circuit board in most appliance, tv , stereo, garage door openers will most likely will fry on a genie that also goes for battery chargers for cordless power tools will have a shorten life, the sensitive components of these board can not tolerate the unregulated power. hope this helps DON'T FOREGET THE CORD.

daddyrabbit 02-10-2010 07:43 PM

kerry--the honda's do seem to put out cleaner power, but what about the new generac and briggs and stratton that come with an automatic voltage regulator? not all briggs and generac models have them, only a few. I think the generac's are called "true power"--utility quality output for sensitive electronics. The briggs just say automatic voltage regulator. I would think they are the same because briggs and stratton owns generac (since 2001).

AndrewF 02-10-2010 10:10 PM

An APC line conditioner should also do the trick...or even possibly a UPS battery backup unit. (Some brands are more picky with generator power than others.)

All of my electronics are on UPS battery backup, and I do not have any problems running them off the generator. I've never tried to run my air handler though.

http://www.apc.com/products/family/index.cfm?id=67

micromind 02-10-2010 11:25 PM

Most small generators use a capacitor for voltage regulation. This results in a distorted waveform, which electronic switching power supplies cannot handle.

If a gen has an actual voltage regulator, and not a capacitor, then it would produce a very clean sine wave. Quite likely smoother than the utility, especially near an industrial area.

This doesn't mean that it will power anything though. There's still the issue of frequency. The frequency of a gen is directly related to RPMs, nothing else. If the engine has an electronic governor, the frequency can be set exactly. If it's a mechanical governor, the frequency will vary a bit depending on load. Usually about 3%. This might not be close enough for certain electronic devices.

As you can see, there's a LOT more to selecting a generator than just the amount of load it's expected to handle.

Rob

P.S. Around here, if the utility power is out, and a power co. employee or a building inspector sees lights on and a generator running, they have the legal right to enter the property to see if the installation is legal or not. If it's extension cords (not connected to the building electrical system), then you're OK. If it is connected to the building electrical system, and there's not a UL listed transfer switch, they'll order the gen turned off, and write a citation. You'll have to go to court. You'll get a hefty fine.

A suicide cord is not a UL listed transfer switch.


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