# Clean / Dirty Power with Furnace



## matt1124 (Aug 23, 2011)

Did you call Lennox main number or applications department? I can't seem to PM you their number, maybe because of your post count. Applications phone number ends in 4962.


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## byezb (Mar 18, 2017)

I called their main # and my local dealer. The furnace is only 6 months old.


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## matt1124 (Aug 23, 2011)

Looks like it is not against the rules to share my own contact info here. Add 85 to my user name and I use google mail. Applications has the real solution if there is one, they have helped me out of many jams, lots of Lennox knowledge, wherever they are.


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## splatz (May 23, 2015)

This is just my experience, if you get good info from the manufacturer that's better. 

IME a decent conditioner will clean up very crappy power to near perfect, just consult with the conditioner manufacturer before you buy. The conditioners last a long time and it will give you surge and power protection even when there is no power outage. It should be cheaper than replacing the generator. But the conditioner does introduce some inefficiency, the last thing you want when you're using a generator. 

Better power from the generator will be better for other sensitive loads, computers, etc., which may or may not be a big deal in a power outage.


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## brian john (Mar 11, 2007)

More than likely the output of the generator is not a true sine wave. I think there are some Generic installers that visit this forum and can give a better answer.


Do you know what the amperage draw is of the furnace?

There are true sine wave UPS's that you could plug into the generator and assuming the generator output is close enough to a 60 HZ sine wave the UPS MIGHT function without depleting the battery to supply your furnace.


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## brian john (Mar 11, 2007)

splatz said:


> This is just my experience, if you get good info from the manufacturer that's better.
> 
> 
> 
> Better power from the generator will be better for other sensitive loads, computers, etc., which may or may not be a big deal in a power outage.


I THINK Honda has some True Sine Wave generators.


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## nrp3 (Jan 24, 2009)

I suspect that because the portable is mechanically governed and is set no load at 62.5 hz will droop down depending on load to somewhere around 60hz. Somewhere is probably not close enough for this furnace. Not that there is anything wrong with it, its meant to work that way and most portables are mechanically governed similarly. Going to inverter type like Honda may solve the issue. I know a few years back I went to a similar situation, older Generac, but electrically governed and a type that typically runs around 59 hz, changed out the control board to a newer version that held closer to 60hz and it ran fine thereafter. Apparently needs to be close. Looked at Amana variable speed that didn't function during the last power outage. This on a Kohler that was doing a decent job of holding 60hz or close. This set up had heat pump as primary and gas as the backup. Naturally when I was there, it functioned as it was supposed to. Heat pump not on the generator, realized it was falling behind and gas took over.


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## emtnut (Mar 1, 2015)

nrp3 said:


> I suspect that because the portable is mechanically governed and is set no load at 62.5 hz will droop down depending on load to somewhere around 60hz. Somewhere is probably not close enough for this furnace. Not that there is anything wrong with it, its meant to work that way and most portables are mechanically governed similarly. Going to inverter type like Honda may solve the issue. I know a few years back I went to a similar situation, older Generac, but electrically governed and a type that typically runs around 59 hz, changed out the control board to a newer version that held closer to 60hz and it ran fine thereafter. Apparently needs to be close. Looked at Amana variable speed that didn't function during the last power outage. This on a Kohler that was doing a decent job of holding 60hz or close. This set up had heat pump as primary and gas as the backup. Naturally when I was there, it functioned as it was supposed to. Heat pump not on the generator, realized it was falling behind and gas took over.


I'm not 100% sold on that. Off the top of my head, I can't think of any components in a furnace board that would be frequency dependant.

Generally, a cheap generator has a really chitty sine wave, I don't know of a meter that could reliably measure the frequency of that dirty signal.

Maybe the new board you installed had better power conditioning ?

Inverter generators, have fairly clean sine waves, and electronics tend to like that better.

See att waveform from a 'chinese' gen.











and the waveform from an Inverter Gen ....


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## frenchelectrican (Mar 15, 2007)

Emtnut.,,

when ya post the photo of sine wave fourm .,, was both type of generators was running loaded or unloaded ? 

I know those cheap generators when running unloaded they spit alot of dirty power pretty quick but once you get full load it kinda clean up some but not all of it.


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## emtnut (Mar 1, 2015)

frenchelectrican said:


> Emtnut.,,
> 
> when ya post the photo of sine wave fourm .,, was both type of generators was running loaded or unloaded ?
> 
> I know those cheap generators when running unloaded they spit alot of dirty power pretty quick but once you get full load it kinda clean up some but not all of it.


No, the output of the cheap gen was unloaded. It does clean up when loaded ... quite a bit actually, but even loaded, a frequency meter has a hard time measuring the Hertz


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## matt1124 (Aug 23, 2011)

Emtnut, the motor drive on an ECM motor would likely require clean power. 

https://www.marsdelivers.com/images/ECM Technology Overview.pdf


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## brian john (Mar 11, 2007)

I have tested many generators with this issue, If there is a switch mode power supply and this load is the majority of the load, you will have current waveform distortion and this results in voltage waveform distortion and this can result in operational issues.


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## emtnut (Mar 1, 2015)

matt1124 said:


> Emtnut, the motor drive on an ECM motor would likely require clean power.
> 
> https://www.marsdelivers.com/images/ECM Technology Overview.pdf


I agree, the ECM motor, and most electronics in the furnace need the clean wave.

I don't think the ECM motor would care if it was 59 or 62 Hertz was my point.


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## numbers (Dec 23, 2011)

I had the same problem with a Sub-Zero refrigerator and a 20Kw generac generator. Sub-Zero and the Generac manufacturer could'nt figure it out. The refigerator refused to run on the generator. It wouldn't even attempt to start although it would light up. The frequency and sine wave on the generator looked good. The refrigerator started to work on the generator after several months. No changes were made to the wiring, loads, refigerator, or generator. I was never able to figure it out.


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## Bird dog (Oct 27, 2015)

Would a UPS, after the genset, clean it up enough?


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## splatz (May 23, 2015)

Bird dog said:


> Would a UPS, after the genset, clean it up enough?


A "line interactive" UPS probably wouldn't do much since it doesn't switch over to battery power until power fails. It might do some filtering but that wouldn't fix the squared off wave. (I don't think.) 

A double conversion "online" UPS would because it uses utility power to charge the batteries but the load always runs off the inverter, and is generally super clean. 

But it is a lot more expensive to get an online UPS for a given power output than a conditioner, and the conditioner will last longer, IME.


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## samgregger (Jan 23, 2013)

What is the model and draw of the furnace?


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## telsa (May 22, 2015)

http://www.powerqualityworld.com/2011/04/constant-voltage-ferroresonant.html

*Constant Voltage Transformer (CVT) or Ferroresonant Transformer (Ferro)* is a non-linear transformer, which passively provides a regulated voltage output through an electromagnetic phenomenon called ferroresonance (where the term ferroresonant transformer was derived). Ferroresonance is associated with the behavior of iron cores while operating near a point of magnetic saturation, wherein the core is so strongly magnetized that further variation in the input voltage results in little or no increase in magnetic flux. Basically, the ferroresonant action is a flux limiter rather than a voltage regulator. Nonetheless, with a fairly constant supply frequency, the CVT can maintain an almost constant output voltage even as the input voltage varies widely. In fact, the output voltage of the ferro varies about 1.2% for every 1% change in supply frequency, such that even with a considerable generator frequency change (2-Hertz), results in an output voltage change of only 4%.



In short, CVTs are basically 1:1 transformers that are excited high on their saturation curves, thereby providing an output voltage which is not significantly affected by input voltage variations. This special characteristic is the foundation of the application of ferroresonant transformers as power conditioners.

&&&

So now you know.


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## JRaef (Mar 23, 2009)

This isn't a really good scenario all around. The issue is actually a known phenomenon (called the "Middlebrook Critereon") for anything with a "Switch Mode Power Supply" (SMPS) and smoothing capacitors in "voltage control mode" such as VFDs (and by virtue of what they are, ECMs) when running from any high impedance source, such as a portable generator. It's an interaction between the high leakage reactance of the source and the capacitors in the SMPS/VFD/ECM that quickly becomes a resonance circuit that swings out of control. So what most SMPS type devices do is to detect it if it happens and immediately turn themselves off before they are damaged. Adding a higher impedance device like a CVT will likely make it worse, not better. 

The better choice is an L-C-L filter (inductor-capacitor-inductor) similar to what you would find in what's called an EMC filter for a VFD. You can get them for single phase applications, but to make sure you get the right type, look for a "dual stage" EMC filter, meaning it is a full L-C-L, not just and L-C filter (single stage). there's still a chance it won't work, but it's the only chance you have short of replacing the generator. The EMC filters are relatively cheap.

You don't have this issue if the generator has a sine wave inverter output, which is why a lot of them are going that way now.


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## brian john (Mar 11, 2007)

Bird dog said:


> Would a UPS, after the genset, clean it up enough?


A true double conversion UPS MIGHT work, but if the sine wave or frequency is not decent the UPS might stay on battery until it is depleted.


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## nrp3 (Jan 24, 2009)

All I know on the one I changed the control board on, it held it closer to 60hz. The voltage regulator on those is a separate board. It solved that one. Don't know which component that fluctuates is the bigger problem. The frequency, off likely to begin with fluctuates, the voltage fluctuates...

I have tried the double conversion type Tripp Lite with an almost new but mechanically governed Briggs 10kw with a Triangle tube wall hanger boiler from 2008. The ups helped but never pushed the frequency totally back to 60hz. Fortunately the boiler started leaking and got replaced. This thing would crash when the utility would have brief outages. While this isn't an airhandler, has anyone tried it recently with success?


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## byezb (Mar 18, 2017)

Below is what i was sent directly from Lennox...


Lennox recommends when connecting a portable generator or emergency backup generator to a Lennox furnace, the furnace and generator be connected per local electrical codes. In the absence of local codes the furnace and generator must be installed to the current National Electrical Code (NEC). Failure to use a power interlock switch can cause personal injury to anyone servicing the incoming power supply. These codes specifically require proper grounding of the furnace and generator.

The SureLight® integrated control must sense a proper ground before it will initiate sequence of operation. This means the Lennox furnace with a SureLight control will not operate without a proper ground. The ground sense function of the SureLight control is a safety feature and the furnace will not operate on permanent or temporary power without a proper ground. It is also important to remember, that any furnace using flame rectification for sensing flame signal, will have problems without a proper ground.

The unit voltage requirements when used with a generator are:

120 volts + or – 10% (108 volts to 132 volts)

60 Hz + or – 5% (57 Hz to 63 Hz)

It is recommended to use a generator with a low wave form distortion of 3% to 8%, which generally does not require a power filter. Also, a generator certified for computer use would not require a power filter. The generator manufacturer or supplier should be consulted for proper sizing of the generator.

When these recommendation and requirements are followed the normal product warranty applies.


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## emtnut (Mar 1, 2015)

byezb said:


> The SureLight® integrated control must sense a proper ground before it will initiate sequence of operation.
> 
> 
> It is recommended to use a generator with a low wave form distortion of 3% to 8%



I read the first part and thought ... Wow ... so it's a ground issue ... cool, now I know :thumbsup:

Then the last part .... Oh yeah, I'll dust off my distortion analyser and check out the waveform :no:


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## nrp3 (Jan 24, 2009)

I don't know if I've seen a generator actually certified for "computer" use. Those voltage parameters seem to be reasonable.


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## byezb (Mar 18, 2017)

Based on all this information, do you think this Rigid generator would be fine or do I need to go to a full inverter type?

http://www.homedepot.com/p/RIDGID-7...r-with-Honda-GX390-Engine-RD9H7001P/205909662


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## nrp3 (Jan 24, 2009)

I've forgotten, did you test the output to see if it is within those parameters. While that Ridgid unit looks good, it is likely mechanically governed too and may not solve your problem.


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## byezb (Mar 18, 2017)

My volts and Hz are in the range but I have not tested the waves


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## emtnut (Mar 1, 2015)

Interesting that they claim <6% THD on that unit


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## byezb (Mar 18, 2017)

All the Ridgid gens advertise the +\- 6%. It's either this or a honda inverter, but the only Honda inverter with a 240 is 4 times that cost.


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## emtnut (Mar 1, 2015)

byezb said:


> Based on all this information, do you think this Rigid generator would be fine or do I need to go to a full inverter type?
> 
> http://www.homedepot.com/p/RIDGID-7...r-with-Honda-GX390-Engine-RD9H7001P/205909662


No doubt that the inverter gen will work for you.
I'd have no problem buying the Champion inverter gen. Many of the 'off' models can be paralleled to, which doubles the output, and 'I think' gives you 240V ... hopefully someone can confirm that.
If not, still go with a generic inverter (non-honda), they come in 240V in the larger sizes.

Personally, I'd buy the Ridgid and try it out !
The good thing about Home Despot, is you can buy it, try it .. bring it back if it doesn't do the job.


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## PlugsAndLights (Jan 19, 2016)

emtnut said:


> No doubt that the inverter gen will work for you.
> I'd have no problem buying the Champion inverter gen. Many of the 'off' models can be paralleled to, which doubles the output, and 'I think' gives you 240V ... hopefully someone can confirm that.
> If not, still go with a generic inverter (non-honda), they come in 240V in the larger sizes.
> 
> ...


Bought a generac invertor 6-8 yrs ago. It didn't work properly right off the 
bat. No way Rona would take it back. Checked with other stores (including 
HD I think) and found this policy was universal for gas operated equipment. 
Eventually sorted out the problem. Generac customer relations was 
good but I still wouldn't recommend generac based on mine cuz it can 
be impossible to start when cold....as in anything below 0degc. 
P&L


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## emtnut (Mar 1, 2015)

PlugsAndLights said:


> Bought a generac invertor 6-8 yrs ago. It didn't work properly right off the
> bat. No way Rona would take it back. Checked with other stores (including
> HD I think) and found this policy was universal for gas operated equipment.
> Eventually sorted out the problem. Generac customer relations was
> ...


Good point about the return policy on the gen :thumbsup: 

As for the gen hard to start when below freezing, and I know some people won't agree with this ... when it's really cold, I spray a bit of 'quick start' right in the carb ... starts first or second pull everytime 

I use an oil based flammable spray, so at least there is a bit of lubrication in it. My oldest gen (champion 3 Kw) is around 16 yrs old ... still running like a charm !


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## splatz (May 23, 2015)

emtnut said:


> No doubt that the inverter gen will work for you.
> I'd have no problem buying the Champion inverter gen. Many of the 'off' models can be paralleled to, which doubles the output, and 'I think' gives you 240V ... hopefully someone can confirm that.
> If not, still go with a generic inverter (non-honda), they come in 240V in the larger sizes.
> 
> ...


I don't really know enough about it to say but I really like the idea of paralleling two portable generators. If one won't start, you still have the other, and if in some emergency you had to help someone out, you could do it without giving up all your power.


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## nrp3 (Jan 24, 2009)

I know you can do it with smaller honda inverters. I think IQ2000 can be too. Fairly good chance that going to an inverter type would do the job. I bet that Ridgid is a nice generator, but I still have concerns it won't run the furnace as any other mechanically governed type. I'd consider seeing if any of the rental places have a Honda to try out and maybe a different mechanically governed unit to try. I really believe the heating equipment people need to make their equipment of this type more tolerant of generators.


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## HackWork (Oct 2, 2009)

splatz said:


> I don't really know enough about it to say but I really like the idea of paralleling two portable generators. If one won't start, you still have the other, and if in some emergency you had to help someone out, you could do it without giving up all your power.


That's why a lot of people bought 2 EU2000i's instead of an EU3000i.

The cost was very similar but having 2 added redundancy, the ability to separate them, less weight to carry (1 at a time), and more overall power.


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## emtnut (Mar 1, 2015)

I don't have one, so I can't comment on reliability ... But the champion inverter can be paralleled, and is <1/2 the price of the honda

http://www.championpowerequipment.c...ter-accessories/73500i-inverter-parallel-kit/


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## byezb (Mar 18, 2017)

Thanks for all the input. I like the idea of renting a few gens and seeing how it reacts


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## Bird dog (Oct 27, 2015)

Champion also has dual fuel (gas/LP) which is nice for small spaces maybe.


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## Trule (Jan 6, 2021)

nrp3 said:


> I know you can do it with smaller honda inverters. I think IQ2000 can be too. Fairly good chance that going to an inverter type would do the job. I bet that Ridgid is a nice generator, but I still have concerns it won't run the furnace as any other mechanically governed type. I'd consider seeing if any of the rental places have a Honda to try out and maybe a different mechanically governed unit to try. I really believe the heating equipment people need to make their equipment of this type more tolerant of generators.


Yes they should. I am having same issue also a 2300 watt inverter generator-runs fan o k but flame does not come on . My voltage tester did show no ground and it was not earth grounded,just plugged into generator directly


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