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Old 03-17-2017, 08:13 PM   #1
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Default Clean / Dirty Power with Furnace

Hello - new to the forum, but need some advice. Just went through a major power outage in the metro-Detroit area. I'll make a very long story as short as I can.

The new high efficiency Lennox furnaces will not run off "standard" generator power. Lennox is saying generator power is too dirty.

Here is the setup. Generac GP5500 connected to a Manual transfer switch that feeds the main panel. Lennox furnace registers a communication error and per Lennox it is protecting itself and not running because the power is not clean. Their new furnaces are not made to run off generator power.

My question I have to everyone, is what options are there? Can I add a line conditioner to the setup, either at the generator or at the furnace? Do I have to replace generator with an inverter type? I'd hate to think any time power goes, it's just not possible to run heat...
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Old 03-17-2017, 08:32 PM   #2
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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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Old 03-17-2017, 08:38 PM   #3
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I called their main # and my local dealer. The furnace is only 6 months old.
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Old 03-17-2017, 08:43 PM   #4
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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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Old 03-18-2017, 07:16 AM   #5
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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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Old 03-18-2017, 08:48 AM   #6
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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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Old 03-18-2017, 08:50 AM   #7
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Quote:
Originally Posted by splatz View Post
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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Old 03-18-2017, 04:04 PM   #8
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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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Old 03-19-2017, 08:16 PM   #9
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Quote:
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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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Old 03-19-2017, 08:29 PM   #10
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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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Old 03-19-2017, 08:33 PM   #11
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Quote:
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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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Old 03-19-2017, 08:40 PM   #12
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Emtnut, the motor drive on an ECM motor would likely require clean power.

https://www.marsdelivers.com/images/...20Overview.pdf
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Old 03-19-2017, 08:41 PM   #13
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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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Old 03-19-2017, 08:46 PM   #14
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Quote:
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Emtnut, the motor drive on an ECM motor would likely require clean power.

https://www.marsdelivers.com/images/...20Overview.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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Old 03-20-2017, 10:45 AM   #15
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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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Old 03-20-2017, 11:33 AM   #16
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Would a UPS, after the genset, clean it up enough?
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Old 03-20-2017, 12:05 PM   #17
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Quote:
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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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Old 03-20-2017, 12:06 PM   #18
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What is the model and draw of the furnace?
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Old 03-20-2017, 01:39 PM   #19
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http://www.powerqualityworld.com/201...oresonant.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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Old 03-20-2017, 05:28 PM   #20
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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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