Not sure if this has been kicked around yet. I have several customers with portable generators that can't run their furnaces. Nearest thing I can figure is that they are not putting out 60 hertz. I also tested several that had an open ground at the GFCI receptacle and L14/30 receptacle.
So 2 questions:
Is there a simple way to get the output hertz up to 60 if the generator is only putting out 57 or 58.

And separate from the above question
Why is there no ground on the L14/30 receptacle of certain generators.

What size generators are these?

The output frequency is a function of the speed of the alternator and it sounds like they might be being overloaded.

Just a thought.

There's no 'easy' answer.

There are $99 generators, and there are $1300 generators - even at the same modest "20 amp / 120v" output range. Ever wonder why the price range?

One of the big areas where they 'save' expense in in the power regulation. The cheap ones are not putting out a very good waveform. This is just fine for lights and motors, but can be pure nightmare for anything electronic - like modern furnace controls.

Other drawbacks to the cheap genny's are high fuel consumption and high noise levels.

And, as Trumnpy has mentioned, overloading the genny will result in the voltage gropping before the machine simply stalls.

Trumpy,

1 generator was 7500 watts under half load
1 generator was 3500 Honda with no load
1 generator was 2000 Expensive Honda no load
1 generator was 3500 cheapo maybe 1000 watt load

4 different jobs and none would run the furnaces with consistency.

Also in regards to the grounding or lack there of
the honda 3500 had no ground
1 of the honda 2000 did and 1 did not have a ground

renosteinke

That is what i always tell my customers. We always recommend Honda's and typically between 3500 and 7500 with idle/throttle control.

We really did not have a voltage issue but a frequency issue.

Any thoughts to the lack of ground issue too?

How are these generators being connected to the furnaces?

Forgive me if I'm wrong, but I was under the impression that you aren't allowed to supply permanently isntalled equipment from a portable generator.
At least, that would not fly over here.

Hondas do not bond the neutral in the generator as a general rule. I suppose some do but the ones I have seen, don't.

I am still not sure why either of them would not run a furnace. Did you get power to the thermostat?

Crack up the throttle screw ought to boost the freq. I had a portable gen set hooked to an inverter once and the range of the frequency was tight while the generator was all over the place

A furnace should only have about 300-500W running the fans/oil pump at 120v - and with an induction motor, frequency should not be a problem, unless it's so low it causes motor overheating, [which is not immediate anyway]. It may be under or over voltage rather than frequency - many modern electronic burner controllers have voltage protection both sides of the norm and may also baulk at square waves or spikes. Her's the Danfoss spec -
http://heating.danfoss.com/PCMPDF/OBC_82-10_X009114_VDACY202.pdf

First, do not assume all are caused by the same problem. Many cheaper generators have poor regulation. I have seen many that will show 120v but low hz when you raise the rpm to get 60hz the peak to peak wave form will exceed what the equipment will handle. Second issue is grounding. Newer furnaces use flame detectors (Flame Rods) that much rely on grounding. Power with a floating ground will cause the CPU to detect no flame and shut down. I have a Honda EU200 inverter generator, it will not operate my furnace unless I ground the neutral side (It has no internal ground) and make sure all including the furnace and gas line is all bonded together.

Permanently installed appliance powered by a portable generator? I would not expect anything different when the power is out due to a storm.

Heck, I spent Dec. 26th without power for eight hours, in 18F weather. If I had a portable generator available to power the fan and controls of my gas furnace, you bet I would have passed an extension cord through the window, in a heartbeat.

Indeed, I'd prefer furnaces to not be hard-wired, to be plugged into a standard receptacle, for this reason. I don't want folks tying the generator into the main panel with jumper cables or suicide cords.

So, I'm rather distressed to hear that a quality generator won't work- but a cheap one will. That's quite a design issue, IMO.

I'd start with suspicion concentrated upon the CONTROL CIRCUIT.

Modern HVAC controls are digital-analog. They may well be drawing upon power sources entirely different from the HVAC unit, itself. (Think Smart Houses, etc.)

This is entirely different from the ancient days, when a thermostat was entirely powered off of a line running from the HVAC unit, and low voltage at that.

So, the first question must be: is the control circuit being properly fed?

I'd look to see if the customers are trying to exclusively power up critical loads -- and the circuit feeding the 'thermostat' is not recognized by the homeowner as being a critical circuit.

There are now so many variations on HVAC controls -- including DIY retrofits -- I can't hazard a guess as to what you're dealing with.

But, that's where I'd start. It's usually the last thing that a homeowner considers -- if ever.

I am not sure why Honda doesn't ground the neutral but it is easy to remedy.

Unless you're talking about bonding the neutral to the frame of the generator, I really don't see that there is any need to "ground" anything on a portable generator.
If you're talking about driving a stake, that makes it a permanent genny install and then other rules come into play.

You are right, I mean bond.
There may be something in the furnace that returns current on the EGC.

Not this

I have heard of this very problem and I think I heard that is mostly effects the very high efficient gas furnaces. These new HE furnaces don't seem to like the portable power. An EC I know seems to figured out the problem, I will reach out to him to see what it was and how to correct it.

This is still confusing to me. I am not sure about furnaces, we don't have them. High efficiency A/C units are inverter deals and don't even know what the frequency or voltage is. The first thing they do is rectify this into DC at 1.4x the line voltage and chop it into 20kz or so. Then they make whatever voltage they need.
The only thing that makes sense is they are using the ground for something like the igniter or that some control system like the thermostat is not being powered.

Some burners use a flame rod which sends an electric current thru the flame.(to ground) Since most all newer furnaces use electronic control boards to control the motor, burner and other parts, a floating ground can cause problems. Lots of these boards have line filters and such that are referenced to ground thru caps or hi value resistors. A floating ground can produce abnormal voltage reference an cause the CPU to detect problems. Many also have VFD fan motors that will also create odd harmonics on an ungrounded unit. And when I mean grounded I mean bonded to neutral. Odd harmonics or poor freq regulation may also affect the control board. Unlike the inverter AC units these units do not convert all the incoming voltage to DC. Most use a mix of line voltage and control voltage as generated on the control board. I have seen the control board have more components on it than the average home computer. Some use zero point switching on scr controllers that the wave form of some generators have a hard time providing.

My friend got back to me and he said that other EC's are using inverter generators. These gens will not bother the current sensitive HE furnaces. I quickly found this web page

http://www.ehow.com/facts_8515377_honda-inverter-generators-work.html

Greg,

I have an older style oil boiler that has many zones.This has to vent into a chimney. The furnaces that I speak of are high efficiency style that are gas fed. and they use PVC pipes for their fresh air intake and their exhaust. You don't even need a chimney with this style. I haven't had a problem nor have I seen it, in one of my towns, my secretary tried to get her furnace working with a gen and she had that problem.

It sounds like all you have to do is bond the neutral to get these to work. I haven't looked in a while but they used to have instructions about how to do it on a Honda.

The AC is converted to direct current by a microprocessor. This DC is then converted back to AC by the inverter.

Love that description! Most Rectifier sections would just use SCR/diode half bridges with a phase control scheme for bus regulation. That's like saying the black boxes power my car without mentioning the 4 cylinder ICE under the hood.
Joe

I caught that too.

This, folks, is what happens -- all the time -- when journalists write about technical subjects of which they know nothing.

While a four diode bridge is commonly used for low power rectification -- power circuits are now typically using IGBTs.

http://upload.wikimedia.org/wikipedia/commons/7/7f/Igbt.jpg

(Silicon Controlled Rectifiers (SCR) preceded them -- and are still in massive use.)

(Insulated Gate Bipolar Transistors)

They've replaced SCRs in recent years -- pretty much in anything newly designed.

Unlike SCRs, IGBTs are strikingly efficient. They can also handle power voltages with aplomb, surviving overvoltages that would let the smoke out of an SCR.

IGBTs can switch AC or DC -- at blazing speed -- so they can generate 60Hz outputs via PWM on the load side of a low-pass filter circuit...

Or, they can function as more efficient SCRs as an element of the low-pass filter circuit. (They'd simply shut off the AC flow even better than a diode -- considering the voltages involved.)

Such IGBT modules are now being manufactured like Chicklets.

It's only a matter of time before IGBTs are integrated into conventional motor-contactors. The real switching will be done by the IGBT. The conventional relay will operate as a fail-safe back-up and indicator. Such a scheme will extend the life of current contacts up towards centuries, for most of the time the coils will be pulling in and out dead circuits. (IGBTs switch state in micro-seconds -- thousands of times faster than any mechanical system.)

I am using solid state motor and heater control on my spa but I still have a big contactor when I turn it off. I like air a lot better than junctions for the "off" state.

I work on lots of big dryers and ovens. many but the latest use contactors to control the heating elements (Infrared panels) They eat up the contacts. I replace many with SS relays, they rarely fail. Most later model units have SS relays in them. I also have some that have mercury wetted relays. They hold up much better than the contactors.