ECN Forum Forums General Topics of the Trade General Discussion Area 60 Hertz issue with portable generator

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.