OT Furnace

Hey folks. About two months ago I had my new big and bad 80,000BTU 95% gas heater installed. Boy does it work nicely and I hope it really cuts the gas bill.

Now here is why I posted. There have been several posts about how to power your heater with a generator if the power goes out. Some say you will blow up the circut boards or blower motors or a control of some type. This is enough to make you worry. Being a commercial equipment repair tech who works on many pieces of equipment with all kinds of sensative controls and computer controls in them....I did a little research.
Here is what i did. Gave a call to YORK/Johnson control heater systems and talked with one of the service techs. He and I went over many things about types of systems and generator types and power output and hook ups ETC....
These are the facts from him. You need a GOOD size generator of around 4000 watts or up. This is around the $400.oo range at harbor freight. You must have both ground and neutral to GROUND like a cold water pipe or like I have a full house gen. system that is up to code. The flame sensor on these units measure the flame at the micro NOT milivolt level and poor grounds or neutral problems will not allow them to sense the flame for conformation. It will fire and burn for 3 or 4 seconds and then go out.
The next problem with not enough power is the blower fans. You have one for the air in and out for the burner plus the big blower to your house. These have air pressure switches on them and if they do not get the correct pressure ...you get a shut down. Also the house blower is multi speed and it must work at speed. ALSO make sure you have CLEAN air filters with these furnaces. They cause those air switches to shut you down!
The BIGGEST problem is the FREQUENCY of your generator. All three of my generators are on the nose. I have a FLUKE 179 digital true RMS meter that will measure frequecy to 59.95hz or 60hz or 60.10hz etc. The tech support guy said you MUST set your generator on the nose! If you have a very good tach most gen. sets are run at 3600rpm. Many people think you set that generator at 120 volts 0r 115 or 220 etc. This is WRONG. Frequency people!!!! One of my generators has brushes so it puts out a TRUE sine wave like your power grid. The new generators are really alternators and put out a square wave. Big generators like military or hospital or industrial etc. all put out a sine wave.
So a quick set of rules are..
Exact 60hz
Good neutal and ground
Enought power to run your furnace with NO power lags.
As I said, the tech and I went over a lot of questions and answers in about 20 minutes of conversation and he has had several calls from the New Jersey area service people with the hurricane Sandy disaster. There are Generators all over the place around here! This is a good coverage of what he and I went over.
He said a lot of people just refuse to ground their generators and then you get the flame sensor troubles. That is why they have that nut on the generator for a ground wire But he realy wanted that frequecy checked.
That is about all I can tell ya, but this is right from the horses mouth folks. Have a warm winter. Jeffcat

Just to clarify. The service tech when referring to neutrals and grounds . His message was don't be running neutral current through the ground system.
Big 10-4 on the generator sizing. Purchasing a 2250 W generator to run 2100W of load isn't going to work.

I have run my 95% Trane furnace on my 5000W TSC generator with no problems.

Yep. All that is good to know "IF" a person;
A. Understands it.
B. Has the tools and knowledge to put it "on the nose".
C. Owns better than a Harbor Freight genney.

The rest will either zap their boards or find another way to heat until power comes back.
They went far beound nessary safty provisions years ago. I trust thermocouples,flame roll-out,high limit devices and see transister boards overly redundant and failure prone.
Adding insult on top of it is that half the so called repairmen are clueless about troubleshooting electronics so they install parts until it starts working again.

Two mistakes here.
First buying a York furnace, second, buying a HF generator.

A fair amount of misinformation, Jeff.

I don't buy the claim that the flame sensors measure in microvolts. It's hard enough to measure millivolts in a noisy environment; measuring DC levels below a millivolt in a noisy environment is quite difficult. There are several different ways to detect a flame with electronics: you can use an optical sensor, you can measure the flame's conductivity or you can heat a thermocouple. None of these techniques requires reading sub-millivolt voltages.

Why should the frequency be so critical? What is "on the nose"? Sure, any ac motors in the system (such as the blower) want something close to 60 Hz, but the electronics shouldn't care: it's all DC at that point. BTW, a cheap frequency meter is the "Kill-A-Watt" meter. Should be good enough to get you within one or two Hz. The only generators capable of maintaining a precise frequency are inverters; any conventional generator will necessarily suffer from droop as the load changes.

All AC generators are by definition "alternators", and most if not all have brushes. The brushes are necessary to excite the field. The inverter-style generators go through the additional steps of rectifying the ac alternator output, then converting it to a sine or square wave output with solid-state switches. The advantage of this is it decouples the engine speed from the output frequency, so an inverter unit will use less gas and make less noise than a conventional generator. It's a fact that the square-wave output of the cheaper inverter units generates a lot of high frequency noise that can play havoc with electronics, but the high-end units such as Honda put out a reasonably clean sine wave.

If you want to smooth out moidified sine wave output, you can use a reactor in the output, or a 1:1 transformer. The iron in the core will take care of it.

Mark,

You need to get your facts straight also.

Most furnaces use a thermocouple to measure flame temperature. Thermocouples use the effect of dissimular metals to produce a voltage when heated and it is in microvolts. How do they measure these small voltage changes? Lots of filtering.

Cliff(VA)

Here is a little more. This is from the Factory guy. Second they have so much crap from what idiots do that if you follow what I told you it should cover most every possible. These furnaces use a hot surface ignitor with 24vac on it. The equipment I work on has standing pilots, to thermal couples, thermal generators, flame optical sensors, feed back cofirmation systems and a couple I probably forgot. Milli are for the thermal pilots and micro are for the flame sensor systems. Some circut boards have quartz crystal counter systems on them and they either work on 50hz or 60hz and nowhere inbetween. Also some of them can get into the $200-$400 range with little effort. This furnace is a 60hz unit. The idea is to cover all of your bases or would you like to try and explane your warrenty when you blow up your $1700 furnace cause you had a screwed up generator or low voltage etc. The guy "pete" two houses down is my heating and air guy who installed it. His dad is 62 years old and has bin in the business for more that 30 years. I think these guys Know what they are talking about. I also think the service teck line for Johnson controls would also know.
Again.. cover all of the bases. I would rather be safe.

To set the cycles to 60 on my little generator, I plug in a 110 volt clock with the second hand set on "12". Run it with the generator for a set time like five minutes, timed with your wrist watch, and observe the second hand. If you are short of five minutes on the electric clock, increase the speed until you get an exact reading. Accuracy increases with longer time spans.