A/C frequency?

[280plus]

Somehow I knew there was a connection there. 

[230RN]

So is the waffle iron just slowing down the genset enough under its relatively heavy 1100W load to bring the frequency down juuuust enough, or is it somehow filtering out the odd-harmonic square-wave hash?  (The waffle iron being a mostly resistive load, I find that hard to believe.) 

With whatever small inductance the waffle iron may have, since it's in parallel, it would ignore the high harmonic frequencies and act as a high-pass filter and let any high-order harmonics through to the boiler.  Which means it wasn't the harmonics screwing up the boiler's frequency-sensing circuits.

Terry, 230RN

[CNYCacher]

If the generator is the kind where the speed of the motor determines the frequency of the wave, then it must be a sine wave, right?

How does one generate a square wave with a rotating coil in a magnetic field?

[230RN]

"If the generator is the kind where the speed of the motor determines the frequency of the wave, then it must be a sine wave, right?"

Agreed.  Good point.  (I think you mean "shaft speed" there instead of "speed of the motor", though.)

I've gotta think about that some more.

I believe even pretty high-powered generator sets nowadays are inverter outputs, with the active solid-state switches being high-powered Silicon-Controlled Rectifiers (SCRs).  What frequency the generator actually produces doesn't matter with an inverter.  I would bet that the actual generators nowadays are really alternators like a car's, where the frequency (due to rotational speed) doesn't matter much because it is then rectified and fed into a 110V (or whatever) 60hz (or whatever) inverter.  Yours is a good point, and I don't know offhand how much frequency in an inverter would be affected by load.  The SCR switching could be controlled with a crystal oscillator, but then you wouldn't have the frequency problem that 280plus is having in the first place.

I know they use SCRs in some pretty high-powered ultrasonic and induction heating systems, like in the many-kilowatt range.

I believe you can generate a pretty close sine wave with a square-wave input (or better, a triangle-wave input), but you need some pretty good pulse-modulation techniques to do it.  Maybe they've gotten that far in consumer-type gensets.

On the other hand, you could get a fairly good basic sine wave of a specific frequency out of an alternator regardless of the rotational speed by modulating the rotor itself with an input sine wave of that specific frequency.  The alternator then acts as an amplifier, rather than a generator.  (Input power in this case is mechanical, rather than electrical, as in a conventional tube or transistor amplifier --there would be no "B+" or "Vcc.")

I actually put some of the above in my post, but deleted it.

See, I figured by now a "real" techie knowledgeable in actual and practical genset technology would enter the stage and have "real" answers, but noooo.... So I can theorize all I want, I guess.

Terry, 230RN


 

[KD5NRH]

Of course, none of this answers the obvious question; why the hell does a boiler care about the frequency of the supply?  It's a resistive heating element (or a gas valve and spark igniter) and a thermostat.

[280plus]

A. My guess is it drags the gen down just enough to get the frequency right.

B. Fancy dancy new fangled boiler with all kinds of bells and whistles. One being it monitors AC frequency coming in and coughs up an error code if it is out by over 1.5 cycle. Calcs by ML say gen was producing ~61.666 which would be a hair too high.

[zxcvbob]

Of course, none of this answers the obvious question; why the hell does a boiler care about the frequency of the supply?  It's a resistive heating element (or a gas valve and spark igniter) and a thermostat.

Because some idiot figured out that it could monitor the frequency without any extra cost -- and when you monitor for an error you have to handle it.

[birdman]

280,  by and large for really big loads SCR's (and their larger brothers, thyristors) have been replaced with IGBT's. Which can handle LARGE loads.  I've seen palm sized ones that can do 3000V and switch 1800A.

[280plus]

^^^translation pleeeez... 

FYI, power came on at midnight. Figures, Filled the tank on the gen to the brim before going to bed at 10. Now to get it back out of there and into my TRUCK!! dammit. lol...

It's been described to me as a CYA feature by the factory to prevent premature failure of the very expensive control module. As long as I can McGyver my way around it when I have to, it's cool.

As far as the other questions. I did not turn the griddle off and see if it tripped the boiler. I did hook the waffle iron up because it draws smaller watts (gas) and found it would still cycle off even if set all the way up. So during the time the boiler was using to make hot water it DID (the waffle iron) cycle off and the boiler did not hiccup. Now, it's entirely possible however that the boiler had completed it's cycle and had gone off before the waffle iron. This MAY mean that it might have tripped on the next startup as it went through its pre-cycle checkout stage but I had shut it off as soon as we had the hot water up, so I don't know. I don't know if it momentarily looks at frequency on startup or it monitors continuously. I guess I'll have to call them and ask. I wanted to relay the good griddle news to them anyways.

Anyhoo, thanks for all the help and suggestions. Now please turn your atention to the flogging of Fistful for causing the whole problem in the first place. 

Feel free to wet your lashes first if you feel the need. 

[cosine]

280,  by and large for really big loads SCR's (and their larger brothers, thyristors) have been replaced with IGBT's. Which can handle LARGE loads.  I've seen palm sized ones that can do 3000V and switch 1800A.

Ahh, power electronics... where the heavy lifting takes place... 

Those are all three terminal, controlled, semiconductor devices. Like controllable diodes (SCRs, thyristors) or transistors (IGBTs), just capable of handling HIGH power. 

[birdman]

Ahh, power electronics... where the heavy lifting takes place... 

Those are all three terminal, controlled, semiconductor devices. Like controllable diodes (SCRs, thyristors) or transistors (IGBTs), just capable of handling HIGH power. 

Yup, and unlike thyristors, in large applications, they don't need a soft turn on to prevent blowing them up before the entire avalanche is setup, and they switch faster (due to their being array devices).  I personally love them.

[230RN]

^ My technology is limited to relays and Hg-filled thyratrons.  Oh, the occasional SCR.

KD5NRH asked the question:

Of course, none of this answers the obvious question; why the hell does a boiler care about the frequency of the supply?

That's been running through my mind, too, and the only answer I can come up with is "If there's a bell, let's blow it, and if there's a whistle, let's ring it."  Or to force those without waffle irons to buy the company's accompanying line conditioner.

The most expensive phrase you will ever hear is, "Why not go with the latest technology?"

Why.

Not.

Indeed.

There been talk recently of relaxing the power-line frequency standards --I forgot where I read it, but it's been on the net, so it must be true.  So, the question arises:  "Hey, Mr. Boilermaker, with your super-sensitive control modules inccorporating the latest and greatest frequency-sensing-technology, what happens if your latest-and-greatest-loaded-with-whistles-and-bells freakin' boiler is installed in an area where the line frequency is <B₁-flat or >B₁-natural.  Hey? what about that, Mr. Boilermaker?"

They recently installed a microchip-controlled air conditioner in my place with, of all things, a remote control.  I now have five remote controls sitting on the endtable by my couch.  Way to lose weight, Terry!  (But only in my button-pushing fingers.) Now if I could find a remote-controlled coffeemaker that would remote-controlledly (izzat a word?) extend an arm to my coffecup to fill it remote-controlledly I'd be in the sixth level of Nirvana.

Hm.  Hey, why not use the latest-and-greatest word?

Terry, 230RN

REF:

http://www.phy.mtu.edu/~suits/notefreqs.html

[KD5NRH]

It's been described to me as a CYA feature by the factory to prevent premature failure of the very expensive control module.

Uh, it needs the same thing your waffle iron has; a mechanical thermostat.  Costs about $8-15, doesn't give a rat's ass what the line frequency (or voltage, for that matter) is.

[280plus]

Oh, don't think "OK, how do I get around all the BS and make the thing work anyways without blowing myself up or burning the house down?" hasn't crossed my mind. 

And yes, it can be done. 

[230RN]

QST:  General call:

Harbor freight has those little generators for $89.99 on a coupon sale again.  Coupons are available in the American Rifleman pp 20-21, September issue, for your convenience. 

No need to clip the coupons.  Just bring that issue in and they can scan the coupon right from the magazine without cutting up the pages.



DE TERRY 230RN WDØAAA

[230RN]

Harmonics:

I picked up a 400 Watt inverter for $19.95 yesterday and stuck it on a fully charged battery with a known 400W resistive load (small emergency hot plate) on the inverter.

I have two meters that measure frequency.  On one, the frequency was 59.87 Hz.  On the other, it was 179.6 Hz.  Interesting, because 179.6 is exactly the third harmonic of 59.87 Hz.  So it must be putting out a square-ish wave with at least the first odd  harmonic reduced and one meter is a little more sensitive to harmonics than the other.  The blurb on the box says, "Modified sine wave for up to 85% efficiency."

One meter reads RMS voltage directly by sampling the waveform.  The other reads (without saying so ) average voltage, and I stuck a little analog meter which inherently measures average, and they all read about 105 Volts on the output with that 400 Watt load --which implies that it is fairly close to a sine wave output.

For those having any interest.

Terry, 230RN

REF:

Chicago Electric Model 66814 from Harbor Freight. $19.95 with coupon.