How critical is Hz?????

[wildbill hickup]

I have somewhat finished assembly of my Changfa/ST generator and all seems to work well. Voltage remains steady under a moderate load at approx 115VAC per leg. To date load consists of; (2) 2hp motors 1 running heavy 10" table saw one running a small metal lathe. (1) 1 hp motor running another 8" table saw, and about 400 watts of lights. This doesn't even change the sound of the 22 hp Changfa engine, and I would be surprized if it did. So far I have kept the load in my barn with older non-electronic devices, because I am still having trouble getting a frequency reading even under load as someone suggested in responce to my origional post awhile back. It's a little hard to tell but I think the saw is running a little fast at full throttle however an incandecent bulb near the generator seems to burn steady, if I back off on the trottle just a touch the saw seems better but the light has a visible pulse. We are in the 'back-up power' season and my gas generator spun a bearing so it's useless. My question is this. If I need to use this thing for power in the house, what should I NOT run with it(IE computer, TV, fridge, microwave etc)? What will it actually damage if the frequency is off a little?

[thunderhead]

The specifications for mains electricity allow the frequency to vary by a few percent.  Over here in Europe, at least, they guarantee a certain number of cycles per day, but second by second the frequency may vary by a few percent.  If the daily count is running behind, they crank up the turbines across the grid, and the frequency fluctuates.

Most electronic equipment works equally well off 50Hz and 60Hz (it saves the engineers having to design it twice) so they could easily manage 55Hz +/- 10%.  Waveshape is likely to be far more important than frequency, unless the frequency is grossly out.  Bad waveshape will certainly fritz electronic equipment, which is why people have to be careful with cheap invertors.

The obvious exception is mains powered timers, timeswitches and so on, which need exactly 50Hz (60Hz in the USA) if they are to keep good time.

There are probably obscure exceptions, too, so insert standard disclaimers here.  But I'd not worry about my equipment.

[Nando]

let me give You a technical point of view.

The generator operating frequency, for every large electric plant in the country or even other countries, is kept to a very fixed and stable frequency because the power transmission lines are interconnected, in USA a large plant in New York may be linked to another one 400 miles - the frequency in N.Y can be a master and the one far away a slave and due to distance there is a difference in PHASE because it takes certain time to arrive to each other and "say Hello" do not fight me.

Now your system, most electric equipment is designed to work with a known frequency like 60 Hz in USA and 50 HZ in Europe, ETC.

The design of such equipment that may have moving parts ( motors) is done to operate to the frequency of the country with a certain %, AC motors generate their RPM as a multiple of the AC frequency and MOST of then if they are not overloaded, they work OK if the frequency is lower and they may work better ( with more power and higher RPM) if the frequency is higher.

The rest of equipment, like Radios, amplifiers, TV, ovens, they take a lot of frequency variation toward the upper end ( 70 + ), lower frequency has less range, for 60 Hz possible about 54 HZ without presenting heating problems.

You case: Keep the engine at the proper RPM for best stable output AC voltage and let the frequency to go high.

If you have motors running, just check their temperature and give them a cooling resting time and You will be OK ( this is you are loading the motor greater than 3/4 of its capacity).

Nando

[wildbill hickup]

Hey folks,

Thanks, for your quick responce. As usual you've answered all my questions. We are haveing a pretty bad ice/sleet/frezeing rain etc. storm as we speak with winds to 40 mph. Wind genny is caked with ice so can expect much from that. Just waiting for the grid power to quit as the trees and lines are starting to get very heavy. It's nice to know I can now hook up the house to that monster. I think I'll go do some experimenting BEFORE I loose power, hehe.

Thanks again

Wildbill

[wooferhound]

All electric clocks, (Digital or Analog) work by counting the cycles of the power they are plugged into. So a different frequency will cause your electric clocks to drift off time.

[TomW]

woof;

Not to be a smart acre but "all electric clocks" is pretty broad.

My watch is analog and uses quartz crystal for an oscillator. Runs off DC so no "frequency" on the power source.  Have had a few quartz controlled alarm clocks that also used a crystal timebase, too.

Just had to point that out. You would probably be correct if you said "most", however.

Cheers.

TomW

[thirteen]

some types of mutimeters have a setting for cycles, amp draws, ohms, and of course voltage AC-DC.  You might have one or maybe get a meter that reads cycles and put it on the output of the genset it will help you have a closer setting on your throttle setting. Does your generator that spun a bearing have guages on it you could use until fixed.  I am not sure how to make one. would be a challenge but over my head.

[thunderhead]

We are haveing a pretty bad ice/sleet/frezeing rain etc. storm as we speak with winds to 40 mph.

We had winds to 140kph (about 90mph) last night, so we had a candle-lit New Year's Eve -- as did most of the rest of Connaught, according to RTE.  The grid went out around 2pm.

Only the 12v equipment would work, which luckily includes a 'fridge.

So my New Year's Resolution: sort out our hone-brew invertor.  Fortunately this was with the agreement of the wife, so there might be some progress. :-)

[Dennisd]

From working with motors driven by Variable Frequency Drives, the rule of thumb was below 50% nameplate speed causes overheating (cooling fans won't move enough air) and 150% overspeed was limited by bearings. Power supply's (AC to DC) have a greater % ripple the lower the frequency, so generally work better at higher frequency's. Heating elements don't really care. Clocks that count cycles will be off if frequency is off. Quality of waveform is more important regarding heating, with a true sine wave running coolest. As a side note, if you are running a modified sine wave inverter, motors rated for VFD's have better quality winding insulation to withstand the high frequency's present in the leading edge of square waves.

Talking to oldtimers that used to work in the provincial (grid)system control center for Alberta, they had a mechanical clock on the wall next to an electric one. depending on the difference in time, the system frequency was adjusted to match the mechanical clock.  

[Flux]

As others have said, most things tolerate a reasonable variation in frequency. The main thing to watch is single phase motors with a centrifugal switch. If frequency is too low the switch will fail to operate and the starting winding will stay energised and the capacitor will go bang fairly quickly.

Best to err on the high frequency side for nearly all loads.

No form of synchronous motor clock will keep time on any generator so don't worry about it . You can however use these clocks to get an accurate idea of frequency, timing the sweep second hand of a synchronous clock will give you a precise frequency when it roughly keeps time.

Flux

[powerbuoy]

Keep in mind that a lot of stuff is rectified nowadays internally. Often, some electrical devices work on both, Euro and US systems by flipping a switch from 120VAC 60Hz to 240VAC 50Hz. This could be a hair dryer for example. While the voltage adjustment is probably solved by adding a resistor, the frequency is probably not being regulated at all in these types of loads.

A trypical space heater does probably not care too much if it fluctuates from 45 to 65 cycles.

[wildbill hickup]

Once again thanks for all you answers this group is the greatest. Now if only I could find a group as good on Dodge/Cummins engines I'd be set!!!!!!!!!

Wildbill