How do I measure Hertz?

[Chris142]

Someone mentioned that I should see what Hertz my generators are running. I know it's supposed to be 60 Hertz.

Under a full load I'm seeing 113volts. Do I need to raise the voltage?

 

[JHZR2]

Voltage and frequency may or may not be related in your generator. Id guess not. Youre seeing low voltage (is this at the generator or at the load?) because of inefficiencies in the generator itself. If you are straying from 60Hz (some droop, especially under high transient load is acceptable), it is because your engine is not governed properly to stay at the right speed to ensure 60Hz output from the generator.

So if youre off of 60Hz, it may be because of the setpoint of the governor and how it is operating to ensure constant speed and proper fueling under load changes. Some of these things are just a cheap spring and a flimsy arm which may not do the job well, thus the comment of checking it.

If youre seeing 113V at the loads, under load, then Id say not to worry about it that much (especially because if you take it too high you may be at over 120V under light load, which isnt what you want). If youre seeing 113V at the generator, you may actually be below 110V at the loads, which would be out of spec for some of them potentially.

But again, you need to check voltages lightly and heavily loaded, etc. It may be that your generator just cant really support the load that you are presenting properly.

IMO, the best thing to do is go to HD and buy a kill-a-watt meter, and plug it in at one of your loads or at the end of an extension cord. Measure frequency and voltage. Try to put some motor loads of relevance on there so that your PF is down at about 0.8 to get real insight into performance.

 

[Chris142]

I measured it at the generator. Voltage is ajustable and I wanted to check the Hertz.

 

[JHZR2]

Again, you need a meter to do so. Some multimeters will do it, but your best bet is to get a kill-a-watt from HD and plug it in at the load. Ill bet if youre seeing 113 at the generator, youre at or below 110 at the loads unless all your conductors are very heavy.

But again, be careful that at light load, youre not over 120V if you take it up a bit. Do it very slow and incrementally.

 

[XS650]

Originally Posted By: Chris142
Someone mentioned that I should see what Hertz my generators are running. I know it's supposed to be 60 Hertz.

Under a full load I'm seeing 113volts. Do I need to raise the voltage?


The standard for power companies is 120V +/- 5% or 114V to 126V.

You are close enough but if you want to get closer, be sure you don't get all crazy too high on the light load end.

Kill-a-Watt meters are widely available for under $30 and also useful for checking power consumption, voltage and power factor. A man can never have too many toys tools.

Older frequency meters used to use a series of vibrating reed and you adjusted the speed until the 60Hz reed gave max movement. New ones are usually expensive but you might find a used one of flea bay or surplus store. They are limited though, all you can do is measure power line frequency with them. Once you have a Kill-a-Watt you will figure out other things to do with it.

Another way would be to use a tachometer if the generator is direct drive. Low priced direct drive generators usually run at 3600 rpm (60 revs/second).

 

[engineerscott]

You can buy a Kill-A-Watt plug in power meter for around $20-$30 that will show the line frequency. It will also give you an indication of the load power so that you can make sure you're not overloading the generator.

Barring that, you can look around for a multi-meter that will display frequency. If you get a Fluke you'll be looking at something in excess of $100 I suspect (it's been a while since I bought my last Fluke meter). There are some cheaper multi-meters around that will measure frequency, but I can't name a brand off the top of my head, you'll just have to look around.

On quite a few generators the voltage and frequency are not independently adjustable, but they are designed to put out about 120VAC at 60Hz (most will actually make about 130VAC @ 60Hz under a no load condition, not a problem). Don't get too worried about the line voltage, most utilities will only guarantee delivered line voltage to be 120VAC +/- 15% and some have even wider tolerances than that. Likewise, if you're within a few Hz of 60Hz you are good, very few loads are highly sensitive to line frequency within reason.

 

[daman]

I asked a similar question a wile ago maybe it'll help you.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1333211

 

[oilboy123]

+ 1 on the kill a watt. Plus you can use it to measure appliance loads etc.
Originally Posted By: engineerscott
You can buy a Kill-A-Watt plug in power meter for around $20-$30 that will show the line frequency. It will also give you an indication of the load power so that you can make sure you're not overloading the generator.

Barring that, you can look around for a multi-meter that will display frequency. If you get a Fluke you'll be looking at something in excess of $100 I suspect (it's been a while since I bought my last Fluke meter). There are some cheaper multi-meters around that will measure frequency, but I can't name a brand off the top of my head, you'll just have to look around.

On quite a few generators the voltage and frequency are not independently adjustable, but they are designed to put out about 120VAC at 60Hz (most will actually make about 130VAC @ 60Hz under a no load condition, not a problem). Don't get too worried about the line voltage, most utilities will only guarantee delivered line voltage to be 120VAC +/- 15% and some have even wider tolerances than that. Likewise, if you're within a few Hz of 60Hz you are good, very few loads are highly sensitive to line frequency within reason.

 

[jaj]

Frequency tolerances for most electronic equipment is +/- 5%, or 57 to 63 Hz. It really only matters for magnetic loads (things with transformers and ballasts), and then it only really matters if it's too low for a long time.

To measure it, you need a frequency meter, and frankly it's not worth the trouble. If the voltage is right, most equipment will work fine if the frequency is off a bit.

I'm not sure what the current practice is on voltage, but back when it was my job to know this stuff, the target voltage for consumer distribution was 117.3 VAC, usually +/- 5%, although in my experience most utilities delivered more stable power than that.

 

[Chris142]

I took the voltage reading at the Generator. It's on the end of a 50 ft extension cord(biggest wire cord they had, think it's 16 guage wire).

I'm running a 750w heater, a 12v battery charger and a TV/ VCR combo off it. Ocasionally I will turn on a 60w light for a few minutes.

I'm letting the generator, heater and tv warm up now. I will post the voltage in the trailer in a few minutes.

 

[eljefino]

If you can get your hands on a magnetic ballast flourescent or maybe one of those green sodium lamps and ran it off the generator, you could aim a NTSC camcorder at it. When the frequency gets "close" you'll see a pattern, related to the 30 frames/ 60 fields per second.

 

[Chris142]

No load voltage is between 125 and 128volts.Tv and vcr player both on drops it to 122volts.Adding the 750w heater brought it down to111-113v.Leave well enough alone?

 

[JHZR2]

If it is 111-113 in the trailer with the loads on, then youre OK. Frankly, 125-128V is a bit high for me, but it is likely OK since it drops with low load.

 

[JimPghPA]

110 to 126 Volts RMS is OK.

Set the frequency at half of maximum continuous rated load. Resistive heaters or light bulbs work well for a load.

You do not want the frequency to be fast, because higher than 3600 RPMs is hard on engines.

You can set the frequency by using an old mechanical alarm clock that runs on 120 AC. Compare the second hand to a wrist watch or battery powered clock with a second hand. If the frequency is slow the 120 AC clock will be slow. And if the frequency is fast the 120 AC clock will be fast.

A frequency meter is another way, but some (most) generators have noise. The spark-plug is one source, and some frequency meters are sensitive to noise. I had to build a simple RC filter to use either of my two frequency meters.

The Kila-Watt meter is probably a good one to use. It probably already has a circuit to filter noise.

 

[JimPghPA]

BTW, you set the governor to set the frequency. This is only for direct drive gen-sets. Inverter gen-sets do not have any way for you to do anything regarding frequency.

 

[engineerscott]

How many watts is this generator rated for?

 

[JHZR2]

Originally Posted By: JimPghPA
BTW, you set the governor to set the frequency. This is only for direct drive gen-sets. Inverter gen-sets do not have any way for you to do anything regarding frequency.


An inverter generator should have the switch timing set automatically to provide a 60Hz vaveform.

 

[Chris142]

Originally Posted By: engineerscott
How many.watts is this generator rated for?
hf says 800 constant and 900 surge.Same genny is sold at other places and they rate it at 1000/1200

 

[engineerscott]

Originally Posted By: Chris142
Originally Posted By: engineerscott
How many.watts is this generator rated for?
hf says 800 constant and 900 surge.Same genny is sold at other places and they rate it at 1000/1200


You're good to go then. You're very near rated capacity at the load you outlined. My HF 800/900W makes about 116V around 800W, and it's reasonable to assume that you're dropping a couple of volts across your 50ft cord. If this was a 3500W generator then I might think it a bit low. BTW, most AC powered equipment is designed to run down to something around 96V and rated to 100V.

 

[Slick17601]

I tried a Kill A Watt on my HF genny today.....it was putting out 152 volts at no load. Adjusted it to 60Hz which gave 123 volts at no load. Good enough for me.