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Thread: Generator frequency

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    Default Generator frequency

    Hi folks I have recently had a generator repaired. It's a Honda engine driving a 5.5KVa Meccalte alternator. The fuel tank was RS, as was the carby, so they were replaced by my local small engines shop, and I was quite happy with the job, EXCEPT: it appears they didn't calibrate anything.

    The genset is used as backup power for my off-grid PV + lead-acid system, and it's been working fine for many years. When I got the genny back from repairs, it worked fine except that it didn't seem to work as well as it had before - it was taking longer to charge the batteries. I thought there must have been something wrong with the battery charger.

    So, when my solar guy was here last month replacing some old panels, I asked him to check it out. We put a multimeter across the input terminals of the charger and it was only reading ~180 volts! (His multimeter is a "proper" RMS meter). So I went and adjusted the genset (a screw adjuster on the carby) until it was giving us ~240 volts. He was going to check it to make sure we were getting 50Hz, but his frequency meter wasn't working.

    Now, as far as I'm aware, these gensets are supposed to supply 240 VAC @ 50Hz, so if if I'm reading 240 VAC, it should be pretty close to 50Hz. This genset only runs the battery charger which states that it can cope with 40 - 70Hz, and the tumble dryer. What sort of damage will it do to the dryer (or any other appliance) if the frequency is way out of spec? The weather here in SE Qld over the last few months means I've been using the genset a lot to charge the batteries and dry clothes, so if there's going to be a slow degradation of something because of out-of-spec frequency, I'd like to know about it.

    cheers



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    I am guessing the Voltage output is based on the engine doing a minimum RPM so its understandable if the reading was low until raised the Rev's.
    I have no idea how the frequency is set but I think it needs to be close to 50 Hz as possible.
    Until others can advise, I remember many years ago that Appliances for the Eastern States used 240V, 50 Hz but Western Australia was either 250 or 260V at 60 Hz and people were warned NOT to take or try to use those appliance there as the diffence would damage them.
    Another problem USED to be that some TV's and refrigerators would not 'start' on a generator, a problem with the SINE wave?

    In a now closed Coal Fired Power station during an Open day, we were taken past the Generators (size of a railway carriage) being spun at EXACTLY 3000 RPM and happily generating a shit load of Voltage, now there was a GENSET !!!

    Better to spend a Dollar and get it checked to your satisfaction than have to replace something.

    PS, back when Home Computers were coming onto the Market in Australia, many found the Computer clock could not keep the correct time and this was put down to the US with their 110V mains but I cant remember at what frequency.
    Last edited by gordon_s1942; 04-04-18 at 07:50 PM.
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    I would suggest when the fuel tank and carby were replaced there was no tuning done as you rightfully suspect.
    The voltage output is controlled by AVR (Automatic Voltage Regulator). When your genset is loaded and the engine doesn't get the right amount of fuel - let's say less than it needs, it will run at lower RPMs as it won''t be able to develop enough power. The output frequency will drop affecting the output voltage.
    Gordon have you the right advice - get someone who knows what is he doing to check and re calibrate the engine fuel system. By simply adjusting AVR in order to get the right voltage will not change the frequency. Most likely you run different Voltage to Frequency ratio risking damaging the alternator.

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    In the US standard residential voltage is 120/240(110~220) vac @ 60hz.

    Most home items are 120vac, with only heavier draw(current) appliances Pumps/Heaters/AC using 240vac! (Twice the voltage = half the current)

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    Thanks, Fromaron. I believe it's capacitor-regulated, as I had to replace the large capacitor a few years back. I'll chase up my solar guy to fix his frequency meter and check it for me.

    The adjustment was actually a screw that moves the carby butterfly to change the engine RPM. A new carby is bound to result in a change in RPM, and I think it wasn't checked to see that the base RPM was correct. My understanding is that the engine at X RPM gives 240VAC @ 50Hz - if it's less than X RPM, you don't get 240 volts and you don't get 50Hz.

    If it cooks the tumble dryer, so be it - they're not expensive. The battery charger OTOH, is upwards of $2K - fortunately it's very forgiving as to what it's being fed

    cheers
    Last edited by dwywit; 05-04-18 at 09:28 AM. Reason: additional

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    If you have any smart computer UPSes, they will usually show the mains frequency.

    There are also some cheap / generic plug in "Power Usage Meters" that also show the mains frequency. Kogan sell one for $35, I guess Jaycar and Altronics would both have something similar and eBay will probably get you one significantly cheaper than Kogan.


    (see the link to the user manual for details).

    I was given one a while back and found it surprisingly accurate when compared to a much more expensive and sophisticated meter. It shows "real power" as opposed to "apparent power". Might be a handy thing to have kicking around if you're running off solar / generator.

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    Quote Originally Posted by dwywit View Post
    Thanks, Fromaron. I believe it's capacitor-regulated, as I had to replace the large capacitor a few years back. I'll chase up my solar guy to fix his frequency meter and check it for me.

    The adjustment was actually a screw that moves the carby butterfly to change the engine RPM. A new carby is bound to result in a change in RPM, and I think it wasn't checked to see that the base RPM was correct. My understanding is that the engine at X RPM gives 240VAC @ 50Hz - if it's less than X RPM, you don't get 240 volts and you don't get 50Hz.

    If it cooks the tumble dryer, so be it - they're not expensive. The battery charger OTOH, is upwards of $2K - fortunately it's very forgiving as to what it's being fed

    cheers
    I am guessing then if it has a large capacitor its not AVR regulated ? so base idle is important.This type of regulation is pretty crude and the frequency can vary between 45 and 55 HZ most electrical equipment will tolerate this ok but more sensitive electronic devices don't. Most devices these days will run 90 to 260 volts happily @ 50 or 60 HZ Just a note test voltage and frequency under full load as well as I have seen Generators @260 volts because they are revving to high under load.

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    Quote Originally Posted by shred View Post
    If you have any smart computer UPSes, they will usually show the mains frequency.

    There are also some cheap / generic plug in "Power Usage Meters" that also show the mains frequency. Kogan sell one for $35, I guess Jaycar and Altronics would both have something similar and eBay will probably get you one significantly cheaper than Kogan.


    (see the link to the user manual for details).

    I was given one a while back and found it surprisingly accurate when compared to a much more expensive and sophisticated meter. It shows "real power" as opposed to "apparent power". Might be a handy thing to have kicking around if you're running off solar / generator.
    OH, SNAP! Of course, i used to have one of those - plugs in between the appliance and the wall to show and record energy usage. Mine went unresponsive a few years back so I threw it out. Now I've got the incentive to get another one. Thanks

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    I'll get one of the meters suggested upthread and test it under light and heavy loads to see what's what. The only appliance I run directly off this is the tumble dryer, the battery charger seems to be OK with the supply - it's a model specifically designed to run off unregulated power.

    All the rest of the household devices run off the battery bank via the sine-wave inverter.

    cheers

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    Perhaps order a cheap impulse tacho from fleebay ($15) or there abouts. Just wrap the sens wire around the plug lead. If the alternator is NOT an inverter type {I suspect it is not due to its age} then there is something wrong. I believe it's better to run the device @ 3000RPM as that is what it's designed for. Some gensets have regular problems with caps & also slip ring brushes. As suggested earlier better to have someone (electrical) check it out.

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    Quote Originally Posted by Softek2 View Post
    Perhaps order a cheap impulse tacho from fleebay ($15) or there abouts. Just wrap the sens wire around the plug lead. If the alternator is NOT an inverter type {I suspect it is not due to its age} then there is something wrong. I believe it's better to run the device @ 3000RPM as that is what it's designed for. Some gensets have regular problems with caps & also slip ring brushes. As suggested earlier better to have someone (electrical) check it out.
    That's a good idea. It's not an inverter genset. I wonder if I can take the digital speedo off the motorbike and use the impluse tacho wire from that?

    It's a good quality engine (Honda) and a good quality alternator (Meccalte) and it's been reliable for years - perhaps it needs a full-on service of the electrical bits.

    cheers

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    I would suggest getting the right frequency is far more important than the " Right" Voltage.

    For one thing, the standard in Australia for about the last 20 years has not been 240V but 230. Regardless, everything ( including those so called " Sensative electronics) these days will run happily on a fairly wide range of voltage, at least 220-255V and many beyond. What things do get iff with is Frequency.

    I have purchased new and used gennys and converted induction motors and I alsways set them at about 1/3rd load ( or what ever the main load is if the machine is specific purpose) to output the correct FREQUENCY.

    Rarely does this give any correct voltage. It's usually 237 or 229 or something very non standard. Thing is, it don't matter. the margin is too small to compensate but that frequency can be important. If you are running dumb loads like heaters, motors or things with stepping circuitry like a battery charger, don't much matter ( although your motor speed may vary slightly).
    Electronics -can- be more sensitive with things like internal clocks.

    You can get multimeters off fleabay now that have frequency and are surprisingly cheap. Don't think they are rubbish. I have bit of a multimeter fetish and have a load of them and even the cheapest ones when checked against a calibrated meter are surprisingly accurate.

    In any case, you would be far better off setting the frequency of the gen where it normally operates and let the voltage go where it wants within reason than do it the other way round.
    Especially on an Non avr set, you will be winning the jackpot to find a unit that has the correct frequency and spot on voltage at the same time.
    But it does not matter as long as you get the frequency close.
    That is directly controlled by engine speed so it is a good idea to put a load or the regular load on the unit when setting it.

    Be also aware it can shange due to ambient temp, running in of new components, load and other things even like the fuel you use. Ideally, use non ethanol fuel so it does not condense water in the tank which will give you no end of problems and is just crap fuel that an older genny may have trouble with anyway.

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    Thanks for the info. The genset is only used for 2 things: battery charging, and tumble dryer. It's *never* used to power the household directly. No electronics except the internals of the battery charger ever encounter the output of the genset. The tumble dryer is an older type with a clockwork dial timer, and a hot/warm setting.

    The charger is very forgiving regarding frequency - the front plate states that it will accept 40-70Hz, confirmed by my installer. He was the one who noticed that the readings were a bit low. It's rated at 70amps, but it was only putting ~50 into the battery bank. He measured the voltage at the input terminals (using a true RMS meter) and it was only 180 volts. His frequency meter wasn't working, but he suggested adjusting the genset until the voltage hit 240. It was then putting 68 amps into the battery bank.

    I know not to use ethanol fuel blends, but once in a while I'll put a cupful of metho in before filling it. It slowly gathers a little puddle of water at the base - probably condensation.

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    In an article I read on the story of the invention and introduction of Electricity and the War between Tesla (AC) and Edison (DC) there was a mention of generated frequency and it said as an example that parts of New York still had a '25 cycles per second' service and this was noticeable because this caused the lights to 'pulse' (my words) unlike other areas that were using '60 cycles per second' which give a steady glow.
    I cant remember the Voltage but I would suspect it would be no more than the 110V that is still the US standard today.

    Voltage must play a part in the supply because until a few years ago, appliances sold in the Eastern States were unsuitable to be used in Western Australia due to their higher Mains Voltage (250V).
    I have a small Gen set of 2400 Watt output and have used it to power up a 50 inch TV, Cordless telephone and 2 TV MHA's along with a floor lamp with a 40 watt incandescent bulb during a power outage.
    The longest I have run it is about 6 hours and had no problems with the appliances.
    While all around us was in the Dark, with the fire going and the TV on beats playing 'I spy' in the dark anytime.
    I did want to run a fridge/freezer but was a bit wary to do so.
    Since last year I have been 'baby sitting' a much newer and powerfuller genset and if its still here and the power goes out, I will see if it supports the 2 small fridges and Freezer and maybe the TV etc.
    Experience has shown that with care we can keep most things safely cold for over 48 hours.

    Make sure you only plug into the Genset what appliance you need to power up and dont connect into the House wiring !!!
    Last edited by gordon_s1942; 29-05-18 at 12:25 PM.
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    As I recall from my early days in the electrical distribution industry, the 'nominal' system voltage allows for a range of +/- 10% so legally a 240V service can be in the range of 216V-264V. Supply authorities target a range using half that tolerance before they take action to reduce network affects on a customers voltage IE phase-neutral voltage between 228V and 252V means no action required.

    If you're close to the local distribution transformer you can experience voltages higher than nominal at minimum load times (middle of the night). If at the end of the run from the transformer lower than nominal voltage will occur at maximum load times. High voltage is corrected by a tap change in the transformer, low voltage requires either heavier distribution mains or new transformer nearer to the customer, or both.

    So a local alternator with voltage and frequency within 10% of nominal ratings should not cause any grief to any appliance. Where they get into trouble is supplying the DOL starting current of a loaded motor in something like a washing machine, fridge, pump etc.
    Last edited by Skepticist; 29-05-18 at 01:23 PM.

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    I am the first house off the pole transformer located outside my house and I havent bothered to check the Voltage for years but I expect it to drop around the evening peak and rise during the 'midnight hours'.
    Many moons ago the Supplier came here in response to complaints of power variations that was causing a TV screen to shrink and they used what looked like an old style wire wound household radiator to 'load' up the mains and noted the voltage.
    I gathered it was less than what it should have been and it didnt seem that long later that they changed how the Village was supplied with power by dividing it and adding a new transformer.
    I stand unequivicably behind everything I say , I just dont ever remember saying it !!

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