240v generator output monitoring

Discussion in 'Electronics & Electrics' started by noober69, Oct 7, 2015.

  1. noober69

    noober69 Member

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    Hi, I have a 2700kva generator (old applied power model) run by a honda motor. It would be at least 10 years old if not more but was serviced 2 years ago, and hasn't been run since. It runs ok with new fuel.

    It was recently serviced but I am finding the voltage output low. There is a screw on the carby that adjusts rpm and voltage but when I monitor the voltage going into a ups (with input v display) it is all over the place, up and down by 10v.

    1. Is there a cheap plug in pass through style 3 pin voltage meter I can use to give me a readout of the voltage from the generator?
    2. Does anyone know if these generators are ok for domestic loads, or is it typical of their voltage to fluctuate a lot with load, and therefore not really useable with TV's, pc's etc?

    Thanks.
     
  2. aXis

    aXis Member

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    Up and down by 10V seems pretty good to me. And yes, their voltage and frequency will vary quite a bit as their load changes and the generator recovers.

    Most modern electronics with switchmode power supplies have universal 80 - 240V 50/60Hz capability, they really don't care much about the voltage or frequency as long as the voltage stays below the limits of the input stage. Arguably they would cope with an old genset better than a cheap UPS / square wave inverter as there are less harmonics.

    The things that really care about voltage and frequency are motors - give them the wrong power and they can overheat due to stalling or the change in reactive impedence.
     
  3. fR33z3

    fR33z3 Member

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    in my experience, most line interactive UPS's get real unhappy with the varying voltage and frequency of small gens. I've never tried with a double conversion UPS - I'm assuming they would handle things a bit better. Otherwise if it becomes an issue, maybe run without the UPS?
     
  4. 2xCPU

    2xCPU Member

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    2.7KVA?
    What is the 'normal' output you are reading?
    I've got the smaller model (2.2KVA), which when I got it, only put out 180V under load. Replacing the cap across the field winding brought it back to life.

    2.
     
  5. RobRoySyd

    RobRoySyd Member

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    For some reason that I don't understand some such generators require an earth for their controllers to work well.
     
  6. OP
    OP
    noober69

    noober69 Member

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    Thanks for the replies.

    I will check for an earth, there may be a spike somewhere I can put in, that and a new cap may help. I wonder replacing the cap is within the scope of a store that services small Honda engines, like a mower/garden equipment store. Unfortunately I cannot find a manual for mine online.

    Yes, line interactive ups seem not to like generators. Given that they claim to accept dirty power and filter it, even if only to knock of spikes etc, I would expect them to be more robust than the power supply on my pc, but maybe not.

    And yes, 2.7kva, I got carried away.
     
  7. 2xCPU

    2xCPU Member

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    If it's the same as mine, it has no controller (and output is highly rev. dependent). If it's a later model, it'll have an AVR, but shouldn't show this behaviour.
    Don't get hung-up on the job, it's not that hard. If you decide the cap needs replacing, this is what I found in mine:

    Rear guard removed

    Click to view full size!

    Diodes for half the rotor

    Click to view full size!

    Schematic

    Click to view full size!

    The cap you "may" need to replace is the silver FACON cylinder in the first pic. It has 1/4" spade terminals and is held in with a cable tie. It's a 5min job with the most basic toolkit.
    The replacement cap I used was just a 380V motor run cap (not a start cap).

    2.
     
    Last edited: Oct 9, 2015
  8. aXis

    aXis Member

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    Line interactive UPS's are expecting to go into trim / boost only a few times a day, not every 10 seconds as could happen with a poorly running genset. Cheap line interactive units might even have physical relays rather than solid state switches and so they would have a limited life too.

    Full conversion should be a lot more capable, but you may have to wind out it's alarm limits to stop it being a nuisance.
     
  9. paulvk

    paulvk Member

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    If the generator is a 240V output do not use a 380V capacitor it will have a shorter life, use a 440V motor run capacitor.
    380V is for USA 210V-220V
     
  10. 1shot1kill

    1shot1kill Member

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    Killawatt style meter, but it probably won't work if the generator output isn't PSW.
     
  11. 2xCPU

    2xCPU Member

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    The cap I replaced was rated 270V iirc. The replacement was considerably higher.

    The cap is on the exciter coil, not the output. I never measured the voltage applied to it.

    2.
     
  12. RobRoySyd

    RobRoySyd Member

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    Yes, without an AVR all you have is a simple governor which will try to keep the frequency (RPM) constant. A basic AVR is pretty simple.

    AUTOMATIC VOLTAGE REGULATION (AVR).

    If rolling your own is a challenge, they're under $15 on eBay.
     
  13. TERRA Operative

    TERRA Operative Member

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    I used to fix these things for a living.

    By far the biggest cause of failure was that cap, and replacing them is super easy, we usually installed an uprated cap from RS Components (we used a higher voltage rating cap that is also rated for 'motor run' use IIRC).
    I don't think I ever found faulty diodes on the rotor, and if they ever did die, you'd often be replacing the rotor anyway...

    The AVR (if fitted) was the second most replaced part, followed by the stator (the outside windings) if something got shorted out or the insulation failed from age, usually 30+ year old machines that are sitting on a farm somewhere..

    The smaller generators are pretty loose with their output voltages, so the fitment of an aftermarket AVR will definitely help smooth things out.
     
  14. OP
    OP
    noober69

    noober69 Member

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    Ok, thanks for all the info.
    Bearing in mind I am not sure it is out of spec, but it was running a little lumpy and boltage was up and down. I would like to improve it in case I have to use it for stuff like tv's, pc's, and a microwave. The microwave really killed it with its cycling heavy load.

    I pulled out this:

    http://imgur.com/9LXxC11

    This is the back of the generator.
    http://imgur.com/2wa8dJ4

    So my question is, can I just replace the capacitor with one like this:

    http://au.rs-online.com/web/p/polypropylene-film-capacitors/3778813/

    or would an avr be better? If so, any suggestions for a 3kva system? Ebay seems full of cheap no-name but perhaps that is enough. If I think about it, shouldn't the avr be in addition to the cap and in line with the output to in effect accept the AC input and regulate AC output?
     
  15. 2xCPU

    2xCPU Member

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    Yes, that'd be a good match
    If it's like mine, it has no slip rings, so retrofitting an AVR may not be straight forward.

    2.
     
    Last edited: Oct 13, 2015
  16. paulvk

    paulvk Member

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    What state are you in have about 2000 of those, very common can beat that price any day! Fellow I work for occasionally, imports from italy just do not do cards as not much retail mostly large customers but do bank deposit.
    Also that gen looks like it could do with a clean and service!
     
    Last edited: Oct 13, 2015
  17. OP
    OP
    noober69

    noober69 Member

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    I am in Vic but already ordered a new cap, sorry.

    The generator portion probably could do with a clean. Not sure how I would go about that.

    I spoke to a mower repairman and he said with generators he just looks at the motor, which was serviced only a few engine hours ago (although probably more than a year ago).

    Might get it another service as it shouldn't cost a lot, spark plug and air filter he reckons.

    I am guessing not an easy fit for an avr?
     

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