Generator power

JESSICAJESSICA Solar Expert Posts: 289 ✭✭
Maybe this is a stupid question, but since I don't know the answer, I ask anyway:

Electricity produced by an ordinary generator, like, say, a Coleman, Generac or Craftman, is it modified sine wave or pure sine wave?

Thanks.

Comments

  • solar_davesolar_dave Solar Expert Posts: 2,394 ✭✭✭✭
    Re: Generator power

    From the Generac spec sheets:
    TRUE POWER® ELECTRICAL TECHNOLOGY: Superior harmonics and sine wave form produce less than 5% Total Harmonic Distortion for utility quality power. This allows confident operation of sensitive electronic equipment and micro-chip based appliances, such as variable speed HVAC
  • BB.BB. Super Moderators, Administrators Posts: 32,800 admin
    Re: Generator power

    In theory, a generator (alternator) produces pure sine wave power (rotating magnets and coils).

    In practice--Under some conditions, such as very heavy loads, poor power factor loads, and non-linear loads (non PF corrected electronic loads), the actual output can be distorted from a true sine wave (basically, when the current output exceeds the capability of the generator design).

    Also, for some devices, accurate frequency is very important (less than 0.1 Hz variation from 60/50 Hz)--And many generators will vary by 1-2 Hz (or more).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Generator power

    It should also be noted that the frequency (Hz) of most generators (non inverter types) is dependent on rpm. A cheap generator will run at 3600 rpm, which happens to be a multiple of 60. More expensive industrial duty generators tend to run at 1800 rpm, also a multiple of 60. The result is that any variance of speed will lead to a variance of frequency, at least momentarily.

    What typically happens, a large load comes on line, this leads to a momentary drop in engine rpm which drops the freq a few hz. The engine then recovers, often time overspeeding for a bit, leading to the freq being a couple to high. The bigger the generator the smaller the effect.

    So while the generator produces sine wave power, it may not be real stable sine wave power.

    Tony.

    PS The reason cheap generators run @3600 is that a manufacturer can get more net output out of a smaller engine with higher RPM. Most 3600 generators that I know of have trouble carrying their rated load, while most many 1800 rpm units will carry way more than rated load for long periods of time.

    T
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Generator power

    JESSICA,

    It is the inverters that are either MSW or PSW, not the alternators. The Honda, Yamaha and Kipor inverter generators do have PSW inverters, but the cheaper inverter generators use a MSW inverter.

    Regular generators don't use an inverter, just a nice smooth rotating alternator - at constant 1800 or 3600 rpm - which puts out PSW, but since they have to stay at the same RPM all the time, they just use a governor which opens up the throttle under load to keep the engine from slowing down - so they use more fuel.

    The advantage of an "inverter" generator, is that it will produce 60hz regardless of RPM. So instead of running at 1800 or 3600 rpm continuously, it will throttle up or down depending on load - and save a bunch of fuel.
  • Ralph DayRalph Day Solar Expert Posts: 986 ✭✭✭✭
    Re: Generator power

    In a perfect world, 1800 and 3600rpm sure. In the real world...

    I purchased a Subaru diesel 5kw genset and had some problems right away. After checking with a Killawatt meter it showed the Hz at 63. The Hatz company who manufactures the diesel engine told me that they leave the factory with the governor set for 3700rpm translating to 63 hz on the alternator. This is fine when you're loading up with saws, compressors, all the good things on a construction site, but maybe not for your inverter or home electronics.

    My 10kw diesel 1800rpm genset I have cold/no load running at 62Hz. Once charging starts it hits the 60hz mark most every time.

    Ralph
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Generator power
    Ralph Day wrote: »
    After checking with a Killawatt meter it showed the Hz at 63.

    And in real life, you won't notice a thing, except your clocks will be of a tiny bit. 3 hz is not enough to cause a problem. Many things are labeled 50/60 hz.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Generator power

    I have always spun my generators up to ~63 hz with no load (depending on the size of the genny and the expected loads) That way, when loaded with the expected load they come in pretty near 60hz.

    As Mike suggests, it has been suggested to me that within ~5-10% of hz cycle is close enough, and that almost nothing will complain. (except clocks as Mike also said). So ~55-65 hz really shouldn't effect much.

    Tony
  • Ralph DayRalph Day Solar Expert Posts: 986 ✭✭✭✭
    Re: Generator power

    You all are right, it wasn'tthe hz being a problem on the Subaru, it's voltage regulation was capacitor type, not electronic. When hooked up to the p240 autotransformer it acted wonky. Turns out the neutral was carrying current back to the genset unbalancing the two legs of the 240. By isolating the neutral the problem went away. Never even noticed the unbalanced performance with the Simpower 10kw unit.

    I have a load service again, so all generators are for emergency use only now...except for exercising them. Even peak at 10 cents per kwh is cheaper than diesel at 75 cents per liter x 2.5 liters per hour. (except for the monthly charges etc...total diesel bill last year $300, Hydro one ???)

    Ralph
  • JESSICAJESSICA Solar Expert Posts: 289 ✭✭
    Re: Generator power

    Once again: Thanks!
  • soloronesolorone Solar Expert Posts: 257 ✭✭✭
    Re: Generator power

    I just found this thread.

    I have a 6 YO Kubota diesel, it has given great service with minimum of problems.

    Biggest issue is Hz stabilization, mainly by keeping the alternator belt tight.

    I did a complete service last month, new pump belts and tightening, I am seeing some HZ fall off. Now this could be age, lose of compression, maybe needs a top end done.

    Or could it be brushes?? I have never changed the brushes, but have them in my spare parts box. Wondering if I should fool with them.

    If the brushes were bad wouldn't it show up some other way???
  • BB.BB. Super Moderators, Administrators Posts: 32,800 admin
    Re: Generator power

    I would guess that worn slip ring brushes would be seen as a loss of output current (and possibly lots of electrical noise). The slip rings provide power to the rotor--more current through the slip rings, more current/voltage output by the alternator.

    The brushes (for generic equipment anyway) are usually pretty easy to take out. It would not be a bad idea to pull one out and see how it looks. If you let them wear completely out--It is possible that you will damage the slip rings on the rotor (need to be turned smooth again).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Generator power

    First place I'd look is the fuel delivery system. Any leaks? blockages? I had an issue where the Hz would vary a bit when the set wasn't under load, turned out to be tiny air bubbles from a leaking fuel filter.
  • soloronesolorone Solar Expert Posts: 257 ✭✭✭
    Re: Generator power
    BB. wrote: »
    I would guess that worn slip ring brushes would be seen as a loss of output current (and possibly lots of electrical noise). The slip rings provide power to the rotor--more current through the slip rings, more current/voltage output by the alternator.

    The brushes (for generic equipment anyway) are usually pretty easy to take out. It would not be a bad idea to pull one out and see how it looks. If you let them wear completely out--It is possible that you will damage the slip rings on the rotor (need to be turned smooth again).

    -Bill

    Ummm, Slip rings do not sound good at all, sounds like a major repair. I guess a brush inspection is in order, thanks for the nudge.
    stephendv wrote: »
    First place I'd look is the fuel delivery system. Any leaks? blockages? I had an issue where the Hz would vary a bit when the set wasn't under load, turned out to be tiny air bubbles from a leaking fuel filter.

    Thanks for input. With all lines 6 YO I guess that could be a possibility.
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Generator power

    Phase stabilization is generally a function of engine/genset rpm.

    Take the brush cover of, and run the genny under load in the dark. You should only see minimal arcing. If you see significant arcing , either the brushes have worn far enough to be riding on the copper connector wiring, or they are sticking. A sticking brush can cause the brush to wear unevenly so that it eventually may only be riding on a very small point.

    Brushes are cheap, and pretty easy to install in most gennies. I would check the engine rpm and the bush seating.

    Tony
  • MangasMangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Generator power

    To Bill's excellent point , "I would guess that worn slip ring brushes would be seen as a loss of output current".

    This is a very important maintenance item which many people fail to perform. Slip rings need to be periodically cleaned up to preserve brush life and protect the voltage regulator from frying itself. I didn't do this service and paid the price. On my SG 015 propane unit, I have them service the slip rings every 200 hours.

    I am considering replacing my brush unit with an Onan 1800 rpm 15 KW water cooled propane industrial genny which I believe has an exciter instead of brushes. Normally you find exciters on the larger units above 20KW.

    I'm researching this with my power generation outfit. Also, I need some education on how an exciter works. I know the power generation can with the exciter is much larger than a brush unit's can. They claim the exciter equipped gennys' need less maintenance and reliability is increased.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • BB.BB. Super Moderators, Administrators Posts: 32,800 admin
    Re: Generator power

    Alternators with rotor windings (not Permanent Magnet Types) all need some sort of Exciter to supply current to the rotating field (rotor).

    The "simple" Alternators use slip rings to supply DC current to the rotating field (which moves the current in the external stator to generate your AC power).

    There are brush-less exciters which are (can be?) sort of the reverse of the Alternator you are getting power out of.

    Have an external field coil, and internal rotor which generates AC power, which then goes through a diode bridge (which itself rotates with everything else to make DC current which is then wired over to the rotor to create the variable magnetic field to make your AC power without using slip-rings or commutators or brushes (how is that for an engineering run-on sentence?).

    Or, look at page 4 of this synchronous motor description PDF. Page 3 shows the slip ring type (with a DC generator + commutator + brushes in this case.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MangasMangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Generator power

    Thanks Bill for explaining how the thing works.

    Always count on you guys.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
Sign In or Register to comment.