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Small commercial gas generators

Discussion in 'Renewable Energy' started by Bach On, May 25, 2013.

  1. Bach On

    Bach On New Member

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    I've seen several smaller gas powered generators advertised lately. I'm talking about 800 watts to 1200 watts. Some are described as generator/inverters.

    My understanding is that a real generator usually puts out fairly clean sine wave voltage.

    I'm wondering if these smaller generator/inverters tend to be true sine wave or the less expensive modified sine wave? I already have a couple of modified sine wave inverters. They don't play so nice with some appliances and electronics. I've been considering a small portable generator that would provide a better quality power. True sine wave inverters are cheaper than they used to be. But they are still way more expensive than the modified sine wave models.

    Has anyone here used some of these generator/inverters?

    As an example, Harbor Freight has an 800 watt model on sale for around $100. It is described as a generator/inverter.

    Thanks in advance for any input or responses.

    Bach On
    .
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Do you have a link? - I can't find any such thing on Harbor Freight (only a normal 800W generator on offer at $129).

    Googling found this from Honda:

    http://powerequipment.honda.com/generators/inverter-generator-advantages

    And this:

    http://www.electro-tech-online.com/custompdfs/2013/05/Inverter-Generators-1.pdf

    EDIT:

    Spent some more time googling, generator/inverters are FAR more expensive than normal generators, so $100 is unlikely to be a sinewave 800W one (they look to be about £300 or so in the UK).
     
    Last edited: May 25, 2013
  3. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    I wouldn't classify those little units as commercial by any means. They are more a light duty recreational use generator with a life expectancy of maybe a few hundred running hours if you treat it real nice.

    A real commercial grade genset has a life expectancy measured up into the thousands of hours to tens of thousands of hours.

    As far as one of those being sine wave output it is possible. The only real difference between a modern sine wave inverter and a modified sine wave inverter is a $1 IC and a simple LC output filter circuit.;)

    The rest of the higher cost is just markup. :mad:
     
  4. dave

    Dave New Member

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  5. Bach On

    Bach On New Member

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    That Harbor Freight model is not listed as a generator/inverter. I made a mistake. (BTW: it is on sale through this weekend for $99. 5/25/2013). I have no idea about the quality of this model. I wouldn't expect terrific longevity.

    Here is a link to some models I was talking about. And there are lots of them on eBay:

    http://www.electricgeneratorsdirect...erators.html?gclid=CKaL0LWVsrcCFcuj4Aod0FAATg

    The Honda and Yamaha models claim to have a clean power signal. Some of the others don't seem to specify the kind of power. You will note the Honda and Yamaha models are far more expensive.

    I said 'commercial' - meaning only that it was commercially manufactured - rather than some homebrew generator using a lawnmower type engine and a car alternator. I'm wanting to build one of those. And I've been exploring the cost. That search is what got me investigating these models.

    The inverter is the part I'm interested in on these models.

    I understand what you're saying about the difference between a modified sine wave inverter and a true sine wave inverter. I've used both. The electronics may not be all that different, but the retail price difference is still substantial. And the electrical output is very different. Most people don't have the knowledge or skill set to modify them - at least not safely.

    BO
     
  6. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I would disagree with tcmtech, the electronics involved is substantially different and much more complex - a true sinewave inverter is basically a class-D (switching) amplifier.
     
  7. Bach On

    Bach On New Member

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    I was reading at a site last night that caters to the Recreation Vehicle crowd. Many there were telling people with questions about inverters that THEY use modified sine wave inverters for most everything except microwave ovens and some compact fluorescent lights.

    I have two modified sine wave inverters. One is a Cobra 800 watt unit that accepts short surges up to 1200 watts. The other is a 2000 watt unit that accepts surges up to 2500 watts (I've forgotten the brand name).

    I can run my refrigerator on the large one. But I've read that it may damage the motors on many compressors - or at least cause them to run hotter than usual.

    I've never tried delicate electronics with either. But people at this site were claiming they could run TVs, battery chargers, computers, DVD players, and Hi Fi systems with the modified sine models. They were discouraging others from buying true sine wave inverters. Go figure!

    I'd like to have a nice 1500 or 2000 watt generator in the under 40 pound variety. But I would want something that puts out a true sine wave. And the Honda and Yamaha models are very expensive - at least for my budget. My original question was about the generator/inverters. I was asking if the less expensive models were modified or true sine wave varieties?

    Seems like it would be great if there was some sort of filter than would smooth out the signal. But that would probably cost a fortune too.

    Thanks for the input,
    BO
     
  8. RCinFLA

    RCinFLA Well-Known Member

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    Inverter generators are permanent magnet three phase alternators rectified to DC. The inverter takes the high voltage dc and converters to a high freq PWM'd sinewave. They have the advantage over non-inverter syncronous generators in their engine rpm can be modulated based on the load need. When operating in 'econo' mode, the voltage peaks of the sinewave will chip off as engine rpm is brought up to speed to meet a sudden heavier surge load. For example, start up of a refrig compressor would not like the slump so should be run at full rpm non-econo mode. Freq is much better controlled as it is not dependent on engine rpm of syncronous generator.

    I have not seen a modified sinewave inverter generator. It does not really make too much sense as the manf would not save any significant money in making them modifed sinewave versus sinewave output and be a competitive disadvantage. There are some reasonably priced copy cats, like Kipor and other China models.
     
  9. Bach On

    Bach On New Member

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    Decided to roll my own. I've got a five HP Briggs % Stratton engine. Plan to mate it with an aftermarket GM alternator. I think the finished product will be able to put out something like 100 amps at a nominal 12 volts. My plan is to use it to run an inverter and charge a pair of deep cycle batteries.

    60-100 amps is probably too much current to hit the batteries with. So I figure I'll need some charge controller capable of feeding maybe 15-20 amps to the batteries.

    Some of these charge controller units such as for solar panels can be costly. Is there a cost-effective automotive equivalent that would work well?

    I think this alternator is the 3 wire unit with built-in voltage regulation. It can produce up to 140 amps at 12,000 RPM. I don't envision speeds that high, so I'm figuring a high around 100 amps.

    Bach On
     
  10. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    I wouldn't worry about the charging currents. You are aware that if that alternator was used in a vehicle or other machine of some sort with a larger engine it would put its full 140 amps into the battery if the battery so needed it. :confused:

    Think of it this way whatever the batteries cranking amps rating is that is also it's peak charging rating as well. If the battery puts out 500 cranking amps for 30 seconds without problems it will also take 500 charging amps for 30 seconds without problems. ;)

    Even with a very run down battery it wouldn't put a full 100+ amp load on the alternator for more than a minute or so of which after that you would see it naturally taper down to 20 - 30 amps for a few minutes followed by 10 or so for a very long time.
     

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