Email of the day 12/25/2010

—–Original Message—–
From: Douglas B. 
To: George B
Subject: RE: Contact Form: changfa

 Thanks for the reply George. I have enjoyed your book and CD on home power generation. Would you please make your best comment on quality and value here for back up power in my on grid home essential  electrical items.

Is a half gallon/hour reasonable efficiency for the output ?

Reply: There’s a few thing to consider here, this looks like a nice machine, but they’re not giving it away. We need be a little more precise in our fuel usage data. What we find with the >OLD< Lister CS clones is about .125 gallons of fuel used per KWH out of a typical generator head. We know that diesels are most efficient when loaded at 80% or more.  If we look at their fuel usage figures, we first ask.. Did the Salesman run the test, or a DIYer? If this number is real, it equates to .136 gallons per KWh at half load. That’s an impressive figure (for me) and I’d expect an even better figure (fuel/kWh) at 4000 watts output.

Now.. for the question? Who made the Yanmar engine? How different is it than the Chinese knock off with totally  interchangable parts? I’m sure I don’t know, but I bet this engine was made in China, and I’d love to learn if it came off the same production line as the Changfa Branded Engine or if there are surperior parts and more attention to QC when it gets the Yanmar name slapped on it? I have the question not the answer…

In this set up, we have a non adjustable drive system, we have an engine with a taper shaft and a need to spin at 3600 RPM. I believe this engine will live a far longer life at 3000 RPM, and I also believe that most of us can get by with about 4000 watts, the Yanmar with a serpentine pulley system running at 5:4.2 ratio allows the engine to run a little slower, and I believe this could allow the engine to run a lot longer before you toss it or overhaul it. 

Building your own may not save you money, but you might have a spare engine, or a spare generator head for back up, plus you can tune the drive for the max power downward and potentially better the fuel/kwh figure and increase the life expectancy of the power plant. Here’s a link to a DIYer built unit. Learning to wire feed weld is fun and easy. A skill that self reliant people can use now and in the future.


I am also looking at a construction light tower generator. It has a 3 cylinder 17 hp. kubota (D850) and is rated for 4800 watt continuous power output. This is possibly more power and fuel consumption than I want.

At what speed does this power plant run at? It may be that the 17hp figure is at 3600 RPM, and they are running it at 1800 RPM with a directly driven 4  pole head? If so, this >could< be far more desirable. 

Perhaps I should just buy a Lister CS type and limit my power needs to 2500 watt.

Question? Where will you find the engine and how much work will you do on it to make it reliable? I do hear there are clones out there, but Quality is always an issue. I wonder what the warranty is like on the Yanmar? 

Thanks for any help you can offer.

I wasn’t much help, let us know what you decide to do…

George B.

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5 Responses to Email of the day 12/25/2010

  1. John says:

    AFAIK the Kubota d850 is HP rated at 1800rpm. I see that engine in the Onan generators I work on.

    • George B. says:

      Thanks John, I would think the 17hp engine rating and 4800 watt output power rating are a little unusual in a commercial product, IF the power ratings are both at 1800RPMs (60hz).

  2. Hi George,

    I agree with your surprise George – I have emailed you the performance curves for that particular engine. Kubota Australia show the D850 is rated and tested to be 11 HP @ 1800 rpm for continuous operation and 13 HP for lintermittent loads @1800 rpm.
    I hope that information helps – the file also has curves for D750 and D950 in case others are stuck working out this family of engines. There is a big difference between the salesmans Gross HP and usable HP in a 24/7 genset application.


  3. George B. says:

    11hp and 4800 watt electrical output rating sound about right, and maybe a few thousand feet elevation above sea level are still possible.

  4. Doug B says:

    Thanks Steve for the comment. I am happy at lower than expected HP and the resulting lower fuel consumption. I also am happy with the 1800 rpm as people have incorectly told me this engine runs at 3600. Would you please send the Perf. curve for the engine as I bought it yesterday. It needs some work but the price was too good to turn up.
    Doug B.

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