7KW powertech

[robertglines1]

200 hrs diesel   Whats it worth? Enclosed cabinet ;looks new. Owner wants  $4,000  Bob

[RickB]

If its the same powertech that they're putting into entertainers they are around 10 k new

[robertglines1]

Came out of wrecked toter home. 200 hrs didn't sound band to me but just wanted to make sure. It sounds good and has all hardware transfer switches and auto start.

[luvrbus]

I ordered a 7.5 Onan quite diesel in a cabinet from Southern Plains Cummins for a friends conversion cost 6346.00 with shipping, might want to give Dick Wright a call on a price of his 7.5


good luck

[robertglines1]

Thanks for info -decision time now   Bob

[PP]

Bob, all that hardware and switching stuff adds up fast when you add it to the cost of a new Jenny, but you probably already know that. Happy New Year!

[Charles in SC]

Came out of wrecked toter home. 200 hrs didn't sound band to me but just wanted to make sure. It sounds good and has all hardware transfer switches and auto start.

I had a toter with one of those in it. It was a good basic technology generator. The thing to remember is that it is not an inverter generator . That means that it runs wide open all the time and is much noisier than a 7kw Quiet Diesel Onan. If that does not bother you then go for it. The generator head bearing needs to be changed every 2000 hours.

[neverlearn]

Bob, for reference I paid $1500 for mine with 5000 hours on it. 

[Sean]

... The thing to remember is that it is not an inverter generator . That means that it runs wide open all the time and is much noisier than a 7kw Quiet Diesel Onan. ...

The Onan Quiet Diesel is not an inverter generator, either.  Perhaps you are thinking of the newer HQD (Hybrid Quiet Diesel).

Also, "wide open" is not a correct characterization of how these generators run.  Most quality generator manufacturers, and here I would say Power Tech and Onan are virtually identical, carefully match the prime mover to the generator head rating.  The result is that the chosen prime mover is in the sweet spot of its power band at 1,800rpm (3,600rpm for single pole units, and correspondingly 1,500 or 3,000rpm for 50hz models).  The sweet spot will not usually be "wide open"; you can get the wide open spec from the prime mover's manufacturer.

It would be more appropriate to characterize this style of generator as "constant speed."  But note that even constant speed generators can be made nearly completely silent, even in ratings of 20kw or more.

If your experience is that Onan Quiet Diesels are quieter than Power Techs, that has little or nothing to do with inverters and everything to do with sound enclosures, exhaust and intake baffling, isolated radiator fans, and many other methods that have been detailed on this board over the years.

What an inverter style generator gets you (aside from a much larger price tag) is improved efficiency over a wider range of power outputs.  Constant-speed generators are most efficient at full rated continuous load, and the efficiency drops off rapidly as the load decreases.  An inverter style generator is most efficient somewhere just below full continuous rated output, and drops off more slowly above or below that number.

It is a side benefit of this technology that the noise level will, in fact, drop as the load on the generator drops.  But a 7kw inverter-type generator and a 7kw constant-speed generator will produce essentially identical amounts of noise (all else being equal) when they are producing their full rated output.

For the best efficiency, fuel consumption rate, and generator longevity, you want to engineer the rest of your conversion to operate the generator as close as possible to its rated output every time you run it.  So you are best served to select a generator and design your installation such that the noise level is acceptable to you at full rated load, rather than count on the slight reduction in noise an inverter unit will buy you when operated at lower outputs.

I'm not trying to talk anyone out of an inverter style generator if that is their preference -- it certainly will get you more fuel efficiency over a wider range of outputs, and most of us have to have a bunch of extra capacity there that only gets used when A/C is needed.  Neither will I talk anyone out of something like a Quiet Diesel, which gets you a pre-packaged sound-reduced system, if you prefer to go that route rather than roll-your-own.  But if you are on a more limited budget, you can still have an extremely quiet and pretty efficient system by carefully choosing and designing the other elements of the installation.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

[Depewtee]

(Quoted from Sean) For the best efficiency, fuel consumption rate, and generator longevity, you want to engineer the rest of your conversion to operate the generator as close as possible to its rated output every time you run it.

Sean - You mentioned during your Thursday Bussin' 2011 seminar (I was watching the live Internet stream), and I have heard you mention it before, that you could function in Odyssey with a smaller generator.  Coming into this whole BusNut obsession I thought "the bigger the better" when it came to the genset, but after owning two buses with 12.5KW generators I am now convinced bigger is not always better.  My MCI has two 15,000 BTU roof airs and the Prevost has three 15,000 BTU roof airs.  Last summer the two in the MCI were more than sufficient in the humid Florida summer.  In the Prevost, we never used all three at one time.  In my humble newbie opinion, bigger generators are noisier, vibrate more, more expensive to maintain, and more costly to run - your quote above is spot on!  I need to do some calculating, but I am hoping when I replace the genset in the Prevost I can get by with a 7.5KW or 8KW model (I really like the idea of the Onan Quiet Diesel, though I am not sure I can afford one.  I am happy with the roll-your-own in the MCI and will likely go a similar route with the Prevost).

Brian S.

[luvrbus]

I really don't get it about running the generator at close to max most use the same head like 10 to 12 kw with the different kw ratings accomplished by the hp on the engine and that is pretty easy to change on most.
I know a bigger engine running at 1/2 the load will use less fuel than a smaller engine at full load and these new smaller diesel engines are not bad about wetness that I have been around 


good luck

[James77MCI8]

The RPM of a generator is determined by the number of poles on the generator armature. A 2 pole will operate at 3600 RPM for 60Hz . A four pole will operate at 1800 for 60Hz.

[Sean]

The RPM of a generator is determined by the number of poles on the generator armature. A 2 pole will operate at 3600 RPM for 60Hz . A four pole will operate at 1800 for 60Hz.

Not true for the inverter style generators mentioned above.  These generator heads produce a DC output and that is fed into an integral inverter to produce the desired frequency.  As such the engine RPM is varied by the generator control circuitry to produce the desired amount of power.  The prime mover operates at lower RPM for lower demand levels and higher RPM at higher demand levels.

Note technically that for constant-speed generators (not inverter units) it is the frequency of the generator that is determined by the number of poles and engine RPM and not the other way around as you presented it.  The engine RPM is determined strictly by the governor, which may be mechanical or electronic, and that in turn determines the frequency.

Many 60hz generators can be converted to 50hz models by changing the governed RPM, however at a loss of power rating.

You are correct that a generator with a single set of poles operated at 3,600 RPM produces 60hz.  Likewise this same generator operated at 3,000 RPM will produce 50hz but must be de-rated by 17%.  One and two sets of poles, while most common in low-power contractor, residential, and RV generators, are not the only choices.  Generators are also commonly made with three or four sets of poles.  A generator with three sets of poles need only turn at 1,200 RPM to produce 60hz power (1,000 RPM for 50hz) and this is an extremely common speed for generator prime movers.

Note also that the subject of generator poles can be confusing when one starts to talk about anything other than straight single-phase power, as the number of different windings goes up and how each winding passes through the various pole pairs is a complex subject.  It is not uncommon for a three-phase generator to have six separate windings and three pole pairs (six poles).

This site has a nice animation of the effect of multiple pole pairs on a single winding:
http://www.wisc-online.com/objects/ViewObject.aspx?ID=IAU14108

Note also that poles always come in pairs -- there is no such thing as a magnetic monopole.  I have a lazy habit of sometimes leaving the word "pair" out which is probably confusing and I should not do.

-Sean
http://OurOdyssey.BlogSpot.com

[TomC]

It is interesting to note the differences in engine speed between a constant speed generator and an inverter generator.  The constant speed generator (heavy duty Diesel) runs at 1800rpm.  While the inverter generator will be variable speed between 1600rpm and 2400rpm.  The inverter generator has to run at a faster rpm since typically the inverter generator uses a smaller engine then the constant speed.  Hence you could have a bit more noise with the variable speed inverter generator with all things being equal.  I personally don't like the inverter generator just because of the variable speed fact.  If you're running in hot weather with 2 A/C's on during the night, the generator speed will be rising and falling all night-for me at least would make for an uncomfortable night waking up with every change in engine speed.  This is why I like the constant speed generator-it creates a low drone that never changes (slight dip when a compressor starts).  Plus with a constant speed generator, you don't have all the electronics involved with an inverter generator that can (and do) fail.  Good Luck, TomC

[Sean]

... You mentioned during your Thursday Bussin' 2011 seminar ... that you could function in Odyssey with a smaller generator. ...

Yes, I did, and some here may remember that a year or so ago I was trying to make a trade right here on this board for something half the size or less.

The generator we have now came with the bus.  I ripped out all the start/stop wiring and safeties and completely rewired that system to make it much less complex and more reliable than the original converter had done.  We also relocated it, put a hush box around it, and remote-mounted the radiator with an electric squirrel-cage fan.

In hindsight, when it was out (and I had finished the rewiring) I should have tried harder to trade it for a unit half the size.

This generator is probably 15kW continuous, 17kW standby, and possibly made sense in the extremely inefficient original conversion, which had no natural ventilation whatsoever and even featured a 240-volt cooktop and household size refrigerator.  If I were buying a generator today, I would buy a 6kW model, enough to run three roof airs simultaneously with power to spare.  Everything else on the bus operates on the inverter and so with 6kW we could operate absolutely everything on board simultaneously.  With air conditioners generally cycling on and off at least during the night, that's plenty of capacity to recharge the batteries from any other daily needs.

I would expect a 6kW unit to use perhaps half the fuel that our current unit uses, and it would also require less oil, coolant, and other expendables.  The assessment we made at the time of the conversion, however, was that it would be a very long time (if ever) until the cost of the extra fuel and other items would surpass the cost of replacing the generator.  I would have needed to find someone willing to trade more or less straight across, but few people were interested in a generator with an unknown number of hours assembled by an unknown integrator.

The biggest problem we have is trying to get enough load on the darn thing once every few months or so to make up for any wet stacking and keep the cylinders healthy.

-Sean
http://OurOdyssey.BlogSpot.com