That Fischer Panda
is a pretty good model of how not
to design a small genset. This is absolutely horrifying: Fischer Panda: The Final Chapter
. The multitude of engineering problems with this device are extremely well documented here.
One of the things mentioned in the Sail Whisper blog is that the Kubota 1-cylinder diesels are rated (according to Fischer Panda) for only 1500 hours service
life, and cannot be used at rated power for long periods. Fischer Panda told him that anything over 125 amps is "overloading" the genset. That's 1.6kW; less than half of the advertised power of that genset. Yikes.
Other comments on the one-cylinder Kubota engine
"They used a 2cylinder Kubota. Mine was a one cylinder model
. They run at a much higher RPM
, and thus produce more heat, and heat is the enemy of mechanical stuff. Mine ran at a crisp 2800rpm, and was so loud even the guys with the reefer units would park elsewhere. It lasted about 3 years, then puked coolant
out the top and died. Disposable engine
. 7hp commercial
rototiller engine I later found out."
Marine Generator. Low revs or high revs?
I like Lloyd's generator
very much, much better than the Fischer-Panda. But if I were designing a bullet-proof, trouble-free small genset for cruisers, I would do it somewhat differently. For one thing, I would not use the one-lunger Kubota engine at all, much less at its maximum output, trying to produce 3.6kW of power, which based on all of the above reports seems like a recipe for trouble to me.
I would make it as simple as possible, and I would make it "open source" -- which means (a) designed with the most commonly available, off-the-shelf parts
possible; and (b) designed with as many parts
as possible which can be easily fabricated in a third-world machine shop; and (c) publish all of the engineering drawings so that parts can be made up in the field.
I would make it extremely simple, and I would significantly derate both motor
for trouble-free and long life.
I would probably use the two-cylinder Kubota and derate it to 1800 RPM
or so. Driving with double v-belts an off-the-shelf schoolbus alternator
like a Leece-Neville or Prestolite which can be rebuilt anywhere by any third-world auto electric
shop. Best of all if the alternator is the same one you are using on the main engine -- then you can keep one whole spare alternator for both positions and Bob's your uncle. Alternator derated to about 70% of its maximum power. Regulated with a common three-stage regulator
like a Balmar
or Adverc (again, best of all if this is the same regulator
you are using on your main alternator -- one spare for both applications).
Power take-off like Lloyd's for refrigeration
, hydraulics, dive compressor
control system at all and no electronics
(other than the off-the-shelf regulator). Hand throttle, by cable if necessary (if direct access to the genset is awkward). You watch the current
draw and throttle down manually when you need less power. Thus one less complex component to fail.
from the Yanmar
parts bin, and mounted in a way that just about any old marine heat exchanger
lying around can be used in a pinch (and drawings supplied for fabricating one in a real pinch). Ditto with the water
pump and exhaust elbow
. Location of all of these parts designed for totally simple accessibility from one side, with plenty of room to get to everything.
Who would like a genset like that?
To my mind, a DC generator really only has one significant advantage -- you don't need an accurate RPM control, and you can vary the motor speed for quieter and more efficient running at lower loads. That is because converting AC to DC or DC to AC is just not a problem if you have a modern inverter/charger, so I really don't think you care whether you are getting AC or DC power from your generator.
Therefore, low speed, heavy duty AC gensets, available off the shelf, fulfill most of this mission. They have simple air-cooled alternators which are rarely used at maximum output. They use simple, heavy duty, low-speed, large displacement
, three-cylinder Yanmar
or Lugger engines which at max load are still only putting out 50% or less of their designed maximum power.
makes a 4.5kW marine
genset which I often drool over. For anyone with space for it (and it's quite small), that is just as good a solution as my Open Source Genset, I think, in most respects. And it would have one huge advantage in being much quieter. Disadvantages are that it is more expensive, heavier, and bulkier, and has proprietary parts. But if you take care of a genset of that type, you will rarely need any parts at all, proprietary or otherwise.