# Diesel generator duty cycle

• posted

I am studying a diesel-electric propulsion system for an inland waterway boat to be sailed on the continent. This boat would have electric motor(s) powered by a large secondary battery, and the battery would be charged by whatever electricity I will find (exemple power outlet in a marina). But the main source of electricity would be a diesel generator. My project is to find the best compromise between the power needed to run the boat, the capacity of the battery and the power of the diesel generator. The way it would be used would be the following : The power of the generator would be something like 1/4 to 3/4 of the peak power required to run the boat. The battery would buffer the power so that at full power, the generator would produce part of the required power, the balance coming from the battery. The battery would be charged whenever the boat is idling or runs slowly -- an event that occurs more than often on a canal, because of the many locks to go through. In the case of high-speed sailing, the total run time of the generator would be more than the actual sailing time each day (typically we sail 6 hours, with a break for lunch). This occurs when sailing on rivers or large canals. In the case of low-speed sailing (such as in narrow canals), the generator would be more powerful than required. Remember that the power is roughly proportional to the cube of the speed, that is to say at half peak speed, only 1/8 of the peak power is required. I think it would not be a good idea to draw such a low power from the generator, since it would run with a less than ideal efficiency then. Rather, the generator would run for say one hour at full power, then wait several hours before the energy stored during this hour is spent by the propeller. Then the generator would restart, and the process resumes. I need an advice on the on and off periods that will perform best. I imagine that if the generator would be run for only five or ten minutes with maybe an hour of rest in between, it would run cold most of the time, which I think is not advisable. So what is the minimum period of time that would make the diesel work virtually without heat-up period problems? should the engine run at partial power for the first minutes, or can it run at full power from start time? How would the expected lifetime of the engine be reduced, as compared to a continuous operation? would this require a special maintenance (oil change, etc.)? Any comments welcome. Sorry for this lengthy text. Jean-Marc

• posted

What voltage battery are you going to use, and what HP are the propulsion motors?

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

• posted

I did not decide for the voltage yet, I am concentrating on the power for the time being. According to my estimates, it can be something like

21 kW for a 43-foot l> >
• posted

Well, you'd not want to go much less than 48 volts for that kind of power, and

110V might be better to reduce cabling losses.

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

• posted

and 110VDC will not only kill you, it will also cook the corpse

the OP's idea is bloody silly

he needs a constant duty generator running 12 hours a day and two motors on the same shaft, one high power for when the donkey is running, and one low power for accumulators only

basically he's copying WW2 submarine propulsion, it's going to be EXPENSIVE

the generator needs to be MORE powerful than the main leccy motor, the shore power he is planning on using better be 3phase, the way he wants to do it is impractical and he clearly hasn't done ANY of the sums.....

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diesel - electric (sans batteries) is viable, but for a ditch crawler the hull shape doesn't load in favour of this separation as much as it might in a seagoing hull.

drawing 20kw DC from a battery bank is 200 amperes at 100 volts DC more or less

deep cycle batteries you're looking at a 5 hour rate tops, as he wants to draw this sort of current for 3 or 4 hours.

100 Ah deep cycle traction cell may give you 3 amps at a 5 hour rate, and thats a 2 volt cell, 50 of em in series for your 100 volts and and you do not have 50 times the capacity, you have 50 times the voltage, you have to parallel batteries to increase capacity...

a 40 foot LWL ditch crawler will move along nicely on 5kw, if you use the right prop.

5kw on a 48 volt system, much cheaper and easier to source parts, is 100 amperes.

12 deep cycle traction cells in series get your 48 VDC

100 amperes on a 5 hour rate you're looking at something like 1100LL's, provided you fit cooling to them, 200 x 550 x 600 mm each cell, for a DIN43531 bank, 950 odd kilos for the entire bank (oops, there goes trim) 95 mm cross section area cable, the diesel might as well be AC, then you only have to buy one battery charger and charge controller whether running off shore power or diesel, but it's still take about twice as much juice on 240 VAC as you can pull through a single 13 Amp plug so you're back to 3 phase.

don't even THINK about asking "how much" because it will make a new quality diesel engine installation look cheap, then there's all the health and safety and rules and regulations and insurance and certification stuff.

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