Atleast 5 Demerits of .. Dc motor & AC Generator?
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A/C generators:
They have the disadvantage of requiring transformers, which complicates the circuitry. They must be designed so that the higher voltage on one side doesn’t discharge (arc). High voltages are not generated efficiently, so low voltages are generated and the voltage has to be transformed to a higher level for long-distance transmission .safety-related disadvantage of A/C is the increased danger of electric shock due to the use of higher voltage for long-distance transmission. This is why long-distance transmissions use power lines kept high up off the ground.
especially the high rpm models (due to having a smaller engine and a cheaper alternator for the same power output) are that they are unreliable, or at least in harsh duty service. A correctly-specified DC generator is more reliable. It is used to charge 12v, 24v or 48v battery banks connected to inverters.
In my experience 3kW is the heaviest load that should be used for this application, therefore people who want to run A/C and freezers must use an AC generator. To get an AC generator with even the minimum of acceptable reliability on a boat, it is necessary to choose the largest capacity diesel (therefore physically the largest engine) at 1,500rpm with the most capacious sound cabinet (or preferably none) that is available. Cutting costs on a boat AC generator purchase is the single worst mistake in fitting-out, and it leaves people regretting their error permanently. Generator breakdowns leaving the boat stuck in port are a common complaint on forums. There are just so many issues with these generators, the list is endless. For example: does your sound cabinet include a high-output fan directed exclusively onto the alternator, to cool it? Does it have a dead fan alarm? If not, chances are the alternator is going to fry one day. And so on.
Diesels are almost exclusively used on boats for a number of reasons. A petrol (gas) AC suitcase generator may be used on smaller boats with no space or budget for a diesel generator, if the load is small, typically less than 1kW. These are used to run laptops and hairdryers, and similar.
DC motors:
High initial cost
Increased operation and maintenance cost due to presence of commutator and brush gear
Cannot operate in explosive and hazard conditions due to sparking occur at brush ( risk in commutation failure)
Speed regulation in the series motor is quite poor. With the increase in the load speed of the machine decreases, DC shunt motor maintains almost constant speed from no load to full load.
With decrease in the speed torque of the dc series motor drops sharply.
DC series motor should always require being loaded before starting the motor. Therefore series motors are not suited for the application where load on the motor is completely removed and where motors are driving the belts.
Mishap to the belt leads to motor operates on no load and attains dangerous speeds which damage the motor.
They have the disadvantage of requiring transformers, which complicates the circuitry. They must be designed so that the higher voltage on one side doesn’t discharge (arc). High voltages are not generated efficiently, so low voltages are generated and the voltage has to be transformed to a higher level for long-distance transmission .safety-related disadvantage of A/C is the increased danger of electric shock due to the use of higher voltage for long-distance transmission. This is why long-distance transmissions use power lines kept high up off the ground.
especially the high rpm models (due to having a smaller engine and a cheaper alternator for the same power output) are that they are unreliable, or at least in harsh duty service. A correctly-specified DC generator is more reliable. It is used to charge 12v, 24v or 48v battery banks connected to inverters.
In my experience 3kW is the heaviest load that should be used for this application, therefore people who want to run A/C and freezers must use an AC generator. To get an AC generator with even the minimum of acceptable reliability on a boat, it is necessary to choose the largest capacity diesel (therefore physically the largest engine) at 1,500rpm with the most capacious sound cabinet (or preferably none) that is available. Cutting costs on a boat AC generator purchase is the single worst mistake in fitting-out, and it leaves people regretting their error permanently. Generator breakdowns leaving the boat stuck in port are a common complaint on forums. There are just so many issues with these generators, the list is endless. For example: does your sound cabinet include a high-output fan directed exclusively onto the alternator, to cool it? Does it have a dead fan alarm? If not, chances are the alternator is going to fry one day. And so on.
Diesels are almost exclusively used on boats for a number of reasons. A petrol (gas) AC suitcase generator may be used on smaller boats with no space or budget for a diesel generator, if the load is small, typically less than 1kW. These are used to run laptops and hairdryers, and similar.
DC motors:
High initial cost
Increased operation and maintenance cost due to presence of commutator and brush gear
Cannot operate in explosive and hazard conditions due to sparking occur at brush ( risk in commutation failure)
Speed regulation in the series motor is quite poor. With the increase in the load speed of the machine decreases, DC shunt motor maintains almost constant speed from no load to full load.
With decrease in the speed torque of the dc series motor drops sharply.
DC series motor should always require being loaded before starting the motor. Therefore series motors are not suited for the application where load on the motor is completely removed and where motors are driving the belts.
Mishap to the belt leads to motor operates on no load and attains dangerous speeds which damage the motor.
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