21-06-2012, 05:14 PM
Small Generator Voltage Regulation and Electronic Voltage Regulators
[attachment=25034]
We are all used to connecting electrical equipment to the local utility and getting all of the power that
our equipment demands. That’s because the utility is part of a grid that is powered by generating plants
with combined capacities measured in hundreds of millions of kW (kilowatts). Even a large industrial
load represents but a very small fraction of the capacity of the power available from the grid. So, when
you turn on your washing machine or home theater, the impact on the grid is so insignificant as to be
almost incalculable.
Small/Home Generators
Due to recent power interruptions caused by weather and other situations, many people have felt the
need to invest in small engine-driven generators in order to have power when utility service is
unavailable. Unfortunately, many purchasers have the expectation that their small generator will deliver
power just like the utility, and many sellers of these small generators do little or nothing to dispel this
notion. The truth is that small generators cannot deliver power in the same unlimited fashion that the
utility does. This may be why you could be having an issue with your small generator.
Small Generator Power Problems
In technical terms, the issue with small generators and their inability to provide smooth, steady power is
a matter of rotating mass and generator size.
To a small generator, the starting of a home appliance or tool can represent a significant step change in
load. For example, refrigerators, freezers, HVAC, etc. can all be seen as major changes in load to a
small generator. The small generator simply does not have enough rotating mass to absorb this change,
so the generator controls have to call on the engine to produce more power (torque) to permit the
generator to produce more electrical power.
As an analogy, imagine your 5 hp push-type lawnmower running into a patch of tall, thick grass.
Because of your mower’s engine size and the small mass of the blade, the mower bogs down in the
heavy grass. Now, think about cutting the same grass but with a 75 hp industrial riding mower; it
probably barely notices the heavy grass because of the power of the engine and the rotating mass of the
huge blade. Now, imagine mowing the same grass with a 10,000,000 hp mower, then you can get an
idea of the difference between getting your power from the utility and a small generator.
A Larger Generator
Buying a generator that is several times larger than the total load is not only expensive, but may not
solve the problems of a smaller unit. At very light loads, like less than 10% of the generator rating, the
generator may suffer from poor regulation. Running a generator at light loads can result in a problem
often called “wet stacking”. In this instance, engine exhaust gases condense in the exhaust
stack/muffler because the exhaust is not hot enough to evaporate the gases. You see this in car
exhausts (as water dripping out the exhaust pipe) when the car has not been driven long enough for the
muffler and tailpipe to heat up. Wet stacking can lead to premature failure of engine exhausts and other
engine problems.
[attachment=25034]
We are all used to connecting electrical equipment to the local utility and getting all of the power that
our equipment demands. That’s because the utility is part of a grid that is powered by generating plants
with combined capacities measured in hundreds of millions of kW (kilowatts). Even a large industrial
load represents but a very small fraction of the capacity of the power available from the grid. So, when
you turn on your washing machine or home theater, the impact on the grid is so insignificant as to be
almost incalculable.
Small/Home Generators
Due to recent power interruptions caused by weather and other situations, many people have felt the
need to invest in small engine-driven generators in order to have power when utility service is
unavailable. Unfortunately, many purchasers have the expectation that their small generator will deliver
power just like the utility, and many sellers of these small generators do little or nothing to dispel this
notion. The truth is that small generators cannot deliver power in the same unlimited fashion that the
utility does. This may be why you could be having an issue with your small generator.
Small Generator Power Problems
In technical terms, the issue with small generators and their inability to provide smooth, steady power is
a matter of rotating mass and generator size.
To a small generator, the starting of a home appliance or tool can represent a significant step change in
load. For example, refrigerators, freezers, HVAC, etc. can all be seen as major changes in load to a
small generator. The small generator simply does not have enough rotating mass to absorb this change,
so the generator controls have to call on the engine to produce more power (torque) to permit the
generator to produce more electrical power.
As an analogy, imagine your 5 hp push-type lawnmower running into a patch of tall, thick grass.
Because of your mower’s engine size and the small mass of the blade, the mower bogs down in the
heavy grass. Now, think about cutting the same grass but with a 75 hp industrial riding mower; it
probably barely notices the heavy grass because of the power of the engine and the rotating mass of the
huge blade. Now, imagine mowing the same grass with a 10,000,000 hp mower, then you can get an
idea of the difference between getting your power from the utility and a small generator.
A Larger Generator
Buying a generator that is several times larger than the total load is not only expensive, but may not
solve the problems of a smaller unit. At very light loads, like less than 10% of the generator rating, the
generator may suffer from poor regulation. Running a generator at light loads can result in a problem
often called “wet stacking”. In this instance, engine exhaust gases condense in the exhaust
stack/muffler because the exhaust is not hot enough to evaporate the gases. You see this in car
exhausts (as water dripping out the exhaust pipe) when the car has not been driven long enough for the
muffler and tailpipe to heat up. Wet stacking can lead to premature failure of engine exhausts and other
engine problems.