| There
are so many generators to choose from How do I make up my mind ?
In this
age of consumer freedom the choice for many items including generators seems endless,
this can make choosing seem somewhat daunting. Before you choose a generator you
may wish to consider the following : What
size of generator do I require: All electrical products have a data plate
with information regarding their power usage, for most power tools i.e. drills
sanders etc their listed wattage is all the power they require to run. Household
items such as central heating pumps, lights, TV's, Video recorders etc. fall in
the same catergogry. Items such as freezers, fridges, washing machines, some lawn
mowers are normally different, whilst they can state a wattage rating, due to
the type of motor they use can require a much greater requirement on start up,
when started they then require a smaller usage. If
you are unsure as to what power usage a product has it is always advisable to
contact the relevant manufacturers sales or technical dept, quoting model number
and requesting the START UP wattage & RUNNING wattage of your item. With this
information you will be able to determine accurately the size of generator you
require.
Do I require a Generator that has a long run fuel tank:
Generators are available in either standard run or long run versions. A standard
tank will last for 2-4 hrs, where most long run generators can run through the
night, if you are looking to purchase a generator for back up for powercuts then
we would recommend a long run tank machine.
Do
I want to run a Computer off my Generator :
Running home computers from a standard generator is not advisable, you
require a generator that utilises AVR (automatic voltage regulation such as the
Briggs Pro Max 4500A or a Inverter such
as the Honda EU & EM Range these systems
will give you more stable electricity than the mains. Please note !!! that as
a generator runs out of fuel, the engine is likely to surge. To avoid this affecting
electronic equipment an Uninterruptible Power Supply (UPS) can be used. These
are typically sold for use with computers so that data is not lost in the event
of a power cut. I
have bought a generator, and I am concerned about safety. Can I use a personal
power breaker? Answer
: The generator is configured differently to the mains supply. The generator
has a ‘floating earth’, whilst the mains has an earthed neutral. Whereas
it is definitely recommended to use a personal power breaker (RCD) from the mains,
for the majority of cases, it is not necessary to use one with a generator. The
generators are safe as they are designed.
Personal power breakers are designed
to operate from the mains. If one is to be used with a generator, then it is necessary
to modify the generator so that it is configured in the same way as the mains.
This is a relatively simple modification for a qualified electrician involving
adding a link wire from the neutral terminal to the earth terminal. However, once
the generator has been modified, it is necessary to then always use a personal
power breaker and to also always use an earth spike, which connects between the
generator frame and the ground. Since this is difficult to ensure, it is generally
recommended not to modify the generator. If
you still find that you are unsure as to what particular generator you require
either
Tel 01263 820202 Fax 01263 826190 or e-mail enquiries
@justgenerators.co.uk
Question
: I have bought a generator, and would like to connect it to my house in case
of mains failure.
What do I need to do? 
Answer
: When using a generator as an alternative supply to the mains, there are
several precautions that must be observed.
It is vital that the generator
is completely isolated from the mains supply. This ensures that the generator
is not attempting to power up the whole neighborhood, but also ensures that it
does not electrocute a utility worker trying to restore the mains supply.
To achieve
this, a double-pole, break-before-make, changeover switch must be installed by
a qualified electrician. Briggs & Stratton manufacture a manual transfer switch
for this application. Click Here To View the BTS9200M.
This should be fitted between the electricity meter and the building consumer
unit. The switch connects the building to either the mains supply or to a lead
which can be plugged into the generator.
Most
buildings now have an RCD built into the consumer unit. This is configured to
operate from the mains supply with an earthed neutral, and not from a generator
with a floating earth. To utilize this protection device, it is necessary to modify
the generator so that it is configured in the same way as the mains supply. This
is a simple modification for a qualified electrician, involving adding a link
wire from the neutral terminal to the earth terminal. It is recommended to make
this connection in the plug that is to be used to connect to the generator. This
ensures that the generator is unmodified when it is disconnected from the house,
and therefore remains safe.
The
plug should be labeled “Do not connect to mains: Neutral-Earth link fitted”.
The lead between the generator and the transfer switch is not protected by the
RCD, it is therefore recommended to use a steel armored cable for this connection.
Finally a local low-impedance earth spike needs to be installed.
What Type Of Sockets
do Generators Use: Generators
for use within the UK use the following sockets.
Please not the white
230V 15A Schuko sockets are for European use only. 
Question : What
is the difference between kW and kVA? What is Power factor? Answer
: There are 3 types of electrical: Real
Power, measured in Watts (W). This is the power drawn by a resistive load, e.g.
a heater element in a kettle, and has a power factor of 1. (unity power factor,
cos F=1, 1.0pf or pf=1) Reactive
Power, measured in Volt Amperes reactive (VAr’s). This is the power drawn
by a reactive load (a load with a winding around a core), e.g. an electro-magnet,
and has a power factor of 0. (zero power factor, cos F =0, 0pf or pf=0) Apparent
Power, measured in Volt Amperes (VA). Many loads have a combination of resistive
and reactive elements. (in fact it is not possible to produce a purely inductive
load, since the wire used to form the windings has a resistance). This combination
of elements means that both real power (W) and reactive power (VAr) are drawn
together. The
proportion of Real Power to Reactive Power is defined as the power factor. [Nearly
all resistive load (e.g. Universal motor used in hand tools) then power factor
0.95 to 1.0, nearly all inductive load then power factor ~ 0.3]
The vast
majority of single-phase loads have power factors approaching 1. Therefore, single-phase
generator power ratings are taken at power factor =1, and are consequently in
Watts (W) or kilo Watts (kW), where 1 kW = 1000 W. Three-phase
loads tend to have lower power factors, approaching 0.8, therefore, three phase
generator power ratings are taken at power factor =0.8 and are in VA or kVA. There
is obviously a relationship between real power, reactive power, apparent power
and power factor…. i)
Apparent Power (VA) = Ö [(real power (W))2 + (reactive power (VAr))2] And ii)
Power factor = Real Power (W)
Apparent Power (VA) Therefore… Apparent
Power (VA) x Power factor = Real power (W)
If the Power factor =1, then all
the Power is real, and
Apparent Power (VA) = Real Power (W)
(W = VA @
1.0 pf) For
a single-phase generator, the rating should be at 1.0 pf, in which case
Watts
= Volt Amperes.
But, for a three-phase generator the rating is at 0.8pf. This
is where confusion can arise! Example.
A three-phase generator has a continuous rating of 5 kVA at 0.8 pf. Now,
at this rated load, the Real power (kW) will be … Real
Power (kW) = Apparent Power (kVA) x Power factor Real
Power = 5 x 0.8 = 4kW This
means that a generator producing 5kVA at 0.8pf is actually producing 4 kW of Real
power, but it is also producing some reactive power. From
i)…
5000 VA = Ö [( 4000 W)2 + ( Reactive Power)2]
Reactive Power
= 3000 VAr’s It
is this combination of 4kW of real power and 3kVAr’s of reactive power that
has defined the limit for the generator rating. If
the same generator was loaded with a resistive load only, then it may be capable
of more than 4kW, however, there is no formula that can be used to find this limit
from the 0.8pf rating. It can only be found through testing of each machine.
Similarly, a single-phase generator rated at 4kW, cannot be expected to produce
5kVA at 0.8pf !!!!
Question
: Can I operate sensitive equipment from a generator? Answer
: The output from a portable generator is not as stable as the supply from the
mains. The speed of the engine driving the alternator is controlled by a simple
mechanical governor; consequently, the speed drops as the load is increased. The
frequency of the output voltage is directly dependent on the engine speed; therefore,
the frequency of the output varies with load. In addition, the output voltage
will vary with load, and with temperature. The output voltage of most standard generators
will remain within 230V +/- 10% from no load up to the rated load current quoted
on the dataplate. This is the guaranteed range of voltage supplied from the mains
utilities.
The
frequency of the output voltage will vary typically from 53Hz at no load to 49Hz
at rated load current, whereas the mains supply is unlikely to vary by more than
0.1 Hz.
Most electronic equipment is designed to cope with these fluctuations
and will operate normally. However, it is always recommended to ask the equipment
supplier whether their equipment is suitable to be operated from a portable generator.
As a generator runs out of fuel, the engine is likely to surge. To avoid this
affecting electronic equipment an Uninterruptible Power Supply (UPS) can be used.
These are typically sold for use with computers so that data is not lost in the
event of a power cut.
Honda Inverter Produces Power Stability
Computers
and power-sensitive testing equipment require what is referred to as "clean
power." Clean power is electrical current that is consistent and has a stable
"sine wave" or signal. If the lights or other basic appliances in your
home were being powered by a generator and there was a fluctuation in the AC power,
you’d probably see the lights dim and then return to full brightness—no
problem! However, if your computer was being powered by a generator and the voltage
fluctuated, chances are the computer would either shut down or at least interrupt
the program you were working in.
In
order to overcome this problem, Honda engineers developed a revolutionary form
of inverter technology. This process takes the raw power produced by the generator,
passes it through a special microprocessor that provides ultra-clean power that
boasts a sine wave equal to or better than the current from your household AC
wall outlet. This means that, you can operate a computer or laptop direct from
a generator.
Models Recommended Honda EU10i, EU20i, EU26i, EU30iS & EM70iS Click Here To View These Models
What
size generator do I need to start a motor ? Answer
: This is a tricky one, since there are many different designs of motor, each
with different characteristics
Some motors, e.g. Induction type motors (capacitor
start/capacitor run) require additional current to start them, therefore requiring
a larger generator.
Motors fitted to hand tools generally do not require any
additional start-up current.
Consequently, it is recommended to ask the supplier
of the equipment that you wish to run whether it requires additional start-up
current.
As a rough guide only, allow for a generator that has a continuous
rating of 2 ½ to 3 times the motor rating.
Motors can be rated in kW
or HP. To convert HP to kW, multiply by ¾.
E.g. What generator to
run a 3HP motor?
3HP = 3 x ¾ = 2.25kW.
This motor would require
a generator of between;
(2 ½ x 2.25) = 5.625kW
and …
(3 x 2.25) = 6.75kW
What
size generator do I need for my welder ? Answer
: A welder is rated by its output current. To estimate its input power, divide
the output rating by 30.
E.g. A 130A welder will have an input requirement
of approximately 130/30=4.3kW. A 200A welder will have an input requirement of
approximately 200/30=6.7kW.
This is only an estimate; therefore, it is recommended
to choose a generator of the next size up. However, bear in mind, that many users
will not actually require the full capacity of their welder, a smaller generator
would still operate the welder, but would limit the welding current.
|