are available as built in or portable units. Built in models are usually
only found in larger motorhomes, the emphasis here is the smaller
The aim is to produce a stable and constant voltage and frequency, for
Australia this is 240V at 50 Hz.
Portable generators are
available with 2 stroke and 4 stroke engines.
Models are available with electrical outputs of 240V AC from 150 VA to
over 5000 VA and often with a 12V battery charging output ranging from
60 to 150 Watts.
Many are understandably confused with the term VA and how it is related to
AC generators are almost always rated in VA (Volt-Amps) rather than Watts.
Put as simply as possible VA = Watt when the load is resistive (such as a
However most AC loads are reactive (such as electric motors, transformers)
where current and voltage are out of phase to varying degrees.
The degree to which they are out of phase is known as the power factor
By definition, power factor is the watts consumed by the load divided by the VA necessary to deliver that power.
The relationship between between watts, volt-amps and power factor is . . .
= W / pf
= VA x pf
= W / VA
generator manufacturer doesn't know what the load will be they rate their
product in VA or occasionally Watts @ pf. For example the
manufacturer may express the rating for a particular generator as 1 KVA or
800 W @ .8 pf . (Of course 1000 VA is the same as 1 KVA)
Conventional Two Pole Generators.
Ignoring the new inverter models, this requires an engine speed as per the
( Hz )
generators are almost the exclusive domain of larger stationary and marine
units due to the physically larger generator and also engine which must
produce the required power at lower RPM.
These generators all require mechanical engine speed governors to maintain
a constant frequency and some form of electrical regulation to try to
maintain a constant voltage under varying load conditions.
When selecting a generator you need to be aware that the name/model does
not necessarily indicate the real output power for us in the 50 Hz part of
Because most generators are made for the world market, the model name is
usually related to the maximum short term output at 60
The exception to this is inverter generators and locally manufactured or assembled
conventional two pole generators for the local 50Hz market.
To use a fictitious example, the "Supagen 1000", refers to the maximum 60Hz output.
In this case a typical output would be . . .
As you can
see the "Supagen 1000" is really only capable of 640VA continuously
at 50Hz, not 1000VA as many may expect.
Why the difference between the 50 and 60 Hz rating ? Because the power of these
small engines in this RPM range is almost
directly proportional to the
RPM. In other words engine power at 3000 RPM is 20% less than at 3600
RPM and this is translated to a corresponding 20% reduction of the
electrical output capability.
Often the de-rating from 60 to 50Hz and maximum to continuous may be a
little less than my example but it's fairly close, if you use 20% in both
cases, you will be erring on the safe side.
The new inverter generators are quite different in design. The engine
is coupled to a multi phase alternator which produces an output that is electronically
converted to a stable single phase 240V at 50 Hz.
Because the engine speed does not
govern the final frequency or voltage, only the output power, the engine can idle when
power demand is low and can spin at 5000 RPM or more at maximum output.
This results in both engine and alternator being considerably smaller and
lighter for a given KVA rating. Another benefit is a much cleaner and more stable output and
lower noise levels when operating at the lower output.
The photo on the left shows the new Yamaha 1KVA inverter generator weighing
only 13 Kg.
The day is coming soon when all small generators, particularly
portable ones will be inverter types. Not only for the reasons
just given but manufacturing costs would have to be lower
too. Pity that isn't reflected in the present retail
price, hopefully it will when they become the norm.
What size generator do you need
Of course this depends on what you want to operate, where you
want to use it and how much can you comfortably lift.
You must be realistic here, to comfortably lift it in and out of the
storage area, you really don't want to exceed 20-25Kg and if you don't want
to invoke the wrath of neighbours and rangers look for noise levels of
60dB/7M or lower.
This will almost certainly rule out powering your air conditioner but may include the micro wave oven.
(An exception is the new Honda EU20i - with an output of 1.6/2.0 KVA,
59bD/7M, 21Kg - which will run a small air conditioner**.)
I should also mention that the 12V output of these generators is almost
always unregulated and suitable only to charge a 12V battery, it shouldn't
be connected directly to a load.
The output, often peaking 18V and more under no load conditions will most
likely be detrimental to devices directly connected.
Even 12V batteries will need to be monitored to ensure they are not overcharged,
although a generator is not likely to be run long enough for this to be a problem
Remember when calculating a generator size to allow for loads that require
a high initial starting current such as electric motors, particularly in
The micro wave oven is another appliance that is often misunderstood.
When calculating the size generator you would need to run the micro wave, you need to appreciate that the advertised power rating is the RF cooking power, the total power consumed by the microwave oven is approximately double that. For example, a 600W microwave will consume around 1200W.
In our application where we want to operate them with an absolute minimum of
impact on the environment and any neighbours, we should be looking at a
quiet four stroke model.
In my own case the generator, a Honda EM650, with an output of 2A @ 240V
and 8.5A @ 12V is an excellent backup for the times when the solar
panel/battery/inverter system can't satisfy needs. It has the
ability to simultaneously run the fridge, TV, video, laptop computer, lights and charge the
I find this a very useful size for caravanning.
This model weighs 22Kg and noise level of 54dB/7M.
Reason for choosing this particular brand and model - small, very very quiet, light(ish),
very reliable (always first pull starting), spare
parts readily available, good "old fashioned" technology (repairable and rebuildable).
Frequency stability is good, voltage stability is acceptable and wave
form distortion, well that's another story although it's no worse than others in
this capacitor regulated class.
Although rated at 8.5A for battery charging purposes, like most others,
it will only do this into a dead flat battery. Once the battery
starts to charge, this falls off rapidly so that when battery is only half
charged, charging rate is only a couple of amps.
this, I have built a battery charger tailored to the characteristics of
this particular generator. It will now charge a battery initially
at 20A falling to 15A when fully charged. (Obviously, putting 15A into a
charged battery for any length of time is not desirable so this must be
constantly monitored manually or I have provided for the ability to fed in
to my PL20 regulator.)
I am sure there are other brands that fall into this category but
when I have inquired about availability of parts, I have come away less
For the same weight and noise level and three times the output, the
Honda EU20i inverter model previously mentioned is the only new model
that fulfils my same criteria that is available at the moment (except for
the "old fashioned" technology), that I know
about. It also has the advantage of most inverter models, that of
excellent voltage and frequency stability and low waveform
distortion. If I could justify an outlay of $2200, this would
be my first choice. (Aust dollars Feb 05)
Update April 07
If you shop around and at caravanning shows,
the EU20i can be had for A$1750.
Also, in and email from Pat & Ralph Michod, "We also have a Honda 20i which is 4 years old and running sweet as a pie. It runs the A/C in the van with no effort, it is very miserly with
fuel, runs caravan frigde & Waeco for 11 hours on a tank of 5 lt. Hope this info is of some help."
and in a later email from them "The A/C is an Air Command Heron Q 2.5kw heat & 2.5kw cool max current draw of 5.5A and is tested by Air Command on that Gen."
If I had a medium size motorhome or much larger caravan, another Honda,
the EU30iS on a slide out mounting would be my choice for $4100, (also inverter type,
electric start, 3 KVA, 58dB/7M, 59Kg) or the new Honda EM50is for $4550
(inverter model, 5 KVA, 62-68dB/7M, 95Kg)
Also, another good choice in this larger class are three new Yamaha inverter models,
the YG2800i (2.8 KVA, 67dB/7M, 30Kg - yes 30Kg), the EF3000iSE (electric
start, 3KVA, 57dB/7M, 67Kg) and the EF3000iSEB (electric start, 10 sec 500W
boost feature, 3KVA-3.5KVA, 57dB/7M, 68.3Kg)
** See Honda Aust
brochure HE 5781 09/02
Recently a range of portable generators has flooded the Australian
market originating from China. They have various brand
names reflecting the identity of the importer.
I was originally sceptical of their worth but at the price asked, I have
come to believe they may
be good value.
For example, what looks like a clone of the Yamaha ET900 that used to sell
for around $900 is available for $149. I even saw it briefly on sale
for $98 by a major retailer.
( However, it is a two stroke so I wouldn't recommend it for reasons given
Also available are fully enclosed "suitcase" four stroke models
rated at 850VA @ 50Hz for around $600, almost half the price of a
As recently as last week, I looked at a 1.2 KVA inverter model for $800,
half the price of the Japanese equivalent.
How do they compare with the major Japanese brands, probably like a Hyundi
compares to a BMW, although should be quite serviceable.
I have spoken to some owners of these generators and have not heard many
While I haven't had the opportunity to personally explore the quality of
construction of any of these generators, I have been favourably surprised
with the quality of several Chinese built electrical devices that I have
pulled apart recently (and not ones built for Western or Japanese
companies). But I have also seen some absolute garbage
including some very poorly designed and dangerous DC/AC
inverters. The problem is that you can't tell without looking
If you do purchase one, I think it would be wise to give it a lot of
running time within the warranty period and if they come through that OK
they should last with occasional use for some time.
A major downside as I see it would be the availability of spare parts for
the proliferation and turnover of "brands" &
models. You may well have a worthless piece of junk once
the warranty period is over.
Another downside I fear will be that, unfortunately, many thoughtless
caravanners will take advantage of the very cheap price of the two stroke
generators and we will have to put up with the smelly things at our
They should have a beneficial effect of reducing the exorbitant retail
price of Japanese models too.
(Several years ago
when I was pricing a Honda EU10i, the most often quoted price was (from
memory) around $1600 but one retailer was happy to sell me one for $1200
claiming he was still making a reasonable margin.)
Would I purchase one for a primary source of power - definitely not, would I purchase
one for occasional non critical use - maybe.
But remember, buying one of these rebadged Chinese imports is a lottery,
you may pick a winner - you may not.
A readers contribution on the subject of cheap generators. Jan 05.
The following is an email I received which you may find interesting, I have
included it un-edited.
I was looking at your website to find some information regarding
generators, thank you for clarifying some issues, and noticed that you made
some comments about the cheap Chinese imports maybe being worthwhile.
I will relate my experience with one of these and you may wish to
We bought a GMC from Bunnings as these carried a two year warranty against
the Scorpion (one year) being sold by ( I think) Repco and various ther
brands being flogged by others some with only six months warranty.
The cost was $189. I had been warned by other grey nomads to check that all
the bolts were tight so I duly did this as several were a bit loose.
I then filled the tank with the required 50:1 mix and noticed that it
leaked fuel like a sieve.
Tightening the screw at the bottom of the carby solved that. I then
started it up and put a AC voltmeter on the output, it read 180 volts.
I found the throttle control and adjusted that to 250V. Connecting it
to our caravan batter charger/regulator (switchmode type) promptly dropped
it back to 200V and then it fluctuated between that and 300V as the charger
altered the load. After talking with more grey nomads on the road I
also plugged a 60W globe on the output and that seemed to stabilise it a
bit, fiddling with the throttle I could get it to stay in the range of 200V
to 270V. That was fine while the charger was in the "BULK"
and then "ABSORPTION" modes but as soon as it went to the
"FLOAT" mode the load reduced and the voltage shot to 350V.
I have solved this by cuting it off in the absorption mode when the battery
monitoring voltage gets to 14.2VDC, I realise that the battery is only
about 85% charged at this point but after burning out a couple of
powerboards by not cutting it off quickly enough I decided that I would
live with this. After reading your piece I now understand that the Hz
rate probably also fluctuates wildly as a result although I have no means
We are now in the market for an inverter (ACV stable) generator.
I hope that this may help someone in a similar situation and prevent some
John (on the road somewhere)
It is worth noting that most small generators, including premium Japanese
brands, utilising (cheap) capacitor regulation suffer from some degree of
voltage instability and less than perfect waveform which is improved by
adding a resistive load such as John's 60W light globe.
(However, expect voltage variations of 210V to 255V from no load to maximum
load with this type of "regulation", often worse but anything
like John's is totally unacceptable rendering the generator practically
On the occasions that I run our little Honda EM650 generator, I load
it up with the 3-way fridge's 240V 175W element for this very reason (saves
a bit of LPG too).
Generators with "proper" voltage regulation, often termed AVR
(automatic voltage regulation) or some similar terminology are considerably
better in this department.
However I would only purchase a known and well supported brand with AVR.
(Almost all generator faults with which I have been associated over many
years have been a failure of the electronic regulation circuit, and be
aware, the cost of all the AVR circuit boards I have seen has been
astronomically high, often rendering small generators to the scrap
heap. Most are not repairable, being either potted in epoxy
and/or having their components defaced, forcing you to buy a new
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