"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Stuart wrote:

Recently took delivery of the Wolf 800 Generator, at just under a 100
notes I thought it would come in handy for our all too common power
cuts, not much output at 650 watts but will run the gas central
heating and the tele!

Reasonabale little genny set it up runs fine does the job i want,
however looking thru the instruction booklet I came accross the
following table, http://www.stuartstuart.fsnet.co.uk/misc/gen1.jpg
and I am clueless to what it is going on about, maybe someone on this
group can explain.

Lighting,
Power Factor = 1
Load = ~650W

Power Tools
Power Factor = 0.8 ~ 0.95
Load = 520W

Electric Motors
Power Factor =0.4 ~ 0.75
Load = 220W


The first bit seems reasonable enough, use lighting up to its max
output of 650W

The next two bits is where I am getting confused. Is there some
difference between a power tool and an electic motor, after all I
can't think of a power tool that dosn't have an electric motor!
(maybe a Soldering Iron ?) So what does it all mean? Presumably the
power factor is a percentage, so power tools 80 - 95% of 650Watts.
does this mean that the (80% 0f 650=) 520W is a minimun, if it is the
maximun then what does the 95% represent?

Anyway, I have plugged it all in and it does what I want, but I am
curious as to what that table is all about, I have emailed the
manufacturers but I won' hold my breath for their reply!

Another Question, can these types of generators ever damage TVs,
Videos or computers? should I use a surge protector?

Let me have a go at a simplified version of John Rumm's explanation.


Or even more simplified. There are two different types of Electric Motor,
Inductive, which doesn't use carbon brushes to make it work, and Power Tool
Electric Motors that do use carbon brushes to make it work.

Inductive loads have a huge variation in the voltage and current they draw from
a gennie, and cause the output to swing positive and negative a lot more,
especially on start up, than an electric motor that uses carbon brushes to send
the voltage and current through the winding coils.

The table seperates them into two catagories of "Electic Motors" and "Power
Tools" and that's the only difference.

Simple.

For any AC device, the voltage and current are not constant - but vary
sinusoidally (as in a sine wave) 50 times per second.

When the load is purely resistive - as in a normal light bulb, or soldering
iron - the current is exactly in phase with the voltage - i.e. the phase
angle is zero.

When the load is reactive - as in electric motors etc. with capacitance
and/or inductance - there is a phase shift so that the current is no longer
in phase with the voltage, but leads it or lags behind it by a phase angle,
which varies from device to device.

In all cases, the power consumed is calculated by multiplying the RMS (Root
Mean Square) Voltage by the RMS Current by the Power Factor - where the
Power Factor is the cosine of the phase angle.

Your generator is apparently capable of delivering 650 watts for resistive
loads (where the phase angle is zero, and the power factor is 1). So, at
240v, it can deliver a current of 650/240 = 2.7 amps.

But it can *still* only deliver 2.7 amps when reactive loads are used. So if
you have a device with a power factor of 0.4 (phase angle 66 degrees), you
only get a power output of 240 x 2.7 x 0.4 = 260 watts rather than the
original 650.

As someone else said, the generator has an output of 650 VA rather than 650
watts. This is a measure of volts x amps (ignoring phase angle) and only
equates to 650 watts for purely resistive loads.

HTH.
--
Cheers,
Set Square
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