I have bought a 4 stroke genny from good old Nettos for under a 100 quid.
I am about to test it on powering up my house in the event of the next power
failure (of which we have many and prolonged...the last one was over 12
Other than a limit on th current drawn by things like kettles, cookers, hobs
etc how do the switched mode power supplies within user equipment like TV's
PC's videos, DVD's cope with a genny?...that is always of course providing I
limit the power drawn to the stated max of the genny.
I was thinking in terms of frequency control, or any harmonics which may be
there or spikes.
Anyone got experience of what not to connect to the generator please?
Modern electronics with switch mode supplies take the input and
immediately turn it to dc - so won't generally care about frequency or
harmonics and are pretty excellent at dealing with spikes too.
Of course, things like electric clocks will not have the same accuracy*.
Things like motors with high starting currents may trip the genny whilst
trying to get up to speed.
*Some modern (typically "lightweight" models) genny often generate at
high frequency, convert to dc and have an inbuilt, crystal-controlled
inverter for producing mains frequency output. These vary prime-mover
speed in response to load but keep their output frequency very accurate.
They use much less fuel on light loads than a normal genny. Much cheaper
to run, IME.
If you are planning to be out for hours, regularly, it may be worth
considering getting a couple of big deep discharge batteries and a good
charger and inverter. You then only run the genny on full load
(supplying the household load and fast charging the batteries). Then
have periods of blissful silence when the household load is being met
from the batteries alone. Typically, you can run the genny for an hour
and then have 4 hours running off the batteries - but it does depend on
batteries, loading, etc.
One problem with a small genny is the waveform tends to not be a
"perfect" sinewave but has a flattened top and bottom.
If you run the house off a battery bank and inverter, you will find that
the inverter's inbuilt charger section performs very badly off a small
generator. They usually are designed only for running off mains supply
when it is available. It typically needs a 6kW genny to run the inverter
and charge the battery bank, even when you are only loading it to 1.5kW.
Buy an inverter/charger designed to run off a small genny or get a
separate charger meant for the purpose.
Thanks for that...extremely informative but I dont want to go to the trouble
of providing power via batteries using a UPS.... the reason i bought a Netto
genny was because of its low cost, and to be frank the power problem I have
is local to my street rather than the town I live. If the problem develops
to become national rather than very local I may consider upgrading.
One thing I have found though is that the genny output voltage is quite
severely affected by load....and it seems a struggle to get it to strike up
I know its not quite IEE regs, but because of the (hopefully) temporary
nature of the installation I am feeding the house via the garage which is 10
yards away(normally it is the other way around). In this case the voltage
dropped to 200V and I have raised the voltage output to 220V or thereabouts
in the garage but it is obvliously quite low in the house (the cable feed
being 1.0mm2 should handle that ok) but the volt drop appears to be too
great. When I isolate the house supply from the generated garage supply the
genny output goes up to 280V on low load (6 garage lights)! It has to be
genny voltage control thats the problem because when its loaded to about
800W it drops to 220V.
Anyway...the good news is that it runs my central heating (the no. 1 reason
for having it) all my high efficiency fluroescents even the telly....and Ime
happy enough with that.>
Unless your meter is an (expensive) true rms type, its
readings will mislead you into thinking the voltage control
is not working.
Basically, as I mentioned previously, a small genny doesn't
produce a true sine wave under load - it has flattened tops
A true rms meter will show you what is really happening -
the genny voltage control is working and is maintaining a
near constant *rms* output voltage. But as the load goes up,
the waveform shape distorts and the peak voltage will drop,
as measured by a "normal" meter. The rms voltage will remain
For things that "use" the peak value of the mains - like
some chargers, as I mentioned, the effect can be dramatic.
Switch mode power supplies (eg computers) use the peak value
too - but have normally been designed to cope with a very
wide range of suppply voltages, so are ok. Things like
photocopiers and lamps basically "use" the rms value - so
don't care that the waveform is distorted either.
The proof will be an (incandescent) lamp plugged into the
genny and watched as your measured voltage changes so
dramatically as you put extra load on. The light should
hardly vary in brightness at all (it "uses" rms) - whilst
your meter ("using" peak) changes a lot.
If small genny manufacturers regulated on peak, rather than
rms voltage, your lamps would be going really bright and
really dim with every change in the load - and you very
surely would be taking it back to the shop...
The "lightweight" inverter-type small gennys synthesise the
sine wave output - so they don't have this problem. Their
waveform (and hence both the peak and rms values) remains
almost constant irrespective of load. They do have
disadvantages (particularly their ability to handle large
transients as they have little stored energy) - but
generally they are a pretty good idea unless you are trying
to power motors with large starting currents with them.
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