On Mon, 29 Jan 2018 18:35:03 +0000, newshound wrote:

I rent some stables and a field where there is no mains electricity. I
manage with cordless tools for most jobs, and with a 900 W (inverter)
genny which will run the angle grinder, a mains drill, or circular saw
on the rare occasions I need them.

I'd quite like to use a larger Bosch shredder up there soon and I doubt
if the current generator will do it. I see that you can get basic
nominal 3 kW ones for between £200 and £300 (not inverter, obviously)
and I suspect these would run the shredder.

Aldi used to sell cheap 2.8KVA 4 stroke petrol powered emergency gensets
cheaper than that several years ago. My first one cost me 180 quid about
5 or 6 years ago. The following year they were selling them for a mere
150 quid. In the light of that, I think those cheap Chinese examples are
way overpriced (and that's assuming they were made to at least the same
shoddy standard as the Aldi unit!).

The last time I was checking out 3KVA rated inverter gensets (some 5 or
6 years ago now) to replace that entirely useless for my needs
conventional genset (see below), the lowest price point was around the
600 quid mark (a far cry from the 1800 quid being asked by Honda for
their i3000e inverter genset!). You might be able to purchase the much
more flexible inverter type 3KVA genset for not much more than the 300
quid priced Chinese units you've mentioned (are you absolutely sure
they're not the inverter type?).

At the time, even this price gave me pause for thought so I held back on
making a purchase. I suspect such inverter gensets will be a little
cheaper by now but I haven't checked out the pricing recently since I'm
hoping to snap up an Aldi or Liddle 1.2KVApk unit for a mere 150 quid or
less the next time they make them available. A recalculation of my
requirements suggests this might be all the emergency power I'll be
needing. In any case, I'll be able to verify compatibility with my
existing UPS before committing to a more expensive inverter genset
purchase.


I know these will not cope with the inductive load of a traditional
stick or MIG welder, but I've recently got one of the little Lidl
inverter stick welders (nice toy, BTW). I guess that might have a kinder
load characteristic, any ideas whether a cheap generator might cope?

Any other views or advice? I realise that hiring a petrol shredder would
be cheaper, but I like collecting things.


Inductive loading is the only type of reactive loading such gensets
*can* cope with (and take in their stride provided you don't draw more
than the genset's maximum current rating).

What such basic gensets can't tolerate is capacitive loading since this
causes self excitation of the rotor which the AVR module cannot
compensate for. For example, I discovered that a mere 4700nF (fluorescent
lamp ballast PFC capacitor) wired across the output terminals of a 230v
2.8KVA genset head was all it needed to send the output voltage north of
the 270v mark.

This proved to be the true nature of the "Dirty Mains Supply" so oft
referred to when powering electronic loads (particularly when such loads
are protected by a UPS) since the capacitance of the PSU mains input
filters could prove to be sufficient to cause the genset to start over-
volting.

In my case, it proved particularly problematical when the APC
SmartUPS2000 presented a couple of 4700nF capacitors effectively in
parallel across its mains input terminals, causing the genset to go north
of the 275v mark until the UPS switched to battery power which
disconnected the capacitors and the load from the genset which then
reverted back to its nominal 230v output, triggering the UPS into
switching back to 'mains power' which then set off another cycle of 'Bad
Mains Supply Voltage' triggered fallback to battery power ad infinitum
until I switched back to the Public Supply Utility's source of power (the
actual mains supply).

Since most households are now using a mix of CFL and LED GLS lamps where
most of the LEDs use a wattless capacitor dropper, a market for cheap
1.2KVApk inverter gensets seems to have opened up, creating a demand for
cheap mass production of these modestly rated inverter gensets which the
likes of Aldi and Liddle put on sale about every 12 months or so.

The small classic 720VA two stroke powered gensets if used just 'to keep
the lights on' are now more likely to result in blown lamps due to over-
volting from a largely LED lighting based lamp load which I suspect is
the reason for the appearance of relatively cheap inverter gensets (circa
150 quid in Aldi and Liddle stores... whenever they become available)
which are free of this over-volting response to both capacitive and
inductive loads.

--
Johnny B Good