Quietening a generator

[Dave Osborne]

Well, it's all a matter of scale. The 500MW alternators at your friendly local power station do produce a very nice sine wave.

Coming down the scale, a 100kVA diesel genset provides a pretty good sinewave (certainly nothing to sneer at for the vast majority of applications).

Even smaller gensets down to 10 or 20 kVA will be OK if they have a quality alternator and a reasonably resistive load.

However, when it comes to very small generators (of the order of 1kW), the waveform is not so good. Rubbish alternators connected to underpowered, poorly regulated engines with very little flywheels mean that (among other things) the load regulation is poor, which leads to a squiffy waveform. Also, the pureness of the sinewave from a small alternator is dependant upon the characteristic of the load. If you put a 500W halogen floodlight on your 750W generator, you would get a pretty good sinewave. On the other hand, if you put a few compact fluorescents and a few switched mode battery chargers and the portable TV set on your

750W genny (only pulling about 150W total), these things add up to being a horrible non-linear load and the waveform would likely be all over the place.

[Andy Dingley]

Not enough cylinders to keep it rotating at constant speed, two strokes in particular. This isn't a big problem though, as the harmonic output of those is still pretty low. It's nothing like as ugly a waveform as most inverters.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Andy Dingley saying something like:

A cautionary tale: Last year I had three one-day-long power outages and was running the basics (TV, lights, UPS->PCs) from a cheapy Chinese inverter. Two months after the first outage the TV gave up, and I got it fixed for ¤30 (East-West chip fault). A couple of months after the second outage, the TV failed again, with a psu fault - again, ¤30 repair. I didn't connect the two at the time, but it became much more obvious when the TV failed shortly after the third occasion, with the same fault as the second time.

At the time it was a bit inconvenient, but it spurred me into biting the bullet and buying something new rather than spend any more cash on an elderly telly. Pity really, because it was a cracking set and I'd hoped to keep it going for another year or two.

Sure as shit, I won't be running the new TV on a crappy inverter. I will risk a laptop on a UPS, purely as a stopgap for the day.

[tony sayer]

OK point taken so if we have a rather light load on our Homebase 750 watt jobbie we may well get a half decent sine wave, but for the same power genny can we assume that an inverter type will produce better results..

Come to think of it the mains waveform round here, City area underground cable fed substation 400 yards away isn't that much cop;!...

[Dave Osborne]

I couldn't say Tony. I don't have any experience of using very small gensets for anything other than powertools. Any gensets I get involved with (for festivals) are usually in the order 60~125kVa 3-phase jobbies and with these, I've never had a problem with incompatibility of sensitive gear (including lighting control desks, video equipment, general PC's, etc).

Mostly get problems with caterers (1) with sh*t installations popping RCDs and (2) lying (or being clueless) about their max demand and popping the laughably inadequate 16A supply they ordered on overcurrent.