Power Cuts/Generators yet again

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I'm not quite sure why you'd want a microwave to work as part of an emergency installation. Fine if you're providing a *proper* standby generating facility, but few would - unless they live somewhere subject to frequent cuts. Surely some form of calor gas cooking would be easier for emergency use - assuming you don't have mains gas and can't just use a hob.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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In an earlier contribution to this discussion,

I guess it's simply a matter of keeping my options open. We have gas for the central heating of course - but an all-electric cooker! I'm thinking of a situation where power lines get brought down by ice and where it takes the electricity board 2 or 3 days to restore the supply. [This *did* happen to some near neighbours of ours a few years ago - who are fed from a different sub-station from ours]. Provided the path from the house to the caravan is not blocked by a 6 foot snowdrift, we would probably use the caravan's cooker, powered by propane. Even so, the microwave would be useful for thawing any frozen food we may wish to eat.
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In an earlier contribution to this discussion,

Well, I'd do it with the widow - or even door - open. More likely, I'd put the generator outside - but I'd then need to keep the electrics dry if it rained.

My microwave is rated at 650watts cooking power - but when I measured the actual consumption with my plug-in meter it was just over 1200 watts. That's why I said I would need the 1600 watt generator rather than the 900 watt version.
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On Sat, 10 Jan 2004 23:36:50 -0000, Set Square wrote:

Under an upturned wheel barrow with the handles supported on a couple of garden chairs? Have the barrow facing into the prevailing wind direction to minimise rain blowing under.
Also I suspect the smell might penetrate rather deeply into any soft furnishings. Are these little Hondas 2 or 4 strokes?

But your probable other load is 250 x 2 for the freezers and 150 for the CH = 650W. You only have 400W "spare" on the 1600W when it's driving the uWave. I guess you could switch the freezers off use the uWave and then (hopefully!) remember to switch them back on again...
Not to mention that all those loads are probably pretty inductive, that always brings in some derating of a genny.
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In an earlier contribution to this discussion,

They're 4 stroke.

Yes, I wouldn't run it all concurrently - see my previous post.

Ah, now that's interesting! The little plug in volt/amp/watt meter which I have bought also displays phase angle as cos-phi (can't do Greek symbols in plain text!). What use should I make of this information when determining genny load?
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On Sun, 11 Jan 2004 12:37:42 -0000, Set Square wrote:

Was that ScrewFix? I remember the price 20. I have one but that's more sided to costs rather than techy things like V I phase difference. It also doesn't like light loads (below about 50W).

Donno, only did AC theory up to A level, 25 years ago and not used it since. That's what google and the web is for... B-)
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In an earlier contribution to this discussion,

No, I got it from Machine Mart. It's made by brennenstuhl - and the model is PM230. It incorporates a 13A plug and socket, and has an lcd display - plus several buttons to select function/mode etc.

Ah, well I did it over 40 years ago - and it's sort-of coming back. I seem to remember that watts = rms volts x rms amps x cos(phi) - where phi is the phase angle [so that cos(phi) is the power factor (= 1 for a phase angle of zero or less than 1 for a non-zero phase angle, as with an inductive load)]
Assuming that is correct, how do I use it to de-rate my genny? For example, when the CH is running, it is taking 118 watts = 240v x 0.56a x 0.88 Should I multiply the volts and amps together and ignore the phase angle to get 134VA - and treat this as 134 watts as far as the genny is concerned?
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On Sun, 11 Jan 2004 18:04:36 -0000, Set Square wrote:

25.00ish inc VAT and delivery. Tempted but there is a dearth of any real information on the net including the Brennenstuhl site. B-(
Any chance of posting up a spec sheet for it? Always assuming that information is supplied with the unit... Nearest Machine Mart is Carlisle (50+ miles RT) and we rarely go to Carlisle.
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I bought one from Maplin a while back when it was on special offer (12 IIRC). I compared it with a true power meter, and there are some load types for which it wasn't very accurate. I don't seem to recall what those were now though.
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On 12 Jan 2004 01:28:05 GMT, Andrew Gabriel wrote:

Well I wouldn't expect a precision instrument for <20. B-)
I have an "Econometer" bought about 10 years ago which is pretty good for loads above 100W or so but anything less is is decidely doubtful. What is the minimum power this one says it'll measure?
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I don't think it says. The display goes down to 0.00W. Just tried a few wall-wart PSU's in it with no load on them. Two registered 7W (but are clearly nothing like that), and a third registered 0W.
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In an earlier contribution to this discussion,

You can see brief details at http://www.machinemart.co.uk/product.asp?p 0916213
The spec printed in the instruction leaflet says: Operating Voltage: 230V~ 50Hz Operating Current: Max 13A Lowest measurable current: 0.02A Voltage Display (VAC): 190v - 276v Current display (amps): 0.00A - 16.00A Wattage display (watts): 0W - 4416W KWh display (in kWh): 0.00 - 999.99 kWh Frequency display (Hz): 40 - 70 Hz Power factor display: 0.20 - 1.00 ACCURACY: Voltage: +/- 3% of measured value Current: +/- 3% of measured value +/- 0.04A Wattage: +/- 5% of measured value +/- 10W kWh: +/- 5% of measured value +/- 0.1 kWh
It's clearly not a high precision instrument - but is nontheless useful in getting an indication of consumption when, for example, speccing an emergency genny. -- Cheers, Set Square Please reply to newsgroup. Reply address is Black Hole!
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On Mon, 12 Jan 2004 14:16:31 -0000, Set Square wrote:

Yes I found that and the makers site with not a lot more information. Indeed the MachineMart site and another resellers site where almost verbatim the makers page...

I make that 4.6VA, this is somewhat better than what I have. If you (or Mr Gabriel) have a 15w bulb does it read 15W +/- ballpark?
Does more techy things than mine as well, like current, volts and frequency. I think I want one, note want not need... B-)
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In an earlier contribution to this discussion,

Just tried it by taking a 15w bulb out of my Goblin Teasmade (blimey, that dates me!) and putting it in my lead lamp. It reads as follows: Voltage: 237/238/239 (fluctuating) Current: 0.07A Power Factor: 1.00 Watts: 16.66/16.75 (fluctuating)
With a 60 watt bulb, it read 59 watts.
All this makes me feel that it's resonably believable - and that the tolerances stated in the spec are rather conservative.
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Ah, but bulbs are resistive loads. Know a fellow who'd tested a few, and found that the cheaper ones didn't do too well with inductive and capacitive loads.
That said, it should be fine for getting the numbers in the right ballpark.
Thomas Prufer
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In an earlier contribution to this discussion,

Well, with the inductive loads on which I've tried it (e.g. central heating pump) the displayed numbers stack up - in that displayed watts = displayed volts x displayed amps x displayed power factor. I know that doesn't prove that its *right* - but it's got a fighting chance!
The fact that it displays these parameters separately means that you can also work out VA (ignoring power factor) which is probably more relevant than watts when considering the use of gennys or inverters for emergency standby use.
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And VA would be broadly accurate, I'd expect -- phase is the trickiest of the three to measure cheaply.
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On Tue, 13 Jan 2004 13:36:12 -0000, Set Square wrote:

Volts and amps are easy to measure fairly accurately the phase angle not so easy but once you have that the rest is just maths.
Nice to know that the device does produce reasonable answers, thanks for running the tests. Pity you're not on commission...
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In an earlier contribution to this discussion,

I think we all benefit from sharing experiences of devices we have bought. I have certainly benefitted from other people's input on other devices - and am quite happy to do experiments.
Just to show that I'm not biassed, I'm not claiming that this volt/amp/meter is the best thing since sliced bread - but simply that it does a reasonable job and seems to be reasonable value for 20.
I did have one minor problem with it on the first day - when it locked up and wouldn't respond to any of the buttons. The reset button also didn't work, and I had to take the batteries out for several minutes and start again. It has been ok ever since.
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Generators (and UPS's) normally care about the VA of the load. So for practical purposes, simply measure the current drawn by the appliances and ignore the phase angle and power.
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