On 7/9/2015 6:40 AM, Larry Jaques wrote:
On Thu, 09 Jul 2015 04:02:35 -0700, mike wrote:

On 7/9/2015 3:32 AM, robobass wrote:
On Thursday, July 9, 2015 at 12:10:02 PM UTC+2, mike wrote:
On 7/9/2015 2:47 AM, robobass wrote:
I know this is a metalworking site, but there is quite a bit of expertise on subjects like this here.

I just bought a 200/300Watt 230v inverter. I attached it to a car battery on the bench (nothing else attached) and plugged in a few lamps. The output measured 330v with loads of 50 and 150 watts. The lights did seem brighter, but not excessively so. The voltmeter is a cheapie, but seems generally accurate. I know that these devices produce a modified sinewave, and I should expect a different reading, but I thought the reading should be lower if anything. Is this inverter a dud, or do I just not know how to measure?

Thanks

Probably the latter...
But
since you provided zero information about the inverter,
zero information about the lamps,
zero information about the meter,
It's hard to tell.

That the lamps didn't explode suggests you may not have
330V...maybe...depends...

Well, Have a nice day to you too!
Here is the picture of the inverter.
http://i.ebayimg.com/t/SPANNUNGSWANDLER-200W-300W-12V-230V-WECHSELRICHTER-INVERTER-USB-PKW-LKW-BATTERIE-/00/s/ODAwWDgwMA==/z/18IAAOSw3ydVhsoL/$_57.JPG
It lists specs:

Eingangsspannung: 12V DC (10-15V)
Ausgangsspanung: 230V (AC) +/- 10%
Effizienz: 85%
optimale Arbeitstemperatur: 5 - 45°C
Kühlungsmethode: Lüfter
Dauerleistung: 200W
Spitzenleistung: 300W

I know it's in German, but it should be clear even if you don't speak it. I don't have like a schematic diagram for it or anything. Bought on Ebay.

The lamps were two 220v 50w halogen spots and a 53w Edison bulb.

The meter is a typical multimeter you get from an electronics shop for under 50 bucks. It measures the mains at 220v.

What specific information do you suggest I provide?

Well..I don't do German and the text tells nothing about the waveform
supplied. The link is just a picture.

There is no such thing as a typical multimeter. Your results are
atypical, so exactly what the meter measures might be the clue.

mike, if the meter measures mains at 220 and the inverter at 330 (WITH
a load), I would trust the meter reading. YMMV

I can't come up with a
voltmeter topology that would produce the observed responses.
So, that's weird.
It's hard to judge a secret meter.

But!
How long will a 220V Halogen light burn on 330V?
I claim it ain't very long.
And the difference in brightness would be BIG.
That info alone suggests that the output ain't 330V RMS.

Sometimes, you just need a friend with a scope.

Every meter I've ever used has measured within a couple percent of any
others I've tested them with, so I consider that a typical multimeter.
If you need more precision, buy an expensive multimeter with metrology
documentation and certification. The rest of us can use the $5 HF
versions with impunity, joy, and a _much_ lower cost.

Typical??
Statistics are great when you are sizing a power plant or sewer system.
But, when YOU are the one who doesn't fit the pattern, the statistics
are no comfort. It's either pass or fail for your specific atypical
instance.
When the meter is a secret, conjecture is all you get.

Bottom line is that we'll probably never know.

--
We are always the same age inside.
-- Gertrude Stein