On Thu, 9 Jul 2015 03:32:18 -0700 (PDT), 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?

Sounds like a bogus inverter. I'd take it back (with meter in hand)
and check the replacement or go to a different vendor. 5% is the
usual tolerance for power fluctuation.

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