12v inverters - Output voltage too high?

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...

se on subjects like this here.

ry on the bench (nothing else attached) and plugged in a few lamps. The out put measured 330v with loads of 50 and 150 watts. The lights did seem brigh ter, but not excessively so. The voltmeter is a cheapie, but seems generall y accurate. I know that these devices produce a modified sinewave, and I sh ould 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?

Well, Have a nice day to you too! Here is the picture of the inverter.

$_57 .JPG It lists specs:

Eingangsspannung: 12V DC (10-15V) Ausgangsspanung: 230V (AC) +/- 10% Effizienz: > 85%

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 unde r 50 bucks. It measures the mains at 220v.

What specific information do you suggest I provide?

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

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"Note 3: A general-purpose digital volt meter (DVM) is not usually suitable to measure a distorted waveform (not pure sinusoid)."

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.

I've never experimented with Halogen, but I expect that 330V would burn a 220V one out rather quickly.

A modified sinewave converter typically puts out the peak voltage of the 230VAC RMS spec. (~320V) and sets the duty factor to provide an RMS value of 230V.

Sounds like a meter problem to me, but can't tell cuz it's still a mystery meter.

Trying to think of another way to measure, I attached a small 220v axial fan to the inverter. The pitch of the fan was about a major third higher than when run on the mains, meaning about 25% higher.

Well, Have a nice day to you too! Here is the picture of the inverter.

$_57.JPG It lists specs:

Eingangsspannung: 12V DC (10-15V) Ausgangsspanung: 230V (AC) +/- 10% Effizienz: > 85%

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?

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The German power line frequency is 50 Hz. Dauerleistung is continuouspower, Spitzenleistung is peakpower.

You really need a scope to measure the output voltage, frequency and duty cycle. The voltage of a changing signal is calculated from its heating power, which varies as the square of the voltage, not its average which is what a non-RMS meter displays. They fudge their average reading to show what the RMS value should be, but only for a sinusoidal waveform.

-jsw

As to the meter, I actually found the manual online and the only relevant t hing was "Corrected mean corresponds to the sinusoidal RMS".

Not having a scope or the knowledge how to use one, I tried another test. I plugged in a 230vac to 24vac transformer in parallel with a 60w tungsten b ulb and compared the no-load voltage of the step down transformer. It was p ractically the same, as was the observable bulb brightness, between running off the mains or the inverter. So, I guess I'm OK. The fan test is still w orrisome for me though.

Some types of of AC motor respond to voltage control of the speed, IIRC shaded pole was one. I have a Comair Rotron axial fan and have used it with an EBM Ziehl speed controller intended for fan speed control to slow it down but it was run off 240V 50Hz mains, I presume if you can slow them down by reducing the voltage then the opposite may also hold if your inverter is seen to put out a higher voltage.

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.

Right. The frequency should still be around 50 Hz with the inverter. All th is "RMS" and "Modified Sinewave" stuff is way out of my pay grade, but I as sume that different types of load will respond differently to the voltage p roduced by a cheap inverter compared to what comes from the local power com pany. I was aware that the measurement with my multimeter would be dodgy be cause of this, but I kind of freaked when I saw 330v. I'm starting to think that I may have nothing to worry about. Any other laymen tests I could do? I'm only going camping.

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

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. ;)

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.

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.

Cheap inverters put out a stepped voltage that roughly corresponds to a sine wave. Furthermore, the inverter will put out a higher voltage when lightly loaded and the voltage will drop as more load is put on the device. The stepped voltage may rise above the rated voltage because the inverter maker is expecting the load to average the voltage to the rated voltage. Try plugging an induction motor into the thing and then measure the voltage. Your digital meter may not be very good at averaging the stepped voltage output of the inverter and so will show a higher peak voltage instead of the averaged voltage. An analog meter would probably be more accurate for this measurement. If you put a diode in series with one wire of an AC supply it will rectify the AC into pulsed DC. If you then measure this DC voltage it will be 1.414 times the measured AC voltage. This is because the sine wave shape of the rising and falling AC voltage shows that it has a peak value of 1.414 times the RMS voltage. And the RMS voltage of AC devices is what is printed on the label as the voltage rating. So your typical AC 120 volt rated motor is expected to run on AC that peaks at 169.68 volts. Eric

Right. The frequency should still be around 50 Hz with the inverter. All this "RMS" and "Modified Sinewave" stuff is way out of my pay grade, but I assume that different types of load will respond differently to the voltage produced by a cheap inverter compared to what comes from the local power company. I was aware that the measurement with my multimeter would be dodgy because of this, but I kind of freaked when I saw 330v. I'm starting to think that I may have nothing to worry about. Any other laymen tests I could do? I'm only going camping.

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If you have a (possibly sacrificial) way to heat water with the inverter you could time how long a measured amount of room temperature water takes to boil on the inverter and on Netzstrom. They should be pretty close to each other.

-jsw

The first bubbles you see at around 80C will be dissolved air coming out of solution, not steam.

Incandescent lamp _life_ is highly dependent upon RMS voltage. At 330v, a 230v lamp's life would be very short! If you have a 220 to 110 transformer? If so, connect as a boost to your 220 to get a real 330v and put one of you 220v lamps on it. The difference in brightness and life will be dramatic. And will demonstrate that the inverter is not really producing 230v RMS.

Bob

Tell us the model number of the meter.

To get a proper (RMS) reading, you will need a 'true RMS' meter. Otherwise, it reads the peak a nd scales that down by sqrt(2) which is only valid for a sine wave. If you don't know what kind you've got, some electrical whiz can tell you.

Amen to that. A nominal 230VAC (rms) sine wave will be 650VPP. and will rea d right around 230V on a "normal, cheap, non-rms" meter. A square wave with an RMS voltage of 230V will be 460VPP, but the cheap meter won't know what to make of it. Once you add the word "modified" to the waveform, all bets for an accurate reading are off with the cheap meter.

Later in the thread, it was suggested that plugging a transformer into the inverter and into the mains produced the same output voltage. That suggests to me that the transformer is filtering the waveform enough that the meter is less whacked out. My GUESS is that the inverter is doing what it's supp osed to do, and the meter is just confused.

On 7/9/2015 1:26 PM, Bob Engelhardt wrote: ... is not

Brain fart! _330v_