I thought of that, but the most likely cheap-meter equivalent would be a square wave, which would read lower.
I suppose that a meter that takes the average of the absolute value and then scales _up_ may be off in this manner, however.
-jsw
You should read about 0.7 x the rated voltage on a modified square wave inverter.
I am amazed no one has suggested using a good old Simpson 260 or similar ANALOGUE meter and get the real answer. All this waffle about transformers and peaks and average is typical of the impractical answers so common in some of the electronics groups. KISS Keep It Simple Stupid. :-?
Won't work any better than the DVM, it'll just give yet another misleading value.
My impractical waffle is to use two identical lamps with clear envelopes, a variac, and a voltmeter. Connect one lamp to the inverter and the other to the variac. Arrange them so the filaments are nearly superimposed as you look thru both envelopes. Adjust the variac so there's no difference in the color of the of the two filaments. Measure the output voltage of the variac - that's the RMS output of the inverter, within, I'll wager, a couple percent.
Switch the lamps and repeat the experiment to check for any detectable difference between them.
on the bench (nothing else attached) and plugged in a few lamps. The outpu t measured 330v with loads of 50 and 150 watts. The lights did seem brighte r, but not excessively so. The voltmeter is a cheapie, but seems generally accurate. I know that these devices produce a modified sinewave, and I shou ld 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?
Obviously not a dud as it does produce AC. But the real question is does t he inverter do what you bought it to do. And if so why do you care about t he voltmeter reading? If it is just that you are curious why the voltmeter reads high, I think you need to see the waveform on some kind of a scope.
The suggestions to compare heating water and comparing lamp filament bright ness will let you know what the power output is.
Dan
are you sure?
How many people who ask Electric Questions in a Metalwaork Group have a Variac sitting around for such experiments?
I have several, but would have to look to see if any are rated for 240 volts.
Dan
Quite sure.
Good question. But if a fellow was curious enough, small used variacs are easy to come by.
I've gat 4 or 5 of them- from itty bitty to HUGE.
Anyone thought about using a "true RMS" meter.
CP
Bingo! An electric coffeemaker's brew time for a given water fill is a better RMS voltage meter than most inexpensive electronic meters.
I thought of that, but my water kettle is 2200w. As to getting a scope or v ariac or true RMS meter, I'm the only one I know who even owns a DVM! Some of my friends are aircraft engineers, but couldn't jump start a car with a gun to their head. No, I'm all alone here as to equipment. I think I'll jus t trust my step down transformer test. I was only worried that with such a high reading I might burn up a power supply or maybe even have a fire.
Thanks all!
PS. The meter is a TopCraft TMMH-930. You can download the manual, but woul d need to speak either Dutch or German to read it!
The heater's power draw would have to be within the capacity of the inverter and battery, perhaps an immersion heater or single-serving hot pot for a dorm room or office desk. A 1000W coffee maker would pull over 80A from the 12V vehicle battery.
-jsw
I thought of that, but my water kettle is 2200w. As to getting a scope or variac or true RMS meter, I'm the only one I know who even owns a DVM! Some of my friends are aircraft engineers, but couldn't jump start a car with a gun to their head. No, I'm all alone here as to equipment. I think I'll just trust my step down transformer test. I was only worried that with such a high reading I might burn up a power supply or maybe even have a fire.
Thanks all!
PS. The meter is a TopCraft TMMH-930. You can download the manual, but would need to speak either Dutch or German to read it!
=== I'm back on dialup for a while, no joy trying to download a German Bedienungsanleitung, and I don't read Dutch.
-jsw
Yes, I figured my 2200w kettle would stress an inverter which is rated at 3
00w peak. At the moment I only see chargers for the laptop and tablet, and maybe a boombox being used, but I'm sure other things will creep onto the l ist. It's pretty cool the availability of warm white LED lamps now, especia lly in 12v. I will be able to have plenty of lighting in the tent run from a car battery. Won't even need the inverter most of the time.
Yes, I figured my 2200w kettle would stress an inverter which is rated at 300w peak. At the moment I only see chargers for the laptop and tablet, and maybe a boombox being used, but I'm sure other things will creep onto the list. It's pretty cool the availability of warm white LED lamps now, especially in 12v. I will be able to have plenty of lighting in the tent run from a car battery. Won't even need the inverter most of the time.
======= I've measured substantial variation in the low voltage cutoff of my inverters. One doesn't shut off at all, it will happily drain a 12V battery to 7V. I tested it with a variable power supply, not by ruining a battery. The others shut down somewhere between 10V and
11.5V.I wouldn't run one off a car battery all night away from home because they consume a fair amount of current internally and you might not be able to start the engine in the morning.
-jsw
Right. I know mine is sucking power even when switched off. Where we're goi ng I need to leave the car a fair distance from the tent and will be using a spare battery, mostly without the inverter attached. Still have to work o ut options for recharging in the morning...
Back in the day, the whole idea of going "camping" is to get away from all that stuff that uses electricity. If you're not rubbing sticks together to start a fire, you ain't camping ;-)
Yeah. You're right. I can still go for actual hours without checking my ema il, and still carry a "dumb" phone. My wife would prefer to live like that, but her job makes it impossible. And the kids, well, if they had to go a w hole week without Netflix I'm not sure they'd survive!
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.