Author Options:

Q: why does a 220v (down-step) regulator output 300v? Answered

hi, bought this 220v regulator (see photo). strangely enough the volt-meter shows almost 300v on the output (at zero load). otherwise it works fine. any ideas? gracias



4 weeks ago

If it is from China....
Could also be displaying the peak to peak voltage or a resulting DV voltage - you never know with these toys....

la xerraDownunder35m

Reply 4 weeks ago

one more thinkg to learn in life... (ok, ´ll do some homework, cheers)

Jack A Lopezla xerra

Reply 4 weeks ago

I also do not know this, "DV voltage," and when I search for this phrase, my search-fu fails me. But if I had to guess, I would guess it has something to do with a voltage waveform having higher than expected peak-to-peak voltage, because it has some spikes in places.

I don't know if I want to try to explain why spikes, or ringing artifacts, will creep into otherwise square, or sinusoidal, waveforms, but they often do.

To show some pictures of what these spikes look like, I am just going to point to an image search for, "oscilloscope spikes", here:

Peak-to-peak voltage is the highest voltage seen, in one period, minus the lowest voltage seen in the same period.

So with spikes, peak-to-peak voltage will be measured higher than without spikes, compared to some other way to measure voltage, like root mean square (RMS), which is the square root of an average of the square of the signal.

For another feat of hand waving, I am going to claim that sometimes adding a resistive load will make the spikes go away, by like, absorbing the energy in these spikes somehow.


4 weeks ago

Connect the load with a proper resistor
The value of resister should design by the load current

la xerraarunbabu179

Reply 4 weeks ago

you got the set-up right (voltmeter and converter mounted in p.e.t. > plugged into outlet).

_resistor: yes, will try that (always some electronic dinosaur ready to be butchered flying around here on my playground=junkyard)

_ plug/outlet: yes, european stuff (although the brits have ´brick´-like plugs etc... but then, the brits arent really europe, are they, haha)

_knob: no, w/o load the voltage doenst change... once something is plugged in: yes, always stays below 220v

thanks jack

Jack A Lopez

4 weeks ago

These pictures of other people's electrical outlets always look so strange to me.

Maybe you would feel the same way if you could see what the outlets in my house look like? Actually the Wikipedia article, "Mains electricity by country", can show you what they look like.


Getting back to your picture: I am guessing I am looking at two gizmos mounted inside, what used to be a plastic water bottle. I am guessing the gizmo on the left is an AC voltmeter with mains power plug on the back. I am guessing the gizmo on the right, with the black knob on it, is the mysterious power converter module.

I am also guessing, a little bit further to the right, is a wall outlet, supplying mains power.

I have a few ideas.

One is to try plugging the voltmeter gizmo into the wall outlet directly, to see what it says when just measuring the voltage at the wall outlet.

Another suggestion is to to try the same setup, but with a small (in terms of power) load that would be hard to destroy. But what would that look like?

Supposing you wanted a resistor that would dissipate around 10 W, at 300 V AC (rms). That would be 9000 ohm, since P = (300V)^2/(9000 ohm) = 90000/9000 = 10 W. A 10 Kohm (10 W) resistor , or 10 * 1Kohm (1 W)resistors wired in series, would be close enough.

The trouble is, if you're like most normal people, you do not have resistors like that in your junk collection. But what do you have?

A low wattage heater, or light bulb, might be the next best choice. Again I was thinking something in the range of 1 to 100 watts. Basically I just wanted to load that power converter a little bit, without making it work too hard. I think a plug-in "night light" or "fragrance heater" might be something in that range.

Regarding the property of being hard to destroy, incandescent light bulbs are actually pretty easy to destroy through overvoltage, but they might be cheap so that destroying one would not be big loss. I have no idea what the cost of incandescent lightbulbs is in your local market, but they might be cheap, especially if they are considered "obsolete", but are still available on the used, junk, thrift market.

Another possibility for an electrical load, with wide range, hard to destroy, is a big water resistor, like KOR's, "Scariac", in this instructable,


Something like that would best be used together with an actual power meter.

I think I mentioned power meters on a topic you posted previously, but I did not link to any examples.

I am guessing Harbor Freight Tools (a company that sells Chinese tools in stores in the former United States) does not have any stores in your country, but I am going to link to their page for the "Kill-a-Watt" power meter, made by "P3 international"


Obviously, the version of this made for your electrical outlets, would have connectors shaped to fit your electrical outlets.

But homemade Scariac plus power meter, that is like a whole big project, just to build a thing, to test a thing...

Getting back to your mysterious power converter: My last piece of advice is to try turning that big black knob, and see if that does anything to the voltage measured at the converter's output. I am guessing it will. That was the promise, right? I am guessing this is an adjustable power converter, and the big knob is the means by which the adjustment happens.