Tester that connects AC load at peak voltage

[slugrustle]

I'm looking for a piece of off the shelf test equipment that connects an AC load to an AC source at the peak of the AC source's voltage waveform.   Ideally it would work with a 240VAC 50Hz input.

The goal is to stress test the AC source.

I'm not looking for something that turns on at the peak every half cycle and then turns off at the zero crossing.  Rather, I'm looking for something that turns on at the peak and stays on.

It's a little hard to search for this... is anyone aware of an off the shelf tester that works like this?

Thanks in advance.

[David Hess]

I did a quick search for an AC load which can do that, but did not find anything.  Hopefully someone else knows.

If I needed such a thing, I would design and fabricate the control circuit over an afternoon.

[slugrustle]

If I needed such a thing, I would design and fabricate the control circuit over an afternoon.

I have built one of these before, for 120V 60Hz, with a TRIAC.  In that case, the load and heatsinking requirements weren't very high.

For various reasons, in this instance, am looking for something a little more professional than I could cook up quickly, and time is important.  Hence putting "off the shelf" in the original post twice.

[TimFox]

You will have a problem sensing the time of the peak voltage, since the first derivative goes to zero at the extreme.
If you have a clean sine wave, you could phase shift it by 90 deg and sense the zero crossing of the resulting cosine wave.

[slugrustle]

The source has consistent phase, so the concept would be to detect the zero crossing and delay by 90°.

[David Hess]

You will have a problem sensing the time of the peak voltage, since the first derivative goes to zero at the extreme.

That can work, and I have done it, but derivative circuits are almost always a bad idea.

If you have a clean sine wave, you could phase shift it by 90 deg and sense the zero crossing of the resulting cosine wave.

In a more comprehensive design, that is what I would do.  Phase lock a clean local oscillator to the noisy AC power signal to remove the noise, and then use a phase comparator to phase lock a second local oscillator in quadrature.  Or a quadrature oscillator could be used to do it all in one shot.

But that is a long way from a simple design which will do what slugrustle requires.

[TimFox]

My comment about the derivative at the extremum is not a suggested method, but an indication of the difficulty of seeing the maximum when it happens.
Your suggestion of cleaning up the sine wave with a PLL is practical, since many PLL designs inherently lock to the input with a 90 deg phase shift.