Boy, I know even less than I thought about diodes

[rp58]

Can someone please explain how this simple circuit:


can generate this waveform?


That's an almost dead 12v SLA, a 50v 3A diode, and the scope is dc coupled. When I flip the diode it conducts and displays normally.  The frequency looked suspicious, but it does not equal my mains frequency which is 59.56

[xrunner]

Just picking up 60 Hz noise from the surrounding lines. The battery/diode has nothing to do with it per se, except acting as a slightly better antenna.

[ataradov]

And you can't rely on the frequency value as measured by the scope. It is on the ballpark of the 60 Hz, it is mains.

[rp58]

Ok, got it.

As a follow-up, what I was preparing to do was protect my benchtop power supply while I reverse charged this battery.  But then I realized there is no way to do that, is there?  You can use a diode to forward charge a battery, but how do you protect the power supply for reverse charging?  (This is an experiment in desulfation)

[ataradov]

No, your power supply need to be able to sink current. Many supplies can do this, but usually for a limited amount of time.