(No, not comic strips or movies…)
With 230V experiments becoming more commonplace here at JeeLabs, I’m worrying about safety again. It doesn’t take much to get sloppy once you do things over and over. But sloppiness and 230V don’t mix well!
Given the recent trials, and some great comments, I’d like to get back to a safer voltage level for day-to-day testing. Using the isolation transformer only for incidental cases because no matter what, 230V is tricky.
Until now I’ve been using my lab supply, which goes up to 30 VDC. But that’s limited, and more importantly it doesn’t let me see the effects of AC rectification and ripple. It’s time to come up with a better test setup:
A couple of small well-insulated PCB transformers, one rated 2x 18V @ 45 ma and two with 2x 28V @ 20 mA secondaries, respectively. The 18V and 28V secondaries are completely safe (by themselves) – they might damage a circuit, but they won’t harm me.
When combined, these can produce from 18 to 148 VAC. Note that 148 VAC is still over 400 Volts peak to peak, so this is serious stuff. The best way to keep the risks down is still to use low voltages as much as possible, of course.
One reason why these voltages are less risky than AC mains, is that the output current is very limited. I picked the weakest transformers I could find, meaning that their secondary coils have a high internal resistance and small magnetic cores. That and magnetic saturation should keep maximum currents limited to 20..30 mA.
Tomorrow I’ll describe a convenient hookup for all these little power sources.