capacitor on series with transformer primary?

Sounds like it was there to limit the current... at 60 Hz 0.15uF looks to be a bit more than 10k ohm....(Assuming I'm ready the chart correctly.. I'm too lazy to punch in the numbers.) something like

100mA of current.

George H.

Ah, so would a 10k resistor in series with the primary do something similar?

Seems odd they would choose a capacitor...?

Also I realized I made a mistake: the TRANSFORMER was less than 1 cu. in., not the capacitor.

It's a really cute transformer; I was planning to desolder it for use elsewhere, but wondered what would happen if say a couple of 1.2V NiCd batts want to suck too much current from the secondary...

Thanks,

Michael

It's a ballast (current-limiting) component; probably the transformer will burn up if you short across it. The capacitor doesn't heat up like a resistor, and is cheaper than a series inductor.

It's a common trick, seen in lots of plug-in-the-wall emergency flashlights.

Only very vaguely. That cap may also be there for galvanic isolation from the mains.

The cap limits current without dissipating heat. A 10k resistor with

120V across it will dissipate 1.5W (120V^2 / 10k). Assuming that most of the voltage drop is in the cap, you'd throw away more energy to heat than you would spend charging the battery.

They wouldn't, because the capacitor would limit the current -- if you left it in there.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

Nice! Limiting current without dissipating heat.

I'm guessing capacitor polarity is not important, since it's AC? (It wouldn't be an electrolytic, would it?)

I'll desolder that puppy too for future experiments.

Thanks,

Michael

It will _not_ be a 'lytic!

Those things are generally poly-something, with generous over-rating to take transients into account. IIRC the dielectric is somewhat self-healing, too, but that memory is coming out of a pretty dusty storeroom, so it may not be accurate.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

Oh good... no kablooeys to worry about.

Thanks!

Michael

"Tim Wescott"

** Nonsense.

150nF is way to big a value for safety isolation and there would also need to be two of them for that job - one in each AC supply line.

The shaver is made safe by virtue of having " class 2 " insulation provided between all live and contactable parts.

.... Phil