On Sat, 11 May 2019 08:24:12 -0700 (PDT), wrote:

On Saturday, 11 May 2019 15:46:05 UTC+1, Archibald Tarquin Blenkinsopp Esq wrote:
On Sat, 11 May 2019 07:28:51 -0700 (PDT), tabbypurr wrote:
On Saturday, 11 May 2019 11:38:18 UTC+1, Fredxx wrote:


As others have said, using a capacitor dropper for a variable load
simply doesn't work.

I've used that arrangement without problems enough times. It's just more issues to address, less situations where it's ok.

It makes the term variable somewhat interesting.

A bank of capacitors to dim a light bulb perchance?

Even high st discounters flog regulators to do that for a few quid.

I cannot think of an instance where you would want to supply a varying
load through an impedance, or even a resistance, with the intention of
dropping the supply Voltage to a useable value. There is just no
point.

the point is obviously to reduce v and/or i

A Triac or SCR can select the chunk of the sine wave you want
and the scource impedence is so low that it can be ignored.

Lots of appliances use a C dropper to supply varying loads. It's cheaper.

I wasn't aware that it was common practice, I would have thought that
in practical terms battery charging or similar might be feasible.

What loads are you aware of?

Some loads need their v limiting with a zener, some can accept the variation.

The power dissipated by the zener must limit the practicality of the
Wattless dropper. A variation of any significance ie a few watts,
would be better served by a transformer.


I seem to rcollect that train sets and model car race tracks used
resistors to drop the supply from 12V, but I would guess that they are
fully electronic now. The lack of back EMF was painfully obvious when
using the early ones.

the early ones just used a series lightbulb to the track, with IIRC 110v train motors. Yes, for children.

Happy days!

Would have been more fun with 240V.

AB