On 28 Sep 2020 at 10:48:04 BST, "Chris Holmes"
wrote:

Hi All,

I recently bought and installed a Manrose timer board for one of their inline
fans (so it runs on after the lights are turned off). I installed it this
weekend (actually driving a similar fan from another manufacturer).

It's working fine, but I found it a little curious...€¦.

It's a tiny PCB with quite small tracks. It only has about 10-12
components, from memory, a small transistor at the input end together with a
pot to adjust the delay, a big resistor, a handful of tiny things most of
which are probably resistors, but one or two could be diodes or something
else a chip, and another little transistor at the output end. The permenant
live is just a track that goes straight to the output, and the neutral goes
most of the way there and then gets switched to the output.

Thing is, in my limited experience, transistors and chips required a power
supply of some sort to convert mains to 5V and or 12V DC. But I couldn't see
anything on the board that I recognised as being capable of doing this.
Are there now 240V AC chips? Have there always been and I've just not come
across them before?

I got it for about £10 by the way (on special offer, reduced by 50-ish %), so
a nice cheap simple way to add a timer to something that doesn't require much
wattage.

I think the secret is low current consumption. To drop (most of) 240V at,
say, 5mA needs only to dissipate 240 x 5 x 10^-3, that is about 1.2W and the
large resistor can probably do that even air cooled. Only few low power
components are needed to voltage limit, smooth and regulate the low voltage
supply. There should be an electrolytic capacitor though, unless anyone can
give a clue how to avoid it.

--
Roger Hayter