On Mon, 28 Sep 2020 07:14:34 -0400, Paul
wrote:


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.


Plugged "Manrose timer board" into Google and got an iFixit link
with a Youtube reference.

"How to Fix an Extractor Fan Timer"

https://youtu.be/UxU-ZQp2ag4

CD4001BE, big-ass RC (analog) timer circuit ?
Like making an amplifier out of CMOS logic.

Have a look and see if it's similar to yours.

There is a large resistor that does the dropping
to bring the 240V down to some lower level. Notice
in the video that his resistor is cracked or has some
surface damage of some sort. Looks safe and reliable.

A non-isolated circuit ? What's not to like ?

I was hoping for a schematic, but that's too much
to expect.

Paul


I followed your tracks and found a better video. The PCB in yours was
marked 1998, but the one in mine is 2008, and has a big copper PCB
land on one leg of the big resistor in an attempt to add more cooling.

(The presenter sounds like an aircraft pilot welcoming passengers).

I've worked out the circuit and added an explanation. See:
https://www.dropbox.com/s/hmxsxtxt0x...Timer.jpg?dl=0

I am guessing that the IC runs on 12V and the trimmer is 2M to give a
delay of 1 to 20 minutes.
--
Dave W