On 05/10/2020 09:55:25, charles wrote:
In article , Dave W
wrote:
On Sun, 04 Oct 2020 22:42:45 -0400, Paul wrote:
Dave W wrote:
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.
Neat. That looks about right. Fast attack, slow decay circuit. The diode
in the upper left could be a 1N4007. For the price, probably not that
much more for a higher rating. I think they're the same diode, just some
are tested to higher voltages.
Does this mean the triac only conducts on half-cycles ???
The only hobby triac circuits I've had here, they were fired by a diac.
Paul
I forgot to include a link to the video that I used for source material:
https://youtu.be/3sumou4ScDM
Triacs conduct in both directions when the gate is held +ve, so give
full-cycle operation.
er, no. Triacs are diodes. To get full cycle conduction you need a pair of
triacs.
They are more complicated than a "diode".
FYI
A Thyristor conducts in one direction
https://en.wikipedia.org/wiki/Thyristor
A Triac can conduct on both negative and positive going part of the cycle.
https://en.wikipedia.org/wiki/TRIAC
Triacs can be turned on by passing a current in the gate. If the gate
drive has been removed they stay on until the end of the cycle when
current is lower than the holding current.