Low-power transformer - and other stuff

[Pete Verdon]

Hi,

As part of a bathroom project, I want more sophisticated control of the
extractor fan than just turning it on with the overhead light. At
present, I'm thinking in terms of a flow-switch on the shower supply (so
it extracts steam while showering) and a push-switch (for occasional
toilet-related necessity ). Both of these would also involve
over-run timer(s).

Since in the UK I can't legally have a mains (240v) switch in the
location I'd want (well, except for a high-IP-rating one, all of which
are ugly) I'm thinking in terms of a 6-12-ish volt "signal" circuit
going down to the switches in the room, and a suitable timer
module/relay/etc assembly in the (accessible) roof-space above the
bathroom where the fan will be. I envisage a very simple circuit on
stripboard or similar, in a project box.

My main question is how best to power the "signal" circuit with minimum
wasted energy when not in use. I've had a quick look at small
transformers (eg
http://docs-europe.electrocomponents.com/webdocs/0029/0900766b80029e0c.pdf
) but don't understand all the figures. Things like "efficiency 30%" and
"core losses 1.8W" scare me when all I want to do is energise a relay a
couple of times a day - but perhaps these only apply under load? In
addition, I'm a little confused by the apparent two outputs - do I get a
different voltage across each compared to across both or something like
that?

Secondarily, any advice on "chunky" self-contained parts for things like
my overrun timers? I don't really want to get into detailed electronics
on this project, just slap together big chunks of ready-made
functionality on a dumb board. It's electrics more than electronics.

Cheers,

Pete

 

[Phil Allison]

"Pete Verdon"

My main question is how best to power the "signal" circuit with minimum
wasted energy when not in use. I've had a quick look at small transformers
eg
http://docs-europe.electrocomponents.com/webdocs/0029/0900766b80029e0c.pdf
but don't understand all the figures. Things like "efficiency 30%" and
"core losses 1.8W" scare me when all I want to do is energise a relay a
couple of times a day - but perhaps these only apply under load?

** Core loss will apply with no load.

In addition, I'm a little confused by the apparent two outputs - do I get
a different voltage across each compared to across both or something like
that?

** There are two identical windings - so you can use them in series or
parallel.

The voltage rating will be double in series and the current will be double
in parallel.


...... Phil

 

[Steve Sousa]

Hi,

As part of a bathroom project, I want more sophisticated control of the
extractor fan than just turning it on with the overhead light. At present,
I'm thinking in terms of a flow-switch on the shower supply (so it
extracts steam while showering) and a push-switch (for occasional
toilet-related necessity ). Both of these would also involve over-run
timer(s).

Why not replace the single switch on the outside with a double were one
turns on the light, the other light+fan ?
Cheap, simple, safe, foolproof and uses no power...

 

[Randy Day]

Hi,

As part of a bathroom project, I want more sophisticated control of the
extractor fan than just turning it on with the overhead light. At
present, I'm thinking in terms of a flow-switch on the shower supply (so
it extracts steam while showering) and a push-switch (for occasional
toilet-related necessity ). Both of these would also involve
over-run timer(s).

Since in the UK I can't legally have a mains (240v) switch in the
location I'd want (well, except for a high-IP-rating one, all of which
are ugly) I'm thinking in terms of a 6-12-ish volt "signal" circuit
going down to the switches in the room, and a suitable timer
module/relay/etc assembly in the (accessible) roof-space above the
bathroom where the fan will be. I envisage a very simple circuit on
stripboard or similar, in a project box.

My main question is how best to power the "signal" circuit with minimum
wasted energy when not in use. I've had a quick look at small
transformers (eg

Does your house have an electric doorbell?
Maybe you could tap off the transformer for that.

If not, you could buy a doorbell transformer from
a local home supply center.

HTH

 

[amdx]

I like the two switch idea, but why not make the light+fan a mechanical
timer. Turn it to the time needed. 5 minutes for me, 30 minutes for my teen
daughter
Mike

 

[Jasen Betts]

Hi,

As part of a bathroom project, I want more sophisticated control of the
extractor fan than just turning it on with the overhead light. At
present, I'm thinking in terms of a flow-switch on the shower supply (so
it extracts steam while showering) and a push-switch (for occasional
toilet-related necessity ). Both of these would also involve
over-run timer(s).

Since in the UK I can't legally have a mains (240v) switch in the
location I'd want (well, except for a high-IP-rating one, all of which
are ugly) I'm thinking in terms of a 6-12-ish volt "signal" circuit
going down to the switches in the room, and a suitable timer
module/relay/etc assembly in the (accessible) roof-space above the
bathroom where the fan will be. I envisage a very simple circuit on
stripboard or similar, in a project box.

have you looked at pneumatically operated remote switches, often the
buttons for them aren't so ugly.

My main question is how best to power the "signal" circuit with minimum
wasted energy when not in use. I've had a quick look at small
transformers (eg http://docs-europe.electrocomponents.com/webdocs/0029/0900766b80029e0c.pdf
) but don't understand all the figures. Things like "efficiency 30%" and
"core losses 1.8W" scare me when all I want to do is energise a relay a
couple of times a day - but perhaps these only apply under load?

I think 'core losses' is related to magenetising current and so you
pay that all the time. 30% is extra costs while you're using the power.

In
addition, I'm a little confused by the apparent two outputs - do I get a
different voltage across each compared to across both or something like
that?

yeah , there's a number of different ways you can hook them up.
basically you can either have two isolated outputs, or parallel them
or connect them in series.

and I'm guessing you're wanting DC ad then end...

http://en.wikipedia.org/wiki/Rectifier

But I'd consider putting an outlet in the ceiling crawlspace/attic and plugging
a plugpack DC supply into it,

 

[Rich Grise]

As part of a bathroom project, I want more sophisticated control of the
extractor fan than just turning it on with the overhead light. At present,
I'm thinking in terms of a flow-switch on the shower supply (so it
extracts steam while showering) and a push-switch (for occasional
toilet-related necessity ). Both of these would also involve over-run
timer(s).

I just replaced the switch with a dupllex one and fished a new wire to
the fixture.

Have Fun!
Rich