Home Automation - Timer on reduced-frequency circuit

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Timer on reduced-frequency circuit

Lacustral

2007-07-31, 9:25 pm

I'm thinking of using a variable speed control and a timer in series.
Would a timer have trouble with the lowered frequency electricity from the
speed control? WOuld an electronic timer run OK that way?

Thanks
Laura

Arfa Daily

2007-08-01, 9:25 am

"Lacustral" <lark@lightlink.com> wrote in message
news:Pine.GSU.4.58.0707312021220.14042@adore.lightlink.com...
> I'm thinking of using a variable speed control and a timer in series.
> Would a timer have trouble with the lowered frequency electricity from the
> speed control? WOuld an electronic timer run OK that way?
>
> Thanks
> Laura

Firstly, a variable speed control does not affect the 'frequency' of the
supply current. It does, however, have a profound effect on the waveshape,
if it is electronic rather than passive, and this may well affect an
electronic timer's ability to work correctly, as opposed to keeping time,
which I presume is your reason for asking about frequency. If you put the
timer ahead of the speed control, there will be no such issues, as the timer
will only be fed with 'standard' line power, which it will then pass thru'
to the speed control during one of its 'on' periods.

Arfa

Jasen Betts

2007-08-01, 9:25 am

On 2007-08-01, Lacustral <lark@lightlink.com> wrote:
> I'm thinking of using a variable speed control and a timer in series.
> Would a timer have trouble with the lowered frequency electricity from the
> speed control? WOuld an electronic timer run OK that way?

maybe, but the easy fix is to put the timer before the speed control.
you don't need to power the speed control when not using the fan.

Bye.
Jasen

Sam Goldwasser

2007-08-01, 9:25 am

Lacustral <lark@lightlink.com> writes:

> I'm thinking of using a variable speed control and a timer in series.
> Would a timer have trouble with the lowered frequency electricity from the
> speed control? WOuld an electronic timer run OK that way?

I assume you mean a common thyristor phase control, not one that actually
changes the frequency of the power, though the same comments apply.

If you mean put the timer first which plugs into a wall socket and then the
switched output of the timer goes to a variable speed control, there should
be no problem. The timer will run off the unmodified power.

However, if it is an electronic timer that is in series with the load ONLY
then this is probably not a good idea unless the timer manufacturer
specicially states that it is permissible.

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Lacustral

2007-08-01, 5:25 pm

Sam Goldwasser (sam@red.seas.upenn.edu) wrote:
>Lacustral <lark@lightlink.com> writes:

[color=darkred]
>I assume you mean a common thyristor phase control, not one that actually
>changes the frequency of the power, though the same comments apply.

Probably. A guy at an electric store said it changes the frequency, which
sounded weird to me. But no, it would be an ordinary speed control. I
vaguely remember reading about phase affecting power delivery in a physics
book.

>If you mean put the timer first which plugs into a wall socket and then the
>switched output of the timer goes to a variable speed control, there should
>be no problem. The timer will run off the unmodified power.

I see - that makes sense.

Thanks
Laura

Jasen Betts

2007-08-03, 9:25 am

On 2007-08-01, Lacustral <lark@adore.lightlink.com> wrote:
> Sam Goldwasser (sam@red.seas.upenn.edu) wrote:
>
>
>
> Probably. A guy at an electric store said it changes the frequency, which
> sounded weird to me. But no, it would be an ordinary speed control. I
> vaguely remember reading about phase affecting power delivery in a physics
> book.

Some speed controls do (a device called a variable frequency drive),
but that is for large industrial motors, small fan speed controllers
just reduce the voltage that the fan gets.

Bye.
Jasen

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