Re: Resistor vs transformer

On Wed, 08 Feb 2006 09:26:30 +0100, Weinberger Hans
<weinberger@xxxxxxx> wrote:

On 7 Feb 2006 13:45:00 -0800, bill.sloman@xxxxxxxx wrote:


Weinberger Hans wrote:
On 7 Feb 2006 06:49:00 -0800, cs_posting@xxxxxxxxxxx wrote:

Weinberger Hans wrote:

Thanks and all those who gave "useful" replies.
Its a wireless receiver unit which calls the fire department in case
of a fire.

You probably need to figure out how it converts 120v to whatever it
needs. It may be that you could rip out its power supply and
substitute one for your line voltage.

Is that time/cost efficient?

No. Get a transformer with a dual 115V+115V primary, connect the
primaries in seires, and hook your fire alarm across one of the
primaries. Ignore the secondary windings.

Cost goes by size, but 6VA transformers have rotten regulation. The
2002 Farnell catalogue lists a 12VA part (stock number 159-591) whcih
cost 6.58 euro and would presumably do the job, You'd have to put the
transfomer in a box to protect the outside world.

Farnell have a whole range of boxes - I'd probably go for the 525-625
(which cost another 5.65 euro back in 2002), and mount the transformer
on the lid. You might be able to get cute and mount the fire-detector
on the other side of the same lid (leaving it outside the box).

This ought to work - the transformer will run a bit warm, but it would
run warm without any load at all.

I easily/cheaply find dual 230V at the primaries in my area. I guess
it would do the job too.

---
Not necessarily.

Sloman's trick of using the 120V primaries in series and having your
device connected in parallel across the primaries causes the
transformer to become an autotransformer, which would work.

Using the scheme with a transformer with dual 240V secondaries
likely wouldn't work well because of the much higher winding
resistance you'll encounter causing, I would expect, _very_ poor
regulation.

--
John Fields
Professional Circuit Designer
.

Relevant Pages

  • Re: Resistor vs transformer
    ... Its a wireless receiver unit which calls the fire department in case ... No. Get a transformer with a dual 115V+115V primary, ... primaries in seires, and hook your fire alarm across one of the ... Cost goes by size, but 6VA transformers have rotten regulation. ...
    (sci.electronics.design)
  • Re: Resistor vs transformer
    ... Its a wireless receiver unit which calls the fire department in case ... No. Get a transformer with a dual 115V+115V primary, ... primaries in seires, and hook your fire alarm across one of the ... Cost goes by size, but 6VA transformers have rotten regulation. ...
    (sci.electronics.design)
  • Re: Resistor vs transformer
    ... Its a wireless receiver unit which calls the fire department in case ... No. Get a transformer with a dual 115V+115V primary, ... primaries in seires, and hook your fire alarm across one of the ... Winding resistence doesn't depend ONLY on input voltage range. ...
    (sci.electronics.design)
  • Re: Resistor vs transformer
    ... Its a wireless receiver unit which calls the fire department in case ... No. Get a transformer with a dual 115V+115V primary, ... primaries in seires, and hook your fire alarm across one of the ... Cost goes by size, but 6VA transformers have rotten regulation. ...
    (sci.electronics.design)
  • Re: Resistor vs transformer
    ... Its a wireless receiver unit which calls the fire department in case ... No. Get a transformer with a dual 115V+115V primary, ... primaries in seires, and hook your fire alarm across one of the ... Cost goes by size, but 6VA transformers have rotten regulation. ...
    (sci.electronics.design)