Re: Resistor vs transformer



bill.sloman@xxxxxxxx wrote:
Fred Bloggs wrote:

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.


It makes no sense to use a transformer this way. If he can buy a
transformer then he should get a 230->115 step down.


It's a question of price and availability. Split primary transformers
are a commodity product available off the shelf in a vast range of
sizes. Auto-transformers are a niche product, and you are likely to
have to buy a bigger transformer than you need at a consumer price.

Phil Allison's example cost some $A59 (including tax) equivalne to
$43.60 or 36.5 euro which is a couple of times more than you'd have to
spend on a regular transformer and a box to put it in.


We don't really know what's going on here. If all the alarms are on a dedicated circuit then you can consolidate all the transformer cost into a single transformer. The prime power converter market for 220-110 runs the full range from pricey designer models to low end utilitarian cheapies. Here is a low end utilitarian cheapie:
http://www.alldual.com/trans/VolTRANS/StepDown.htm

.

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 ... 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)
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