halogen lamps & dimmer switches
Stewart Duncan
anyone know if they should be fitted on the 12 volt circuit or on the 220
volt mains circuit? Thank you.
Looksy Malone
240 voly circuit but make sure you have a dimmable transformer and
proper dimmer switch.
Dave Plowman
Looksy Malone <mys...@looksy.fsnet.co.uk> wrote:
> 240 voly circuit but make sure you have a dimmable transformer and
> proper dimmer switch.
Since you like making smart ass replies, here's one. *All* transformers
for 12 volt lighting can be operated via a dimmer.
--
* Depression is merely anger without enthusiasm *
Dave Plowman dave....@argonet.co.uk London SW 12
RIP Acorn
Looksy Malone
<dave....@argonet.co.uk> wrote:
>In article <3a72a39b....@news.freeserve.co.uk>,
> Looksy Malone <mys...@looksy.fsnet.co.uk> wrote:
>> 240 voly circuit but make sure you have a dimmable transformer and
>> proper dimmer switch.
>
>Since you like making smart ass replies, here's one. *All* transformers
>for 12 volt lighting can be operated via a dimmer.
No, Not the case. Or at least it wasn't a few years ago. There were
dimmable transformers and non dimmable ones.
Yes, i do like making smart arse replies but on this i am right. I
admit things may be different with latest technology but worth
checking.
Dave Plowman
Looksy Malone <mys...@looksy.fsnet.co.uk> wrote:
> No, Not the case. Or at least it wasn't a few years ago. There were
> dimmable transformers and non dimmable ones.
The non dimmable 'transformers' are not transformers but switch mode power
supplies.
--
* I couldn't repair your brakes, so I made your horn louder *
Looksy Malone
<dave....@argonet.co.uk> wrote:
>In article <3a70cf0c....@news.freeserve.co.uk>,
> Looksy Malone <mys...@looksy.fsnet.co.uk> wrote:
>> No, Not the case. Or at least it wasn't a few years ago. There were
>> dimmable transformers and non dimmable ones.
>
>The non dimmable 'transformers' are not transformers but switch mode power
>supplies.
Sorry but no. I dont care what they are they are all sold as
transformers. About 6 years ago I had some which were not dimmable.
The guy simply asked for some advice and i gave him some good advice.
You are being silly and trying to complicae things. And you say i
like to give smart asrse answers!
ian_c...@my-deja.com
Dave Plowman wrote:
>
> The non dimmable 'transformers' are not transformers but switch mode power
> supplies.
Hi Dave
Isn't that a rather picky point, given that at most outlets you'd be
hard pushed to get the staff to clarify what the method of operation of
the voltage reducing device was?
And in relation to Stewart Duncan writing:
> I have ceiling mounted halogen lamps and wish to fit dimmer switches. Does
> anyone know if they should be fitted on the 12 volt circuit or on the 220
> volt mains circuit?
the answer remains unclear. How does one figure out if the transformer
is actually a switched mode power supply, and if it is can the 12V
circuit be dimmed?
I'm interested in the answer too.
IanC
Wapimak
off of a solid state (switcher) or transformer on the 240V side.
My reasoning is as follows:-
Most lamp dimmers are only designed to feed a non reactive (ie purely
resistive) load, as they are switching devices, either controlling the phase
angle delay in turning on the mains cycle to the device, or are 'burst' mode
whereby they let several cycles of complete mains sinewaves through, and
then turn off at the zero crossing points. If you feed a reactive load with
either you will generate large voltage transients within the dimmer which
will strain its internals and possibly nuke it short term.
Anyway any form of dimming for halogens, 240V, 12V or otherwise is a no no
as it shortens the life of the bulb. The life of a halogen bulb is
maintained by the halogen cycle which has to run at a very high temperature.
This prevents the filament from evaporating and condensing onto the
surrounding quartz envelope.
Looksy Malone <mys...@looksy.fsnet.co.uk> wrote in message
news:3a704c3f....@news.freeserve.co.uk...
Brian
<mys...@looksy.fsnet.co.uk> writes
>On Thu, 25 Jan 2001 00:20:28 +0000 (GMT), Dave Plowman
><dave....@argonet.co.uk> wrote:
>
>>In article <3a70cf0c....@news.freeserve.co.uk>,
>> Looksy Malone <mys...@looksy.fsnet.co.uk> wrote:
>>> No, Not the case. Or at least it wasn't a few years ago. There were
>>> dimmable transformers and non dimmable ones.
>>
Is the difference because dimmers work by switching at different points
in the phase of the input voltage. The output is therefore non-
sinusoidal and contains harmonics of 50 Hz for which a normal mains
transformer is not designed to handle. The energy in the harmonics will
then be dissipated in the transformer rather than passed on to the lamp
with consequent overheating.
--
Brian
Dave Plowman
Looksy Malone <mys...@looksy.fsnet.co.uk> wrote:
> Sorry but no. I dont care what they are they are all sold as
> transformers.
It tends to be one of the features of this group that many will give
better advice than counter staff.
But when you nit-pick at others on this group, prepare to get as good as
you give.
--
* A conclusion is the place where you got tired of thinking *
ch...@areti.co.uk
>
> Well I think you are all wrong, and you cannot dim 12V halogens which run
> off of a solid state (switcher) or transformer on the 240V side.
> My reasoning is as follows:-
> Most lamp dimmers are only designed to feed a non reactive (ie purely
> resistive) load, as they are switching devices, either controlling the phase
> angle delay in turning on the mains cycle to the device, or are 'burst' mode
> whereby they let several cycles of complete mains sinewaves through, and
> then turn off at the zero crossing points. If you feed a reactive load with
> either you will generate large voltage transients within the dimmer which
> will strain its internals and possibly nuke it short term.
But a transformer feeding a lamp won't be reactive. A 'perfect' real
transformer will be 'invisible' in electrical terms, you will see the
exact equivalent load at a different voltage.
In practice you will see a little more inductive reactance when
looking 'through' the transformer but it shouldn't have too much
effect.
--
Chris Green (ch...@areti.co.uk)
Dave Plowman
<ian_c...@my-deja.com> wrote:
> > The non dimmable 'transformers' are not transformers but switch mode
> > power supplies.
> Hi Dave
> Isn't that a rather picky point, given that at most outlets you'd be
> hard pushed to get the staff to clarify what the method of operation of
> the voltage reducing device was?
I was just attempting to tell the one who does not want to be identified
that I don't like him slagging off others. Do a search of this newsgroup
if you want to see what I mean.
> And in relation to Stewart Duncan writing:
> > I have ceiling mounted halogen lamps and wish to fit dimmer switches.
> > Does anyone know if they should be fitted on the 12 volt circuit or on
> > the 220 volt mains circuit?
> the answer remains unclear. How does one figure out if the transformer
> is actually a switched mode power supply, and if it is can the 12V
> circuit be dimmed?
I'm afraid their is no universal answer - some electronic types *are*
suitable for dimmers.
> I'm interested in the answer too.
The main difference between the two will be in the weight - a SMPS type
will be smaller, lighter and usually cheaper. IMHO, the most suitable
transformers for 'dimming' are toroidal types which are usually in
circular housings.
Something like the TLC cat lists types which are and aren't suitable.
--
* Starfishes have no brains *
mar...@my-deja.com
"Wapimak" <wap...@4u.net> wrote:
> Well I think you are all wrong, and you cannot dim 12V halogens which
run
> off of a solid state (switcher) or transformer on the 240V side.
> My reasoning is as follows:-
> Most lamp dimmers are only designed to feed a non reactive (ie purely
> resistive) load, as they are switching devices, either controlling the
phase
> angle delay in turning on the mains cycle to the device, or are
'burst' mode
> whereby they let several cycles of complete mains sinewaves through,
and
> then turn off at the zero crossing points. If you feed a reactive load
with
> either you will generate large voltage transients within the dimmer
which
> will strain its internals and possibly nuke it short term.
> Anyway any form of dimming for halogens, 240V, 12V or otherwise is a
no no
> as it shortens the life of the bulb. The life of a halogen bulb is
> maintained by the halogen cycle which has to run at a very high
temperature.
> This prevents the filament from evaporating and condensing onto the
> surrounding quartz envelope.
OK, I'll bite. Untrue. Sounds good in theory, but in practice doesn't
happen (or is insignificant). For my evidence, I'll cite the two
dimmable mains halogen lamps that I have had running for around 3-5
years. The 5 year old one is used about equally at 50% power an 100%
power, and is on the original bulb, with no blackening evident. The 3
year old one is used almost exclusively at around 30% power, every night
(on a timer switch) with very infrequent use at full power. This is also
on the original bulb, with no blackening of the glass. Finally, have a
look at you car headlamp bulbs - when they're switched to 'sidelights'
with the ignition on, modern cars run the main bulb at a very low power
level (dim-dip) through a line resistor. I doubt if they would design
the system
this way if it was likely to cause bulb damage.
Mark
Sent via Deja.com
http://www.deja.com/
Dave Plowman
Brian <br...@guarlfrd.demon.co.uk> wrote:
> Is the difference because dimmers work by switching at different points
> in the phase of the input voltage. The output is therefore non-
> sinusoidal and contains harmonics of 50 Hz for which a normal mains
> transformer is not designed to handle. The energy in the harmonics will
> then be dissipated in the transformer rather than passed on to the lamp
> with consequent overheating.
A toroidal transformer is rather happier with a non sine wave than a
conventional 'core' type.
--
* The average person falls asleep in seven minutes *
Andy Wade
>But a transformer feeding a lamp won't be reactive. A 'perfect' real
>transformer will be 'invisible' in electrical terms, you will see the
>exact equivalent load at a different voltage.
>
>In practice you will see a little more inductive reactance when
>looking 'through' the transformer but it shouldn't have too much
>effect.
Yes, but isn't the problem this?... In an 'ordinary' dimmer the triac is
fired with a very short pulse from a capacitor and break-over diode (diac).
If at the end of the firing pulse the load current hasn't reached a value
sufficient to hold the triac in conduction then you end up with no output
for the remainder of the half-cycle -- and therefore, to all intents and
purposes, no output at all. If the firing pulse is only of the order of
microseconds, it wouldn't take much in the way of transformer leakage
reactance to reduce di/dt to the point where the triac won't hold on. And am
I not right in thinking that there are 'hard-fired' dimmers available which
use more sophisticated firing circuits to circumvent this effect?
If I'm right I'd expect, torroidal transformers to be more likely to work
with an 'ordinary' dimmer than laminated core types (due to the lower
leakage inductance). Also connecting some (resistive) load on the primary
side of the tranny might also help. Maybe.
--
Andy
Dave Plowman
Andy Wade <ajw...@dial.pipex.com> wrote:
> I not right in thinking that there are 'hard-fired' dimmers available
> which use more sophisticated firing circuits to circumvent this effect?
Certainly, not all dimmers will work with an inductive load - but the
ones specified for 'low voltage' work will work OK with a 'normal' load.
--
* 'ome is where you 'ang your @ *
Andrew Gabriel
"Andy Wade" <ajw...@dial.pipex.com> writes:
>And am
>I not right in thinking that there are 'hard-fired' dimmers available which
>use more sophisticated firing circuits to circumvent this effect?
Yes - they either use a snubber network (resister in series with
capacitor) to conduct the triac's holding current for a very short
time until sufficient current builds up in the inductive load, or
they use an extended pulse into the triac.
The other thing you can do is to add a regular resistive load such
as a mains 40W lamp. Some ~25 years ago, I used this technique to
enable me to dim fluorescent lamps with cheap dimmer and regular
control gear (with minor addition) - details available at
http://www.misty.com/people/don/f-dim.html
--
Andrew Gabriel
Consultant Software Engineer
Peter Parry
>the answer remains unclear. How does one figure out if the transformer
>is actually a switched mode power supply,
Weight and (usually) shape. The switched mode are lightweight (few
ounces) and often long and thin to fit through the hole in the
ceiling. Conventional 50Hz transformers are much heavier and
normally circular or square.
>and and if it is can the 12V circuit be dimmed?
Some switched mode units are marked as dimmable however there is as
far as I am aware no absolute way other than this of telling a
dimmable from a non-dimmable.
--
Peter Parry.
http://www.wpp.ltd.uk/
Chris Burrow
Lots of good stuff about this but there is a rather complicated point that I
only became aware of recently that may be of interest.
Most iron cored inductors or transformers are built with slightly less iron
than than they should be for obvious bean counter reasons, normally this
should saturate the core and cause problems but in the real world when a
core is magnetised, reminance leaves the core marginally magnetised. When
the current switches over to the other direction this reminance, or perhaps
hysteresis, must be overcome by the manetic force applied by the current and
consequently the core does not saturate.
So when you next switch on your big transformer and it makes a thump and
even blows a fuse, it's not because you happen to have switched it on the
top of the mains cycle - as I previously thought - but you have switched it
at the bottom of the cycle and there is no reminant field to prevent the
core saturating.
Relevance to dimmers and transformers, older dimmers switch on as near as
dammit to zero when at full I think, not sure how they get round this other
than switching supplies or some fancy circuitry.
Regards,,
Chris
Dave Plowman
Chris Burrow <g7...@rem0veme.hotmail.com> wrote:
> Most iron cored inductors or transformers are built with slightly less
> iron than than they should be for obvious bean counter reasons, normally
> this should saturate the core and cause problems but in the real world
> when a core is magnetised, reminance leaves the core marginally
> magnetised. When the current switches over to the other direction this
> reminance, or perhaps hysteresis, must be overcome by the manetic force
> applied by the current and consequently the core does not saturate. So
> when you next switch on your big transformer and it makes a thump and
> even blows a fuse, it's not because you happen to have switched it on
> the top of the mains cycle - as I previously thought - but you have
> switched it at the bottom of the cycle and there is no reminant field to
> prevent the core saturating.
Most 'low voltage lighting' transformers are toroidals - they don't have
a core. But they do have rather a greater 'switch on' surge.
--
* I'm not a complete idiot, some parts are missing *
JimJam
A good rule of thumb is
Electronic dimmable tranny - can any standard dimmer
Standard Transformer - use a LV dimmer.
Mark
"Dave Plowman" <dave....@argonet.co.uk> wrote in message
news:4a42112b26...@argonet.co.uk...
ch...@areti.co.uk
>
> Most 'low voltage lighting' transformers are toroidals - they don't have
> a core. But they do have rather a greater 'switch on' surge.
>
--
Chris Green (ch...@areti.co.uk)
Phil Addison
>Dave Plowman <dave....@argonet.co.uk> wrote:
>>
>> Most 'low voltage lighting' transformers are toroidals - they don't have
>> a core. But they do have rather a greater 'switch on' surge.
>>
>??? Of course they have a core, it just happens to be a toroidal one.
Oh dear... definitions time.
A toroid is the shape you get when you wind a wire around a ring shaped
former (I was going to say doughnut shaped but not all doughnuts have
holes in them these days). Alternatively it is a helix bent round so the
ends touch.
A toroidal transformer has two such windings, primary and secondary (you
guessed that?), wound around a solid core. The core is invariably a
Feroxcube type of material, i.e. moulded and sintered from a high tech
magnetic powder. It makes a much more efficient core than steel
lamentations as used in rectangular E-I section transformers. You
*could* have an air-cored transformer but it would pass very little
power at 50Hz. Such things are used it telecomms at much higher
frequencies.
HTH
Phil Addison
Dave Plowman
<ch...@areti.co.uk> wrote:
> > Most 'low voltage lighting' transformers are toroidals - they don't have
> > a core. But they do have rather a greater 'switch on' surge.
> >
> ??? Of course they have a core, it just happens to be a toroidal one.
'Course you're right. Must take more water with it.
--
* If tennis elbow is painful, imagine suffering with tennis balls *
Dave Plowman
JimJam <underwea...@btinternet.com> wrote:
> Sort of but you need to ensure you have to correct dimmer.
> A good rule of thumb is
> Electronic dimmable tranny - can any standard dimmer
Nearly, but in the strict sense of the term, a transformer isn't
electronic. The 'electronic dimmable tranny' is a switch mode power supply.
--
* "I am " is reportedly the shortest sentence in the English language. *
Andy Wade
> The core is invariably a
> Feroxcube type of material, i.e. moulded and sintered from a high tech
> magnetic powder.
No, the core of ordinary torroidal mains transformers is made from a long
thin strip of high permeability silicon-steel wound into a ring (like a
roll of sellotape). Iron powder and ferrite materials are much more
expensive and probably wouldn't work any better at 50Hz in any case. They
come into their own at the much higher frequencies (10's of kHz upwards)
used for SMPS's.
Torroidal xfmrs are quite easy to strip down, so if you don't believe me
find an old one and take the windings off. This 'feature' also makes it
relatively easy to rewind or adjust secondary windings for different
voltages. (The mains primary is invariably wound first, with the
secondary(ies) on top.)
--
Andy
Phil Addison
<ajw...@dial.pipex.com> wrote:
>Phil Addison wrote ...
>
>> The core is invariably a
>> Feroxcube type of material, i.e. moulded and sintered from a high tech
>> magnetic powder.
>
>No, the core of ordinary torroidal mains transformers is made from a long
>thin strip of high permeability silicon-steel wound into a ring (like a
>roll of sellotape). Iron powder and ferrite materials are much more
>expensive and probably wouldn't work any better at 50Hz in any case. They
>come into their own at the much higher frequencies (10's of kHz upwards)
>used for SMPS's.
Yes, I stand corrected. I was thinking of the switcher cores.
>Torroidal xfmrs are quite easy to strip down, so if you don't believe me
>find an old one and take the windings off. This 'feature' also makes it
>relatively easy to rewind or adjust secondary windings for different
>voltages. (The mains primary is invariably wound first, with the
>secondary(ies) on top.)
You are referring to stripping of just the secondaries, or all windings?
In pedantic mode, is there a special name for a rectangular section
'toroid'?
Phil Addison
Andy Wade
>You are referring to stripping of just the secondaries, or all windings?
Both: the secondaries if you want to rewind for a different voltage, all
windings if you want to find out how the core is made.
>In pedantic mode, is there a special name for a rectangular section
>'toroid'?
Pass.
--
Andy
Phil Addison
<ajw...@dial.pipex.com> wrote:
>Phil Addison wrote ...
>
>>You are referring to stripping of just the secondaries, or all windings?
>
>Both: the secondaries if you want to rewind for a different voltage, all
>windings if you want to find out how the core is made.
Ahh, just stripping. I assumed you meant strip and re-wind rather than
strip and bin. Without doing the sums I would think the primary has too
many turns to be rewound by hand, not to mention safety issues.
Phil Addison
Andy Wade
>Ahh, just stripping. I assumed you meant strip and re-wind rather than
>strip and bin. Without doing the sums I would think the primary has too
>many turns to be rewound by hand, not to mention safety issues.
Yes, several thousand turns for a small size one, and several hundred for
medium size (100 - 500 VA sort of size). But you'd only need to rewind the
primary if you wanted to cater for a different input voltage. Since
ex-stock transformers are readily available with 115, 230 and 400V inputs
it'd be better to buy one of those and just adapt the secondary if you want
a particular o/p voltage.
--
Andy
ne...@river-view_dot_freeserve.co.uk
>> as it shortens the life of the bulb. The life of a halogen bulb is
>> maintained by the halogen cycle which has to run at a very high
>temperature.
>> This prevents the filament from evaporating and condensing onto the
>> surrounding quartz envelope.
>
>OK, I'll bite. Untrue. Sounds good in theory, but in practice doesn't
>happen (or is insignificant). For my evidence, I'll cite the two
>dimmable mains halogen lamps that I have had running for around 3-5
>years. The 5 year old one is used about equally at 50% power an 100%
>power, and is on the original bulb, with no blackening evident. The 3
>year old one is used almost exclusively at around 30% power, every night
>(on a timer switch) with very infrequent use at full power. This is also
1) Even infrequent use at full power is sufficient to redeposit the
filament, apparently.
2) If you _always_ (ie 100%) run at bulb at 30% power, I wouldn't
expect it to have a blackened envelope (until it actually fails
anyway), the filament will be deposited as a thin metal layer,
which probably wouldn't even be visible.
'1' is fairly commonly stated, and seems plausible to me, '2' is
just a guess, open to suggestions :-)
Nigel