Home |
Search |
Today's Posts |
|
UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
I installed have two halogen light circuits, each consisting of three
12V 35W halogen bulbs. Each circuit is fed by its own 150W 230/12V transformer. Both circxuits are connected in parallel to a 500W dimmer. I put in the lights about five years ago, and all was fine until about two weeks ago, when both transformers failed about the same time. The transformers gave off an overheated smell, and a cable that must have been in contact with one of the units was badly charred. Strange coincidence, I thought as I replaced the transformers two days ago. Even weirder, I thought as the lights worked fine for about one day and again stopped working, with the same symptom: overheating of the transformers and even melting of one of the transformer plastic casings. I checked the bulbs and are all rated 35W, so the 105W load per circuit is confortably within the rating of the transformer. So my attention turned to the dimmer. Can this be causing the problem? Do dimmers fail with symptoms like this? |
#2
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
ppmoore wrote:
I installed have two halogen light circuits, each consisting of three 12V 35W halogen bulbs. Each circuit is fed by its own 150W 230/12V transformer. Both circxuits are connected in parallel to a 500W dimmer. I put in the lights about five years ago, and all was fine until about two weeks ago, when both transformers failed about the same time. The transformers gave off an overheated smell, and a cable that must have been in contact with one of the units was badly charred. Strange coincidence, I thought as I replaced the transformers two days ago. Even weirder, I thought as the lights worked fine for about one day and again stopped working, with the same symptom: overheating of the transformers and even melting of one of the transformer plastic casings. I checked the bulbs and are all rated 35W, so the 105W load per circuit is confortably within the rating of the transformer. So my attention turned to the dimmer. Can this be causing the problem? Do dimmers fail with symptoms like this? you should NOT use dimmers with toroidal transformers. Use electronic ones designed to work with dimmers. However this begs the question of why its worked OK for 5 years. |
#3
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
In article ,
The Natural Philosopher wrote: you should NOT use dimmers with toroidal transformers. Use electronic ones designed to work with dimmers. That was the only way you could dim them before electronic PS became available. You need a dimmer designed for an inductive load, though. -- *Ham and Eggs: Just a day's work for a chicken, but a lifetime commitment Dave Plowman London SW To e-mail, change noise into sound. |
#5
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
"ppmoore" wrote in message ... I installed have two halogen light circuits, each consisting of three 12V 35W halogen bulbs. Each circuit is fed by its own 150W 230/12V transformer. Both circxuits are connected in parallel to a 500W dimmer. I put in the lights about five years ago, and all was fine until about two weeks ago, when both transformers failed about the same time. The transformers gave off an overheated smell, and a cable that must have been in contact with one of the units was badly charred. Strange coincidence, I thought as I replaced the transformers two days ago. Even weirder, I thought as the lights worked fine for about one day and again stopped working, with the same symptom: overheating of the transformers and even melting of one of the transformer plastic casings. I checked the bulbs and are all rated 35W, so the 105W load per circuit is confortably within the rating of the transformer. So my attention turned to the dimmer. Can this be causing the problem? Do dimmers fail with symptoms like this? If an old fashioned TRIAC dimmer, I would guess that at part load there's a significant DC content, which lead directly to heat in your transformers. A TRIAC triggering is inherently asymmetrical, and I'm guessing this has deteriorated over time. |
#6
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
Fredxx wrote:
"ppmoore" wrote in message ... I installed have two halogen light circuits, each consisting of three 12V 35W halogen bulbs. Each circuit is fed by its own 150W 230/12V transformer. Both circxuits are connected in parallel to a 500W dimmer. I put in the lights about five years ago, and all was fine until about two weeks ago, when both transformers failed about the same time. The transformers gave off an overheated smell, and a cable that must have been in contact with one of the units was badly charred. Strange coincidence, I thought as I replaced the transformers two days ago. Even weirder, I thought as the lights worked fine for about one day and again stopped working, with the same symptom: overheating of the transformers and even melting of one of the transformer plastic casings. I checked the bulbs and are all rated 35W, so the 105W load per circuit is confortably within the rating of the transformer. So my attention turned to the dimmer. Can this be causing the problem? Do dimmers fail with symptoms like this? If an old fashioned TRIAC dimmer, I would guess that at part load there's a significant DC content, There is not actually. Ther is however a sigificant harmonic component. which lead directly to heat in your transformers. A TRIAC triggering is inherently asymmetrical, and I'm guessing this has deteriorated over time. Not that I know of it aint. |
#7
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
In article ,
"Fredxx" writes: "The Natural Philosopher" wrote in message ... Fredxx wrote: "ppmoore" wrote in message ... I installed have two halogen light circuits, each consisting of three 12V 35W halogen bulbs. Each circuit is fed by its own 150W 230/12V transformer. Both circxuits are connected in parallel to a 500W dimmer. I put in the lights about five years ago, and all was fine until about two weeks ago, when both transformers failed about the same time. The transformers gave off an overheated smell, and a cable that must have been in contact with one of the units was badly charred. Strange coincidence, I thought as I replaced the transformers two days ago. Even weirder, I thought as the lights worked fine for about one day and again stopped working, with the same symptom: overheating of the transformers and even melting of one of the transformer plastic casings. I checked the bulbs and are all rated 35W, so the 105W load per circuit is confortably within the rating of the transformer. So my attention turned to the dimmer. Can this be causing the problem? Do dimmers fail with symptoms like this? If an old fashioned TRIAC dimmer, I would guess that at part load there's a significant DC content, There is not actually. Ther is however a sigificant harmonic component. which lead directly to heat in your transformers. A TRIAC triggering is inherently asymmetrical, and I'm guessing this has deteriorated over time. Not that I know of it aint. Perhaps you should look up the various gate sensitivities depending on the quadrant of operation. I can assure you there will always be some small difference between any quadrant leading to a small voltage leading to a disproportionately high DC current flowing through the transformer primary. Gate sensitivity doesn't factor because triacs in dimmers are not driven at levels close to gate sensitivity. However, asymmetry of a firing diac does factor in for very simple dimmer circuits where they are used as the firing trigger, but not for higher quality dimmer circuits where hard firing is used. Also, with cheap dimmer circuits, symmetry of the triac's holding current will become significant if the load is at or near the dimmer's minimum load. It is something the OP could do with a DVM. Whilst there are significant harmonic in any TRIAC dimmer, an inductor will present a higher impedance to these frequencies, and any flux in the transformer is inversely proportional to frequency. The first significant harmonic should be the 3rd. A couple of points: Core losses at higher frequencies are also higher, as the stamping thickness is optimised for quenching 50/60Hz eddies, so you get more core heating with higher frequency harmonics. However, I can't see where OP said that a old style transformer was being used. Triacs often die in one direction whilst continuing to work in the other direction, leading to very high DC component (in either case of a short or an open circuit on the failed side). Connect an ordinary filament lamp and check the dimmer still goes from nearly nothing to full brighness. If the triac has partly failed, the light will either go from 0 to half, or from half to full, but not 0 to full. -- Andrew Gabriel [email address is not usable -- followup in the newsgroup] |
#8
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
Fredxx wrote:
"The Natural Philosopher" wrote in message ... Fredxx wrote: "ppmoore" wrote in message ... I installed have two halogen light circuits, each consisting of three 12V 35W halogen bulbs. Each circuit is fed by its own 150W 230/12V transformer. Both circxuits are connected in parallel to a 500W dimmer. I put in the lights about five years ago, and all was fine until about two weeks ago, when both transformers failed about the same time. The transformers gave off an overheated smell, and a cable that must have been in contact with one of the units was badly charred. Strange coincidence, I thought as I replaced the transformers two days ago. Even weirder, I thought as the lights worked fine for about one day and again stopped working, with the same symptom: overheating of the transformers and even melting of one of the transformer plastic casings. I checked the bulbs and are all rated 35W, so the 105W load per circuit is confortably within the rating of the transformer. So my attention turned to the dimmer. Can this be causing the problem? Do dimmers fail with symptoms like this? If an old fashioned TRIAC dimmer, I would guess that at part load there's a significant DC content, There is not actually. Ther is however a sigificant harmonic component. which lead directly to heat in your transformers. A TRIAC triggering is inherently asymmetrical, and I'm guessing this has deteriorated over time. Not that I know of it aint. Perhaps you should look up the various gate sensitivities depending on the quadrant of operation. I can assure you there will always be some small difference between any quadrant leading to a small voltage leading to a disproportionately high DC current flowing through the transformer primary. It is something the OP could do with a DVM. Very small by comparison with the actual rated currents of the transformers. And most dimmers are not 'just' triacs these days. The ons switching is controlled by a chip or some other method usually. Whilst there are significant harmonic in any TRIAC dimmer, an inductor will present a higher impedance to these frequencies, and any flux in the transformer is inversely proportional to frequency. The first significant harmonic should be the 3rd. what about the capacitors uses to snub the switching :-) And various other stray capacitance effects.. Mind you its true to say that largely toroids present a greater danger to dimmers, than dimmers to toroids. |
#9
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
Andrew Gabriel wrote:
In article , "Fredxx" writes: "The Natural Philosopher" wrote in message ... Fredxx wrote: "ppmoore" wrote in message ... I installed have two halogen light circuits, each consisting of three 12V 35W halogen bulbs. Each circuit is fed by its own 150W 230/12V transformer. Both circxuits are connected in parallel to a 500W dimmer. I put in the lights about five years ago, and all was fine until about two weeks ago, when both transformers failed about the same time. The transformers gave off an overheated smell, and a cable that must have been in contact with one of the units was badly charred. Strange coincidence, I thought as I replaced the transformers two days ago. Even weirder, I thought as the lights worked fine for about one day and again stopped working, with the same symptom: overheating of the transformers and even melting of one of the transformer plastic casings. I checked the bulbs and are all rated 35W, so the 105W load per circuit is confortably within the rating of the transformer. So my attention turned to the dimmer. Can this be causing the problem? Do dimmers fail with symptoms like this? If an old fashioned TRIAC dimmer, I would guess that at part load there's a significant DC content, There is not actually. Ther is however a sigificant harmonic component. which lead directly to heat in your transformers. A TRIAC triggering is inherently asymmetrical, and I'm guessing this has deteriorated over time. Not that I know of it aint. Perhaps you should look up the various gate sensitivities depending on the quadrant of operation. I can assure you there will always be some small difference between any quadrant leading to a small voltage leading to a disproportionately high DC current flowing through the transformer primary. Gate sensitivity doesn't factor because triacs in dimmers are not driven at levels close to gate sensitivity. However, asymmetry of a firing diac does factor in for very simple dimmer circuits where they are used as the firing trigger, but not for higher quality dimmer circuits where hard firing is used. Also, with cheap dimmer circuits, symmetry of the triac's holding current will become significant if the load is at or near the dimmer's minimum load. It is something the OP could do with a DVM. Whilst there are significant harmonic in any TRIAC dimmer, an inductor will present a higher impedance to these frequencies, and any flux in the transformer is inversely proportional to frequency. The first significant harmonic should be the 3rd. A couple of points: Core losses at higher frequencies are also higher, as the stamping thickness is optimised for quenching 50/60Hz eddies, so you get more core heating with higher frequency harmonics. However, I can't see where OP said that a old style transformer was being used. Triacs often die in one direction whilst continuing to work in the other direction, leading to very high DC component (in either case of a short or an open circuit on the failed side). Connect an ordinary filament lamp and check the dimmer still goes from nearly nothing to full brighness. If the triac has partly failed, the light will either go from 0 to half, or from half to full, but not 0 to full. All my dimers that have failed, have failed completely. Either full on, or the board burned out, or both in fact as I discovered when I repaired a track. |
#10
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
In article ,
The Natural Philosopher wrote: All my dimers that have failed, have failed completely. Either full on, or the board burned out, or both in fact as I discovered when I repaired a track. I've got some 75 watt halogen mains spots (a bit like a small PAR38) on a dimmer, and when one failed it not only blew the dimmer to bits but tripped the 10 amp MCB. -- *Husbands should come with instructions Dave Plowman London SW To e-mail, change noise into sound. |
#11
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
|
#12
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
In article ,
Skipweasel wrote: Bulbs have fuses in them lately, but they still don't seem to actually work, hence the blown bits. The purpose of the triac in the dimmer is to protect the fuse in the lamp.;-) -- * I like you. You remind me of when I was young and stupid Dave Plowman London SW To e-mail, change noise into sound. |
#13
Posted to uk.d-i-y
|
|||
|
|||
Using a dimmer with 12V halogen lamps
In article ,
says... Bulbs have fuses in them lately, but they still don't seem to actually work, hence the blown bits. The purpose of the triac in the dimmer is to protect the fuse in the lamp.;-) More likely to work than one of these... http://www.voltimum.co.uk/news/9428/...ing-Alert.html -- Skipweasel - never knowingly understood. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
What is it with halogen lamps? | UK diy | |||
Low energy lamps with dimmer | UK diy | |||
halogen dimmer | Electronics Repair | |||
replacing halogen lamps | UK diy | |||
Halogen lamps ... Low voltage or mains? | UK diy |