Lightprocessor Dimension 610 Dimmer

[KevinE]

The snubber versions are required by these dimmers

 

You really need to fit the right ones. The -W on the end of an SGS-Thomson triac means they are snubberless. The sensitivity is the letter before it, eg S, A, B, C with S the most sensitive and C the least. There is also a T which means logic-level gate drive.

 

The snubberless ones really come into play with regard to reliability when driving inductive, transformer or motor loads as this is when they may cause trouble. It shouldnt matter either way if it's just lamp loads.

 

The PSC does make a difference in that it affects the current that flows under fault conditions.

I'm sure that since Liteprocessor have made dimmers for years, they'd have noticed if they had designed a suicidal product like yours seem to be! Try FF fuses and see how you go.

[swampman]

The other item that should be in line inside the dimmers is a choke. I have not had the opportunity of disecting one this model, so: do they have one, if so at least what size is it, how many coil turns are visible, what shape ... ?

The dark world of inductors and maths associated leads to a basic comparison on these parameters.

 

Why do I refere to the choke ? Becuase in a short circuit fault situation the intensity will lag behind V and it will also saturate causing a higher Z. (I stand to be corrected on this explanation but dimmers with butch chokes seem to survive more torment :D )

[Don Allen]

If I repair a dimmer with a low current triac , less than twice the rated load, I always replace it with a triac that is at least 4 times the rated load current, looking up data sheets to match gate sensitivity and other characteristics. I have a folder of triac data sheets to help cross reference.

 

So for a 2.4kW 10 amp dimmer channel I would fit a 40 amp triac with a case style to suit the dimmer.

 

If you look at manufacturers such as Jands in Australia, they dont use low current triacs.

[DrV]

The other item that should be in line inside the dimmers is a choke. I have not had the opportunity of disecting one this model, so: do they have one, if so at least what size is it, how many coil turns are visible, what shape ... ?

The dark world of inductors and maths associated leads to a basic comparison on these parameters.

 

Why do I refere to the choke ? Becuase in a short circuit fault situation the intensity will lag behind V and it will also saturate causing a higher Z.

I think this is a good point although...

(I stand to be corrected on this explanation but dimmers with butch chokes seem to survive more torment :D )

I think what you mean is that when the choke saturates it will become a lower impedance as it becomes purely resistive at that point. Net result is the same - less impedance in the way -> higher fault current.

 

And regarding the issue of fitting devices with the right gate sensitivity, the only place I have seen sensitive gate devices fitted has been cheap sound triggered disco lights where there is very little electronics between the mic and the triac. Even the cheapest dimmers usually have a "proper" firing circuit, either using a pulse transformer or an opto/opto-triac. In the repair business it makes sense to fit a high current device - the cost differential is negligible, but when you are buying thousands of them perhaps manufacturers sometimes make savings where they shouldn't.

 

Dave

[srslight]

- the cost differential is negligible, but when you are buying thousands of them perhaps manufacturers sometimes make savings where they shouldn't.

 

Thats 100% true - we're using only BTA48/800 or BTA48/600 for each unit - the most important thing is look on i2t parameter - must be higher than i2t of the protecting circuit that means that fault will start the protection - not firing your triac. The other thing is have good choke with high risetime - because energy of the short circuit can be stored on good choke until the breaker tripped... But good chokes and triacs COST money.

[swampman]

The other item that should be in line inside the dimmers is a choke.

...

Why do I refere to the choke ? Becuase in a short circuit fault situation the intensity will lag behind V and it will also saturate causing a higher Z.

I think this is a good point although...

(I stand to be corrected on this explanation but dimmers with butch chokes seem to survive more torment :D )

I think what you mean is that when the choke saturates it will become a lower impedance as it becomes purely resistive at that point. Net result is the same - less impedance in the way -> higher fault current.

 

The opposite would be the case the rush of current would in fact be filtered since it is a "high" frequency occurence in contrast with the normal 50Hz mains load.

[DrV]

The other item that should be in line inside the dimmers is a choke.

...

Why do I refere to the choke ? Becuase in a short circuit fault situation the intensity will lag behind V and it will also saturate causing a higher Z.

I think this is a good point although...

(I stand to be corrected on this explanation but dimmers with butch chokes seem to survive more torment :D )

I think what you mean is that when the choke saturates it will become a lower impedance as it becomes purely resistive at that point. Net result is the same - less impedance in the way -> higher fault current.

 

The opposite would be the case the rush of current would in fact be filtered since it is a "high" frequency occurence in contrast with the normal 50Hz mains load.

 

True up to the point where the choke saturates, but we are dealing with a fault current here. And the chokes in your average dimmer rack aren't of such vast reactance that they offer any substantial impedance to 50Hz - they are designed to filter out the sharp edges caused by the semiconductor switching. Consider the risetimes quoted in dimmer manufacturers' literature; 100uS standard, 450uS for a quiet version.

 

Dave

[bigclive]

The science of a lamp failing and taking out the triac is that when the filament breaks it sputters metal vapour which turns the lamp into an unballasted discharge lamp briefly, often turning the interior of the lamp a shiny black in the process as the metal vapour condenses on the glass.

 

The main thing is that it does effectively go short circuit, so the total circuit impedance/resistance is the only current limiting factor.

 

Fuse choice is important. A glass fuse is only designed to break a short circuit current of about 35A and current higher than this will result in a brief sustained arc in the fuse as it happily passes hundreds of amps. If the fuse has exploded or gone black inside, then this is what has happened. Sand filled ceramic fuses are rated to break over 1000A and will do so in a fast controlled manner. The FF fuses are expensive but probably easier to change than a triac. The quick-blow fuses will probably save a few triacs. The slow-blow fuses will not really save triacs.

 

Yes I know that the glass fuses are cheaper and you can see through them to check if they've gone boom, but seriously, you need to use ceramic fuses in mains circuits subject to high current faults.

 

Big fat chokes do indeed limit the current of a dead short enough to save robust semiconductors. They also limit the current of a wiring dead short, but lets not go there, it's scary. You might as well throw your breaker trip characteristics manual in the bin for a partially dimmed short circuit with a fat choke in line. The choke will get hot. The breaker will not trip in a hurry.

 

A BTA12 is a fairly lightly rated triac. A BTA16 would be better in the same package form, but a BTA26 or higher would be best, although the package is bigger and may not fit in some triac mounting arrangements. The peak current rating of these components is typically 10 times their normal rating, so using a high current triac gives a more significant short circuit current handling capability.

 

The snubberless triacs have a higher DVDT rating, which basically means they can handle sharp transients better then ordinary triacs. These transients could be from an inductive load, and in some cases can cause false triggering of the triac.

 

The best dimmers either use enormous indestructible switching devices like inverse parallel thyristor modules, or have easy to change triac assemblies so that changing a triac is almost as easy as changing a fuse.

[KevinE]

I know this is an old thread, but it might be useful for someone.

I've just had a batch of these in for repair...a leaky roof had drenched them. The correct triac is a BTA12-600BW and uses a quick-fit pressbutton terminal block and philips screw through the tab. The factory fitted fuse is F10A ceramic. Yes, they have large chokes, mounted behind the chassis plate. Firing is by optotriac coupled to the gates by fusible resistors. Each channel also has RFI RC networks.

 

Some of the channels had blown triacs and several of those had damaged or blown the gate drive circuitry. There is a cut-out on the chassis plate to enable you to repair this without taking the pcb off the plate.

 

A couple of the packs had 'domed' power supply capacitors.

 

The pcb-mount fuseholders are easily 'opened up' by careless fitting of fuses and there was evidence of hot spots on the clips.

 

Build quality is superb and on a par with the paradime stuff.

 

:)

Edited February 9, 2017 by KevinE

[rowifi]

For better or worse .. I designed these. If I remember correctly the big paradims were the same component designs excepting the Triac size.

I'm here because I just found one in my cupboard after a clear out and then checking out ebay :)