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1267 posts

Uber Geek

  #1581419 27-Jun-2016 19:39
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Here's a heads-up and a question:


I took richms's suggestion of using a cheap PWM dimmer, together with a brick and an LED strip. Interesting exercise.


JCAR Electronics sell a very reasonable strip option - One 3-light segment of an LED strip for $3.60. For experimentation purposes I purchased a strip of 9 lights. It's about 200mm long.


As to the brick, the shop next door (a major lighting chain) had a driver for a very good price - $8.70. The data sheet says it's a 'Eurolite Ultra Series Electronic Transformer'.


That left the 12v dimmer, which cost me $19.20 from JCAR. It's an inline model with a rotary control that's also supposed to be an on\off switch.


I've got these components breadboarded together.


The dimmer's box states 'Dimming 0-100%'. That's not completely accurate - the LEDs never turn off. Very low output, of course, but certainly not '0-100%'. So the on\off part of the gizmo doesn't work.


My question: The transformer's spec sheet also says, 'dimmable with leading edge or trailing edge dimmer'. I take this to mean that the transformer itself is actually dimmable, ie, with the dimmer placed upstream of the transformer, rather than after it, where it's rigged now.


Obviously, I can't use the 12v JCAR dimmer in that situation, but I also have the unused 240v HPM dimmer that I described in my opening post. The model is an 'XL400TWE trailing edge dimmer' and the box says 'suitable for electronic transformers'.


I ask because:


1) It's a better quality dimmer than the JCAR 12v unit and


2) It comes with an on\off switch on the faceplate, something the 12v JCAR dimmer lacks. As I said, its on\off switch doesn't work.


Comments, please.









'Ask not what you can do for your country: Ask what you can do for me'. Donald J.Trump. US President 2016 - 2020.





3885 posts

Uber Geek

  #1581546 27-Jun-2016 22:01

You will need a proper 12V power supply. Those electronic transformers normally output a high frequency pulsed DC, or High frequency AC. If they are intended for halogen lights. Or constant current DC if intended for LEDs. Either way they are meant to be directly connected to the light, not have another controller installed on their output.


The Jaycar 12V dimmer will most likely be a pulsed output with the ratio of On Vs off varying to change the light output. It will not be able to go completely off. But when it is used with a filament lamp. At very low outputs, the filament doesn't get hot enough to start glowing. So the lights appear fully off. While the LEDs (as you have found) will glow with even the smallest current.


You can try your original dimmer on the input of your electronic transformer. But don't expect any miracles. As there are lots of problems with trying to get LEDs to dim properly using a mains dimmer. Filament lights will always work better off a mains dimmer compared to LEDs.


Get an actual 12V power supply, And install a separate switch (or just unplug the power supply) to make it go completely off. And the LEDs should work really well.


And be careful - as some of those electronic lighting transformers might not have full isolation between the input and output. Which means that if the phase and neutral get swapped over, the output becomes live with mains. But it otherwise works correctly. Not a problem for something that gets wired in permanently by an electrician, and in in a ceiling where it can't easily be touched. But when it has a plug on the end - meaning you can't control what it gets plugged into, it is in an area where it can easily be touched, and the output wiring is definitely not intended to handle mains voltages. If something goes wrong, it is more likely to go very wrong.



1267 posts

Uber Geek

  #1582416 29-Jun-2016 08:20
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Thanks, Aredwood.


I didn't want to connect the expensive HPM dimmer to the electronic transformer and strip light until I knew I couldn't damage it.


Turns out, it works fine upstream of the transformer, into which the LEDs are wired.


The light output is no different than before - the 9 LEDs still glow at minimum dimmer output, but they don't appear to flicker at all. And the whole rig is much simpler.


The only unknown is the longevity of the cheap transformer, but it'll be in housed inside a secure wall box so if it fails it can be replaced.



'Ask not what you can do for your country: Ask what you can do for me'. Donald J.Trump. US President 2016 - 2020.





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