DC Dimming Board

[tconley]

I am just putting this out to see who might be interested in a dimming board designed specifically to handle dimming? I was planning on using dc to drive led MR-16 and it sounded like other might be interested as well.


This would be similar to the dc-16 from d-light.

[FireGod]

Per the thread:
http://www.christmasinshirley.com/forum/viewtopic.php?t=315&postdays=0&postorder=asc&start=0
I am fairly sure that the standard SSR board can be used for dimming if you look at the posts of July 10. Any DC dimming will need to be PWM if the power supply is DC. Someone needs to test the parts mentioned in the July 10 post in the thread above. I think they will work and Phil seams to think they will work, we just need a brave volunteer.

[wjohn]

Ok,

I was not very nice to a MR16, however it was for science.

Today, I broke open a LED MR16 with a hammer, not very graceful, however I did get inside the lamp.

Here is a pic. The MR16 was a BLUE 20 LED unit I purchased last year, It had been in my pool-light, until recently. Salt water ingress into the bulb caused it to fail and become a science experiment candidate.

The original rating of the bulb was 12VAC, 1W, Blue LED MR16. Make, unknown.

Looking at the pic, you will see a small PCB in the neck of the bulb. This PCB has four IN4007 diodes configured in a bridge rectifier.
The Red (+) and Green (-) wires contect the Diodes to the main PCB.

The Main PCB contains 20 blue 5mm LEDs. The LEDs are configured in a 5 x 4 matrix. The matrix is connected to a current limiting resistor with a rating of 7.5 ohms and a filter capacitor 47uF 25VDC.

The LED was put onto the bench, and a DC voltage was applied to the bridge rectifier. the LEDs illuminated at ~10VDC applied, with about 50% illuminating, until the supply voltage was increased to 11V DC.

Full brilliance was acheived at 13V DC. The current drawn at 13VDC was 87mA.

a PDF of the schematic diagram is attached.

The measurements were taken with two Digital Multimeters, and illumination measurement were taken using a Mark I Eyeball.

[P. Short]

That much capacitance may make it hard to dim (the capacitor counteracts any attempts to quickly turn the LED off). It may need special firmware to do PWM at a lower frequency than 120 Hz, risking flicker.

--

Phil

[tconley]

What funny is look at the post from dman776 he is doing it with the d-light board. How does it work differently?


http://www.d-light.us/index.php?option=com_weblinks&task=view&catid=26&id=17

Dman776 original post
http://www.christmasinshirley.com/forum/viewtopic.php?t=298

[ErnieHorning]

Since there probably won’t be a lot of these on one controller, you could apply a variable first on pulse that would be related to the difference between where it is and where it’s going to be (kind of a sticky first on). That way, the capacitor will get there quicker and you’ll still be able to do the quicker frequency.

[ErnieHorning]

Another thought…. Isn’t the next version of Vixen supposed to have dimming curves. This could be taken care of as part of that.

[snething]

I have a DC SSR designed and waiting for parts to test. They should be here the end of the week. I believe the board will dim using PWM. I will post all info after testing.

[P. Short]

First, I am sure that the MR16 LED bulbs can be dimmed. The question is how well can it work. What is the range of dimming, how course are the levels within that range, how consistent is it from bulb to bulb?

The issue with the cap is that it makes the turn-off time fairly long. The bulbs will turn on very quickly, but the charge on the capacitor means that it will take some time to turn off (on the order of 5-10 ms, or so), and this time will vary from bulb to bulb due to the capacitor tolerance.

So far I've been having trouble finding bulbs locally to play around with. The local Rat-Shack, OSH, and electrical supply places did not have any in stock, and mostly didn't even know about them

--

Phil

[snething]

Ebay has the MR16 LED bulbs in both the AC/DC or DC only versions.

[FireGod]

I have a DC SSR designed and waiting for parts to test. They should be here the end of the week. I believe the board will dim using PWM. I will post all info after testing.

So, how did it go???????

[RJ]

snething,
If I can be of help let me know. The Lynx dimmer I created dims on DC so I have a bullet proof DC ssr designed.

[teberle]

RJ, I would love to see that DC ssr design.

[tconley]

does it work with the standard renard boards? I need dc dimming for halloween

[snething]

Thanks for you interest!

I have posted the information in the SSR section.

Please let me know how we can improve the SSR.

Thanks
Scot