How to do low-voltage dimming with COB LED Spots?

[Russ]

Hi there,

We're just starting our Loxone install in our reno, having finished one room. We're wanting to use DMX for all the lighting controls which works great with the RGBW & W LED strips we used so far. 

However, I'm having a problem with the 5w COB LED Spots we wanted to use for the next room.  They came with a separate LED Driver and are dimmable, so I thought it would be a simple matter of removing the driver, checking the voltage, and using the same sort of dimmer as the LED strips with the correct voltage and power rating.

I first tried with the normal 12v power supply hooked up to the DMX dimmer and the spot without the provided driver and it lit, but was dim.  The voltage out from the LED driver was 24v so I hooked up a 24v power supply to the dimmer.  The spot went on much brighter but then went out and never worked again.  The dimmer still works as does the power supply.

I bought a pack of 10 so I can experiment a bit more, but would like to do so intelligently.

Anyone else done this before?  Do I need to use a constant current dimmer?  Other ideas of what to check?

Here's a link to the spots on Amazon:
https://www.amazon.fr/gp/product/B00Z9H2UI4/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

And here's a link to the dmx dimmer I used:
https://www.amazon.fr/gp/product/B00Q1N1GZS/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

I realize this topic is only tangentially related to Loxone: apologies if some think it not appropriate.  Just looking for some help.

Thanks.

[Simon Still]

On Monday, 1 August 2016 14:47:49 UTC+1, Russ wrote:

Hi there,

We're just starting our Loxone install in our reno, having finished one room. We're wanting to use DMX for all the lighting controls which works great with the RGBW & W LED strips we used so far. 

However, I'm having a problem with the 5w COB LED Spots we wanted to use for the next room.  

I was looking to advise a friend on something similar.  Is there some reason you've rejected the Loxone spots?

http://shop.loxone.com/enuk/led-spot-ww.html

The price looks very reasonable for what they are and you should be able to control them easily with low cost DMX dimmers designed for LED strip.

My install has constant current LEDs with 1-10v dimming which seemed the best solution at the time.  Constant current DMX LED dimmers seem harder to find and are more expensive - 

https://www.downlightsdirect.co.uk/dmx-driver-constant-voltage.html?fee=8&fep=13603&gclid=CNzXy6W5oM4CFVFuGwodkE0ELQ

 

[Russ]

Hi Simon,

Thanks for the reply.  At 40 euros each, the Loxone spot are over ten times as expensive; I only paid 29 euros for a pack of 10...  (although I see now that they've great increased the price on amazon)

The link you sent is for the constant voltage dimmers, but the constant current ones are there too.

My alternative is to keep the original drivers and get a DMX 220v dimmer; a four channel version can be had for around 100 euros it seems.

Russ

[Duncan]

i think the driver with your downlights would be a constant current driver - so applying 24v has just killed the led due to overcurrent.

if you have an ammeter, but it in series between the driver and the led and measure the current - it will probably be around 700ma or 350ma, but may be another odd number depending on the led configuration inside.

the problem with these is the configuration of the cob leds - they are usually constant current but already have a number of chips in series, so require quite a high drive voltage. supposing each downlight needs approx 24v at 700ma, if you want to put say 4 on a circuit, you would in theory put them in series but that would reqire a dmx contant current that can deliver approx 100v at 700ma and you wont be able to find one.

if you try to drive each one separately then your wiring gets mighty complex and expensive.

you could convert them to contant voltage, by measuring the current needed (say 700ma) and voltage required (lets say 22v) to drive that current, then add a series limiting resistor to each led fitting so that your chosen voltage (lets say 24v in this case) is sufficient to deliver the required current through the current limiting resistor (this is how the led strips work). - you can then use a constant voltage dmx driver and wire them in parallel for each group/circuit that you require. its not that difficult, google the idea of contant voltage leds, but you need to juggle the mixture of psu voltage, available dmx driver, typical drive voltage for the particular cob led and calculate the appropriate current limiting resistor

mains dmx dimmers with the original dimmable driver will be far easier, but the cob leds may not dim very well at the bottom 25% or so of the range, where as constant current or constant voltage would give a much smoother and better range of dimming

the big problem with the loxone dmx leds is they have a silly wide angle - they arent a spot at all but a wide flood and dont provide the accent lighting that you expect, and tend to give eye glare as well

[Russ]

Yes, I think you're right (mains dmx dimmer being far easier).  I started doing some calculations for current + voltage and realized it's more of a pain than I thought.  I've already ordered a 4ch dmx 230v dimmer (around 100 euro from Thomann).  We'll see about the bottom 25% thing, but in my experience that's not such a useful range anyway.  We seem to more often keep things in the 60% - 90% range.

Thanks.

On Monday, 1 August 2016 17:37:32 UTC+2, Duncan wrote:

...mains dmx dimmers with the original dimmable driver will be far easier, but the cob leds may not dim very well at the bottom 25% or so of the range, where as constant current or constant voltage would give a much smoother and better range of dimming

[Simon Still]

Ah - sorry - I think i saw 30euro and assumed that was per lamp.  

These 220V DMX dimmers are very cheap http://www.yozop.com/index.php/dmx-triac-dimmer-led-controller-ac90v-240v-3-channels-dmx302.html but they're not wholly successful dimming LED GU10 bulbs in my experience.   I'm finding the dimming range very limited - maybe to 50% with Sylvania RefLED+ ES50 5W dimmable LEDs.  

With a single bulb I get a bright flash after it has dimmed even a small amount. With 3 bulbs together it's better but below 40% they do not work properly - bulbs start to flicker.  Because of this you can't fade them in or out either - need to use 'jump' in Loxone.  

 

 

[Andrew B]

I went low voltage DC DMX. Used a pair of 32 channel PWM controller boards, and found some awesome 24v downlights (about as thick as drywall) with 92 CRI. For the rest, E26/E27 fixtures with LED bulbs intended for marine and RV use. Took a bunch of hunting around to find acceptable bulbs, and even then it turns out that they work better at 15v, so I got some DC-DC voltage converters (adjustable). With constant voltage bulbs that need to work with a range of voltages (12-24v or 24-36v, for example), it seems that the circuit in the bulbs has... interesting characteristics. Took some experimentation and a few blown fuses (each channel has an automotive fuse on it) and fried channels... but in the end it seems to be working well. Still keeping an eye out for better bulbs, but the downlights are awesome (Lauren Illumination).

[Simon Still]

On Monday, 1 August 2016 16:37:32 UTC+1, Duncan wrote:

the big problem with the loxone dmx leds is they have a silly wide angle - they arent a spot at all but a wide flood and dont provide the accent lighting that you expect, and tend to give eye glare as well

That is an odd decision.  Tiltable units and they appear to have optics but they're a not a spotlight.  

[Peter van Es]

Hi,

I have a room full of COB LED's. Different brand, but the experience will be the same. My LED's require a constant current, 350mA per LED. The power is supplied via a dimmable LED driver (Constant Current) which is dimmable through one of three ways:

1. Pulse Width Modulation
2. 0-10v analog dimming
3. resistive dimming (using a simple potentiometer)

The driver I bought is one of these: Meanwell LCM-40 (https://www.meanwell-web.com/nl/producten/ac-dc-power-supply/led-driver/21-40-w-led-driver/lcm-40). Costs approx Eur 28 (a bit more at dealers). It can drive a string of up-to 8 LED's if yours are 5W each. 

I use the 0-10v analog dimmer, by connecting it to a Loxone analog output. Works like a charm.

The LED's I have are: Klemko Venice 3,3W warm white (www.klemko.nl/producten/aluminium-lumiko-venice-cob-led-module-3-3w…) You can get these for between Eur 18-28 each depending on seller

Peter

[Russ]

So, wait, are you using one dimming channel PER light?  If so, that sure eats up the DMX channels quickly, and would be interesting to program I would think.  Could be expensive depending on how much you paid for the controller boards... 

On Tuesday, 2 August 2016 04:34:07 UTC+2, Andrew B wrote:

I went low voltage DC DMX.  Used a pair of 32 channel PWM controller boards...

[Russ]

Thanks for the info, Peter.  That driver is interesting, although I was hoping to stick with DMX so as not to run out of outputs.  Those LED spots look nice but the price is a bit high for me.

OTOH, that driver would probably work with any constant current LED spot.

[Andrew Brownsword]

I'm using constant voltage so I can put multiple LEDs per channel.  My channels can handle up to about 8A, so I have 1-5 lights or bulbs per channel (I try to stay under 5 or 3A and use appropriate fuses).  Fried two channels while experimenting, and I think I have one spare.  The boards were quite economical, unfortunately the guy has decided not to sell them anymore (although I bet that if a large order were to appear at his door, he might consider a production run).  The nice thing about DMX is that you can trivially daisy chain any devices and there are many on the market... so I have many fallbacks in case of large a bad system failure.

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[Liteworx AV]

I've just installed around 30 of these units which do exactly what you require, they'll normally run a couple of cob fittings with no problems

http://www.ltechonline.com/uploads/pdf/en/DMX-25-180-700-F1P1.pdf 

 

[Duncan]

they look very interesting - do they dim nicely right down to say 10%?

[Andrew B]

Not clear about what product you are asking about with the 10% question...?

[Duncan]

sorry, i was referring to the itech dmx dimmers mentioned by liteworx av

[Simon Still]

They look interesting.  When I was speccing my house I couldn't find that type of unit (DMX, 240v to constant current LED).  My lighting is predominantly PhotonStar constant current LEDs driven with 1-10V dimming drivers.  These *should* happily dim to 10% without flickering though I had a few quality control issues with drivers - a few were unreliable in the 1-2v range.  I'd expect those DMX drivers to be the same.  

Incidentally - I now have my 1-10v dimmers dimming in 10% steps.  Using larger dimming steps might be a way to remove issues with other dimmers.