# Advice on power supply for SORAA MR16 to minimize flicker?



## Bytefield (Jan 1, 2017)

Our home has three 12V track lighting installations. Originally MR16 halogen, I switched to Cree LM16 bulbs several years ago and was happy with them except for color rendition. And of course I could add many more bulbs....

I purchased several cases of SORAA 95 CRI bulbs a few months ago (SM16-09-927-03, 9W, 0.9A) and I've been incredibly pleased with the color, our wood is beautiful again! But my wife and I are both sensitive to flicker, and this is much more of a problem with the SORAAs. I understand why a PS adequate for halogen has a flicker problem with LEDs, so I'd like to replace them with units that will reduce this as much as possible.

I also want each of the tracks to handle up to 20 bulbs and be dimmable. I would welcome any advice on which PS to choose, both brand and watt/amp ratings. SORAA's compatibility list seems to be mostly commercial products. I'm not trying to do this on the cheap, making the flicker stop bothering my wife is the priority.

In retrospect, I wonder if I should have gone with SORAA's constant-current bulbs and a CC power supply like the Meanwell HLG-320H-C series. Would that be a good choice for futureproofing in case I later upgrade to CC bulbs? Or am I overthinking this, and any well-regulated power supply will reduce flicker enough? 

Many thanks for any advice.


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## Str8stroke (Jan 1, 2017)

Since you said, "any advice" I am not a expert in cabinet lighting. But I have played with them a little. 
Reading your light bulb specs, it looks like each bulb is drawing almost a Amp. So, I would multiply the number of bulbs you are planning to run, then add say 10% for line loss to get a rough idea of the size supply you need for each run.
The flicker you see is most likely the LED Driver. It is using what is called Pulse Width Modulation PWM. Some folks are sensitive to this. Basically think of it as a super fast strobe that the human eye can barely detect. So check on your driver and see if that can be changed to a unit not using PWM. 

However, having the proper supply can help. Some cheap supplies will cause some non PWM leds to flicker. 

There are thousands of power supplies out there designed specifically for lighting. 

For my led cabinet lighting, I run a 20amp hobby power supply I had already. It is made by Astron. They are designed for 100% duty cycle. They may not work for your project. They are large, lol. Anyways, make sure when you look for supplies, you consider the Duty Cycles. Meaning, not all 20 amp supplies are built equally. 

Hopefully, others more knowledgeable in those lights can help. Good luck and welcome to the forum.


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## Lithopsian (Jan 1, 2017)

Are you sure that the flicker isn't due to a transformer incompatibility rather than just a 12V output that isn't very smooth? The bulbs you have are designed to operate from 12v AC with essentially undetectable unsmoothed-DC flicker. Low voltage MR16s are renowned for problems when used as a retrofit with halogen transformers, especially electronic types. Pronounced flickering is just one potential problem. Even quality lamps may turn out to be incompatible with particular transformers. SORAA do publish a list of compatible driver technology for their lamps. Are you also running a dimmer?


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## Bytefield (Jan 1, 2017)

Str8stroke, thanks for the advice. 

These are actually track ceiling lights (GK Lightrail). Size is not an issue, I can easily hide the supply. I once used a 500W computer PSU to power early 3W Crees as my office lighting and never noticed flicker. Since I want dimmability and no fan, that's not an option of course. And since I'm buying three I want to make sure I'm getting something reliable with minimal flicker.

Thanks for the welcome!


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## ssanasisredna (Jan 1, 2017)

Dimmability will require phase-cut on the AC which means you need AC if you want to dim. Seems to be an issue with the SORAA supply and/or as noted, incompatible halogen transformer and bulbs. If you have an electronics transformer, may want to try with a standard magnetic to start (and make sure dimmer is compatible).


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## Bytefield (Jan 1, 2017)

Lithopsian said:


> Low voltage MR16s are renowned for problems when used as a retrofit with halogen transformers, especially electronic types. Pronounced flickering is just one potential problem. Even quality lamps may turn out to be incompatible with particular transformers. Are you also running a dimmer?



Lithopsian, thanks very much for your help.

Incompatible halogen transformers is exactly what I assume is the problem, thank you for confirming. I was mostly hoping to get some advice on replacements, especially if it futureproofs a bit for later constant-current LEDs. Or is that not worth pursuing?

When I looked at the SORAA compatibility list, I found only a few rated for 20 bulbs. I don't care about brand, I just want some examples of power supplies that will handle the number of bulbs and minimize flicker.

One track is on a dimmer, the other two are not, but I'd like them to be. The dimmer doesn't make any difference in flicker.


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## ladylites1 (Jan 1, 2017)

Please see the Soraa website under "Resources" and "Compatibility" and "FAQs". All Soraa lamps made in the last year are flicker-free and have a 2-stage driver that eliminates it. Check the number above the barcode on the lamp or box, it should be a 4-digit number starting with "16" which means 2016 manufacture.

You can only use a magnetic transformer for long runs, electronic ones only go 6 feet. You have to derate the transformer power and divide by 1.4, so 214W of lamps can go on a 300W transformer. If you use a dimmer, then you have to use fewer lamps, and derate by dividing by 2.0, or 150W for a 300W transformer.

If you still experience flicker, then I would use a DC power supply with the same restrictions. A constant current lamp is only used in case where very low dimming to 1% or DALI dimming is used.

You can also email at [email protected] for additional help.


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## Lithopsian (Jan 2, 2017)

You mention looking at constant current drivers, but are they even compatible with your track lighting system? Normally track systems are essentially just 12V rails that you can hook up lamps to, and then it is up to each lamp to decide what to do with that 12V. It is a parallel circuit, and driving it with a constant current driver will cause all sorts of problems. Constant current drivers are typically designed and used to drive a series of lamps all at the same current, and it will produce as much voltage as needed to do this (within limits). When used to power several lamps in parallel, the fixed driver current will be shared by the lamps. Adding another lamp to the track would mean they all get less current and less bright. Also, the drivers are usually designed to deliver the amount of current needed for each lamp and enough voltage to power several of them in series, not loads of current at the voltage needed by one lamp.

It is worth mentioning that a "constant current" MR16 lamp is simply a dumb bulb that takes whatever current and voltage is thrown at it and lights up. You are responsible for carefully controlling the current and providing smooth DC at the necessary level. The lamps you have currently are smarter than that and will identify whether they are being powered with DC or AC, rectify and smooth as required, and limit the current to safe levels. That's great for retrofits, but can interfere with the way a constant current driver tries to control the lamp, for example to dim it.


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## Bytefield (Jan 2, 2017)

Thank you for your detailed response.



ladylites1 said:


> Please see the Soraa website under "Resources" and "Compatibility" and "FAQs". All Soraa lamps made in the last year are flicker-free and have a 2-stage driver that eliminates it. Check the number above the barcode on the lamp or box, it should be a 4-digit number starting with "16" which means 2016 manufacture.



The compatibility list is the first thing I looked at. Most transformers listed don't have enough wattage to handle my current runs. Those that do appear to have the same specs and halogen labeling as the two electronic transformers I have. That's why I'm concerned that I need a DC source to solve the flicker problem.

Four cases of SM16-09-927-03 say 1551 ABPT above the square barcode. These were purchased in September from a major online lighting retailer. Two failed, so I had to buy some more. Another case I bought last month from another major retailer says 1643 ABPT, the label is otherwise identical to the others.



> You can only use a magnetic transformer for long runs, electronic ones only go 6 feet. You have to derate the transformer power and divide by 1.4, so 214W of lamps can go on a 300W transformer. If you use a dimmer, then you have to use fewer lamps, and derate by dividing by 2.0, or 150W for a 300W transformer.


The longest run uses this monster 12-pound magnetic transformer, which is not on a dimmer:
http://www.minkagroup.net/products/gktf03-467

I don't know what brand of transformer is inside, and Minka doesn't provide many specs. So I am concerned that even a magnetic transformer certified compatible by SORAA will have the same flicker.



> If you still experience flicker, then I would use a DC power supply with the same restrictions. A constant current lamp is only used in case where very low dimming to 1% or DALI dimming is used.


That was my question: will a DC power supply eliminate flicker? Is there any benefit from a constant-current supply? I don't need dimming below 10%.

I really appreciate the help from everyone here.


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## ssanasisredna (Jan 3, 2017)

Can you better describe the flicker effect you are seeing? Is this 2x line rate flicker or is it random flicker?

There are big differences between different electronic transformers so whether they have the same specs or not, they may behave quite differently, especially if you try to dim them (with LED bulbs).

Exactly how many bulbs are you putting on the 300W transformer? How many on the electronic transformers and what wattage are those transformers? 

Are you seeing flicker with both the magnetic and electronic transformers?


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## Bytefield (Jan 3, 2017)

ssanasisredna said:


> Can you better describe the flicker effect you are seeing? Is this 2x line rate flicker or is it random flicker?


The flicker is 120Hz. 

I found an iPhone app called Flicker Tester that shows an ugly square wave in the light output for both the electronic and magnetic transformers. 
http://www.visosystems.com/products/flicker-tester/

Electronic transformer: Ramps up quickly to 178%, trailing edge drops instantly to 0%. 100% flicker, 0.4 flicker index. 
Magnetic transformer: Ramps up quickly to 148%, trailing edge drops instantly to 0%. 100% flicker, 0.3 flicker index.



 



So that explains why it's so perceptible. The transformers are not on dimmers.

I also tested some SORAA and Cree E26 bulbs, they show nice sine waves, 40% flicker, 0.1 index.



> Exactly how many bulbs are you putting on the 300W transformer? How many on the electronic transformers and what wattage are those transformers? Are you seeing flicker with both the magnetic and electronic transformers?


Both electronic and magnetic runs have 16 bulbs each, 9W, 0.9A, so 144 watts, 14.4 amps total.

I assume I need a DC power supply to eliminate the flicker, especially since I seem to have been sold older SORAA bulbs lacking the newer drivers.

But my original questions remain: which PS to choose? Will constant current help, hurt, make no difference? If no difference, does it make any sense to spend a little more for CC models so I can use CC bulbs in the future?


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## ssanasisredna (Jan 4, 2017)

Use CV. CC will not work.


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## Lithopsian (Jan 4, 2017)

It appears that the bulbs are simply not very good at rectifying AC. I'd look for a different brand, plenty of high CRI offerings out there. You already know the Cree's work better, and I'd expect better from any reputable bulb and many not-so-reputable ones. Or since you have two failed lamps, which is really not acceptable even from the substantial number you bought, you might try to exchange them for newer stock and see if this problem has been resolved.

A DC driver should avoid this sort of issue, although who knows what these bulbs will do. Even a poor quality DC power supply will produce a better waveform than this, with any flicker just down to the level of smoothing.

I think you need to forget the constant current direction. It is a solution for many subtle problems, but the problems you have seem to be more gross. Constant current drivers are not well-suited to track systems. In practice you'd need one driver per bulb. Some track systems have bulky lamps containing individual constant current drivers but I don't think you need or want to go that route.

I've lost track of where we are with the dimming question. The magnetic transformer should be dimmable (already is?) but I'm not sure about the electronic ones. Maybe, maybe not, and maybe with a different dimmer. Dimming performance through the transformers might not be great?


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## Bytefield (Jan 4, 2017)

Thanks Lithopsian, and everyone else for their help. 

Yes, constant current is not an option with the bulbs I have. I haven't found any affordable bulbs (< $30) that rival the SORAAs for color rendition. The difference going from 85 CRI Crees to 95 CRI SORAAs was huge, and I'm not going back.

I once tried dimming the magnetic transformer using a Leviton magnetic dimmer. It buzzed terribly, so I gave up on that.

I just ordered a 320W constant voltage 12V supply, we'll see how well it tames the flicker...


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## Mkala (Jan 4, 2017)

Bytefield said:


> The flicker is 120Hz.
> 
> I found an iPhone app called Flicker Tester that shows an ugly square wave in the light output for both the electronic and magnetic transformers.
> http://www.visosystems.com/products/flicker-tester/
> ...



Tried this app with a 10w LED with small power from a DC Laboratoy power supply : 100-200% flicker 
Does not looks to work


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## Bytefield (Jan 4, 2017)

Well I got relatively consistent results for the bulbs I tried, although of course I don't expect very accurate results from this app.

Did you put a diffuser in front of the lens? That makes a big difference. I used a couple of layers of Scotch translucent tape. You also need to ensure you're testing only a single bulb.


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## Mkala (Jan 4, 2017)

Not tried with a diffuser like recommendations, perhaps here is my mistake


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