LED and driver questions

[consumer]

Hi there, I have a few questions regarding an LED setup that I'm going to be building myself. I have been researching this for a while now but just have a few questions:

First of all, the cree LEDs. Why is it that on sites like ledgroupbuy or rapidled that the price of a typical cree LED is around ~$3 but on ebay you can get the same ones for about ~$1 or so. Granted they come from HK/China, I guess there is no guarantee that what you're getting is genuine or the advertised bin...?

If I want to run a bunch of xt-e crees for example which are 1.5A 5W, why would I want to get a led driver that only does 700mA? I have come across some forums and youtube clips where they get 5W cree leds but run it on a 700mA driver, which means you're not getting as much light as what you could have with a bigger driver. I undrestand that you shouldn't run these at the maximum rated amps but if you're going to get a 5W 1.A then why not run it with at least a 1A or 1.2A driver?

I would like a driver that can do dimming. I understand that there are different dimming types such as PWM or using a potentiometer. PWM is for interfacing with a microcontroller right? Where as using a potentiometer it's just a basic dimmer. Are there any drivers that support both (PWM plus internal dimmer or external potentiometer)? I would like to start off with a driver that can do basic dimming but with the option to interface to an Arduino board. In fact it looks like the Mean Well drivers all have an internal current adjustment and optional PWM module so I guess they would be good.

Ok thanks for any replies! I have done so much research so far on lights... feels like information overload at times!

 

[perkint]

LEDs give more lumens per watt (generally) when driven lower (eg 2 identical LEDs driven at 0.7A will give more light than 1 LED driven an 1.4A, will generate less heat and will actually use slightly less power). And LEDs generally give more light per watt when kept cooler. So by running on lower drive you get more light per watt, keep things cooler (which again increases the light) and potentially extend the useful life of the LEDs. Can increase initial cost and complicate the build, but does give more bang for your electricity

As for cheaper from China, you have hit on most of the reasons. A cheap bin is worth a lot less than a decent one and that's assuming they are what they are saying they are. Having said that, there are some sellers that seem genuine and will provide binning information if asked.

As for drivers - IMO the LDDs (or similar) make for an easy and flexible build and you can use an arduino nano (less than $2), a few potentiometers and some very (very!) simple code to have a set up that works from the pot's but can be updated to a full controller very easily

Tim

 

[consumer]

Thanks for the reply...

I have heard of these LDD drivers, never knew much about them ("why would I want to convert dc to dc?!") but now I think the light (ha ha) has come on - so correct me if I'm wrong but does that mean I could use some other, relatively cheap power supply and then connect it to the LDD (which has a dimming module) that connects to a controller/arduino?

That would be awesome, because I'm needing to power up to 60 or so LEDs and that would mean I would need a few expensive Mean Well drivers (want to dim different colours). The cost of those drivers over here are more expensive than in the US.

Thanks for the answers to the other questions. Makes sense.

 

[consumer]

Just to follow up, I could run something like a Mean Well SE-350-48 which is 350w, then run a bunch of LDDs off of it, each LDD running their own array of LEDs that can be independently dimmed. That power supply could easily power the number of LEDs I need.

At least, I'm pretty sure that power supply would be ok. It has 48v output at 7.3A, but I'd only be running at most 1A per LDD.

Awesome! Those power supplies aren't too expensive and the LDDs are cheap, much better than one driver per array of LEDs. You are right, it is much more flexible this way.

 

[perkint]

I think it is much more flexible and yeah, your idea is correct. So long as the one PSU is rated at at least the voltage of the fV LED string and another 3V (for the overhead of the LDDs), less than 56V (max input of the LDD-Hs) and it has more than enough power for the LEDs (and again a bit for the LDDs) you can run lots of strings from one supply using individual LDDs.

For example using 3V LEDs at 1000mA, a string of 15 would be about 45V. 3V for the LDD means the required voltage is 48V. This string would run about 48W, so you could run about 6 strings and still be OK on an SE-350-48

That is just an example using easy numbers rather than based on actual values (more of the LEDs we use will draw more than 3V at 1A) but hopefully it helps make the point

Tim

 

[oreo57]

Just keep in mind that unlike the "all in 1" drivers the LDD's require a voltage differential so your power supply becomes 45V...
Roughly 42W per "string"..(3.5V(f) x 12 x1A). Running lower current allows more diodes /power supply.
Lower currents usually mean lower heating and higher l/w efficiency. Kind of a trade off more diode/lower amps vs less diode/higher Amps
So 12 3W diodes per LDD is usually about the limit. General guideline. Some "colors" have lower V(f)s so you can run more in series but not blue or whites

(perkint beat me to it..)

 

[perkint]

(perkint beat me to it..)

Makes a change :lmao:

Tim

 

[perkint]

To add a couple of points - it is fairly important to know the specs on the LEDs to work out what you are going to do. Most LED data sheets have a chart showing the fV at varying currents, so you can work out the typical fV at the drive current you use, and then you can work out what LEDs you can string together with an LDD and the PSU you have/will get.

And the other benefit of the LDDs is that you can run a string maxing out the voltage of the PSU (eg 15 to use my example from before) and also another string of for example one red at 2.5V and the LDD will just "sort it out"

More efficient to run similar voltage strings and only feed them "just enough" voltage, but not actually a requirement.

Tim

 

[consumer]

Thanks to both

That pretty much all makes sense regarding the voltage/power side of things. I could just use any PSU for the time being as long as the voltage and amps is high enough to drive the LDD + LEDs.

perkint you mentioned the LDD-Hs, it looks like there is LDD-Hw (as well as LDD-Ls and LDD-Lw), I'm guessing H = high power and L = low power (looking at the specs) but the "s" means SMD and "w" means Wire. Do you know what the difference is between Wire and SMD? I couldn't find much information about it.

Also with the dimming, you said I just need an Arduino Nano... I really have no idea about Arduinos until just recently, but it's true that I can just use one of these to do the dimming? These are similar to the standard Arduino (UNO?) but smaller... The nano boards are so cheap, hard to believe that these things are programmable. The programming side of things doesn't bother me, but the electronic side I have less experience with, but I think enough to do what I need.

Thanks again to both for the replies!

 

[perkint]

There are 4 flavours of LDD - but essentially the all do the same job. The original LDD-H and then the LDD-L. And then higher powers of both. The LDD-L is a little less efficient, bluddy tiny in lower drive currents and accepts a lower max input voltage. The LDD-H has a newer higher drive current variation (available in 1.2 & 1.5A) which accepts a higher max voltage than the LDD-Ls but lower than the original LDD-Hs and there are differences in some of the pin positions between the 4 flavours..

Then you have thru hole, SMD (S) and Wire (W) variations which are available in most of the options, which are more or less the same, be they thru hole, SMD or Wire, just different mounting/connecting options.

Running out of time (lunch break) so will comment on arduino later

Tim

 

[oreo57]

There are 4 flavours of LDD - but essentially the all do the same job. The original LDD-H and then the LDD-L. And then higher powers of both. The LDD-L is a little less efficient, bluddy tiny in lower drive currents and accepts a lower max input voltage. The LDD-H has a newer higher drive current variation (available in 1.2 & 1.5A) which accepts a higher max voltage than the LDD-Ls but lower than the original LDD-Hs and there are differences in some of the pin positions between the 4 flavours..

Then you have thru hole, SMD (S) and Wire (W) variations which are available in most of the options, which are more or less the same, be they thru hole, SMD or Wire, just different mounting/connecting options.

Running out of time (lunch break) so will comment on arduino later

Tim

You forgot the differences in the PWM "ranges" in some. The reason a Bluefish mini will not work w/ lower mA LDD-L drivers..

 

[perkint]

You forgot the differences in the PWM "ranges" in some. The reason a Bluefish mini will not work w/ lower mA LDD-L drivers..

Ah - good point! The LDD-L driver needs at least 3.5V on the PWM signal to turn on, which can be an issue (some controllers use 3.3V), but isn't for the arduino

Looks like they have simply renamed the higher drive LDD-Ls to be the "new" LDD-Hs! Although I think the input max voltage is increased. Sure the LDD-Ls were all 36V but the higher power LDD-Hs are 52V (56V for the other LDD-Hs).

Anyway, enough babbling!

Tim

 

[perkint]

Also with the dimming, you said I just need an Arduino Nano... I really have no idea about Arduinos until just recently, but it's true that I can just use one of these to do the dimming? These are similar to the standard Arduino (UNO?) but smaller... The nano boards are so cheap, hard to believe that these things are programmable. The programming side of things doesn't bother me, but the electronic side I have less experience with, but I think enough to do what I need.

Thanks again to both for the replies!

The arduino nano v3 is essentially the same as the Uno for functionality. It has 6 PWM channels (0-255 levels) so you can easily bolt 6 pot's onto a nano and output a PWM signal based on each pot' reading to each of the 6 channels. The PWM signal goes straight to the LDD (although a pull down resistor can help prevent the LEDs flashing on at full power when rebooting).

You can also code the arduino to automatically fade the LEDs on and off over a few hours, bolt the whole thing to a time switch and have simple sunrise sunset. Or bolt a DS3231 RTC (again a couple of quid) to the arduino and actually have it do proper sunrise and sunset based on time of day!

And if you want more than 6 channels, use a PCA9685 (yet again a few quid) which will allow to control 16 channels rather than the 6 the arduino alone can do. The PCA9685 can also do dimming from 0-4095 which makes for super smooth fade in and out

No limit to what you can do, once you start playing!

Tim

 

[consumer]

Awesome, thanks! I'll get myself a few LDD-Hs (52 or 56V) and an arduino nano, some pots, PSU, etc.

Also........ all this isn't actually for a reef tank (as much as I'd love one) :eek1: This is for a planted tank. I come to this forum because it's big and a lot of DIY'ers hang out on here it seems. But this will all be good knowledge for when I do set up a reef tank.

I have a 150 gallon tank with pathetic lights, I can barely grow a weed. I have read lots about lights and how they work so I pretty much know what type of LEDs and how many I need for a deep tank (24").

Thanks again!

 

[perkint]

No problem

Don't forget decent cooling solutions (is heat sinks & fans if you need fans) for the LEDs!

Tim

 

[consumer]

Yeah I haven't looked in to cooling yet.

I just have one other question regarding the LDDs. Why do people mount them on a board such as like here?

By the looks of it, you can't dim individual strings? I could be completely wrong however...

 

[consumer]

Also, what do you guys think of this here?

20 cree xt-e LEDs for $22.99AUD! (that's about $17USD). Free postage. The binning, according to them, are R4 for the white, but how could you know? The ones on ledgroupbuy are almost $3USD each for an R2(ish) bin. They're from HK, I guess there is just no way of knowing what bin you're actually getting though is there?

Hmmmm decisions decisions...

 

[consumer]

Not sure why it comes up as "clay-boa" but I'm meant to say led-group-bye (buy).. some filter I guess.

 

[perkint]

There is a filter for that trade name. I assume it is non sponsor rules...

LEDs from China are usually much cheaper. Reasons as stated before. And no - it isn't easy to be sure they really are XT-Es or which bin. You can always just get more and plan to run them on a lower drive current (which can improve efficiency and therefore overcome some of the issues if they are a lower bin).

Tim

 

[liquidis54]

Can I piggy back on this thread? I actually came to this site and made an account so I could ask almost the same question. I'm wanting to build my GF a light for her 3g picotope. I want to arduino power it, have an lcd, run 6 cree XP-E2s, and stay fairly small. I'm stuck on the drivers though. I'm not really 100% sure what I'm looking for, but I think I need something that outputs about 10 watts and 1500mah and pwm dimming. I can't seem to find any drivers that are small and meet those requirements though. Only bigger, 30-60W drivers. Any suggestions for me? I'd rather not run the lights off pot's because I'd like to run 3 channels straight from the LCD and be able to do sunrise/sunset.