2.5g Pico Tank LED lighting!

[Jimbo7]

I don't think it'd be a bad idea. I mean (going along the computer power supply idea here), computer PSUs are VERY well regulated. They're powering hundred dollar components in your computer right now. That's a bit more demanding than a few LEDs. I don't know, I'll look into it and let you know.

Wow that didn't take long. I think the "key" is using "series-parallel" arrays. Check out the PDF I found...

http://www.edn.com/contents/images/6615611.pdf

Oh... well.. apparently that PDF concludes that series parallel arrays are useless haha Good read nonetheless.

Ill have to look through that more later, seems interesting. So series is still the way to go.

 

[corrado33]

Ill have to look through that more later, seems interesting. So series is still the way to go.

It looks that way. However, for me with my little LED project, I don't need perfectly equalized LEDs, and I think it's easier for me to just use LEDs in parallel. (Besides, I don't have the ability to run them in series lol)

 

[Jimbo7]

Sorry for the hijack, but how can you not run them in series?

 

[corrado33]

I just have the positive end of both LEDs connect to +V and the negative to the GND (anode cathode ect etc). Therefore they are parallel? It works for me. However, after reading this site, it seems that "parallel-series" arrays work OK. (Not the best, but I'm using 1 dollar LEDs, if one burns out, I'll replace it).

EDIT: The guy uses a resistor to "ballast" the LEDs in series. I don't know if that can be used as a verb, but he did.

EDIT 2: If I were to try to make a long term LED lighting solution, I'd definitely do them in series. However, I don't plan to use this tank much longer (more than a year or two), so I'm sure the LEDs will be fine. I'm really just building a proof of concept thing.

 

[krap101]

Sorry for the hijack, but how can you not run them in series?

When you run a series of leds, they are all strung together, like christmas lights, but when they're in parallel, then each led is individually connected to the power source. When you run leds in series, they split voltage, so on a 21v 800ma power supply, you can run 7 3v leds at 800ma. When you run them in parallel, you'll need to split amperage, so 3v power supply with 5.6A for 7 leds.

HTH

Oh, and you can also run them in series and parallel. Lets say you have a 1.6A 15V power supply. That means you can run 2 lines at 800ma and have 5 leds in each string. (15/5=3 and 1.6/.8=2)

 

[mrg02d]

Hello,
I believe a switching supply is going to put out a constant (with some ripple) voltage no matter the load. If the load isnt sized well, this will cause a lot of power to be dissipated by the supply. So that means no using a 48v SMPS to run a 3v LED. It wont fry the led if the current is regulated, but the power supply and wires will get hot. At least, that is the trouble I had with my high power laser diodes (they would draw 50A) and SMPS.

Now for the diodes in parallel. BAD BAD BAD! Do not do this unless you have a driver for EACH diode. Diodes do NOT share current evenly. Series is much better. The entire string is controlled by one driver. This is how the pros drive $10,000 laser diodes as well. Series is the best way. Each diode will drop some of the SMPS voltage across it according to its particular parameters. Then, to keep current steady, the driver will not allow current to fluctuate.(If a good design).

Resistors are 100% fine is using a battery. A battery will not have a ripple, or be susceptible to changes in the line voltage.
Since we dont use batteries, we need something better than a resistor. Enter the wide world of constant current controllers.

Usually they work by sensing a voltage across a precision resistor and then compare this voltage to a preset voltage. Using ohms law, the driver is able to determine how much current is flowing. It then adjusts its output to the diodes accordingly. Depending on the quality of the design, this can be extremely accurate, or it can suck.

I have no idea how the meanwells work, but I imagine something similar.

Matt

 

[mrg02d]

Quick question, awhile ago I was thinking about doing one of these with a laptop power supply, and I was wondering.. if I use a switching power supply, and lets say there are a few extra volts/amps at the end of a string, do I still need a resistor there, or does the switching power supply make it unnecessary?

You could always put a dummy diode in series with the LED to disspate the extra power. This may be a good idea if the PSU isnt very large and thus not looking to dissipate much more than it has to. You could also put a resistor in series. That would also drop some voltage. Either way, something is getting hot.

At less than 1A draw, it wont be too bad. Id just let the PSU pick up the slack.
Matt

 

[mrg02d]

I have a username for nano-reefs. If you post your question in entirety, i can repost it there.

Krap, thats a good question, its something i was wondering too. The link posted earlier in this, the guy uses 5 LEDs for a 24v PS. Im not sure if he added anything or not to the end.

Hmmm...Here goes a question:
Hello,
I am planning on using the Meanwell 30-27-D dimmable LED PSU to drive 5-6LEDs. Has anyone here any experience with these drivers? If so, would this one be suitable for 5-6LEDs? (Cree XR-E 3W leds).
Thank you!

Nanotuners confirmed they are indeed the 27V output ones. I may ask them if they would be suitable for 5-6LEDs.

Thanks!
Matt

 

[Jimbo7]

When you run a series of leds, they are all strung together, like christmas lights, but when they're in parallel, then each led is individually connected to the power source. When you run leds in series, they split voltage, so on a 21v 800ma power supply, you can run 7 3v leds at 800ma. When you run them in parallel, you'll need to split amperage, so 3v power supply with 5.6A for 7 leds.

HTH

Oh, and you can also run them in series and parallel. Lets say you have a 1.6A 15V power supply. That means you can run 2 lines at 800ma and have 5 leds in each string. (15/5=3 and 1.6/.8=2)

He stated that he was unable to run them in series, I was asking him why that was. I have a pretty firm grasp on how LEDs work already.

 

[corrado33]

He stated that he was unable to run them in series, I was asking him why that was. I have a pretty firm grasp on how LEDs work already.

I have a low voltage, high amperage power supply, that's why.

Well, technically I guess I could run them in series... I'm using a 12V 1A power supply, so it could go either way. Since the LEDs are only (maybe) a hundred milliamps, I'd either have to put some in parallel, or use a bunch of resistors which are going to get HOT.

EDIT: Remember, I'm not using really nice Cree LEDs, I'm using normal ones, which only draw (oh wow really low) 25 mA at 3.3V.

EDIT: Actually I just found an 18v 350 mA wall wort... hmmm... *rethinks design*
EDIT3: Ok I like the 12V power supply better. The fans are 12 V, and I don't want to have to regulate twice...
Sorry for thread jacking

 

[Jimbo7]

Ah, thats what i overlooked. It didn't actually register when i read your post.

 

[mrg02d]

I have a low voltage, high amperage power supply, that's why.

Well, technically I guess I could run them in series... I'm using a 12V 1A power supply, so it could go either way. Since the LEDs are only (maybe) a hundred milliamps, I'd either have to put some in parallel, or use a bunch of resistors which are going to get HOT.

EDIT: Remember, I'm not using really nice Cree LEDs, I'm using normal ones, which only draw (oh wow really low) 25 mA at 3.3V.

EDIT: Actually I just found an 18v 350 mA wall wort... hmmm... *rethinks design*
EDIT3: Ok I like the 12V power supply better. The fans are 12 V, and I don't want to have to regulate twice...
Sorry for thread jacking

Why would you need a lot of resistors? What are you trying to do with resistors, limit current? Current draw doesnt matter, just the LED voltage drop at the current you plan to draw.

Okay, so you have a 12v 1A PSU...How many leds are you trying to run?

Dont worry about threadjacking, I do it all the time!
Matt

 

[Jimbo7]

Correct me if im wrong, but he is planning on running these little guys in parallel, so he would need resistors to drop the excess amperage off. You have a 1000mA power supply and 5-6 25mA leds, so he would need to disperse the extra 850mA at the end along with the excess voltage? correct?

I dont know much about parallel.

 

[mrg02d]

Correct me if im wrong, but he is planning on running these little guys in parallel, so he would need resistors to drop the excess amperage off. You have a 1000mA power supply and 5-6 25mA leds, so he would need to disperse the extra 850mA at the end along with the excess voltage? correct?

I dont know much about parallel.

Amperage isnt something that exists like voltage. Voltage across a load causes amperage. The extra voltage would have to be dealt with, as it will drop across the circuit evenly and causes current to flow through loads. 1000mA is just the rating of the PSU of what it can deliver if required. Actual current draw will depend on the load.

Also, size the PSU right accordingly to the overall voltage drop of the circuit. If you use a 24v supply and 24v worth of LEDS, you get 0A of current. You need a potential difference in voltages for current to flow. Also keep in mind that connecting wires will drop voltage across them as they have a resistance (although small). So 7 LEDs will not run on a 24v supply.

Matt

 

[Jimbo7]

Alright, I'm not sure if you are talking about series or parallel anymore.
In series, amps are constant, and volts drop.
In parallel amps drop and volts are constant.

In parallel, if i understand correctly, amps are caused by the load, so from the beginning of the string to the end, you should drop all amperage, but you still have full voltage load at the end. Are you talking about using resistors to drop that end voltage?

I understand how series work fine, i've been over that with a bunch of people, im just trying to educate myself with you guys talking about parallel.

 

[mrg02d]

Alright, I'm not sure if you are talking about series or parallel anymore.
In series, amps are constant, and volts drop.
In parallel amps drop and volts are constant.

In parallel, if i understand correctly, amps are caused by the load, so from the beginning of the string to the end, you should drop all amperage, but you still have full voltage load at the end. Are you talking about using resistors to drop that end voltage?

I understand how series work fine, i've been over that with a bunch of people, im just trying to educate myself with you guys talking about parallel.

Parallel shouldn't be used IMO. Series is the best way to do this. If its good enough for Coherent and Spectra Physics in their $10,000 diodes, then its good enough for us.

In parallel, each load can/will draw different amounts of current. No two diodes are 100% the same, there will be slight differences and that translates into more or less current draw and imperfect load sharing.

Parallel configurations are commonly used with resistive loads.

Current is a function of voltage and load impedence. It does not exist by itself.

In parallel circuits, the same voltage gets applied to each load. The load then draws current based on its impedence. So, the voltage is the same but the current draw from the supply adds up from all the loads drawing their own current from the line.


Matt

 

[corrado33]

Correct me if im wrong, but he is planning on running these little guys in parallel, so he would need resistors to drop the excess amperage off. You have a 1000mA power supply and 5-6 25mA leds, so he would need to disperse the extra 850mA at the end along with the excess voltage? correct?

I dont know much about parallel.

Like mrg said, in parallel the amperage is dependent on the circuit, however LEDs naturally draw enough current to blow themselves up. (Well, most do, there are some with built in resistors and all that fun stuff.) So I was saying I'd need resistors on each LED to keep it from blowing itself up.

No, that isn't what I meant originally, but it's what I'm pretending I meant. And it's true nonetheless. I think I'm going to go with LEDs in series, then in parallel, like an array. So I'll have (making stuff up here), 3 strings of 5 LEDs, the 5 LEDs will be in series, and the 3 stings will be in parallel.

 

[Jimbo7]

Parallel shouldn't be used IMO. Series is the best way to do this. If its good enough for Coherent and Spectra Physics in their $10,000 diodes, then its good enough for us.

In parallel, each load can/will draw different amounts of current. No two diodes are 100% the same, there will be slight differences and that translates into more or less current draw and imperfect load sharing.

Parallel configurations are commonly used with resistive loads.

Current is a function of voltage and load impedence. It does not exist by itself.

In parallel circuits, the same voltage gets applied to each load. The load then draws current based on its impedence. So, the voltage is the same but the current draw from the supply adds up from all the loads drawing their own current from the line.


Matt

That makes sense, I know series is the way to go but I was just trying to understand what corr just explained above about his plans for a parallel circuit.. I like to soak up any and all information i can

 

[krap101]

He stated that he was unable to run them in series, I was asking him why that was. I have a pretty firm grasp on how LEDs work already.

Oh lol, for a moment there I felt smart

 

[Jimbo7]

Haha, np. It's really good information and explained well. With all the activity these LED threads have been getting, i'm sure it was a big help to someone.