Hey guys, so I figured this forum would be the best place to get some education so here goes.
I am currently building a light to use to grow some macro algae. I am using red and royal blue Cree XP-E2 that I have soldered to the star MCPCB boards. Those little boards make everything nice and neat by the way.
My thoughts were to use a constant current adjustable driver something like the meanwell
HLG-60H-48-A
At full power royal blue is 1000mA at 3.4v
Reds are 1000mA at 2.65v
Was shooting for 80% power.
Anyway i have seen and actually have a high power led array above my reef tank that has two channels one white and one with royal blue and UV Leds. It does not have any series resistors
Could I run these mix forward voltage leds in series as long as I match the voltage.
My mind thinks like this every led has an internal resistance which is why they drop voltage to begin with. And series circuit rules say that the total voltage is the sum of all the voltage drops along the circuit. And current is the same through each component.
I know resistance changes with heat But with a constant current set up it should work correct?
Last night I hooked up 7 reds and 8 blues in series and powered them with 40 volts figured go low to be safe. The circuit was pulling 410mA and each led appeared to be the same brightness. Granted our eyes are a poor judge of brightness but still. I used a IR temp gun, a small one, and measured temp of each diode after about 45 seconds of being on and they were all heating up equally.
Will this work? And if not can someone explain to me the why of why not?
Eventually I am going to putting my overhead lights on a controller that I think I am going to be using an arduino to do so. But I am wanting to learn the ins and outs of leds and drivers before hand. So some smaller projects come first.
LEDs are NON-LINEAR resistors. More current, more heat, less resistance. You have measured the temperature after 45 seconds.What are you using for heat sinks to dissipate that heat?
It’s a large aluminum heat sink the led led stars are attached with thermal paste to it. Basically it’s a led flood light that I gutted because the driver went bad and am repurposing it
As long as you're driving the series string of LEDs with a Current Regulator [i.e. Constant Current], then the only consideration for the LED Forward Voltage is, whether the sum of the Forward Voltages [the highest Forward Voltage they will ever be -- because it changes with temperature], of the LEDs, is less than the maximum voltage the Current Regulator can supply and still be within its ability to regulate the current. Other than that, the Forward Voltage on an LED has no bearing on how an LED is properly driven.
AND, as long as the optimal current is the same for each of the LEDs in series.
Fantastic that is what I was thinking but wanted to make sure. I was going to use a mean well driver that allows me to set voltage and current. Thank you for clearing it up. I don’t feel as stupid now!
I was going to use a mean well driver that allows me to set voltage and current.
A power supply cannot really "control" both current and voltage (because of Ohm's Law).
It's not uncommon for a power supply to have a current-limiting circuit. There are bench supplies with variable voltage and variable current limits. For example, you can set the limit at 1A and as you increase the voltage, current increases to the limit. After that, the voltage knob no-longer increases the voltage.
Or, if you increase the load (decrease the load resistance) the voltage drops so you don't exceed the current limit.
A constant-current power supply is a strange animal... The voltage increases when the load resistance increases (up to the voltage-limit of the power supply). And, it's generally OK to short-out a constant-current supply because the voltage simply drops to (almost) zero and the current keeps flowing.
Ohm's Law defines the relationship between voltage, resistance, and current. It's a law of nature and there's no cheating. The "resistance" of an LED is not constant (it varies with voltage) so we can't really use Ohm's Law, but it's still in force.
DVDdoug:
A power supply cannot really "control" both current and voltage (because of Ohm's Law).
It's not uncommon for a power supply to have a current-limiting circuit. ...
The OP is referring to a device intended to be used to drive high power LEDs ["mean well driver "]. It provides both voltage regulation and current regulation. Thus it controls the current up to the set voltage, and then it voltage regulates.
ReverseEMF:
It provides both voltage regulation and current regulation. Thus it controls the current up to the set voltage, and then it voltage regulates.
No it doesn’t. There is no voltage regulation when the load resistance is too high to get the required current, just the voltage, minus drops, of the supply voltage. You can’t say there is any voltage regulation going on. Not in the sense that the word regulation is normally used.
Grumpy_Mike:
No it doesn’t. There is no voltage regulation when the load resistance is too high to get the required current, just the voltage, minus drops, of the supply voltage. You can’t say there is any voltage regulation going on. Not in the sense that the word regulation is normally used.
From the datasheet of one of the Mean Well devices:
HLG-60H series is a 60WAC/DCLED driver featuring the dual mode constant voltage and constant current output.
It isn’t, it is a data sheet written by someone who’s grasp of English is as poor as their grasp of electronics.
It makes absolutely no sense regulating the voltage into a constant current drive, you might as well feed an unregulated voltage into it and then it has a wider range of constant current capabilities.
If indeed they regulate the voltage before putting it into the constant current supply then they are idiots.
Meanwell is a top name in LED drivers. They make some of the best drivers on the market.
You are making a lot of serious claims about a company you have no clue about. Seems a little irresponsible to me. If you want to know so bad why not contact meanwell directly? I’m sure they would be more than willing to educate you.
From basic physics, it is utterly impossible to simultaneously regulate BOTH the voltage and the current of a power supply.
If there is any confusion about that fact, blame poor writing on the part of the Meanwell folks, and confusion and/or misinterpretation by the readers of their literature.
Meanwell is a top name in LED drivers. They make some of the best drivers on the market
They might but I have never heard of them. The company name is stupid for a start and has all the hallmarks of being chosen by a non native speaker of English. As do the comments that both the voltage and current are simultaneously regulated. That is simply a nonsense and to believe that something like that is possible shows a total lack of understanding about the way electricity works.
From the origional post
My mind thinks like this every led has an internal resistance which is why they drop voltage to begin with.
That is not the case. If it were a resistance then the forward voltage drop would change on a linear way with the current. The best way to think of it is as a constant barrier that has to be overcome irrespective of current. Which is close enough to the physics of the situation which involves the energy gap between electrons in the valence band and those in the conduction band. This gap is defined by the material making up the semiconductor.
Those drivers DO have current and voltage limiting, that can both be adjusted independently.
Sure, you can't have both regulations at the same time.
For LEDs, you use current limiting.
And set the voltage limit to a safe value if/when the LED string gets open circuit.
Think of it as a LAB supply, powering a 3.3volt/300mA LED.
You set voltage to 5volt, or 12volt, or whatever you think is safe when the LED is NOT connected.
Then you set current to 300mA.
The supply is now in current regulation, until the LED is disconnected.
Leo..
You set voltage to 5volt, or 12volt, or whatever you think is safe when the LED is NOT connected.
And set the voltage limit to a safe value if/when the LED string gets open circuit.
That is very silly. If the led string gets to be an open circuit what is the danger? If it is below 50V then it is safe. Under what circumstances will 5V be safe when 12V is not? Remember a child’s electric train set has extensive exposed rails with 12V on them and no one (yet in this safety mad era ) thinks they are not safe.
Like I said they don’t actually understand electronics.
Back when I started a TTY machine would have 300V on the driving lines when not connected and about 3V when it was. That was an 80mA constant current loop system. If you restricted that to 50V then it would not have worked over the required distance.
Could be that max open voltage limit is not only there for the user, but also to protect parts in the power supply. Output decoupling caps, mosfets, etc. One can only guess without actually seeing the circuit diagram.
Leo..
It could be, but if that was the intention then there would be no need to make it adjustable, it would not work. This because if it could be adjusted up to the maximum input voltage then those internal capacitors of insufficient voltage would still blow. A fixed pre voltage regulator would be much safer.
Grumpy_Mike:
That is very silly. If the led string gets to be an open circuit what is the danger? If it is below 50V then it is safe. Under what circumstances will 5V be safe when 12V is not? Remember a child’s electric train set has extensive exposed rails with 12V on them and no one (yet in this safety mad era ) thinks they are not safe.
The constant voltage driver [or "constant voltage" setting] is to accommodate [cheaper] LED strings that are meant to be constant voltage driven (i.e. they have a resistor in series with the LEDs -- and often the "set" is composed of one or more parallel strings of resistor terminated, series connected LEDs, with the advantage being that more LEDs can be powered by one, lower voltage driver). Which, I agree, is a less reliable way of driving LEDs -- especially higher powered LEDs.
The constant voltage driver [or "constant voltage" setting] is to accommodate [cheaper] LED strings that are meant to be constant voltage driven (i.e. they have a resistor in series with the LEDs
The best way of driving LED strings is with a constant current supply, irrespective of if the string has built in resistors or not.
That comment simply does not make sense.
Grumpy_Mike:
The best way of driving LED strings is with a constant current supply, irrespective of if the string has built in resistors or not.
That comment simply does not make sense.
Well, silly -- then I guess "MeanWell" didn't "mean well", when they produced a constant voltage LED driver. Not everyone can be as rational as you, I suppose.
Maybe if you looked at it from a "marketing" perspective ... hmmm.