I am currently in the process of planning a 6x30w led build for a tank, Now the leds are 32-36v 1.7amp each, I have got a 36v psu @ 14amp
Now trying to think how to make the ardunino dim the leds, All the led drivers are no where near the voltage and amperage for the leds so thought of using a 36v 30amp pwm speed controller which has 1-10v dimming function, so thats the psu and dimmer now i would think i cant simply connect all the leds to the speed controller in case one led fails the others will get more power so need a 1.7amp 32-36v regulator do the leds just need the amperage regulated or both voltage and amperage. I have not bought the ardunino yet as i wanted to make sure its all possible. In time i want to make the arduino control the main white leds, the blue lights and the moon lights so will need to find the suitable program also maybe a fan controller controlling the cooling of the heat sink fans.
do the leds just need the amperage regulated or both voltage and amperage.
The key specification for those led arrays are:
DC Forward Voltage (VF): 32-36V DC
DC Forward Current (IF): 1700mA Max
This is telling one that a module won't even start to conduct current until the applied voltage is above 36volts DC, so plan on needing a 48-50 volt power supply rated at around 12 amps or better. These kind of led modules are not controlled by regulating the voltage, but by using (requiring) current regulation with constant current drivers. The expensive part (other then the leds themselves) is that each led module requires it's own separate constant current driver, you can not drive 6 of these modules wired in parallel with one say 10amp current driver as there is no means to force the modules to share the current equally.
So assume you have 6 constant current drivers available and running them at say 1 amp (don't run the modules at their maximum rated 1.7 amp value, it's not safe for the modules reliability), you would require that the constant current modules have a +5vdc enable signal input the turns on and off the current regulation. All six current drivers could have this enable signal wired together and then wire to one Arduino PWM output pin. This would allow all the modules to have variable brightness control via the software you write for the arduino.
Finding the six constant current drivers rated at 50vdc or greater and with fixed or adjustable constant current value of an amp or so, and with a +5vdc enable input signal, will not be easy I suspect. And designing and building six such current regulators with digital input enable signal control is not a trivial effort.
If you do manage to find all the pieces needed, be sure to heat sink the heck out of all those led modules as the combined heat dissipation is going to really surprise you.
Won't say this can't be done, but this is a bear of a project you are taking on. Lots of voltage, lots of current, lots of heat. That adds up to a challenge even for the more experianced of electronics designers.
This circuit should limit current to 1A. The resistor will dissipate 3.3W, so get a 5W one, the transistor (power npn, not darlington) between 0.3 and 1 W, so needs a heat sink. It should be driveable from an arduino output.
----------------------------- +ve
|
LED Load
/ c
Ard --- 56R ------------b |
| \ e npn
| |
4V _ a Zener 3.3R
^ c Diode |
| |
----------------------------- 0V
This circuit should limit current to 1A. The resistor will dissipate 3.3W, so get a 5W one, the transistor (power npn, not darlington) between 0.3 and 1 W, so needs a heat sink. It should be driveable from an arduino output.
But one Arduino pwm output pin will not be able to drive six of these drivers at once without an additonal current buffer amp.
I thought he wanted 3 outputs. Is the limit of 40mA the whole arduino, or can each output pin source that?
I have thought of an improvement to the circuit:
If the transistor warms up, the Vbe falls, so more current will flow, so the transistor could warm up more... This could lead to a current runaway.
To get better temperature stability, put two small signal diodes (e.g. 1N4001), forward biased, in series with the zener, and reduce the zener diode to 2.6 volts. The diodes should be in close thermal proximity to the transistor. As the transistor warms, the diodes warm too, and reduce the voltage across them, since there are two diodes, the voltage Vbe across the transistor will fall and it will
reduce the current.
If you use a darlington pair, and change the Arduino output resistor to 220 Ohms, and the transistor emitter resistor to 2.7 or 2.2 Ohms, it should still work but take only 5mA from the Arduino output.
I thought he wanted 3 outputs. Is the limit of 40mA the whole arduino, or can each output pin source that?
40ma is the absolute max for a output pin, 20ma is recommened test condition continous current in the datasheet. 200ma limit for total chip and output pin consumtion.
The OP didn't really state if he wanted individual brightness control of each of the 6 led modules, or just one brightness control over the whole array. My comments were making an assumption of one pwm control over the complete array. Either way arduino control is not the difficult part of this project, DC power and heat management are where the challenges lay.
I've noticed that most of the constant current higher power led drivers made available from china on E-bay, etc utilize switching circuits in their drivers, which makes sense as we are talking real heat producing current levels here and driver efficiency really counts.
Thanks guys, I kind of knew about needing the driver one for each led, so in theory would the pwm 36v 30amp dim the leds ?
So would it be a better idea getting one psu per led then then try to work out how to dim the leds, I know theres going to be a lot of heat and going to be importing 4-5 large heat sink sand have 6 x 120mm fans cooling
any thoughts on these psus ? i guess this gets rid of the led driver circuit, Thank you for helping
Both those drivers have the same problem. Remember the voltage requirements for your led modules?
DC Forward Voltage (VF): 32-36V DC
That means they are going to require a current driver that has can provide and 'overhead' voltage above the 36vdc value, I would suggest 48vdc to be a minimum driver voltage requirement.
Also both drivers fail to have a interface means that would allow an Arduino to control brightness via PWM commands.
Thats the psu that he sells with the leds which i had told him i could do with dimmable ones, Ok so if i manage to source a psu to use the 36v30amp pwm to run the leds all i need then is an 1 amp current limiter for each led
are these any good ignoring he voltage side just trying to get my head around it all lol
This small power supply provides a regulated voltage, adjustable between 1.5 and 35 volts at 1 Amp. With the LM317 regulator remarkably better ripple and regulation characteristics are given than with conventional regulators. Current limiter and thermal overload protection are included in the IC. Supplied without heatsink.
Specifications
At first i was going to use a 24v psu with 20-24v leds using the velleman vm168, Then just get 14v led constant drivers just so the amperage couldn't go over the max
3 channel 0..10VDC PWM DC dimmer
Selectable: 0..10VDC or 1..10VDC operation
Selectable fast / slow response
PWM frequency: 90Hz
Will work with any 0 - 10V (1 - 10V) controller
0..100% level adjust by means of external potentiometers is possible
DIN-rail enclosure: 2 modules wide
Max output current: 5A /channel
Power supply 12 - 24VDC
But the amperage of the leds was 2.5amps each
I can only repeat that you require current drivers that can provide in excess of 36vdc voltage before those led modules, you posted, will even start to turn on. I suggest 48vdc is the minimum output voltage you require for your drivers if you are going to use those led modules per their stated specifications.
The circuit I posted + darlington output would cope with 2.5A, change the resistor so it drops 2.6V at 2.5A, so about 1 Ohm, to change the current limiting. Of course the heat sinks will have to be even bigger.
The circuit is a current limiter - that is, whatever the input voltage, it will keep the current at the set point. Google for "transistor constant current" on Wikipedia. The input voltage needs to be that required by the LED + about 3.5V (for the current limiter).
None of the power supplies you posted can be controlled*. They would drive a LED, but appear to need adjusting to set the current.
From your last post the vellman vm168 needs a 0-10 voltage input. You cannot get that from an arduino directly; you need an amplifier/converter from the analogue output, and a 10V power supply; or a circuit to convert PWM to 0-10V DC.
This uses the LM317, the 1A is a protection limit, I'm not sure that is how the LM317 is supposed to be used. The LM317 datasheet does not say its a constant current source. You still have a heatsink problem since its going to shut down to protect itself without one, and its not supplied with one. Better to buy a couple of the LM317 and experiment with it.
This small power supply provides a regulated voltage, adjustable between 1.5 and 35 volts at 1 Amp. With the LM317 regulator remarkably better ripple and regulation characteristics are given than with conventional regulators. Current limiter and thermal overload protection are included in the IC. Supplied without heatsink.
And the max input of that unit is 40V which as Retrolefty says, is too little for the LEDs you originally said.
Does that only apply using the drivers then that you need a higher voltage than the leds rated at, Sorry trying to get to grips with it
Yes are two very different but required requirements determined by the leds one is using. All leds have a forward voltage drop rating, Vf, which until exceeded will not conduct any current at all. A simple led led has around a 1.5vdc Vf specification, below that it will simple not conduct any current at all. All leds have a maximum rated continuous current specification. The common simple red led has maximum recommended current specification of 20ma. Above that the led will/can be destroyed due to excess heat dissipation. However the simple red led will light up from anywhere from 1ma on up to it's maximum rated value.
Bottom line, you first have to select the led(s) you want to use and that will determine what kind of supporting components and their ratings you will need.
As I read it, the LED and Driver can be connected together. That gives full brightness. They are matched.
You could try to control it by PWM to a single MOSFET transistor. This could be done with an Arduino. A transistor such as the PHP7N60E would do this, and this can be controlled directly from the Arduino output.
** I don't know how trying to modulate the output of the driver at that sort of frequency (at least 100Hz is needed) is going to interact with the power supply (the driver). It may not work at all. It is possible that it damages the driver.
The MOSFET may also get hot - again a heatsink might be needed.
Driver +ve -------------
|
LED LOAD
|
-| d
|
Ard Pin -------g-| | PHP7N60E
|
-| s
0V, Driver -ve ---------
** I don't know how trying to modulate the output of the driver at that sort of frequency (at least 100Hz is needed) is going to interact with the power supply (the driver). It may not work at all. It is possible that it damages the driver.
That is an important issue. Unless it's stated or been shown to work, one can't assume that a given constant current driver can be 'modulated' with an external MOSFET/PWM signal turning on and off the current path. That's why I would only buy a driver that has it's own pwm input signal and has published the maximum switching frequency of switching it can be used with.