In one of the previous posts we learned how to wire a low power grow light circuit using 5mm LeDs, here we see how the same may be done using 4 watt power LEDs. The idea was suggested by Mr. Jack.
During my exploration of LED lighting and the various circuits employed I would like to post some of my recent finding. Acknowledgements to LED Magazine and Steve Roberts. I've attached several pictures of my recent build,.....28 - 3watt leds, 7 leds, in series per row and 4 row in parallel. I'm using a 24v-32v, 4amp power supply.
These lights were purchased as emitters and the bases had to made and heat sinks applied to each emitter. The leds were mounted to aluminum channel.
Since the completion of the circuit, I've experienced various heating problems and it was continuing to be difficult to balance the circuit, to run cool, stable, and steady electronic output. I decided to look deeper into this and leds in general and here is what I've found.
Even if the LEDs are all from the same production batch and sequentially manufactured, the foward voltage (Vf) of individual LEDs still has a ± 20% tolerance.
The tolerances this high means that the total forward voltage for each led in a string can be very different and therefore the current mismatch can be very significant.
Consider, if we have 5 leds in series with a forward voltage of 4v, that is (4v)(5) = 20v. WRONG!!!
Given the tolerance above, the forward voltage is really, 16v to 24v, that an 8v spread. How are you going to design a circuit that requires you to place things in BALANCE if the tolerances are that hight? This is one of the reasons that things go array. There are many others!!!
For a newcomer or a new hobbyist wiring LED lights could look complex with many hidden intricacies, actually it's not.
Wiring the LEDs
It just needs to be done as per the rules, for getting the correct results.
Referring to the above images sent by Mr.Jack, we can see that the LED strings are not correctly wired and that's exactly why the design is giving erroneous and erratic response.
You should never wire LEDs having different V/I specs in series.
You should always group up the LEDs with identical specs together when a series connection is needed to be implemented.
However if the requirement is in a mix and match manner as in the above images, yet still the same color LEDs must be connected in series and if necessary in parallel with their individual series resistors.
High watt LEDs will emit heat, therefore assembling these devices over a heatsink is imperative and to avoid a thermal runaway we can incorporate a current regulator, that's all right, no issues with these parameters.
But said that the LEDs must be wired up as instructed in the above paragraphs, only then you would be able to acquire an efficient response from the system.
And suppose you have a power supply which is rated to supply a lower voltage but higher current in that case you could simply hook up all the LEDs singly in parallel with each LED equipped with its own limiting resistor, a well calculated one.
Calculating the LEDs for the grow light circuit using power LEDs
I have already discussed this in one of my previous posts, you may read it here
Therefore the correct way of wiring the LEDs for the above example high power grow light assembly should be as expressed in the following diagram.
All the positive and negative ends of the respective strings now simply needs to be integrated with the power supplies (+)/(-) terminals
If you have any questions or doubts feel free to post them in the comment box below.
I think I completely missed something in the above design.
Since the current specs of all the LEDs are same, voltage specs can be ignored, and different color LEDs may be connected within the same strings.
So let's analyze the design correctly yet again.
The first string from left has 4 red LEDs and 3 blue LEDs, supply is 24V, therefore the current limiting resistor for this string could be calculated as follows:
R = supply minus total LED fwd. voltage divided by LED current
= 24 - (4x2)+(3x3.2) divided by 0.6 (600mA)
= 10.66 ohms
wattage =(4x2) + (3x3.2) x 0.6 = 10,56 watts
you can calculate resistors for the other strings too, in the above manner.
The current control for the above set up can be constructed as explained in the following artices: