Connecting high power LEDs to the TC420
This section will deal with connecting High Power LEDs to the TC420. I am looking to add 3w CoB LEDs to my 6' aquarium. I have the theory for this worked out and will post a full guide and tutorials once I have built the lighting and confirmed the theory is correct. Due to other financial priorities, this will most likely be sometime in the first half of 2017
NOTE: I have not built this system, so cannot confirm 100% that it works or that you
will not encounter problems. Use this information at your own risk.
At the moment, I am not going in to depth, so please make sure you understand the electronics side of this before attempting anything.
Using 3/5/10 watt LEDs with the TC420 is possible, however its not a case of simply connecting the LEDs to the outputs from the TC420, you need to use constant current drivers and modify the TC420 to gain access to the direct PWM signal from the processor. What this means is that the main current for the LEDs does not pass through the TC420, it just provides a signal to the drivers, so you can in theory hook up as many LEDs as you like.
For the rest of this guide I will be talking about 3w LEDs, however you could use 5w or 10w LEDs by substituting the correct driver and calculating the correct size power supply.
Standard 3w LED wiring
When you wire up 3w LEDs, you have a transformer which you use to power a constant current driver, which then feeds a chain of LEDs wired in series. The maximum number of LEDs in the series chain will depend on the voltage of the transformer you use. A 3 watt LED has a forward voltage of approximately 3.3v. Therefore, if using a 12v power supply, you can have 3 LEDs in the chain.
floor( 12 ÷ 3.3 ) = Number of LEDs in the chain
floor( 3.64 ) = Number of LEDs in the chain
3 = Number of LEDs in the chain
3 LEDs isn't a lot, however, you can wire multiple drivers in parallel to the same transformer, For example 1 driver will have 3 LEDs, but 5 drivers will give you 15 LEDs.
Now imagine that instead of a 12v power supply, you have a 36v power supply. This will now give you 10 LEDs in the chain of a single constant current driver. This is a much more cost effective solution as it's cheaper to buy a 36 volt power supply rather than many more constant current drivers. Now with 5 drivers we can have 50 LEDs running off of a 165 watt, 36 volt power supply.
Of course, we no need to calculate how many watts our power supply needs to provide. To calculate the
wattage of the power supply, there are 2 calculations to perform; you pick the highest value from the 2
- Multiplying the total number of LEDs by their wattage, for example 15 × 3w LED = 45w. Then multiply this by 1.1 to factor in the 10% overhead; in our example this would equal 49.5w.
- Multiply the Amps of the LEDs by the forward voltage of the LEDs (0.35 × 3.3 = 1.16), then multiply this by the number of LEDs (1.16 x 15 = 17.4), finally multiply by 1.1 for the overhead (17.4 × 1.1 = 19.14w)