 LEDs & Power
Programming

# 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

## The theory

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( Transformer volts ÷ LED forward voltage ) = Number of 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 calculations.

1. 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.
2. 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)
Using the greater number and rounding up (always round up), we find would need a 50 watt power supply. Some power supplies are listed using amps, not watts. To find out the amp rating for our power supply, divide the wattage you have calculated by the voltage of the power supply. For example, our 165w 36v power supply from earlier is a 4.6A power supply.

### Basic Driver Calculator

This calculator will give an estimate for the drivers you need for your application. You should work this out per channel, not as an overall number.

* Please note, use this calculator only as an estimated guideline. The driver you need and quantities of LEDs will vary depending on the exact LEDs you are using. To be the most accurate, use the data-sheet of your LEDs and the Advanced Driver Calculator below to work out exactly what you need. I will not be held responsible for any problems or damage that occurs from basing your lighting on the results of the calculators below.

| | |

LEDs per Driver = | Drivers needed = | Minimum power supply needed = watts
Driver Type:

This calculator will calculate the drivers you need for your application. You must work this out for individual channels. If you use multiple colours on a single channel, you should calculated each colour separately. The information that you need for this calculator will be supplied on the LED's data-sheet, which should be available from your LED supplier.

* Please note, This calculator is only as accurate as the data you enter into it. Please use the data-sheet of your LEDs and not estimated figures.

W | Vf | mA
| |

LEDs per Driver = | Drivers needed = | Minimum power supply needed = watts
Driver Type:

There are a couple of things that we will need to do to add the TC420 to this setup. We need to address the voltage, and controlling the drivers.

### ...but the TC420 can't use power supplies over 24 volts

This is very true. If you're using a power supply between 12 and 24 volts, you don't need to worry about this section. However, if you're using a power supply above 24 volts, something needs to be done so that the TC420 doesn't end up getting fried. There are 2 options that have been considered. The first is using a separate 12v power supply to power the TC420, however, you would need to join the negative connection the that of the 36v power supply to merge the 2 otherwise separate circuits. I don't like this solution, it's not very neat and you need another power supply. My preferred solution is to use a buck converter to reduce the power of the 36v power supply to 12v and power the TC420. This is a neat solution where you only have 1 circuit and power supply.

### Drivers

You will need to use drivers that can be controlled by PWM. You will probably be able to find some cheap drivers on eBay, however I think it would be better to use a proven, reliable driver. For 3w LEDs my choice would be the Mean Well LDD-700H. This has an input voltage of 9 to 56 volts (meaning you could use a 48 volt power supply and have 14 LEDs per driver), is PWM controllable and has a constant current of 700 mA, which is ideal for 3 watt LEDs. For different wattage LEDs you would need to use the appropriate driver, for example the Mean Well LDD-1000H outputs a constant current of 1000 mA, ideal for 10w LEDs.

### Controlling the Drivers

NOTE: Please only attempt this if you are happy soldering. This will invalidate the warranty of the TC420.

To control the drivers, you will need to Frankenstein your TC420. The channels are controlled by PWM, but they cannot be used as a direct link to the drivers. Internally, the PWM signal controls MOSFETs which let the power of the positive input voltage from the transformer through the MOSFET and to the channel connectors. To access the PWM signal directly, we need to attach a cable to the gate of each channel's MOSFET, and let that cable instruct the drivers via their PWM input. You can use this cable to provide a PWM signal to multiple drivers. The MOSFETs are the 5 chips with 3 pins located near the output connectors, labelled Q3, Q5, Q8, Q2, and Q4. The gate pins are the far left pins of each chip, shown here in blue.

### Wiring Diagram

The images below show how to wire high power LEDs using the above instructions. This image is suitable for power suppplies greater than 24v. You can click on it to view a larger version. Please read the page above for details on this wiring diagram. The image below shows a similar diagram for power supplies 24v or below. You can click on it to view a larger version. 