To be clear, if I talk about transformers or power supplys/PSUs, I am referring
to the device you plug in the wall that outputs a constant DC voltage. For LED strips, this will be
If I talk about drivers, I'm meaning actual driver circuits used to provide a
constant current for high power LEDs.
Selecting the right transformer and setting it up
The transformer connects to the input v+ and v- terminals on the right side of the
controller. It supplies power to both the TC420 and the LEDs, so you must get a transformer with
enough power for these devices. Ideally, you should get a power supply with a regulated voltage, so
no matter what the current draw, it will be a consistent 12 volts.
In the previous sections, I showed you how to calculate the amps for your LEDS. To calculate the size
transformer you need, you must add the amps for all 5 channels together and add 10% as a safety margin.
This will give you the smallest transformer size in amps. In the following example, I'll be using the
following amp values for channels 1 to 4: 2, 1.5, 0.6, and 1.1.
amps = (2 + 1.5 + 0.6 + 1.1) x 1.1
amps = 5.2 x 1.1 (Multiplying by 1.1 adds 10% to the amps)
amps = 5.72
So we would need a 12v transformer rated at 5.72 amps or above. If the transformers are sized in watts,
we must multiply the amps by the voltage.
watts = amps x volts
watts = 5.72 x 12
watts = 68.64
So we would need a transformer rated at 70 watts or above.
You can calculate your transformer using this calculator
The power supply needs to be rated for at least 0 watts or 0 amps.
Questions - Drivers
Questions - Lights off
I've been asked about power supplys, what happens to them when the lights are off, and if it's a good
idea to have the power supply on a wall timer; the idea so that the power supply is off when the lights
are off and rely on the TC420's battery backed up memory to keep time. First I'll start with is it
possible, then I'll tackle is it worth it.
Is it possible?
I'm going to start with the battery backup, as if this can't keep time for the hours that the power is
off, then this whole setup is doomed to failure. The average aquarium light is on for 6-10 hours a day,
depending on what you are keeping. For testing the extremes of the battery, we'll go for a 6 hour set-up
which would mean our PSU is off for 18 hours, so that will be the goal for my test. So far, I've had a
TC420 disconnected from a power supply for 12 hours and it was fine. I will test out the full 18 hours
when I get a new TC420 in a few weeks time.
I'm fairly confident that it will easily last the 18 hours. It most likely uses circuitry similar to
that of an electronic wall timer, and I've had those things go without power for months and still be
correct within an acceptable margin. My biggest concern would be the longevity of this, and if the
battery would be happy with daily charging and discharging like that. However, for now I'm going to say
yes, this is possible.
Is it worth it?
To me, this is the more interesting part of the question, and this time I'm pretty sure the answer is
going to be no. Power supplys do not constantly produce the levels on the casing, that is their
maximum level and will only supply what is being asked of it, plus about 10% which is lost in the
efficiency of the transformer its self. When no current is being drawn, a power supply should only be
ticking over at around 0.25 watts; the more efficient the power supply, the less it will be.
I am going to measure the watts of an unconnected power supply, then connect only the TC420 to see how
much that draws. This will give us an approximate figure for the TC420 in, what I'd call, standby mode,
which is when it's connected but no LEDs are on. Once we have this figure, I'll measure some normal wall
timers and see how many watts they use. In the case of a mechanical wall timer, it has to operate a
motor to turn the time dial, and a digital timer is likely to have a circuit very similar to what
is in the TC420.
The questions are:
I'll get these answers here soon, so stay tuned.
- how will a TC420 in standby mode's power consumption compare to a normal wall timer?
- Will it be enough of a power difference to make any significant financial difference?