I have an outdoor lighting transformer (operating at the usual 12VAC) that I want to add a strip of LED lights in a new run. The transformer has two legs, each supplying up to 300W of load at either 12V, 13V, 14V, or 15V (4 contacts per leg). The strip light controller takes 12VDC at up to 12A, but I will only be connecting a single strip that consumes 5A (+1A margin).

I know that to convert the power source to DC I will need a bridge rectifier and then something to smooth the ripple. I'm not sure what the tolerance of the RGB controller is (guessing 0.5V, I might be able to confirm that tonight). Based on my research over the past few days it sounds like the BR will boost the output DC voltage (due to RMS vs peak) so I will need some resistors or diodes to drop the voltage back down to 12VDC. As this converter will be living outside my intent is to keep things compact enough that I can weather proof it without much effort (either small enclosure, or epoxy and heat-shrink tubing).

I have a reasonable understanding of how the circuit design should look, but where I am not confident is on the specs of the components. For the BR, is at least 6A If reasonable or should I pad that with at least 12A If (especially if I want to add another 6A run on the end of this run)? A 20A If BR is only about $2.00 so no big deal on price. All BR's in this range seem to support very large peak reverse voltages (usually 600V+), are there any minimum specs I should take note of?

For capacitance, I am using the C = I / (Vdrop * Ifreq * 2) formula. In my case that is C = 6 / (0.5 * 60 * 2) = 100 mF which seems very high, but perhaps necessary for this type of circuit (with load this high)? Is it more reasonable to use multiple caps instead? I know that I will need 25V caps to handle the 12VDC coming out of the BR. I can pick up a cap with these specs for about $6.00 so again, no big deal price wise.

Are there any other considerations that I should be aware of? I am certainly not a professional electrician, but I understand the general concepts. Building the circuit and soldering the parts together is no problem for me, it's just some of the finer details that I would like some feedback on to make sure I'm on the right track.

Finally, what I am attempting to recreate is a product available on Amazon but not available in Canada (where I live). Based on it's size and shape I'm almost certain that it is composed of a BR and (at least one) capacitor. Possibly some other parts to regulate the voltage?

Here is a (very basic) circuit diagram that I am expecting to build. I just put 1kOhm for the controller as a reasonable amount of load resistance for the LED strip (not sure what the actual value is, but maybe I can figure that out later).


simulate this circuit – Schematic created using CircuitLab

Thanks for any help.

  • \$\begingroup\$ Isn't Canada 60Hz mains? \$\endgroup\$ – Tyler Mar 9 '16 at 19:11
  • \$\begingroup\$ it sure is. oops, i'll correct the typo. \$\endgroup\$ – pjs Mar 9 '16 at 21:59
  • \$\begingroup\$ What DC current do you need at 12V DC? \$\endgroup\$ – Andy aka Mar 9 '16 at 22:04
  • \$\begingroup\$ at least 6A (300 LEDs * 0.24W / 12VDC) \$\endgroup\$ – pjs Mar 9 '16 at 22:42
  • \$\begingroup\$ 12VAC is the RMS value correct? If so, then your DC output would be around 16 V. \$\endgroup\$ – Swarles Barkely Mar 10 '16 at 0:48

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