I need to power a large 180W LED lamp that runs on DC so I got this transformer that is 12v × 15amp. But I don't understand the labeling on the terminals.

  1. There are 2 +V terminals but no -V terminal, why?
  2. What is the 'com' terminal for and why 2 of them?
  3. What is that terminal between 'com' and 'N'? I'm guessing ground.
  4. What grade/gauge/type of wiring must I use for safe and efficient operation?
  5. Any additional equipment devices needed for safe operations?
  6. What is the purpose of 'output adjuster' knob? There is a knob in the corner but it doesn't look like it can be adjusted by hand. What kind of tool is needed here? See image below.

My aim is to use AC from the wall and turn it into DC to supply the LED. Please show me the correct path lest I get electrocuted. Somebody told me the 'com' terminals are -V output and said there are 2 of each -V/+V so you don't have to jam a thick wire in and instead use two smaller wires. This is a bit confusing. Please elaborate and whether this step is even necessary.

  1. If 2x -V/+V terminals present, is total current/voltage split between the two? Can I use just one set of terminals to get full voltage & current, or must I use both? What happens if I use just one set?

Please help. I don't want to hire an electrician for a job that may be very easy. Neither the LED nor the power supply came with any manuals or supporting documents. LED manufacturer said to use the above power supply.

Additional info on power supply,

Link to actual product page

Item description is found at this link


3 Answers 3


Disclaimer: If you don't know what you're working with, I suggest you hire someone to help. I know it's not what you want to hear but it's better safe than injured or dead. You only get once, maybe twice to seriously mess up.

From left to right on the back:

The AC "L" and "N" probably mean "Live" and "Neutral" respectively. The ground next to it is the Earth ground. The V+ and COM are the DC output terminals, which you could also say are V+ and V-, respectively.

Just some clarification: What you're referring to when you say V- is probably "ground" or to be precise, 0 Volts. With respect to the circuit with the LED anyways. COM and V- and Ground can all mean 0 Volts. However, V- is typically reserved for actually negative voltages, like -10V, etc.

The reason why there is a set of two is probably because there are two "rails." A rail acts as an independent supply so that you can easily isolate or distrubute loads so that two separate circuits don't interfere with each other or rob each other of too much power. This is just a guess since there's zero documentation for this supply. Also without documentation we don't know if it's possible to run those outputs in such a manner you can power the one 180W LED without some other external circuitry.

A lot of high power LED's I've seen run at ~30V or so. Power = Current x Voltage, so 180W = Current x 30V, solved: 6A of current. You'd set the output voltage of the power supply by using the adjust potentiometer "+V ADJ" before connecting anything.

According to the following table you probably need 12 gauge or larger wire (allowing more amperage to over-rate so the wires don't heat up easily).


Also another consideration: Be sure the LED has plenty of heat sinking otherwise it will burn up immediately. Even 20W - 50W LED's can require heatsinks as large as a typical desktop CPU's (including a fan).

  • \$\begingroup\$ Thanks for the reply. Heat is not an issue, there is a massive Heatsink in place (72" × 6" × 8"). LED circuit is complete and built by a retailer. The whole system is ready to go, except power supply. So, the manufacturer said to use this [12v × 15a] power supply. 1) Can you elaborate more on "rail" please? 2) Can you guide step-by-step how to connect the pieces (i.e. AC wire L/N goes to L/N terminals, then..)? Thanks. \$\endgroup\$
    – Samid
    May 31, 2015 at 2:57
  • 1
    \$\begingroup\$ @Korozjin - L is "Line", not "Live". \$\endgroup\$ May 31, 2015 at 4:45
  • \$\begingroup\$ @Samid that is pretty large, wow! Also, it just occurred to me both V+ connections might actually be just one rail. So you can have two large cables hooked up, etc. Check with a multimeter to see if they are connected. Either way, an explanation of rails... This is an oversimplification, but here it goes. So, imagine you have two supplies which each only have one COM and V+ connection. Well if you build it so you combine them into one package you call the outputs "rails" to indicate they act, effectively like two separate supplies. So each V+ should connect to different rails if thats the case \$\endgroup\$
    – Korozjin
    May 31, 2015 at 5:00
  • \$\begingroup\$ @Samid The distinction here is that a supply with multiple rails = multiple independent outputs, each from its own "source", usually at the same voltage, whereas a supply with multiple connections and one rail is still only one supply "source". Hopefully that makes sense. \$\endgroup\$
    – Korozjin
    May 31, 2015 at 5:05

1) "I don't want to hire an electrician for a job that may be very easy." On the one hand, you can probably go to any electrician, bringing your power supply and a power cord, and he'll show you where the wires go. For free. On the other hand, how much is your life worth to you? Seriously. Mess this up and you can do serious damage. Respect your limits and don't try for a Darwin Award.

2) If your system is really pulling 180 watts, you are asking for trouble by using a cheap 12 volt / 15 amp supply. You can give it a try (and since you have it, I expect you will). Be prepared for the supply to overheat or otherwise give you trouble. Make very sure you have good ventilation. Driving a power supply right at its rated output is asking for trouble, but you may get away with it.


It is quite common on power supplies to have a remote sense connection adjacent to output. In most cases it may be simply strapped together at supply. On a single voltage supply the output is between +V and com (common). It sounds as though your common is also referenced to ground. Measure -with no power connected- with ohm meter to chassis to verify. Do not have ANY connections between output and power line! Doc


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