pc power supply to power 12 volt outdoor led lights?
I have a parts pc that I’m not using. I recently was given some low voltage outdoor l.e.d. lights. From what i’ve read the lights need a transformer to power them. With these lights being l.e.d.s, the wattage of the bulbs is only 0.375 each x 8 lights for a total wattage requirement of 3 watts. They are also 12 volt. The power supply in the old pc says 12 volt @13 amps. Will this work? or will the amperage be too much? The wiring will be roughly 50 feet long and 14-16 gauge strand copper.
2 Responses
SammiChengHK
16 Jun 2010
Scott P
16 Jun 2010
First, PC are not 12v power supplies. Second, your power supply should have the capability to produce your required current power at no more than 80% of total supply capacity. A circuit will not draw more current then what it needs. LEDs are simply Light Emitting Diodes. Diodes forward bias is .6v generally. The wattage is the amount of heat dissipated (or light in this case) the diodes will generate. You want to know what the power requirements are for a 12vdc power supply to produce 4W. Remember, we are using 4W so that we do not approach the power supply’s max output by more than 80%.
I = P/E Ohm’s law ( I = current, P = watts, E = voltage )
I = 4w/12v
I = .33 amps
Now we solved for current requirements, you know that a 12 volt power supply that will supply a sufficient current of .5amps will be adequate and you meet the max capacity by 66%
Wire lenght should not be included in this calculation. Wire resistance is pratically nill.
Transformers are AC (alternating current) which uses volt-amperes (VA) as a power rating. These are step down transformers (usually from 120vac to 12 – 24vac with no bridge rectifier). This is not the currect application. If you use a plug in power supply that has a 12v output @ 1A, this will surfice. These are plentiful and can be obtain anywere.
It is not practical to use a PC power supply to power outdoor LEDs.
1. The 12V output usually has small current output. It is very unlikely to output 13A which is more likely for 5V output. But it should be able deliver 3W of power.
2. The long wire length (50 ft) may be an issue on the power supply loading.
It would be better to use older transformer type AC adaptor to drive the LEDs.