Hi I woould like to know, I am currently looking to buy a variable DC PSU and I can see some are rated for 30V 10A, 35V 5A etc. I would like to test circuits before implementing them in my project and one of them is a 12V 300W led bar and I would like to know if the PSU could handle more amps at lower voltage than what it's rated for (rated for 30V 10A -> 300W vs 12V 25A -> 300W)

 

Um - what? A 30V 10A PS is capable of 300 watts, but if your LED's are designed to run on 12VDC - Don't try it unless you have all the specs for your LED Light Bar. If you up the voltage you'll probably blow out your light bar.

 

Um - what? A 30V 10A PS is capable of 300 watts, but if your LED's are designed to run on 12VDC - Don't try it unless you have all the specs for your LED Light Bar. If you up the voltage you'll probably blow out your light bar.

a variable PS can be set with a knob 0v to 30v so I would put it to 12v for the 12v led bar ...

 

There’s generally a maximum current listed that is independent of voltage. If you need 300W @ 12V, find a supply capable of 25A. Why do you want it to be variable?

 

Calculate the current required using the formula for wattage:

P = I x V
I = P / V
A 12V 300W LED strip will require 300W / 12V = 25A.

Hence you need a PSU that can deliver 12V @ 25A minimum.
Ignore the voltage and power rating for this part for now. If the PSU is not rated for 25A (ideally 30A or more for some headroom) then it is not going to work for your application.

 

There’s generally a maximum current listed that is independent of voltage. If you need 300W @ 12V, find a supply capable of 25A. Why do you want it to be variable?

Just like I said in my question I want to test my circuits BEFORE implentation in my project there is other circuits with differents voltages that I want to test the 300w led bar was just an exemple

 

Your question was answered. No, a 30V 10A variable supply cannot provide 25A at 12V.

Bob

 

Um - what? A 30V 10A PS is capable of 300 watts, but if your LED's are designed to run on 12VDC - Don't try it unless you have all the specs for your LED Light Bar. If you up the voltage you'll probably blow out your light bar.

Your question was answered. No, a 30V 10A variable supply cannot provide 25A at 12V.

Bob

Let me be just a little bit clearer: If you raise the output voltage to 30 volts on a 12 volt light bar - you're going to have a massive leakage of smoke from all components involved. Like Bob said - "No, a 30V 10A variable supply can not provide 25A at 12V."

 

Unless the PSU has a switching preregulator, it may actually handle fewer amps at low voltages, because so much power has to be dissipated in the series regulator.

 

Power supply ratings are almost always the maximum that the supply can deliver, and often not all of them at the same time. So the zero to thirty volt supply may be able to deliver ten amps at any voltage, BUT the load drawing 300 watts is also specified to require 12.5 volts, and so that is what the supply should be adjusted to deliver. The fact that the load requires 25 amps for full power means that the supply will be overloaded when you connect the load. Some supplies will deliver more current for a brief time, most will not.
So with a power supply the things to check are the volts and the amps capability. Ignore the watts, it is mentioned because it is a big number, not because it is useful.