How many MA for 3528 LED strip

[Troy Shaffer]

I useally use 12v 500ma power supply, but I got an order for 75 edge lit signs and I can't find that many supplies in one place. I can find 12v 300ma but I'm worried about them being dimmer. What I've seen online they can handle up to 1A, But with my 5050 Leds they get hot at 500MA but not at 300MA. I'd just like to know what to expect before I place a big order. The strips are going to be 6inches long. Thanks Troy

[AL Ursich]

I would use a mA meter in line with the positive wire and measure just what it takes to run the 6 inch display. The Meter on the mA setting goes in line with the positive wire.. Positive of meter to the power supply and negative of the meter to the Red positive wire of the Load or LED.

And a word of caution. Buy a quality Wall Wort.... Remember if Houses start burning down, you bought the Wall wort.... Liability...

"Yes, your Honor, I substituted my normal Wall Wort for this smaller version.... I was in a hurry to ship the order."

Don't want to Pi$$ you off, just go into this with open eyes....

AL

[Dan Hintz]

I useally use 12v 500ma power supply, but I got an order for 75 edge lit signs and I can't find that many supplies in one place. I can find 12v 300ma but I'm worried about them being dimmer. What I've seen online they can handle up to 1A, But with my 5050 Leds they get hot at 500MA but not at 300MA.
The strips should only take one value of current... even if your supply is capable of 500mA, a 300mA strip should only use 300mA. Changing the voltage, however, can be a problem for strips that aren't regulated. Providing 12V to a 9V unregulated strip can quickly overheat them as they will pull more current than designed.

[Mark Ross]

Simple ohms law. Find the resistor or resistors that are in series with your LED's. Typically the strips are set up in sets of 3 led's as forward voltage on white LED's is typically 3 volts. You did not mention what color your led's are. Red LED's drop about 2.1, blues and greens tend to go closer to 3.5-4 volts. If it is white, and you are going to supply 12 VDC, then take 12, subtract the value of the forward voltage of the three LED's (lets say 9 volts). This leaves you with 3 volts. Take 3 and divide it by the resistor value and this will give you the current draw for those 3 led's. Multiply the current draw by the number of LED sets you have, that gives you the total current. 6 inch long strips don't need anywhere near 300mA. Typically "wall warts" are unregulated and if they say 12 vdc at 500mA, that means at a load of 500mA, the supply will put out 12 vdc. So for a much less load, the VDC out of the supply will be much greater than 12 and because of that, you are overdriving the strip.

You need a regulated 12 VDC supply or you need to find a supply that will be around 12 VDC at whatever your load is. Heat is what kills LED's more than anything and overdriving them causes them to overheat.