Joh, thanks for the detailed response.

You are of course correct on all points.

I will likely string 54 together roughly 6 strips of 9 LED's per strip
of 5050's I believe will fit in my current case. Using the smaller
3528's would yeild roughly 6 strips of 12 lED's for a max total of 72
LED's..

By the info you provided, 500ma should suffice.

Thus a power supply in the range of 1 amps would appear to be plenty.

Thanks again for straightening me out.

On Fri, 07 Mar 2014 03:27:53 -0600, John Fields
wrote:

On Fri, 07 Mar 2014 00:23:17 -0500, nospamgoingjag
wrote:

Hope this is an appropriate request for this newsgroup.

I have an LED trouble light (as in for working on a car). It is the
style with buld LED's. They started going out at random, so I decided
to check the power supply and it was varying all over the place
exceeding 87 volts. I frankly couldn't determine how the power supply
could be working properly. Since most of the LED's had already blowm,
I decided I would "rebuild" it using strip LED's (5050 SMDs or
3528's). Although I suppose I could run a wallwart and run the 12 V
up the 110 wire, but I would prefer to build a small power supply into
the handle as it is now, I just won't use the existing circuit board.

Could someone supply me with a schematic for a 110v to 12 V DC 5 amp
power supply that would fit in about a 2 inch by 2 inch by 1/2 inch
thick space?

---
30 watts per cubic inch is kinda pushing it for homebrew.

Each of the 3 LED's in a 5050 is rated for 20mA maximum, and by
connecting them in series, they'll drop about 9.6VDC across the
string.

a 120 ohm resistor in series with the string will drop the remaining
2.4V and will dissipate about 50 milliwatts doing it.

Using a 12VDC 5A supply, at 20mA per 5050 you could drive 250 5050
strings in parallel, which seems like a lot of LEDs for a trouble
light.

Is that really what you want to do?

John Fields