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Default LED trouble light power supply

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?

Appologies is this is the wrong place to make this request.
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Default LED trouble light power supply

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
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Default LED trouble light power supply

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

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Default LED trouble light power supply

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.


I used some Cree 1 W white LEDs from Digi-Key
($1.70 each in small quantity) and put 10 in series. I used a 36
V AC or so transformer, rectifier and filter cap, and built the
LM3404HV reference circuit to deliver 300 mA to the string. This
has worked well, and 10 of these lamps are OUTRAGEOUSLY bright!
In fact, you need a diffuser, or you will be temporarily blinded
if you look at them! The 10 LEDs at 300 mA is about 9 W, but it
is almost as much light as a single 48" fluorescent tube, and brightly
illuminates our pantry/laundry area at home, which was horribly dim
with a 60 W incandescent. (Due to the particular ceiling fixture
there, no CFL would fit.)

The only problem with this plan is to find a 10 W transformer that
can fit inside your trouble light handle.

Jon
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Default LED trouble light power supply

On Fri, 07 Mar 2014 12:18:10 -0500, nospamgoingjag
wrote:

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.


---
the info I provided was based on a voltage drop of 12V across each
5050 and its current limiting resistor with 20mA through them, so
that would be 12V across each strip with 20mA through each 5050 and
its resistor, for a total of 180mA per strip.

You'd run all 6 strips in parallel, so the input voltage would stay
at 12V, but the total current would be 1080ma, or about 1.1A for the
5050 array.

Assuming 20mA for each 3528 and 12 3528s per strip would yield a
current of 240mA through each strip with 12V across it, and a total
of 1440mA for the 3528 array.

Thus, using a 12V 1.5A supply should work for either array but,
before any power supply decisions are made, you should characterize
the strips by finding out how they're wired and the values of their
current-limiting resistors.
---

Thanks again for straightening me out.


---
You're welcome.

John Fields


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Default LED trouble light power supply

On 2014-03-07, nospamgoingjag wrote:

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?


You want to pack a 60W PSU into 2ci? that seems fairly ambitious,

--
Neither the pheasant plucker, nor the pheasant plucker's son.

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Default LED trouble light power supply

Jon, thanks for the info, I may pursue that for other lighting
opportunities.

Jasen, John Field has straightened me out on my overbly ambitious
requirements.

John, thanks for the further feedback. I obviously need to revisit
the LED count and layout before pursuing further.

Thanks again for the feedback and ideas.

..On 8 Mar 2014 03:19:54 GMT, Jasen Betts wrote:

On 2014-03-07, nospamgoingjag wrote:

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?


You want to pack a 60W PSU into 2ci? that seems fairly ambitious,

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Default LED trouble light power supply

On Fri, 07 Mar 2014 23:10:58 -0500, nospamgoingjag
wrote:

Jon, thanks for the info, I may pursue that for other lighting
opportunities.

Jasen, John Field has straightened me out on my overbly ambitious
requirements.

John, thanks for the further feedback. I obviously need to revisit
the LED count and layout before pursuing further.


---
Oops...

Earlier I assumed that the 3528 has three LEDs in the same package,
like a 5050, but it doesn't.

It has a single LED per package with specs similar to each of the
LEDs in the 5050.

That is, a forward voltage of 3.2V typical, with a forward current
of 20mA through the LED.

For 6 parallel strings of nine 5050s with 3 series-connected LEDs
and one dropping resistor per 5050, that's 20mA per 5050 times 9
5050s per string times six strings, which equals about 1080
milliamperes with 12VDC across the array.

Since the 3528s only have one LED per package, six strings of 12
LEDs would be 72 LEDs, and wiring them up as 6 parallel strings of 4
parallel groups of 3 series-connected LEDS with their
current-limiting resistors would result in 20mA per group times 4
groups per string times 6 strings, which equals 480mA with 12V
across the array.

John Fields
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Default LED trouble light power supply

Jasen Betts wrote:

On 2014-03-07, nospamgoingjag wrote:

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?


You want to pack a 60W PSU into 2ci? that seems fairly ambitious,

He doesn't need 60 W. With the Cree 1 W LEDs, 10 of them will
nearly blind you!

Jon
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