Using a computer power source to control LEDs, et al..?

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SDHLaw1701
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Using a computer power source to control LEDs, et al..?

Post by SDHLaw1701 »

Hey,
I kind of have what might seem as a silly question. I have heard of others using a computer power supply to power LEDs and other components in a model, given all the varrious wires eminating from the computer power supply how do you properly hook up the LEDs to the power supply with out destroying the LEDs and other lighting components (i.e. flasher boards..etc). Thanks
SDHLaw1701
macfrank
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Re: Using a computer power source to control LEDs, et al..?

Post by macfrank »

SDHLaw1701 wrote:Hey,
I kind of have what might seem as a silly question. I have heard of others using a computer power supply to power LEDs and other components in a model, given all the varrious wires eminating from the computer power supply how do you properly hook up the LEDs to the power supply with out destroying the LEDs and other lighting components (i.e. flasher boards..etc). Thanks
SDHLaw1701
Using a PC power supply to light up some LEDs is overkill. PC power supplies tend to be bulky and have fans. Most modern supplies also require a "power good" signal from the motherboard which you'll have to supply. Also, some power supplies require a current load before they start operating properly. A fully stocked PC mother board is a load. For or five LEDs are not.
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Post by en'til Zog »

Go to "The Realm of Zog" and look up 'Wall Warts'. The little blocks you plug into the walls to power clocks & such. Small, cheap, available.
Madman Lighting
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Post by Madman Lighting »

Ditto what Zog said. You might want to get a *regulated* wort so the output voltage is smoother and ripple free. If you want to spend about $15, goto Digi key or Mouser and buy a regulated switch mode wall wort. Very compact, very efficient.

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Re: Using a computer power source to control LEDs, et al..?

Post by fokkerpilot »

macfrank wrote: Using a PC power supply to light up some LEDs is overkill. PC power supplies tend to be bulky and have fans. Most modern supplies also require a "power good" signal from the motherboard which you'll have to supply. Also, some power supplies require a current load before they start operating properly. A fully stocked PC mother board is a load. For or five LEDs are not.
Overkill. LOL ok, On the 1:350th it's worth it. PC power supplies have fans and rightly so because I wouldn't want a supply like that in my base unit with out some method of cooling. The current load you speak of is easily dubbed by inserting a jumper allowing the power supply to operate with an on/off switch. I strongly suggest the use of one on a model this big with the large number of LEDs involved when considering the total miiliamps. Radio Shack AC power adapters will be taxed to their limits and will eventually fail due to heat buildup.

Now for the smaller kits with, lets say, 20 LED's, then the little wall adapters would be fine and yes, a Computer power pack would be overkill. But not with the 1:350th.
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Post by Madman Lighting »

I just looked at your 1/350th Enterprise, thats really nice work on your part. I've got one of those and its bloody HUGE.

How many LEDs did you use for yours? I'm guessing at least 30, or as many as 50.

I do have to disagree with you about choice of power supply, you dont need a PC power supply, even for that. Each LED draws about 20mA, even with 50LEDs, thats still only 1000mA, or just 1 amp and large wall worts are quite capable of those loads. The newer switch mode worts can do it, Mouser sells them:

http://www.mouser.com/catalog/625/1564.pdf

Nice model work.

-John C.
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Post by fokkerpilot »

Thanks Madman. If I recall there were 68 LEDs total in this puppy. 2 circuit boards run off 12v for the flasher and photons. There's no offense taken to using wall adapters. I just have a slew of desktop computer power packs in the shop. I figured that since I had a fairly large base then why not use a CPU power supply; especially since I could tap the 12v and 3.3v side of it. The fan in this one runs quietly too.

The other good thing about this base is that the top will lift off just high enough to replace the power pack should it ever decide to go on vacation.

Off topic (sort of) but the idea for the base came up when I wasn't compfortable with the orginal design supporting the ship. The idea of the clear rods (martini stirrers) to support the saucer was pretty tacky on behalf of PL. The base they supply is nice but not big enough in my book.
This base I had ordered (custom built) has venting in the front and an exhaust port in the rear to give the power supply adequate airflow.

For those using just the original base, then a wall adapter would be good. My only word of caution is add the total Ma's and make sure that the wall adapter being purchased is rated at least 15% higher that the total Ma's from the build. Otherwise the unit will eventually heat up being pushed to it's limits. And while I'm on the topic of the Wall Adapter, those who need to use resistors to drop down to 3.3volts (for the sake of argument) and are concerned about heat build up may want to consider leaving a window or two open just to allow some airflow within the model. It wouldn't hurt.
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Post by Sparky »

I 've got some pc power supplies laying around too. Found some articles on using them to power all sorts of things, like HAM radios. I think I even found an article on making one into variable power supply. They are well regulated since any fluctuation in the CPU power rail translates to the OS locking up or other un correctable bugs in what ever is running.

I didn’t think that modern PC power supplies required loading to work correctly.
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SDHLaw1701
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Post by SDHLaw1701 »

Thanks for all the advice. I agree with Fuzzy and thats why I want to use a computer power supply. My question is still do I have to be concerned with all the hook up wires comming out of the supply or do I just use the fan (fo example) wire to attach to the main power wires comming out of the enterprise? Thanks
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Post by Sparky »

There is some loading need on the supply rails. Several sites mention useing a car light bulb. Others use a resistor, this isn't a very good solution since it gets warm and is wasteful. Any 5 volt device could be used. Once your circuit is built it may be enough load to do the trick.

A quick look on computer site doesn’t mention the loading resistor:
http://www.duxcw.com/faq/ps/ps1.htm
They have the pin out for ATX power supplies as an image though, good reference.

Here’s a good <A HREF=â€￾http://72.14.203.104/search?q=cache:pJz ... refox-aâ€￾ target=â€￾_blankâ€￾>site that gives an acceptable explanation to why the power supply needs to be loaded</A> Scroll down to
Safe PC power supply loading
It seems it is dependent on the supply, so take a look at the sticker on the supply and see what it says it needs as a minimum load. Brake lights from a car could be used as a load.

I will give this a try myself when I get a chance. Busy with wonderfest projects right now. I will need a power supply for the DC motor that turns the roto caster setup this might do the trick if it doesn’t flame out.


Here's some clips from another guide on all the wires coming from the power supply:

http://web2.murraystate.edu/andy.batts ... SUPPLY.HTM
ORANGE +3.3 V
YELLOW +12 V
BLUE -12 V
RED +5 V
WHITE -5 V (May not be present on recently manufactured supplies)
BLACK GND
GREEN POWER-ON (Active high -- must be shorted to ground to force power up)
GRAY POWER-OK What is this??
PURPLE +5 V STANDBY
BROWN +3.3 V REMOTE SENSING Design Guide Update
. . .
GRAY POWER-OK:
Since the signal is generated by the PS for use by the MPU, the PWR_OK (gray) wire should not be grounded, attached to any of the other output lines or tied to a resistor. It is not required for the PS to function -- its sole purpose is to allow the motherboard to initiate the boot process and to continue to function in the absence of unstable or improper power levels.

Could this signal be of any use when converting a PC powersupply to desktop usage? Realistically, the answer is YES. A voltage on the PWR_OK line indicates that the PS has completed a successful POST and that the output voltages are stable and within design specification. If you wanted to use an LED (light emitting diode) as an indicator that the PS is on, rather than tie it to one of the +5V or +12V lines, attach the PWR_OK line to the anode (+) side of the LED and place a 220 ohm resistor on the cathode (-) leg before grounding it. The cathode leg is normally shorter on new LEDs -- if the legs have been clipped, the cathode will be on the same side as a flat spot on the LED base. The LED should be bright for normal operation -- it could possibly glow faintly if the PS has withdrawn the signal simply due to bleedover.

BROWN +3.3 V REMOTE SENSING:
The second addition is of more importance to individuals converting their power supplies. The +3.3 VDC remote sensing wire (brown) is connected directly to the orange +3.3 VDC at pin 11 of the power connector (pin 13 if a 2x12). The sense wire will usually be of a lighter gauge (22 AWG) than the power wires (16 or 18 AWG) and its purpose is to monitor the voltage at the connector in order to provide feedback for voltage compensation by the supply.

If your PS has two wires attached to the same pin on the motherboard power connector, orange +3.3 VDC and a brown sense wire on Pin 11 for example, then these two wires should be joined when you make your conversion. Some power supplies may also have sense wires running to the +5 VDC and +12 VDC connector pins. If there are multiple sense wires, then they will usually be of the same color as the primary supply wire, but of a lighter wire gauge. These sense wires will also terminate in a different location on the PS printed circuit board than the heavier supply lines. As with the +3.3 sense wire, these additional wires should also be connected to the corresponding supply lines. Failure to complete these connections may result in your power supply not latching into a Power_On mode when switched on.
Ok the main connections:
. . .
For the +5 / +12 volt PS, you will need the following combinations:
GREEN / BLACK Power on Switch (Use a SPST switch; a momentary switch will not work)
RED / BLACK Pre-Load Resistor (See text for recommended values)
YELLOW / BLACK +12 volt source
RED / BLACK +5 volt source
ORANGE / BROWN See the Design Guide Update


I use a single common post (GND -- black) for all voltage sources. Our loads are light and we don't require separate grounds for each

Leave 3 black wires -- switch, load resistor and common (GND) binding post

Leave 2 red wires -- 5 volt binding post and load resistor

Leave 1 yellow wire -- 12 volt binding post

Leave the green wire -- power on switch
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