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post #1 of 12 (permalink) Old 01-12-2008, 09:27 PM Thread Starter
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DC power: mixing LEDs and fans

OK engineers, I've got some LED arrays (3 diode units with resistors from autolumination.com) and some PC fans in my hoods. I run a pair of each using two 12v 500mA DC transformers, moonlights one one, fans on the other. I'd love to save some space on my power strip - any reason not to run all four on a single transformer?

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post #2 of 12 (permalink) Old 01-12-2008, 09:33 PM
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How many fans do have, and what is their current rating? That will be the deciding factor. The LED's pull very little current, but depending on the fans you have you might still need both power supplies.

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post #3 of 12 (permalink) Old 01-12-2008, 09:47 PM Thread Starter
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How many fans do have, and what is their current rating? That will be the deciding factor. The LED's pull very little current, but depending on the fans you have you might still need both power supplies.
Two fans with a current rating of 0.13 AMP. Two LED arrays, each has 3 diodes and one resistor. The arrays have an operational range of 10 - 15.8v and draw (is that the right term?) 60mA.

Thanks for the quick reply, Colin.

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post #4 of 12 (permalink) Old 01-12-2008, 09:55 PM
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You should be able to run everything off one power supply. Switch it over and see how everything works on one. The power supply will probably get kinda warm, so make sure there is a little bit of ventilation for it. If it gets to hot though, switch back to two.

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post #5 of 12 (permalink) Old 01-12-2008, 09:57 PM
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0.13 A = 130 mA
2 x 130 mA + 2 x 60 mA = 380 mA
308 mA < 500 mA

You're fine running everything from one power brick. Here's one reason to keep 'em separate, though. Do you want to run the fans at night and the moonlights during the day?
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post #6 of 12 (permalink) Old 01-12-2008, 10:00 PM Thread Starter
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Originally Posted by colinthebassist View Post
You should be able to run everything off one power supply. Switch it over and see how everything works on one. The power supply will probably get kinda warm, so make sure there is a little bit of ventilation for it. If it gets to hot though, switch back to two.
Thanks a lot for the advice, Colin. I'm going to wire up a brick with all four devices on it, and compare it to my existing rigs that are dedicated to either fans or LEDs. I'll post the results later on.

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post #7 of 12 (permalink) Old 01-12-2008, 10:06 PM Thread Starter
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Quote:
Originally Posted by swylie View Post
0.13 A = 130 mA
2 x 130 mA + 2 x 60 mA = 380 mA
308 mA < 500 mA

You're fine running everything from one power brick. Here's one reason to keep 'em separate, though. Do you want to run the fans at night and the moonlights during the day?
Thanks for the detailed explanation, Swylie. It's a good point you make, too. I'm not sure which is less convenient - the huge bricks taking up all my power strips strip or fans running at night. We'll see, I guess.

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post #8 of 12 (permalink) Old 01-13-2008, 02:07 AM
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Just wire in some switches, you can find some cheaply at radioshack.


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post #9 of 12 (permalink) Old 01-13-2008, 04:01 AM Thread Starter
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Just wire in some switches, you can find some cheaply at radioshack.
Switches would do it, but for me it needs to be timers or nothing at all. I'll forget and end up with a hot tank and stressed fish. The fans are only 19dBA anyhow, probably quieter than my XP3s. The fans do have a third wire for a controller, but that's a whole other project.

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post #10 of 12 (permalink) Old 01-14-2008, 05:02 AM
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I'd keep the two power supplies. The cheap wall wart power supplies usually aren't very consistent in their rating, just because it says 500ma doesn't mean it's good for 500ma of continuous draw. It really depends on the quality of the transformer, some may be okay, others won't. If you switch your fans on and notice the LEDs dim, even momentarily the power supply doesn't have enough headroom to run everything. At best with an underpowered power supply your fans or LEDs will die prematurely, at worst your house will catch on fire. If you want to run everything off of one power supply I'd suggest buying a larger power supply rated for at least 1 amp, they aren't that expensive, chances are you've got one in your junk drawer from an old boom box or an answering machine that will work just fine.
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post #11 of 12 (permalink) Old 01-14-2008, 05:10 AM
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I think I might have some 1000 + Mah transformers that would work good if interested. Currently I have them wired to two switches which control two seperate blowers. I don't have a need for it/them anymore though.

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post #12 of 12 (permalink) Old 01-14-2008, 05:14 AM
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Quote:
Originally Posted by mette View Post
OK engineers, I've got some LED arrays (3 diode units with resistors from autolumination.com) and some PC fans in my hoods. I run a pair of each using two 12v 500mA DC transformers, moonlights one one, fans on the other. I'd love to save some space on my power strip - any reason not to run all four on a single transformer?

The only reason I can see why you wouldn't want everything on one transformer is because you might not want your fans on when your LEDs are running or visa versa. You want to run one during the day (fans) and the other to run at night (LEDs), right?

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Last edited by BiscuitSlayer; 01-14-2008 at 05:16 AM. Reason: wording
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