Picking a power supply

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chiver
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Picking a power supply

Post by chiver » Thu Oct 19, 2017 11:35 pm

I am building a romulan warbird with two Green ish LEDs, and there will be at least three white LEDs. I do have experience with electronics. But not from a design stand point. How do I know,how big of a supply I will need? Should they all be in series or parallel? They do not have any paperwork with the LEDs. I do not know the voltage drop of each of them. Any help is aprecated. Thank you
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Ant
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Re: Picking a power supply

Post by Ant » Fri Oct 20, 2017 2:37 am

Factor a 3.2v forward voltage for the whites, with the greens it's a bit harder to guess because there are different types. Older traditional greeny-yellows have a Vf of around 2v, but more modern pure greens are more likely to be around 3v. Start with 2v and see how that looks. Assume a max operating current of 20mA for all.

Wire them all in parallel (1 resistor per LED) and run for a 3XAA battery box (4.5v). This will give you many days, possibly weeks of continuous run time.

If they are high brightness types, you don't need to put 20mA through them. 5mA or even less may still give you more than adequate brightness, but greatly extend the running time even further.

Ant

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chiver
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Re: Picking a power supply

Post by chiver » Fri Oct 20, 2017 3:13 pm

Thank you, I will give it a try. I have to go back through my books to figure out what size resistors to use
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NX-17000
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Re: Picking a power supply

Post by NX-17000 » Fri Oct 20, 2017 7:04 pm

Based on Ant's parts/Numbers, you'd be looking at anything from 65 ohms to 260. Personally, I'd aim for 120s unless they're not bright enough.

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chiver
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Re: Picking a power supply

Post by chiver » Fri Oct 20, 2017 7:23 pm

I calculated 44ohms lol pretty close. I'll give 120 a try later I don't want the windows overly bright.
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