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Old 01-18-2018, 12:28 PM   #141
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Default Re: How to wire LEDs

GREAT tutorial!!! Thank you!!
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Old 04-08-2018, 07:36 PM   #142
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Default Re: How to wire LEDs

So I found some flashlights I'm gonna cannibalize for the surface mount leds. They're running on 4.5 volts and I'm going to use power from a 3s pack 12v. So using the wizard ,source is 12v , forward voltage is 4.5v? Also how do I figure current? Thanks in advance. Carl
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Old 04-09-2018, 08:40 AM   #143
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Default Re: How to wire LEDs

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Originally Posted by wingnutcrawler View Post
So I found some flashlights I'm gonna cannibalize for the surface mount leds. They're running on 4.5 volts and I'm going to use power from a 3s pack 12v. So using the wizard ,source is 12v , forward voltage is 4.5v? Also how do I figure current? Thanks in advance. Carl
Great project!
Unless the packaging of the flashlight gives you some clue as to the power of the LEDs, you will have to measure the current draw with an ammeter.
If you can post a picture of it, I could guess at it, but best is to measure it.
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Old 04-09-2018, 04:40 PM   #144
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Default Re: How to wire LEDs

so to measure the draw I use an ammeter between the led and the supply? I cant seem to post a photo.
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Old 04-09-2018, 05:00 PM   #145
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Default Re: How to wire LEDs

Type this into google:
"how to use a dc ammeter"
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Old 04-09-2018, 05:04 PM   #146
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https://photos.app.goo.gl/VShXVmPuJEXeXxju1
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Old 04-09-2018, 05:10 PM   #147
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Default Re: How to wire LEDs

My best guess is that is a 3 watt LED.

Put your volt meter on the two white wires on the LED. What is the voltage? This will be the "forward voltage".
Then we can find the current using some math because I (assume!) it is 3 watts, using P=IV
Transpose that to I=P/V
so 3/ your measured forward voltage will give you the current.
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Old 04-09-2018, 05:18 PM   #148
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Default Re: How to wire LEDs

The AAA batteries are kinda low. The voltage coming out of the three batts is 3.67 and the two wires at the led show 3.04
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Old 04-09-2018, 05:21 PM   #149
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Default Re: How to wire LEDs

3 volts is what I would expect.
Now do the math to find the current.
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Old 04-09-2018, 05:36 PM   #150
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Default Re: How to wire LEDs

Here's the math to find the current through the LED
Again, assuming 3 watts of power and we have measured 3 volts across the LED. We can find the current with this formula:
Current (amps) = Watts / Volts
3 / 3 = 1 amp

Now you can plug that number into your LED calculator.
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Old 04-09-2018, 05:38 PM   #151
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Lol sorry math isn't my strong suit. I have no idea how to use the equation. So I is the current?
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Old 04-09-2018, 05:40 PM   #152
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Default Re: How to wire LEDs

Yes.
1 amp is the answer for how much current your LED needs.
Your LED calculator might want the current in mA. If it does, you put in 1000mA (same as 1 amp)
3 is the forward voltage of your LED
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Old 04-09-2018, 05:52 PM   #153
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So if I'm not screwing this up , it needs a 10 ohm 10 watt resistor? Aren't those the huge ceramic kind?
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Old 04-09-2018, 05:56 PM   #154
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Default Re: How to wire LEDs

Yes, that's what it will take if you run one of those LEDs from 12 volts.
There is a cheat that you could do. Connect four of the LEDs in series and run it without a resistor. We can do that because - again, I am making an assumption - you are probably using a 3S lipo for the power. Fully charged is very close to 12 volts and will work just fine.
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Old 04-09-2018, 06:20 PM   #155
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I only have the two. Any other approach besides resistors? Maybe some kinda diode? Or maybe a step down from a fpv quad. They have some that drop from 12v to 3.3 v. Just not to enthused about the ceramic resistor.
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Old 04-09-2018, 06:21 PM   #156
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Oh ya thanks for all the help. It's much appreciated.
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Old 04-09-2018, 06:24 PM   #157
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You're welcome!
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Old 02-28-2020, 08:48 PM   #158
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Default Re: How to wire LEDs

An excellent tutorial with some great links. This has helped me out so much with wiring up led's for a couple of projects. Thanks a bunch for the education!
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Old 02-29-2020, 05:38 AM   #159
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Quote:
Originally Posted by Egorr View Post
An excellent tutorial with some great links. This has helped me out so much with wiring up led's for a couple of projects. Thanks a bunch for the education!
You are very welcome. I'm glad it helped.

Al
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Old 10-31-2022, 04:37 PM   #160
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Default Re: How to wire LEDs

I see this started back in '13, but 9 years later and it still has great info in it.
Thanks for the write up.
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