Subject:
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Re: Need Electrical Help
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Newsgroups:
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lugnet.trains
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Date:
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Wed, 22 Oct 2008 15:41:51 GMT
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Viewed:
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10474 times
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In lugnet.trains, Rob Hendrix wrote:
>
> "L. Andrew Reynolds" <andrew_reynolds@uhc.com> wrote in message
> news:JMvuv7.AF2@lugnet.com...
> > I am trying to setup some LED lights to run from the 9v track or a 9v
> > battery
> > pack for some train signals. I have 1.5v lights and the track is 9v
> > (obviously)
> > how can I step down the voltage. Any help would be great.
>
> Typically, most LEDs have a mA rating of around 20mA. Let's assume this is
> the case for yours as well. I have seen some 1.5v LEDs so I 'm taking your
> word that yours are 1.5v like you say, instead of them being the more
> normally found 2.1v LEDs (assuming you're using red, green or yellow LEDs).
> So now we have all the components we need for the formula to figure out what
> ohm (and what wattage) resistor you need. I'm also assuming you are only
> hooking up 1 LED per 1 resistor.
>
> To calculate required LED current limiting resistor (R):
>
> R = (Vs - Vl)/I
>
> R = Resistor ohm
> Vs = Voltage source
> Vl = LED forward voltage
> I = LED current in amps (remember 20 mA = .02A)
>
> For your LED running at 9 volts, lets put the numbers in the formula:
>
> (9 - 1.5) / .02 = 375 ohm
>
> They don't make 375 ohm resistors, so choose 390 ohm which is the nearest
> standard larger value. Now let's figure out the required wattage of the
> resistor we need.
>
> P = (Vs - Vl) * I
>
> P = Power (in watts)
> Vs = Voltage source
> Vl = LED forward voltage
> I = LED current in amps (remember 20 mA = .02A)
>
> (9 - 1.5) * .02 = .15 watt
>
> That's too much for an 1/8w resistor (.125 watt), so choose a 1/4 watt (.25
> watt) which is the nearest standard larger value.
>
> I can go more in depth if you want or I can simply give you the answers. I
> prefer teaching over telling... If you want to hook up more than one LED
> either in series or parallel, just ask!
>
> -Rob
> www.brickmodder.net
I realize that this is an old post, but I jut found it...If I want to hook up a
bunch of LED's (say they are 2.1 volt and I want to hook up 10) to a 9v system,
what do I need to do? Only hook in four at a time or something like that?
I could wire a whole house, but when it comes to small scale electronics, I am a
complete novice.
I have a LEGO train track going around my son's room near the ceiling. I am
building a Santa Sleigh and rindeer to run on the tracks and I's like to light
up Rudolph's nose with an LED as well as have several LED's along the other
reindeer and the sleigh so that they look like traditional christmas lights.
Thanks.
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Message has 2 Replies:
 | | Re: Need Electrical Help
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| (...) For the DIYers out there: (URL) LED Resistor Calculator> For quick results without having to think: You can run 1 (2.1v) LED from 9v if you hook up a 390 ohm (1/4 watt) resistor between one lead of the LED and the power source. You can run 2 (...) (16 years ago, 22-Oct-08, to lugnet.trains, FTX)
| | | Re: Need Electrical Help
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| (...) If the voltage is going to vary, don't use a resistor as current source, consider a current regulator instead. That way the LED stays brightly lit over a wide voltage range without getting burned out at max voltage. This works for one or more (...) (16 years ago, 24-Oct-08, to lugnet.trains)
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Message is in Reply To:
| | Re: Need Electrical Help
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| "L. Andrew Reynolds" <andrew_reynolds@uhc.com> wrote in message news:JMvuv7.AF2@lugnet.com... (...) Typically, most LEDs have a mA rating of around 20mA. Let's assume this is the case for yours as well. I have seen some 1.5v LEDs so I 'm taking (...) (17 years ago, 17-Aug-07, to lugnet.trains)
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