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Old 17th May 2007, 12:09 AM   #1
Plundering the Planet From the Comfort of Home
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Default Replacement LED

I just purchased this thiel equalizer, but the green power indicator led was broken off. I powered the unit up and measured the voltage at the leads and get 20vdc. I go to Ratshack and thumb thru the Digikey catalog, almost all LEDs are 2 or 3v. Maybe 1 out of 100 is 12v. No 20v. I end up getting this part

http://www.radioshack.com/product/in...tId=2062551&cp

2.1v/25mA/6.3mcd. I'm not interested in a direct replacement, any brightness will do. This equalizer is about 15 years old, are 20v leds not made anymore? Can I use the RS part? (I'm suspecting not).
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Old 17th May 2007, 12:13 AM   #2
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Found this looking for info on LEDs, might be of interest to some.

http://www.smithappens.com/picture/5...positions.html
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Old 17th May 2007, 12:27 AM   #3
Elkaid is offline Elkaid  Canada
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Hi

The 2-3Volt you see is the voltage drop caused by connecting the led in a circuit.

You can put almost any voltage through a led... As long as the current doesn't exceed around 20-25mA.

The led you identified would do the job ! Just make sure the LED's longuest lead is connected to + and shortest one to -

Good luck !
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Old 17th May 2007, 12:29 AM   #4
Elkaid is offline Elkaid  Canada
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Quote:
Found this looking for info on LEDs, might be of interest to some.
Where are the three/foursome pictures ?
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Old 17th May 2007, 12:39 AM   #5
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Is there a resistor in series with the LED? That LED looks quite wide. What is its diameter?

You could substitute any normal LED that will fit as long as you use an appropriate resistor in series. You could also customise it's brightness by changing the resistor.
Start with about 5KOhms and reduce or increase until you get the desired brightness but don't run it too hot or you'll be replacing it soon.

You may find that 20volts will burn your chosen LED if used without a resistor. The average LED cannot handle even a 9volt battery for very long unless you add a resistor in series to limit the current!!

If all els fails then you find these types useful (obviously not in this quantity though!): http://cgi.ebay.co.uk/24V-LED-CHROME...QQcmdZViewItem
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Old 17th May 2007, 12:40 AM   #6
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Did not know that bit about the longer/shorter leads, thanks. If I place my meter on the broken led so that I get the +20v indication on the meter, then the leg with the red probe is + and the black probe is -, right? Not sure if the board is marked.

I also found this led at RS that says is frequently used for power indication. I see the mcd is 620 and the mA is 30. Seems like a significant difference in mcd, which would do a better job, you think?

I don't know if its common knowledge around these parts, but if you walk into a RS and they don't have the part you want you can pay for it right then and there and they will mail it to your home at no extra cost, no need to go back to the store.
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Old 17th May 2007, 12:45 AM   #7
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Quote:
Originally posted by Sonusthree
Is there a resistor in series with the LED?

**No.

That LED looks quite wide. What is its diameter?

**5mm and it has a lip, just like the one I referenced at RS.

You could substitute any normal LED that will fit as long as you use an appropriate resistor in series. You could also customise it's brightness by changing the resistor.
Start with about 5KOhms and reduce or increase until you get the desired brightness but don't run it too hot or you'll be replacing it soon.

**The led has two rigid leads that mount directly on the board, no resistor in series with it. Do some leds have resistance built right in? I thought I came across something like that in the RS led drawer. Don't think it was 20v, though.


You may find that 20volts will burn your chosen LED if used without a resistor. The average LED cannot handle even a 9volt battery for very long unless you add a resistor in series to limit the current!!

If all els fails then you find these types useful (obviously not in this quantity though!): http://cgi.ebay.co.uk/24V-LED-CHROME...QQcmdZViewItem
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Old 17th May 2007, 12:56 AM   #8
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The LED's that are rated for 12/24V usually have a resistor built in already.

A quick Goodle search and 10 minutes if your time will teach you everything that you need to know about LED's and how to use them. Here's a link to get you started: http://www.theledlight.com/LED101.html

And here's a handy calculator that tells you what series resistor to use for your application: http://led.linear1.org/1led.wiz

There are quite a few of these calculators available on the web.

Google is your friend!
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Old 17th May 2007, 05:44 AM   #9
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If the LED is broke, then most probably it is open circuit. Even if there is a resistor in series with this LED, u will read the higher voltage that is supplied. In this case it is 20Volts. Check, there may alredy be a resistor that is installed on the pcb. So all u have to do is connect any color LED of your choice/liking.

Gajanan Phadte
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Old 17th May 2007, 11:34 AM   #10
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OK, I think I got this figured out, thanks for the tips and links. What I need to do is remove the existing LED and check its resistance. The new one is only 1 ohm. If the old is the same as the new, then I can just insert it, there is resistance somewhere else to keep the current to acceptable levels.

If the resistance is in the old LED (the lamp part is sheared off, the base is intact), then I will determine what resistance I need based on the following:

20v supply voltage - 2.1 voltage drop of new LED=17.9v

17.9v/.025A = 716 ohms-- select 1,000 ohm resistor

Calculate current w/ this resistor: 17.9v/1,000 ohm = .0179A

Calculate wattage of resistor: 2.1v/.0179A = .0376, therefore 1/4watt resistor is fine.

Thanks, looks like I'll be opening my own repair shop soon. I'll use some of the figurines from the LED figure link above as my van-side logo...
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