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Resistors...who knows how to identify?


fourseventeen

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fourseventeen

OK so here is my issue...I have some resistors here, I have NO CLUE what size they are but I need to order more of the same ones. They are being used for LEDS going into some turntables (record players as some of you old timers may call them lol j/k). The resistor is very small. Blue body, 5 color bands...both ends have red so who knows which side is left or right....so the color bands are... red, brown, black, black, red.

Any able to tell me exactly what size these are?

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I used to remember it as Bad Boys Rape Our Young Girls But Violet Gives Willingly - Get Some Now meaning -

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They are either 210 ohm or 2000 ohms. It depends on where the tolerance band is. It should be slightly further from the others.

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If they're just dropping voltage before feeding a LED, they're probably 2k ohm.

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chevyguy1969

Just put an Ohm meter on them and you will know exactly what you have in your hands. According to the chart posted above combined with your information it would be 210 ohm + or - 2%.

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frikin scientist all over the place here...i'm impressed...and feel stupid now, thanks!

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fourseventeen

If they're just dropping voltage before feeding a LED, they're probably 2k ohm.

Yes Chad...they are being used to drop voltage for a single LED.

I am seeing 200k but then seeing 1/4 watt. 1/2 watt, 1 watt, etc. Which is the right one? and 1%, 2%, etc.

The color bands all look pretty evenly spread BUT if I had to guess id say MAYBE one red side is a hair farther in from the other side. So if thats the case id say its Red, black, black, brown, red. That is if the left first red band is furthest in.

I do have a multi meter and one of the new resistors I can use if testing it that way would tell me?

Im a smart guy but obviously not that smart...I must have missed the color band thing in school.

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chevyguy1969

red,blk,blk,brown,------red =200x10=2000 ohms plus or minus 2 %

red,brown,blk,blk,------red =210x1=210 ohms plus or minus 2 %

You should be able to go to radio shack and find the exact ones you need. good luck

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fourseventeen

Thanks Chevy. Was trying to find out exactly which I need so I can buy in bulk from ebay. they are 2 bucks a pop on average for resistors at radio shack I need about a dozen of them....I can get 50 of them on ebay for 2 bucks lol.

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fourseventeen

id take a photo with my iPhone but its not showing the lines real well and im not about to set up the real cameras to do this lol.

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Is there another LED and resistor you could check with the multimeter? That's the easy solution.

But, if you want the how & why...

You really need to find the voltage and current used at the LED to identify the wattage needed. Likely 1/2 watt would work, but if you need, you can put 2, 1/2 watts in parallel to achieve 1 watt, just take into consideration which resistors you use since parallel resistors will decrease the overall resistance.

Rtotal = (R1 x R2) / (R1 + R2)

So, if you measure one that's working and find 5v before the resistor (source voltage), and 2v dropped at the LED (red) drawing 150mA, you'd have ~20 ohm resistor. R = (5-2)/.150 and P = 3x.150 = .45 watt (use a 1/2 watt) So, if that resistor is 2k ohm, you're either dealing with high voltage or the LED is low amperage.

More likely, you're looking at 210 ohm which may be used for 5v source & 15mA LED. R = (5-2)/.015 = 200ohm. You have some wiggle room on this. Your LED will be dim with higher resistance, and brighter with lower but it may affect the life of the LED if you push it too hot. 1/4 watt would be fine, in this case.

R = Es(source voltage) - Ef(LED forward voltage) / I

R = E/I (ohms law)

P = EI

Where:
I = current (amp)
P = power (watt)
R = resistance (ohm)
E = voltage (volt)

- from some page I found on typical bulb-shaped, wire lead style LEDs (not the flat, square, board-mounted type) -

what’s typical: for 3mm and 5mm indicator-type LEDs, datasheets often list a typical forward current of 15 - 20mA. Forward voltage will depend on the junction material of the LED, but let’s use a white LED as an example. 3.3V would be a typical forward voltage at 20mA.

Note: different LED colors require different forward voltages. E.g. Red @ ~2V+, Blue @ 3.5V+

Yes... I have a EE degree and find this stuff cool.

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fourseventeen

Thank you again Chad, you rock! BUT oh man you had to really confuse me now....red and blue takes different resistors! lol. I have the blue LEDs here now but I need resitors for both blue and red leds. I would rather then be brighter and only last a year then to make them dim and last forever. I purchased a kit online that included the leds and resistors....I want to replicate this kit by purchasing the items from overseas as opposed to paying 5 times the amount for this kit.

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  • 4 weeks later...
fourseventeen

OK I am still trying to figure this out. I have the LEDS and the resistors supplied in a kit I bought online...I am trying to replicate this exact kit by purchasing the items in bulk. I went to radio shack and dude there was an idiot. He sold me some resistors....well I hooked them up exactly how I hooked the ones up in the kit and BAMM 5 seconds and the resistor was hot as shit and it fried the LED as well. So obviously those were the wrong resistors lol. The resistor that got VERY hot and fried was suppose to be a 200k 2%. (red, black, black, black, red). If it was a 200k instead of a 210k...would it really make that drastic of a difference?

What I am gathering is the ones I need are 210 2% yet I cant seem to find those on ebay. The resistor is blue in color....bands are red, black, black, brown, red if my eyes are seeing these correctly. So if I have this correct...why can I not find these resistors on ebay? and how do I determine the wattage? I see lots of watt options. When using my multi meter on the new resistor from the kit it reads 1.0 on the 200k setting on my meter. If someone knows these things well and can give me a call or a PM I would really appreciate it.

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OK I am still trying to figure this out. I have the LEDS and the resistors supplied in a kit I bought online...I am trying to replicate this exact kit by purchasing the items in bulk. I went to radio shack and dude there was an idiot. He sold me some resistors....well I hooked them up exactly how I hooked the ones up in the kit and BAMM 5 seconds and the resistor was hot as shit and it fried the LED as well. So obviously those were the wrong resistors lol. The resistor that got VERY hot and fried was suppose to be a 200k 2%. (red, black, black, black, red). If it was a 200k instead of a 210k...would it really make that drastic of a difference?

What I am gathering is the ones I need are 210 2% yet I cant seem to find those on ebay. The resistor is blue in color....bands are red, black, black, brown, red if my eyes are seeing these correctly. So if I have this correct...why can I not find these resistors on ebay? and how do I determine the wattage? I see lots of watt options. When using my multi meter on the new resistor from the kit it reads 1.0 on the 200k setting on my meter. If someone knows these things well and can give me a call or a PM I would really appreciate it.

200K ohm vs. 210K ohm used in an LED circuit likely won't even be noticable to the eye, as far as brightness is concerned.

However: red, blk, blk, blk, red = 200*100 (+/- 2%) = 20K ohm, not 200K ohm. You need red, blk, blk, orange. or == 200*1K = 200K ohm. (if you're truly working with a 5-band resistor)

If you have a kit that works... just buy the same components. Your measurement of 1.0 ohm at the 200K ohm meter setting = 1*200K = 200K ohm, so the crap you got at radio shack, depending on the input voltage, I can see catching fire.

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Edit... my math sucked...

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fourseventeen

yes I want to use the same components as whats in the kit...thats why I am going through this hassle. I do not know exactly what resistor is in this kit. I went to a different radio shack today...and again no dice. people there are idiots. 4 employees there and not one knew anything about what I had "thats a resistor right"" one says. And they point me to a drawer of resistors. None they had matched what I have. If I thought I could get a photo that really showed the bands well id take one but i doubt its gonna show. But yea there is 5 bands in total on this resistor. the end color on both sides appears to be the same, red. followed by black black and what appears to be brown (its barely a shade lighter then the red on the ends). I cant believe how much hassle it is to find these resistors in the right size. I need them asap though. I have 100 leds but no resistors for them.

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If you can't tell the colors apart, you need to measure what it is... that's your only other option. Above you said your multimeter was set at 200k Ohm and measuring the resistor showed a 1.0 result. That's a 200K ohm resistor. If you move your meter down, to say, 1K ohm, it should display 200.0 on the meter for a 200K ohm resistor.

If they're truly 200K ohm resistors... you need to buy 4 or 5 band resistors.

4 band : red, blk, yellow, gold (20 * 10K = 200K @ +/- 5% tolerance)

5 band : red, blk, blk, orange, gold (200 * 1K = 200K @ +/- 5% tolerance)

The tolerance band doesn't matter on what you get... they're just for LED's so +/- 10% won't affect the LED much.

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fourseventeen

my meter doesnt have a 1k setting. 20k is the lowest which says 1000 when touched to the resistor. So I will look for a 200k +/- 5% resistor and not try to match exactly what I have now...and see if that works. What WATTAGE? I see 1/4, 1/2, etc. Thanks for all your help Chad....greatly appreciate it buddy.

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If your colors are right, sounds like 2K ohm (2, 0, 0, x10 = 2,000). Don't know why your ohmmeter is reading 1.0? Is the resistor loose or installed in a circuit? You can't measure resistance while it's still connected in a circuit. If it's loose, it appears you might have your colors wrong. Just get a good meter and measure the damn thing. Use the lowest range setting that gives you a reading.

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my meter doesnt have a 1k setting. 20k is the lowest which says 1000 when touched to the resistor. So I will look for a 200k +/- 5% resistor and not try to match exactly what I have now...and see if that works. What WATTAGE? I see 1/4, 1/2, etc. Thanks for all your help Chad....greatly appreciate it buddy.

Not sure about your meter, but the setting should be a range unless I've totally unlearned all my electronics training which is possible. 20K should be the high end of the range it can read. If it's reading 1000 that is your resistance. Sounds like you have a 1K ohm resistor to me.

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Resistance is futile. Assimilate into the collective.

You could just wire a pot in and adjust it and see what happens.

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fourseventeen

man this shits confusing me lol. The resistor I have is brand new...never been hooked up to anything.

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