Wiring Resistors in Series with LEDs

[cedarwoodron]

Just curious- can 2 individual 470 ohm resistors be wired in series to obtain close to a 1K approximate reduction in the current running thru a 20 mA LED? As opposed to going out and buying separate 1K resistors? Just trying to use what I have on hand.... Cedarwoodron

[richg1998]

cedarwoodron

Just curious- can 2 individual 470 ohm resistors be wired in series to obtain close to a 1K approximate reduction in the current running thru a 20 mA LED? As opposed to going out and buying separate 1K resistors? Just trying to use what I have on hand.... Cedarwoodron

Yes they can. Resistors in series add. Get a multimeter and learn how to use it. It will be a great help.

For some years I have used a cheap digital meter. I have three of them and cheap to replace if I mis use them. About $5.00 each from Harbor Freight.

If you want to work at the component level, you will need one.

Buy a set of double clip leads from them also.

Rich

[richg1998]

Sent you a PM.

Rich

[CharlieM90]

 

Yes.

And you can wire resistors in parallel  if you find yourself with a bunch of resistors but nothing small enough for what you need. Formula is rT = 1/((1/r1)+(1/r2)+(1/r3)+.....) where rT is total resistance and r1, r2, r3.... are the values of the resistors used. For example, two 2k ohm resistors in parallel will give you 1k ohm total resistance.

[cedarwoodron]

Thanks for the responses, guys. I guess those basic skills learned with the old Radio Shack breadboard kits back in the late 60s ( 1960s! ) will get used more often as I keep working on those old swap meet specials. I'm a big fan of Harbor Freight and go there at least once a month. Multimeters and clips it is- soon, my workbench will be a cross between Science Fiction Theater and Mr.Wizard!! Cedarwoodron

[Phoebe Vet]

Yes you can, but resistors are about 20 cents each; why bother?

[richg1998]

cedarwoodron

Thanks for the responses, guys. I guess those basic skills learned with the old Radio Shack breadboard kits back in the late 60s ( 1960s! ) will get used more often as I keep working on those old swap meet specials. I'm a big fan of Harbor Freight and go there at least once a month. Multimeters and clips it is- soon, my workbench will be a cross between Science Fiction Theater and Mr.Wizard!! Cedarwoodron

Good solution.

I have the Radio Shack digital breadboard set up I still use a lot.

There is a HF store about 12 miles from where I live.

I started in 1956 with a Heathkit AR3 SW receiver kit and their analog multimeter kit, both of which are long gone. The receiver had some glass things that got really hot. I do not miss working with high voltage electronics. The average TV, audio amplifier or receiver operating voltage could be between 250 to 400 VDC.

I have stripped many componnts from old electronic equipment. Nothing older than say 1985.

Rich

[richg1998]

On line calculators if you do not like math. Take time to save the links.

Posting a formula is nice but many do not like working with paper and pencil.

http://www.opamplabs.com/eirp.htm

http://led.linear1.org/led.wiz

If you have a variety of resistors.

http://www.raltron.com/cust/tools/parallel_resistance.asp

Probably more than you really want to know.

https://sites.google.com/site/markgurries/home/part-sources/led-s/resistors-for-leds-bulbs

Rich

 

[hobo9941]

I guess those basic skills learned with the old Radio Shack breadboard kits back in the late 60s ( 1960s! ) will get used more often as I keep working on those old swap meet specials.

All those old rules still apply.

[hobo9941]

For some years I have used a cheap digital meter. I have three of them and cheap to replace if I mis use them. About $5.00 each from Harbor Freight.

I got one free with a coupon and a purchase.

[Train Modeler]

You can also put the LEDs in series if you have a space problem.   The required resistor is calculated by using the sum of the LEDs required voltages vs Vs, then divided by the mA for one LED

Richard

[D94R]

If you don't have a meter, and have various resistors you don't know the value of, you can use the java script resistor color calculator at the bottom of the link and it will tell you what each resistor is.  Then you can use the calculators for finding final resistance with multiple resistors. 

 

http://www.the12volt.com/resistors/resistors.asp#top

[Train Modeler]

Phoebe Vet

Yes you can, but resistors are about 20 cents each; why bother?

 

I do this if I have several that have sat around for a long time and I just want to free up the storage space.  Also, avoids the hassle of buying more(online or store).

Richard

[rrinker]

 If you're doing headlights for DCC, just buy a 100 pack of 1K from one of the electronic suppliers, more like 2 cents each, instead of 20 cents. For any white LED on typical DCC voltage, 1K is the resistor, so you'll use more of those than anything. $2, resistors for 50 locos.

                  --Randy