What kind of resistor?

[jayson_waltz]

I got a qeustion for you lighting guys. I bought a couple small red led's today for my dad's truck, but the guy at radioshack couldn't figure out what kind of resistor i would need. here are the specs, i don't know which of them you would need:
power dissipation- 110mW
forward current- 40mA
forward voltage- 1.7V @ 20mA

Any idea to make them work on standard 12V vehicles?

[cherrington17]

you need a 560ohm.

no math required. just have it memmorized. :lol:

(someone needs to slap the sales guy you talked to.... ratshack employees are suppose to know how to do that kinda thing)

[bizarre179]

^Yeah ok... lol. Im the only one in my store that know anything about resistors, along with half the other parts in our store.

[YALEROYNOT]

here is a good calculator for leds

led calculator (http://led.linear1.org/led.wiz)

[jayson_waltz]

thanks cherry i was hoping you'd chime in

[cherrington17]

^Yeah ok... lol. Im the only one in my store that know anything about resistors, along with half the other parts in our store.

its funny. any customer who even says the letters "led", any coworker(including manager) immediately looks at me. :lol:

[jayson_waltz]

the guy i asked started punchin stuff in google to try to figure it out lol. figured it'ud be safer to ask someone that i knew would give the right answer

[cherrington17]

when in doubt, i go to oznium.com 's page for leds, then go to "technical info" it gives the voltage, and you can get the resistor value off their main led page.

i looked it up a bunch when i started working with them..then got into my multicolor projects, and all my resistors were the same size/color. :banghead: so i had to check them, then look it up... it got annoying, so i just started remembering what was what.

[jayson_waltz]

lol that would suck to go through all of them
btw, does it matter how many watt resistor? or just ohms?

[cherrington17]

not particularly. technically, 4 leds will produce 1 watt of light. power wise, its pretty close to the same.

So if you had 1W 560ohm resistor, you could run 4 leds off that one.

this would be beneficial to me, where i have maybe 20 leds running off one power block, i could just put one big resistor on the main power line, and run them all off that one, instead of one on each individual. the downside to that is, producing one high wattage resistor in the right ohmage, is pretty hard to do.

so its just easier to make smaller ones, and do individual resistances

[jayson_waltz]

ok thanks that makes sense now

[cherrington17]

i was hoping i explained that in a clear way. :lol:

[Cliff8928]

(someone needs to slap the sales guy you talked to.... ratshack employees are suppose to know how to do that kinda thing)

I thought they just pushed batteries and cell phones :ninja:

[bizarre179]

its funny. any customer who even says the letters "led", any coworker(including manager) immediately looks at me. :lol:

I get that same treatment in my store... or if any customers have questions concerning windows mobile.

I thought they just pushed batteries and cell phones :ninja:

Totally not true... I done like to offer anything. Half the sales ppl in my store are stoners who say "Hey, if you need something, just ask..." THATS IT. My excuse is that I hate the place, and dont make any money if I do make sales.

here is a good calculator for leds

led calculator (http://led.linear1.org/led.wiz)

Oh, and that site for led calculations.... good find. :thumb:

[cherrington17]

I thought they just pushed batteries and cell phones :ninja:

yeah, thats what corporate wants. honestly, anyone about RM level, isn't from the radioshack company. they've all been brought in from other companies, and have no experience. So i couldn't give a crap what they have to say. When i have more sales experience then the CEO or anyone directly under him... thats sad.


and it sounds like bizarre works, like my entire store does. commonly we'll get some noob from another store, who hounds people, and we all laugh about it. Its not what our customers like. We'll point you in the right direction, even ask questions, but we won't be pushy at all. Thats just annoying for me to do, and you to hear. hell, i barely mention cell phones at all. (the new "hot" push, is DISH, :lol: we sell like one of those a year. i guess we'll all be "fired" for this one too :rolleyes2: )