Can not find 340 Ohm 0.4 Watt resistor? Any alternative please??

[Becky]

 
Hello I am new to electronics (sorry if my question is very simple) but am building my first robot with the help of this site (saw it for the first time yesterday and have started ordering my parts today).

Basically I can not find a 340 Ohm 0.4 Watt resistor.  I have found other users making do with 330 Ohm so I think that would do... ...?

...however how important is the watts?  Can not find many 0.4 Watt but loads of 1/4 - 0.25 Watt.  What effect would this have?  (Sorry again - my electronics is very beginner).

Thanks!

Becky 

[airman00]

just use a 330ohm resistor , shouldn't be too big of a deal

[Becky]

   Ok that simple?  So just to double check... the ohms come in different Watts but it doesn't matter?

Kind regards

Becky

[airman00]

1/4 watt would be fine too

[pomprocker]

I'd rather you learn why you are to use a resistor of that resistance rather than just tell you which resistor to get.

Visit the LED wizard page and enter values to see different resistor values. Most LEDs you're going to be using will have a forward voltage drop of 2v, and a forward current of 20ma. And for the source current it depends on how many batteries you will be using. 1xAA = 1.5v, 2xAA= 3v, 3xAA = 4.5v, 4xAA = 6v, etc.  So by entering 6, 2, 20..You will see it will recommend a 1/4watt 5% 220ohm resistor (even gives you the color codes!). Now where does 330 and 340 come from? That is just people being over protective of their Light emitting diodes!! It is current that drives the LED, and resistors limit current. So if you give it less current it will be dimmer but will last longer. Visibly though, you won't be able to see the difference if you use 220, 330, 340, etc. You may however see a difference if you use no resistor (which will blow the LED in a few seconds), or a 1K resistor which will be pretty dim.

If you ever build a circuit with LEDs powered by 2xAA (3v) as 3.3v tolerant components are common in electronics, you will be using LED resistors in the area of 47, 51, or 56 ohms.


http://led.linear1.org/1led.wiz

[Becky]

Thank you for the helpful information I have book marked that page and will use it.

Great answer :-)

Becky

[Soeren]

Hi,

Basically I can not find a 340 Ohm 0.4 Watt resistor.  I have found other users making do with 330 Ohm so I think that would do... ...?

...however how important is the watts?  Can not find many 0.4 Watt but loads of 1/4 - 0.25 Watt.  What effect would this have?  (Sorry again - my electronics is very beginner).

You probably wouldn't find a 0.4W resistor easily, but you can allways use a higher wattage than mentioned.
To get 340 Ohm, you could take two 680 Ohm (0.25W) resistors, which is a standard E-12 value, and wire them in parallel to get 340 Ohm (0.5W).

[pomprocker]

Thank you for the helpful information I have book marked that page and will use it.

Great answer :-)

Becky

Glad I could be helpful  [click for yes] http://www.societyofrobots.com/robotforum/index.php?action=modifykarma;sa=applaud;uid=1765;topic=7092.0;m=53680;sesc=3f92b8411f19d5738a3e6f9782a75265

[SmAsH]

this is for the $50 robot? are you sure its .4 watt and not 1/4 (.25) watt?
and using them for leds adding or subtracting a few ohms doesnt really matter to much.
just for future reference (incase you dont have access to the wizard page.
R=v1-v2/A where v1 is vin and v2 is the amount of voltage needed and A is current in amps.
(eg 5v-2v/.02=150ohms) hope this helped

[Admin]

Unless you are dealing with AC current, resistor and capacitor values don't need to be exact. Even a resistor value 50% from the specified value will often work.

As for wattage rating . . .

power (wattage) = voltage * current

Just do the math, and make sure your resistor wattage is higher than you calculated. Otherwise, the magic smoke will come out (circuits only work when the magic smoke stays inside the components).

[SmAsH]

admin are you saying the current in the buses or that the led consumes? im confuzzled...

[Admin]

admin are you saying the current in the buses or that the led consumes? im confuzzled...

I was referring to Becky's question:

...however how important is the watts?  Can not find many 0.4 Watt but loads of 1/4 - 0.25 Watt.  What effect would this have?

[SmAsH]

admin are you saying the current in the buses or that the led consumes? im confuzzled...

I was referring to Becky's question:

wait so if your led is 3V@20ma the power would be .06W?

[Admin]

wait so if your led is 3V@20ma the power would be .06W?

Total power consumed, yes, but not necessarily the power dissipated by the LED alone.

[SmAsH]

wait so if your led is 3V@20ma the power would be .06W?

Total power consumed, yes, but not necessarily the power dissipated by the LED alone.

hmm yes good point but for that situation i most likely wouldnt need a wattage higher than 1/4