# help with wattages

Discussion in 'General Electronics Chat' started by lokeycmos, Sep 21, 2012.

1. ### lokeycmos Thread Starter Active Member

Apr 3, 2009
432
7
so say i needed a 450.45Mohm resistor rated for 22watts and i wanted to use multiple series resistors to equal those values and i used 10 resistors. each resistor would be 45.045Mohms. does that mean each resistors wattage rating would be 22/10 = 2.2 watts?

2. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,167
777
yes, as they are in series they all take the same current, so each have same wattage which is 2.2w,

you could also put Ten 4504.5Meg resistors each 2.2w in parallel, that will give you 450.45Meg at 22W

Last edited: Sep 21, 2012
3. ### lokeycmos Thread Starter Active Member

Apr 3, 2009
432
7
you said "No". but then you said "so each have same wattage which is 2.2w"

Dodgydave likes this.
4. ### crutschow Expert

Mar 14, 2008
13,521
3,388
The answer is yes, each resistor would dissipate 2.2W.

5. ### cork_ie Member

Oct 8, 2011
348
58
That equates to a working voltage of somewhere close to 100KV

You need to check datasheets of whatever you are using for breakdown voltage as well as just plain resistance & wattage

6. ### Austin Clark Active Member

Dec 28, 2011
409
44
I'd just like to point out, just in case, that all the resistors must be IDENTICAL in resistance for this to be true. If one resistor is of a higher value, it will dissipate more heat than the rest. Also, if you wanted to dissipate 2.2W, you'd want to go for at least 3W to be safe, and try to keep each individual resistor relatively far away, so that heat doesn't "pool" across them instead of radiating away like it should. If it's a LOT of heat, you'd obviously want to use some sort of fan or heat sync, because ambient temperature definitely does have an effect on maximum wattage rating.

Again, just wanted to put that out there. That's not always immediate obvious to some people.