Can I use five 1W resistors instead of one 5W resistor?

Thread Starter

scheua

Joined Mar 17, 2016
9
Hi there. I want to build a power supply unit for my project and the schematic says I need a 5W resistor. Those are rather expensive, and I was wondering if I can use five 1W resistors instead. If I need 10 Ohm 5 W resistor, can I use five 50 Ohm 1 W resistors connected in parallel? Thank you!
 

ErnieM

Joined Apr 24, 2011
8,053
Well... It depends. Are you going to lay them out separately so each gets the proper air flow or are you going to twist the leads together and make a tight package so there is at least one resistor buried under the other four?
 

WBahn

Joined Mar 31, 2012
26,074
Hi there. I want to build a power supply unit for my project and the schematic says I need a 5W resistor. Those are rather expensive, and I was wondering if I can use five 1W resistors instead. If I need 10 Ohm 5 W resistor, can I use five 50 Ohm 1 W resistors connected in parallel? Thank you!
In theory, yes.

A few practical things to consider -- the sharing is not going to be exact, so one of the five 1 W resistors will be carrying more power than the others. So you should probably derate things a bit, particularly if you are going to be pushing that 5 W limit. Just adding one or two additional resistors will take care of that.

You also need to ensure that the resistors you use have a positive temperature coefficient (i.e., the resistance goes up as they get hotter) otherwise you will end up with thermal runaway. Most resistor do have positive tempcos, so that shouldn't be a problem.

Finally, the assumption on the power ratings of the resistors is that they have adequate cooling, even if it is just free air. If you park a resistor near a hear source, then it won't be able to dissipate as much power as when it is properly cooled. So don't make the mistake of parking all of these heat sources close together.
 

wayneh

Joined Sep 9, 2010
16,399
Probably not a factor here, but a wire-wound ceramic power resistor also has a significant inductance. A lower wattage resistor that is not wire-wound, does not. A good design wouldn't rely on the inductance of a resistor, but there will be a difference.
 

Tonyr1084

Joined Sep 24, 2015
4,924
What pink box? And why the language?

I read something and below there were more threads. I noticed this one and responded. If it's that old then why was it being promoted by AAC? Y'know, down below the last post on this page ? ? ?

And what's that thing it says in the reply box? "Remember the human - Be courteous when replying to others."
 

WBahn

Joined Mar 31, 2012
26,074
The "Similar Threads" is to help people find information that might be of interest when searching for something (although I find that the threads it suggests seldom have a relevant relationship to the one I am viewing). It is more archival in nature and not a list of hot threads that you might want to participate in. Something to keep in mind when browsing them.

Whenever you respond to a thread that has been dormant for a year, you get a big warning that asks you to consider whether posting new content is really useful and requires you to check a box in order to proceed. However, the last post in this thread was JUST UNDER one year ago, and so no such warning box would have popped up. Accidentally posting to such threads without taking into account their age is an easy mistake to make that all of us do from time to time.
 

spinnaker

Joined Oct 29, 2009
7,835
Not to mention that posting to a thread that is not yours with your own thread, is called "hijacking". You really should create your own thread.
 

GopherT

Joined Nov 23, 2012
8,012
image.jpeg

I didn't mean to call the poster a dumbass, I was just implying that the language and associated confirmation check-box was quite clear in explaining to any potential poster that the thread has been idle for a long time - Hence the quote marks.
 

GopherT

Joined Nov 23, 2012
8,012
I needed a 6.6k, 6W resistor, and I had a good supply of 1k, 1/4W resistors.
View attachment 121878
It is funny how red can look orange with the new LED flashes (no joke). Just confirm, those resistors are brown, black red (and not brown, black orange (10k)).m

I just looked at a motorcycle online and the photos looked orange until the seller confirmed color with non-flash photos.


In person, this bike is Fararri red..

image.jpeg
 

cognas

Joined Feb 24, 2017
58
Oops! I've just reaslised, by reading through the comments, how old this thread is. It was right near the top of the list, so I thought it was recent. I didn't get the pink box because the more recent comments are - well - recent. Might it be an idea if the pink box appeared, based not on the most recent post, but on the date of the opening post?

GopherT - no the resistors are 1k.
 

GopherT

Joined Nov 23, 2012
8,012
Oops! I've just reaslised, by reading through the comments, how old this thread is. It was right near the top of the list, so I thought it was recent. I didn't get the pink box because the more recent comments are - well - recent. Might it be an idea if the pink box appeared, based not on the most recent post, but on the date of the opening post?
The pink box only appears for the poster that breaks the time warp. Once broken, nobody else gets the warning until the thread sits dormant for another year (or 6-months).
 

WBahn

Joined Mar 31, 2012
26,074
View attachment 121871

I didn't mean to call the poster a dumbass, I was just implying that the language and associated confirmation check-box was quite clear in explaining to any potential poster that the thread has been idle for a long time - Hence the quote marks.
What "language and associated confirmation check-box"? He didn't get one, because the thread had not yet been dormant for a year.
 
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