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

Discussion in 'General Electronics Chat' started by scheua, Mar 17, 2016.

  1. scheua

    Thread Starter New Member

    Mar 17, 2016
    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!
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    Yes, that would work, and 5x 1W resistors will have more surface area than 1x 5W resistor so there is a cooling advantage.
    Last edited: Mar 17, 2016
    scheua and wayneh like this.
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    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?
  4. WBahn


    Mar 31, 2012
    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.
  5. wayneh


    Sep 9, 2010
    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.
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010