Electronics > Projects, Designs, and Technical Stuff

Resistor in series to incrase power rating? legit?

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sean87:
Hi all!

I am repairing an amplifier, so far I have found a 1k, 1/2 watt resistor that my multimeter reads its value like 600 Ohm only. So I guess it has drifted a lot.

I do have some spare 1/4 watt 500 Ohm resistors. Can I use 2 of them in series so that 1/2 watt rating gets satisfied? Or I should say, does putting resistor in series helps achieving higher rating at all?

kfitch42:
I believe that series does not increase power rating, parallel does. You could do 2 parallel strings of 4 resistors each. Or 3 strings of 6 ... might give a bit more headroom.

Then again if you found 1 bad component you might find more... perhaps you should be putting an order into digikey (or RS, or whatever makes sense over there in Europe) for the right resistor and a bunch of caps... and anything else you find that is fishy.

EDIT: Yikes! After reading the rest of  the replies I realized I responded to this WAY toooo quick. I actually 'thought' it through "P=I^2 * R"... and said to myself: "in series the current is the same and the total resistance is the same ... ". Missed the boat there by a pretty wide margin :)

mariush:
You put resistors in parallel to increase the power dissipation capability , so you'd have to use 2 x 2k 1/4w to get a 1k resistor 1/2w

Excavatoree:
Two resistors in parallel or series (if identical) will share the power equally, regardless of whether they are in parallel or series.

That is:

1K ohm  (1/2 watt) =  2 (1/4 watt) 500 ohm in series, or 2 2K ohm (1/4 watt) in parallel.

In the parallel case, voltage is the same, but current is halved for each.
In the series case, current is the same, but voltage is halved for each.

It's a simple ohms law calculation.

alm:
Putting the resistors in series to share load is a fine solution. Carbon film resistors have a negative tempco, so voltage sharing should work fine in the series configuration.