Heat dissip. series vs. parallel

[Kevin Roberts]

I need to fit 20 Ohms worth of power resistor as a dummy load in a
confined space. In practice, is there any difference in terms of heat
disspation between using two 10R in series or two 40R in parallel?

Voltage is 12V giving about 7W dissipation. I would be using 25W rated
resistors just to be sure.

Thank you,

Kevin Roberts

 

[Martin Brown]

I need to fit 20 Ohms worth of power resistor as a dummy load in a
confined space. In practice, is there any difference in terms of heat
disspation between using two 10R in series or two 40R in parallel?

Voltage is 12V giving about 7W dissipation. I would be using 25W rated
resistors just to be sure.

Two 40R in parallel will cost more - not an E12 value (39R is).
A failure in either one of a series pair will go open circuit.

20R is 20R for power dissipation but physical layout could matter in a
confined space. Heatsinking might be helpful to keep it cool.

Regards,
Martin Brown

 

[ehsjr]

I need to fit 20 Ohms worth of power resistor as a dummy load in a
confined space. In practice, is there any difference in terms of heat
disspation between using two 10R in series or two 40R in parallel?

Voltage is 12V giving about 7W dissipation. I would be using 25W rated
resistors just to be sure.

Thank you,

Kevin Roberts

You're stuffing 50 watts of dissipation capability in there where
you need only about 15. I guess if you have room and cost doesn't
matter, it's a case of "why not use a bigger wattage". Series or
parallel doesn't matter. Depending on layout, you could get some
advantage by physically locating the "hot spots" (where the
resistors are installed) to minimize heating of nearby components.
That's about the only reason to use multiple resistors in this
case, where your budget and space allows selection of a 25W
resistor to dissipate ~ 7 watts. Maybe 4 5W 5 ohm resistors
would serve you better?

Ed

 

[Winston]

I need to fit 20 Ohms worth of power resistor as a dummy load in a
confined space. In practice, is there any difference in terms of heat
disspation between using two 10R in series or two 40R in parallel?

Voltage is 12V giving about 7W dissipation. I would be using 25W rated
resistors just to be sure.

In addition to the other responses and at the risk of
appearing nit-picky, please consider how you are going
to get rid of those 7 watts. The 25 W rating on your
resistors is in 'free air' that has an unlimited
ability to absorb heat rise convecting off the body of
your dummy load. Enclose those resistors tightly enough
and you have to derate them, perhaps by a lot.

--Winston

 

[Sjouke Burry]

I need to fit 20 Ohms worth of power resistor as a dummy load in a
confined space. In practice, is there any difference in terms of heat
disspation between using two 10R in series or two 40R in parallel?

Voltage is 12V giving about 7W dissipation. I would be using 25W rated
resistors just to be sure.

Thank you,

Kevin Roberts

A series chain is more likely to fail, one failing resistor takes
out the whole chain.