Bill: Resistors...Parts Express

[Tim A]

PE has been out of stock on the 4 ohm 20 watt resistor for a LONG time. I've tried to order twice in the last 2 months.

Would the 2 ohm 20 watt be ok? What other values would work for the application?

Other sources?

Here's a question: If you wire 2- 8 ohm resistors in parallel, do you get 4 ohms? Does the power handling stay the same?

What about 2- 2ohm in series? Do you get 4? Power handling?

[dbaldock]

These calculations can be extended to more than two resistors, as well.

Parallel Connection

Two resistors in Parallel have a Total Resistance equal to the Product divided by the Sum of their individual resistances:

R1 x R2
---------- = R(Parallel Total)
R1 + R2


8 x 8
------ = 4 Ohms
8 + 8


The Total Power Handling for Parallel connection is equal to all the individual Power Ratings added together.

P(R1) + P(R2) = P(Parallel Total)

20W + 10W = 30W


Series Connection

Two resistors in Series have a Total Resistance equal to the Sum of the individual resistances:

R1 + R2 = R(Total)

2 + 2 = 4 Ohms

The Total Power Handling for Series connection is equal to the Lowest individual resistor's Power Rating. If you put a 20W in series with a 10W, your Total Power rating would be 10W, since all the power has to flow through each resistor.

P(Series Total) = Whichever is Lowest of P(R1) or P(R2)


Take Care,
David

[Bill Fitzmaurice]

Use these
http://www.partsexpress.com/pe/pshowdet ... mber=004-4

[Tim A]

Thanks to both!

Dave, your response was extremely informative, I learned a lot!

But ya gotta' love Bill's "use these"!