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If a power resistor (PR) is rated at say 50 watts, and you put 2 in series...will the resultant rating be 100 watts (as I assume) or will it remain at the maximum rating for any one of the PR's. If so, does the same apply to PR's wired in parallel ? I understand that the value in ohms will vary if wired in parallel or series.

I am considering building a dummy load for my Bandmaster head, as I (AKA known as "the dummy") have powered up the head a couple of times without the speaker jack in...only for a few seconds each time...but enough to cause a panic attack.

The easiest would seem to be using one PR of 4 ohms at 50 watts. However, this value would have to be ordered...so I'm looking at other combinations that I could use that might be in stock at some of the places that I shop at.

All comments/suggestions welcomed (other than references to me being a dummy).

Thanks

Dave
 

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If a power resistor (PR) is rated at say 50 watts, and you put 2 in series...will the resultant rating be 100 watts (as I assume) or will it remain at the maximum rating for any one of the PR's. If so, does the same apply to PR's wired in parallel ? I understand that the value in ohms will vary if wired in parallel or series.

I am considering building a dummy load for my Bandmaster head, as I (AKA known as "the dummy") have powered up the head a couple of times without the speaker jack in...only for a few seconds each time...but enough to cause a panic attack.

The easiest would seem to be using one PR of 4 ohms at 50 watts. However, this value would have to be ordered...so I'm looking at other combinations that I could use that might be in stock at some of the places that I shop at.

All comments/suggestions welcomed (other than references to me being a dummy).

Thanks

Dave
You've got the right idea, Dave! With combinations of equal resistors the power involved is shared equally. So a pair of 4 ohm 50 watt resistors in series will give an 8 ohm, 100 watt load.

Or two 8 ohm 50 watts in parallel will total 4 ohms at 100 watts.

Where it gets really tricky is when the resistors are NOT equal! Then you have to do some PITA math. In case you didn't already know:

Pwatts= V x I

Pwatts=I^2 x R

And of course: V = I x R

If you have a "jumble" of resistors of different values then it helps to remember that when resistors are in series the current will be the same through each and every one of them. If you know that, you can then calculate the voltage drop across any resistor or how many watts will be dissipated by any different resistor carrying that current.

This is why with speakers we all find it MUCH easier to deal with combinations of equal value speakers!:smile:
 

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This is why with speakers we all find it MUCH easier to deal with combinations of equal value speakers!:smile:
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I can certainly understand why...after you explained.



Thanks Wild Bill !!

I'm trying to keep thais as simple as possible...mainly because I don't want to do the math (then post it for confirmation) and find out that I'm wrong in my approach/conclusions.

Maybe someday I'll be more "adventurous" in electronics , but for now I'm applying the KISS principle whenever possible.

Dave
 
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