Re: Wire-wound resistors as dummy test load

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Speck by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-davidspeckmd-dot-org>

Ed,
I think we are speaking different languages, but saying the same thing.

If the 4 resistors are in series, they will total 800 ohms.  Passing 1 
amp through the string will dissipate a total of 800 watts, 200 watts in 
each resistor, with a voltage drop of 200 volts across each resistor. 
 Power (watts) = (I ^ 2) * R. = V * I

If the four resistors are in parallel, they will have a combined 
resistance of 50 ohms.  Putting 200 volts at 4 amps across the parallel 
set will still dissipate 200 watts in each resistor, or a total, again, 
of 800 watts.  

When you series resistors of differing wattages, the current of the 
chain is determined by the power dissipation ability of the smallest 
wattage rated resistor in the chain.  Whatever level of current makes 
the maximum dissipation in the smallest rated resistor will be the 
maximum current the chain can sustain without burning out the smallest 
resistor.

Dave

Tesla list wrote:

>Original poster: "Edward Wingate by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <ewing7-at-rochester.rr-dot-com>
>
>Tesla list wrote:
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>>Original poster: "David Speck by way of Terry Fritz <twftesla-at-qwest-dot-net>"
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><dave-at-davidspeckmd-dot-org>
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>>Rick,
>>Sorry, nope, but in series, each resistor will still be able to
>>dissipate its own 200 watts, quite independently of the other three, so
>>four in series will give an 800 ohm, 800 watt resistor, with maximum
>>dissipation when you put 800 Volts at one amp through the string.  A
>>single resistor would dissipate 200 watts when carrying 200 volts at one
>>amp.
>>Dave
>>    
>>
>
>Hi Dave,
>
>The wattage rating of resistors in series is only as high as the
>weakest link which in this case is 200 watts. Each resistor is still
>being asked to pass an 800 watt total load no matter what each is
>dissipating separately and it won't work for long. If you splice 4
>pieces of wire together in series they still will only handle what a
>single length is rated for in amperes. In parallel the 200 watt
>resistors could handle 800 watts because each resistor handles 25% of
>the load.
>
>Ed
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