[Waverley ARS] Dummy Load calculations

[Adam Carmichael]

Hi Robert,

robert sinderberry wrote:
> Hi Adam, first of all I don't know why you want a dummy load capable of 
> 1000 Watts, nobody can do that much power legally in VK . You don't even 
> need 100 Watts with your licence? (hi) but, anyway...to build a 1000 
It's an exercise I gave myself for part of my (insert tada.wav) advanced 
license reading, just a thought experiment. (And since posing this 
question, a friend of mine tells me he is also getting a few mainly 
unused UPS datacentre batteries; and would like to test them out before 
relying on them at home).

> Watt, 50 Ohm dummy load you need...100x5000 Ohm, 10 Watt resistors. i.e. 
> 1000Watts /10W.res.=100 resistors, all up. Then, because it needs to be 
> 50 Ohms (resistance) it's...50 Ohms x 100 res. = 5000 Ohms. Of course I 
> don't know if resistors like that are available? (ask one of the tech 
> guys i.e. Eric or Henry) if not just re-do the maths. Have fun, 
> 73....Rob VK2LRS
Looks like you came to the same conclusion I did - a confidence boost :)

BTW: They do seem to make 10W resistors, but I don't understand the way 
they're expressed on the Jaycar website - "8R2Ohm" and "6R8Ohm" resistors.

> P.S. To find the total resistance of any number of resistors in parallel 
> the equation is 1/Rt=1/R1+1/R2+1/R3+etc (assuming all resistors are equal).
Hold on, maybe I'm not seeing a division or something similar as it's 
pretty early, but that looks like the general equation for total 
resistance of any number of resistors of mixed value in a parallel circuit?


Thanks for the response, first one in 4 or 5 days :)


Regards,

73.... Adam VK2FNRD

>> From: Adam Carmichael <carneeki at carneeki.net>
>> To: members at vk2bv.org
>> Subject: [Waverley ARS] Dummy Load calculations
>> Date: Sat, 21 Apr 2007 12:25:03 +0800
>> Adam wrote:
>> Hello List,
>>
>> I'm reading into how to calculate the components for a 50 Ohm dummy load
>> - and so I decided to test myself, unfortuneately I cannot grade myself!
>> I was wondering if somebody would be kind enough to check what I'm doing
>> is correct.
>>
>> The question I gave myself:
>>
>> I want to build a 50 Ohm, 1kW dummy load. What resistors are required?
>>
>> So I set out to find out. 1W resistors would mean I would need 1000
>> resistors, which is too much soldering! 5W resistors would mean a lot of
>> soldering, but 200 resistors is still manageable; and so I continue.
>>
>> Total Resistance required: 50 Ohms
>> Number of resistors: 200
>> Power dissipation per resistor: 5W
>>
>> Remembering the equation for parallel resistances of equal resistors:
>>
>> R(total) = R1 / (number of resistors)
>> 50 Ohms = R1 / 200
>>
>> Or, rearranged:
>>
>> 50 * 200 = R1
>>           = 10 000 Ohms
>>
>> Therefore: 200 * 10K Ohm 5W resistors are required to build a 1kW dummy
>> load.
>>
>>
>>
>> Thanks in advance,
>>
>> Adam
>>
>> -- 
>> Adam "carneeki" Carmichael - VK2FNRD
>> p: +61415371990
>> w: http://carneeki.net
>> e: carneeki at carneeki.net
>> i: 2207644
>> _______________________________________________
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-- 
Adam "carneeki" Carmichael - VK2FNRD
p: +61415371990
w: http://carneeki.net
e: carneeki at carneeki.net
i: 2207644