[SOC] Looking to build a Dummy (Load)

[BEVIN ALEXANDER]

Two resistors @ 100 ohm and 100 watts might be a bit safer.  Or, 4x 200 ohm 
at 50 watts; I think there is a big step off in price from 100w to 50w.

I flipped through the Mouser catelog during my "morning constitutional" and 
found several.  These include:
    Arcol aluminum housed wirewound [inductive, but not a lot so if you put 
them inside something metal] [200 ohm, 50w]
    Craddock Power Film Resistors
    Vishay/Dale HL Series [used in power supplies]
    Vishay/Dale RH Series [like the Arcol].

I've used both the aluminum housed and V/D HL series types in power 
supplies, but never as a dummy load.  However, at the cheap prices, it would 
be worth a try.

I just took my generic MFJ 300w dummy load apart.  It has one large 
seemingly wire-wound resistor, housed inside a perforated aluminum cage, 
inside a relatively heavy aluminum box with about 1.0-1.5 cm of space all 
around.  This supports my inference that you can put a group of 4x 200 ohm 
50 watt wirewound resistors inside a couple of RF suppressing aluminum or 
steel boxes.  An ammo can or couple of old paint cans [pint inside gallon] 
would be a good, and would be in the adaptive, salvage spirit of ham 
radio.... :-)

Good luck.

Bevin Alexander
K4ALE


----- Original Message ----- 
From: "Tom McCulloch" <thom2 at att.net>
To: "Second Class Operators' Club" <soc at mailman.qth.net>
Sent: Thursday, January 22, 2009 9:31 PM
Subject: Re: [SOC] Looking to build a Dummy (Load)


> Carlos thanks...good point about needing only 40 watts to handle the 100
> watt load for a short time.
>
> I think in parallel you divide and in series you add, though.
>
> Thanks again
>
> One guy pointed me one 50 ohm resistor at 100watts1  It only cost $9.50 at
> Mouser, I think I;ll go that way.
>
> Tom
> ----- Original Message ----- 
> From: "Carlos J Caro" <ccaro3 at juno.com>
> To: <soc at mailman.qth.net>
> Sent: Thursday, January 22, 2009 9:24 PM
> Subject: Re: [SOC] Looking to build a Dummy (Load)
>
>
>>
>>> 1) I guess I can figure out the value of 20 resistors I'd need to
>>> get a 50
>>> ohm result (well, maybe I can't.)  But what wattage should I use to
>>> handle
>>> 100 watts?  Am I going in parallel (yea, parallel, right? otherwise
>>> I'd need
>>> 100 watt resistors???, right?)  OK, so does that mean I'd need 20
>>> five watt
>>> resistors in parallel?
>>>
>> Tom,
>>
>> All your resistors will be in parallel so 50 ohms times 20 resistors
>> equal
>> 1000 ohms. If each resistor is 2 watts the load 1will be a 40 watt that
>> can handle the 100 watts for a short time.
>>
>>
>> Regards,
>>
>> Carlos K4REI
>>
>> http://www.qrpedia.com
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