[Amps] 47 Ohm 5 watt

[Bryan Swadener]

Be careful of the temperature derating. The datasheet says they start to derate at 25°C and derate to zero at 155°C. Caddock and others produce similar power resistors.  Kanthal/Globar produces suitable single units but, I've not heard of a source for small quantities.  However, a coupla 100Ω/2W carbon composition resistors can be used in parallel. Ebay seller 'bigsmythe74' has new old stock Allen-Bradley but, he wants $4/each. Sorting by price, I see he has 91Ω/2W available for $1.25 each (http://www.ebay.com/itm/400003772794). Add $3.50/order shipping to USA.
vy 73,  Bryan WA7PRC 

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Date: Wed, 08 Aug 2018 16:50:37 +0000
From: Manfred Mornhinweg <manfred at ludens.cl>
To: amps at contesting.com
Subject: Re: [Amps] 47 Ohm 5 watt

Joe,

> I hope someone has in their parts box. (2) 5 Watt 47 ohm non inductive 
> resistors.

Actually I do have a few, apparently metal oxide, but shipping them to 
you would cost more and take much longer than if you buy them...

Maybe you can use this one:

https://www.digikey.com/product-detail/en/ohmite/TNP10SC47R0FE/TNP10SC47R0FE-ND/6165413

It's 10W, but still small enough and not too expensive. You can either 
bolt it to the chassis, or on a little aluminium sheet that acts as 
heatsink, shaped and bent to fit the space you have. These resistors 
have lower inductance than old-style "non-inductive" ones, due to their 
smaller size. Of course you destroy that advantage if you have to use 
long wires to connect them...

Or you can assemble them from several 2W film resistors of properly 
chosen values, combined in parallel. Those are very common and 
inexpensive. Or use a bunch of even smaller resistors.

Manfred

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