[Amps] Dummy Load

[Mark Marsden]

Hi Stefan & Will

That's very interesting to me. I'm looking at a possible 50R 40dB attenuator based on the new thick-film-on-steel planar resistors by TT-electronics/Welwyn. They aimed at the automotive dynamic braking & welding industry, with a very low £/kW ratio.

Farnell part numbers are 
465-9569  50R 2-8kW £13.93
465-9600  50R 5-16kW £23.52

It'll be interesting to see if the meander-line construction can be matched to give a good return loss across the HF spectrum.

Best 73 Mark G4AXX 


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 Stefan,

One way I've seen them built the way your wanting to do it is use 4 narrow PC boards with an etched line down eachs middle. The resistors solder across this line where it made two long copper pads. Each 4 was done this way mounting resistors on each in parallel. The 4 boards were then connected together in a box shape during hookup. Then, the top of each board went to the ground of a RF connector, and it center pin went down through the middle of the boards thus connecting at the bottom. These were built in 1 gallon paint cans to be oil cooled. if I recall, the builder took a piece of aluminum tubing and slid it over the board assembley and left it open at the top and bottom by brackets. That way the oil could circulate through the center easily. I'm not sure how well they worked, I just happened to see one built that way.

Best,

Will

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On 5/23/05 at 5:22 PM Stefan wrote:

>Dear friends
>
>I am trying to build a Dummy load made out of many parallel resistors
>(200x 
>10k/2W), and I am thinking of which would be the best configuration. I
>have 
>seen (and even used myself) a bus capacitor circuit with 10uF MKT caps 
>(power capacitor) which to enhance capacitive behaviour made a very clever 
>layout in which current flew in each device in the opposite direction to 
>cancel thier magnetic fields (and therefore reduce their stray
>inductance). 
>You can place caps on the top and the bottom and if current flows in the 
>opposite direction on each one at its sides and beneath it the parasitic 
>inductnace is reduced.
>
>I have thought of using this idea also for the dummy load. Using to very 
>wide tracks on both layers and placing components on TOP and BOT layers, 
>where current flows in the opposit direction on each one. But which is the 
>minimum distance (clearance) I have to maintain between pins of opposite 
>voltages (for Po=400W, R=50 => V=141V). Would 5mm do it? Or even less?
>
>I hope somebody could share his expertise with me.
>
>Thanks in advance,
>
>Stefan
>EA5FY