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Re: [CQ-Contest] Load testing a 50 amp supply?

To: <cq-contest@contesting.com>
Subject: Re: [CQ-Contest] Load testing a 50 amp supply?
From: "Tom McDermott" <tom.mcdermott4@verizon.net>
Date: Fri, 19 Mar 2004 08:02:21 -0600
List-post: <mailto:cq-contest@contesting.com>
One way to test is to use deveral transistors as the load. I've made one
from junk box parts, works great, completely adjustable.

Use about 5 well heatsunk 2N3055 transistors in parallel, with some 0.1 ohm
resistors in the emitters of each (for load balancing). Emitter balast
resistors go to ground. Collectors of all 5 at the load terminal.

Use another 2N3055 as a driver to drive the base, Darlington style.

Use a potentiometer from the load terminal to the base of the driver
transistor. Adjust the pot for the amount of load current you want. It is
easiest to start with the pot to highest resistance, and use a volt meter
across a balast resistor to measure the current. Then adjust the pot as
needed to increase the current to the desired load current. You can also
couple a little AC into the driver terminal if you want to measure the power
supply performance under dynamic loading.

You may need a pretty husky pot to dissipate the driver's base current
(several watts).

        -- Tom, N5EG

>I just repaired (I think) a 50 amp astron rack supply.  I intend on using
>it to power two hf rigs (SO2R) and accessories.  However, I wish to load it
>to about 30 amps to check ripple and regulation without sacrificing my
>station if something is wrong.
>Any ideas on what I could use to load it up for a test?
>Rich, N8UX

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