I agree with Stan.
A limited current power supply is very useful, especially when first powering on a new build.
If it current limits at something over the expected current, you can usually address the problem
before any damage occurs.? At least you won't blow a hole in the board.
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Lots of them out there that can do up to 30v at 10a for around $50.
Here's one: ?
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I have something similar that I bought 5 yrs ago, my particular model is no longer offered.
It has around 50mV of ripple on the output, so quite safe for verifying that the QMX works
but has too much noise to make? serious use of the QMX receiver.
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Spend a bunch more money and you can get one with far less noise.
I found an old analog bench supply at GoodWill for $20, an HP 6281A.
Has a very clean output, does up to 5A at 7.5 Volts.
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Here's a budget option, but you have to feed it from a DC power supply?
with a voltage greater than the output voltage you expect:
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And if you and your four friends are really cheap, you could get by with something like this:
Since it has no display you will need to use your DVM to set the voltage and current limits,
which is easy enough for occasional use.
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Jerry, KE7ER
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On Sat, May 24, 2025 at 05:29 PM, Stan Dye wrote:
On Fri, May 23, 2025 at 08:51 PM, Donald S Brant Jr wrote:
Current limiting can only do so much; a semiconductor can be destroyed WAY faster than a power supply can limit current
True.
However, a current-limited power supply is an important part of doing first power-on tests, and also debugging if you already have a short.
It may not prevent damage to a part when there is already a full short - but it will prevent further damage while debugging where a short is, and recovering from that fault.
So let's not minimize the importance of using a current-limited supply in diagnosing QMX/QMX+ builds.
Stan KC7XE
