Amps
[Top] [All Lists]

Re: [Amps] SB220 Meter blown

To: "amps@contesting.com" <amps@contesting.com>
Subject: Re: [Amps] SB220 Meter blown
From: Rob Atkinson <ranchorobbo@gmail.com>
Date: Sat, 16 May 2020 06:41:58 -0500
List-post: <mailto:amps@contesting.com>
W8ZR is 100% CORRECT.  You DON'T JUST WILLY NILLY SLAP ANY OLD DIODE
ACROSS A METER!


73

Rob
K5UJ

------------------------------------------------------------------------------------------------------------------
For meter protection I also use back-to-back diodes across meter
terminals. However, rather than using rectifier diodes, I use fast
small signal diodes, like the 1N914a. Aside from responding more
quickly to possible damaging spikes than rectifier diodes, they also
short circuit when overloaded, which is a kind of last ditch
protection against meter damage  Given that the diodes cost only about
$0.05, replacing a shorted diode is cheap insurance.

One other comment: it is important to compute the maximum expected
voltage across the meter terminals in normal operation. This voltage
needs to be smaller than the “turn-on” voltage of the diodes, which is
about 0.7V. Otherwise the meter will read low at large values because
current is shared with the protection diode. This is also a
consideration with rectifier diodes like the 1N4005.
73,
Jim w8zr
Sent from my iPhone
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
<Prev in Thread] Current Thread [Next in Thread>