ORIGINAL MESSAGE:
At 11:17 AM 6/26/2006, R L Measures wrote:
>back to belly 3a
>diodes should be paralleled with the meter movement
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Just paralleling diodes across the meter movement may or may not
work, depending on the meter's internal resistance. The diodes won't
conduct until about .6 volts appears across them, and many meters
have far too low internal resistance to make this happen at any
reasonable current.
The best approach is to add a resistor in series with the meter and
then connect the diodes across the combination of meter + resistor.
The exact value of the resistor depends on the resistance of the
meter and the value of current when you want conduction to begin.
Ohm's law will provide the answers, and you can easily check the
protection by running a controlled amount of current through the
circuit and observing the beginning of conduction.
Bill, W6WRT
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