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A QUICK CHECK OF YOUR GALVANIC ISOLATOR.
Andina Marie wrote:
That is a better analysis, Chuck. But two corrections. 1. Think of the zinc and the prop as joined together electrically so they are at the same voltage as you indicate. Current is flowing between them. The amount of current is limited by the resistance of the water so you can consider the water as a resistor connected between them. I'm with you this far. This resistor (the water) also is connected to the dock, and other boats in the vicinity so the voltage of your boat (at the junction of zinc and prop) will be somewhere between the two. Which end of the "resistor" is connected to the dock? Why not both ends with full cancellation? If there is 0.9 volts available it would be reasonable to assume this makes the boat at about 0.45 volts to the water, and the dock etc. So this voltage will always be present across a galvanic isolator and it is extremely unlikely you would read zero volts with a GI in working condition. Sorry, Ann-Marie, but no cigar. 2. You are incorrect in saying "Regarding the operation of a semiconductor diode, it is good to remember that the voltage across a forward-biased diode is related to the current through it. If a voltage is measured, then there is a current through it. " That is wrong. No current flows through a diode until it reaches about 0.6 volts for silicone. It is like a switch that won't turn on until it gets to 0.6 volts. Once it turns on the voltage across it essentially stays at about 0.6 independent of current. You can't determine the current flowing through it by observing the voltage. It does not behave like a resistor. That is how a galvanic isolator works. With two diodes in series (each direction) NO CURRENT flows until the voltage gets above 1.2 volts. Regards, Ann-Marie Foster, Well, that explains why our discussion is not moving toward closure. Please take a few moments and go the this website: http://www.fairchildsemi.com/pf/1N/1N914A.html Product Folder - Fairchild P/N 1N914A - High Conductance Fast Diode Download the datasheet and on page 2, figures 3 and 4, you will see the manufacturer's take on whether there is a relationship between forward voltage and current. You'll see that there is absolutely nothing magical about 600 mV in a V log I plot. It IS like a (non-linear) resistor. The relationship between current and voltage for a pn junction is well-established and has been for more than half a century. Finally, take a variable voltage source, a 100 ohm resistor and a diode. Put them in series and adjust the voltage so there is, say, 300 millivolts across the diode. You will be able to measure a current through the diode of something like one to ten microamps. Change the voltage and watch the current change. Then go back and read the posts. Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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