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Re: Re: Re: Positive ground..?!
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Posted by uh . . . Dell (WA) on January 29, 2002 at 08:17:27 from (198.81.17.53):
In Reply to: Re: Re: Positive ground..?! posted by MarkB on January 28, 2002 at 16:55:45:
Mark........."12 volt alternators are designed to work with negative ground, not the other way around. You could make a positive ground alternator (just reverse the diodes), but negative ground was standardized by the time alternators were in common use"......NO, NO, NO, you just can't simply reverse the diodes. What ultimately caused 12 volt negative ground to become the standard electrical configuration was the switch to transistorized radios in 1956. Everyone just had to have the latest in radio technology. (Does that sound familiar?) The germanium audio Power Transistor Amplifier needed a heatsink to keep from melting its lil' ol'semi-conductor heart. Cheapest and eaziest heatsink was the metal radio chassis itself. Leave alone the problem of insulating the radio from the dash (which it is not insulated). The germanium power transistor is NPN, which means the collector must have negative potential. The collector is also the physically internally connected to the large metal transistor case for heatsinking. The collector is also the part that gets HOT. Vola...the reason for negative ground. The same line of reasoning for the semi-conductor diode trio in the alternator. HEATSINK! Use the alternators metal case as a heatsink. Manufacture the diode so the diode's metal case is physically internally the cathode for heatsinking purposses. Then the anode supplies positive electricity to the diode pigtail. I assume you realize innna 'lectricity, ya gotts ta hava goes innta annna cums outta. Semi-conductor power diodes use their metalic case for bi-directional duties, heatsink and electrical conductor. And so thats the reason for todays automotive electrical systems being "negative ground", POWER DIODES and POWER TRANSISTORS need HEATSINKS and your semi-conductor factorys manufacture them that way..........respectfully, Dell (WA)
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