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Old 01-27-2009, 07:37 AM   #26 (permalink)
dcb
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I don't know if there is a 100% fix either. I don't know what happens to the hold voltage when the alternator goes out. I am assume it is a function of supply voltage, but it is conceivable that they got fancy with the hold voltage drivers, in which case supply voltage could drop below the hold voltage.

resistor experiments:
r2>=2520 ohms (base current @peak =.005a @hold (11 volts) = .00063a)

A 50k seems to work too for r2, so I don't think it is too critical. And a 50k offers much more protection than 2520 so I might just go with that. it means about 0.0000036 amps through the base in "hold" which is about 72 times the base cutoff current, and .0003 amps at peak.

rx=50k ohms
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Last edited by dcb; 01-27-2009 at 11:33 AM..
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