@Sacto Mitch posted:.Basically, using a cutoff switch to stop a running engine is nonsense up with which alternator diodes will not put.
Of course, you knew that and would never do that, but, you know, sometimes we get forgetful in our dotage.
"The regulator's job is to maintain about 13.5V at your battery +. If your alternator is turning disconnected from the battery, the regulator "sees" nothing, which is equivalent for him to Ov. So it gives more field to the rotor, to increase the output voltage which goes to the rectifier diodes. Voltage can go up to 80ish V, enough to "burn" the diodes. If you use a master switch without a resistor (or uncorrectly wired resistor), that's what happens if you cut your engine with the switch, especially at high revs (emergency, ...) On well built switches, the resistor is between the output and the earth. Low resistance -> high current -> low voltage -> safe diodes. Jeff LHD 1990 BDR"
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Great point, Mitch. I haven't tried that trick (removing the battery from the circuit) since the days of mechanical regulators. It worked fine then, but I can see that some cars might go unregulated if the battery is disconnected.
Remember, I haven't done that, and don't plan to. However, would it really work that way for a type 1? Say the engine is running and the alternator is charging the battery at 13.5V. If you disconnect a battery terminal, the charging light, regulator and alternator are still in place in the circuit, there's just a little less load on the alternator (and the regulator will keep the voltage at 13.5V to reflect the lower load).
It seems to me that to make the regulator runaway, you'd have to remove the feedback from the alternator output to the regulator. At least on my car, that's no where near the battery terminals.
Thoughts? @DannyP?