Battery Cutoff Switch- Question for EE's out there
01-24-2002, 02:48 PM
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Battery Cutoff Switch- Question for EE's out there
Ladies and Gentlemen:
I have to install a battery cutoff switch for PCA Club Racing. But I know that if I just interrupt the battery positive lead with the engine running, the massive voltage spike will destroy the alternator.
So, I have obtained a battery cutoff switch that has four poles, and when the throw is rotated, first one pair opens, then the other. The first pair of contacts is for the alternator, so that the field is killed, THEN the battery is cut off with the second pair of contacts, killing the ignition.
Now, the QUESTION: I have converted to a later, 84-89 Carrera Alternator that is internally regulated. If I were using an EXTERNALLY regulated alternator, I would just run the DF lead (alternator field) and D+/61 lead (exciter/warning light) through the switch, and that would kill the field. But with the internally regulated version, there is no external DF lead, only the D+/61 lead. If I interrupt that circuit, it won't matter, because the alternator field is being energized by the current coming off the diode trio ("bootstrapping"). What if I ground it, bypassing the field?
I think I need to open up the alternator and cut into one of the leads to a brush, and run that to the switch. I'd need a wiring diagram for the Valeo alternator for this.
Does anyone have other guidance? Have any of you "F" stock club racers, Carrera folks in particular, wired up a cutoff switch?
Thanks in advance for any replies.
John
'71 E
'88 Carrera
I have to install a battery cutoff switch for PCA Club Racing. But I know that if I just interrupt the battery positive lead with the engine running, the massive voltage spike will destroy the alternator.
So, I have obtained a battery cutoff switch that has four poles, and when the throw is rotated, first one pair opens, then the other. The first pair of contacts is for the alternator, so that the field is killed, THEN the battery is cut off with the second pair of contacts, killing the ignition.
Now, the QUESTION: I have converted to a later, 84-89 Carrera Alternator that is internally regulated. If I were using an EXTERNALLY regulated alternator, I would just run the DF lead (alternator field) and D+/61 lead (exciter/warning light) through the switch, and that would kill the field. But with the internally regulated version, there is no external DF lead, only the D+/61 lead. If I interrupt that circuit, it won't matter, because the alternator field is being energized by the current coming off the diode trio ("bootstrapping"). What if I ground it, bypassing the field?
I think I need to open up the alternator and cut into one of the leads to a brush, and run that to the switch. I'd need a wiring diagram for the Valeo alternator for this.
Does anyone have other guidance? Have any of you "F" stock club racers, Carrera folks in particular, wired up a cutoff switch?
Thanks in advance for any replies.
John
'71 E
'88 Carrera
01-24-2002, 03:23 PM
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John,
I have an '87 Carrera that I will be doing the same thing to. My mechanic has the Bosch cutoff switch that I am planning on using. He also has a wiring diagram for setting these up. Once I get the diagram I will send it to you. Remember that the switch has to kill the engine at 2500rpm as well as idle.
James
I have an '87 Carrera that I will be doing the same thing to. My mechanic has the Bosch cutoff switch that I am planning on using. He also has a wiring diagram for setting these up. Once I get the diagram I will send it to you. Remember that the switch has to kill the engine at 2500rpm as well as idle.
James
