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That NRHA comment defies electrical physics. They must use some magical wiring system that keeps the battery in the circuit with the negative disconnected. That's assuming that disconnecting the positive in fact kills the engine.
Here the wiring required by NHRA. Notice the alternator wiring on the battery side of the kill switch.
Ok, I can see how removing the positive voltage kills the engine, it kills 12v to the fuel pump. How does the fuel pump keep running if you remove the negative (ground) from the battery? Where does the fuel pump get a connection back to the battery to make it run if the battery is not connected to any other ground?
That NRHA comment defies electrical physics. They must use some magical wiring system that keeps the battery in the circuit with the negative disconnected. That's assuming that disconnecting the positive in fact kills the engine.
When installing batteries in an aircraft, exercise care to prevent
inadvertent shorting of the battery terminals.
Serious damage to the aircraft structure (frame,
skin and other subsystems, avionics, wire, fuel
etc.) can be sustained by the resultant high discharge
of electrical energy. This condition
may normally be avoided by insulating the
terminal posts during the installation process.
Remove the grounding lead first for battery
removal, then the positive lead. Connect the
grounding lead of the battery last to minimize
the risk of shorting the “hot terminal” of the
battery during installation.
You get no current flow with either post disconnected. It can't get back to the negative post to complete the circuit. I don't care which cable you disconnect, the circuit is broken and no current can flow.
In that exact condition with the engine running, the alternator becomes the "battery" for electrical purposes. My previous answer about the rat tail not shorting was not based on the engine running because it wasn't in the question.
We sure are drifting from which post to put a disconnect on, but for battery drain and some small feeling of theft deterrent the post chosen doesn't matter. After the engine is started, I've never used or felt the need for a cutoff. It seems to me that the ignition switch should take care of that.
assume a engine started and running (the battery disconnect is on the negative terminal and is to prevent the car from being started).
the alternator is a one-wire and is energized and grounded through its mount; the battery ground is disconnected; will the car keep running?
Bill
That's the scenario I figured 65GGvert was talking about.
We used to pull a terminal off the battery (when running) to get an idea if the alternator shot. If it died you knew something was up with the charging system. Done it with internal and external reg cars. And yes, that's not the greatest thing to do----please no lectures.
In that exact condition with the engine running, the alternator becomes the "battery" for electrical purposes. My previous answer about the rat tail not shorting was not based on the engine running because it wasn't in the question.
We sure are drifting from which post to put a disconnect on, but for battery drain and some small feeling of theft deterrent the post chosen doesn't matter. After the engine is started, I've never used or felt the need for a cutoff. It seems to me that the ignition switch should take care of that.
... but I do use a green **** on the positive post...
... but I do use a green **** on the positive post...
I guess my scenario was addressing the NHRA post.
Bill
I have a 72 Corvette with the cutoff on the negative post, and a 68 LS1 Camaro with the cutoff on the positive post. That's the way they were when I got them, and I saw no need to change either. I'd rather have the cutoff on the negative on the Camaro too, because as I was tightening a bolt on the a/c compressor the wrench touched against the exposed metal on the blade type cutoff and started quite a fireworks display. When I change it, I'll probably use a **** type that doesn't have several inches of exposed metal to access. Plus the corners and edges of those big blade types are sharp and will take off some skin.
I have a 72 Corvette with the cutoff on the negative post, and a 68 LS1 Camaro with the cutoff on the positive post. That's the way they were when I got them, and I saw no need to change either. I'd rather have the cutoff on the negative on the Camaro too, because as I was tightening a bolt on the a/c compressor the wrench touched against the exposed metal on the blade type cutoff and started quite a fireworks display. When I change it, I'll probably use a **** type that doesn't have several inches of exposed metal to access. Plus the corners and edges of those big blade types are sharp and will take off some skin.
That's the scenario I figured 65GGvert was talking about.
We used to pull a terminal off the battery (when running) to get an idea if the alternator shot. If it died you knew something was up with the charging system. Done it with internal and external reg cars. And yes, that's not the greatest thing to do----please no lectures.
No Lecture from me as I have done the same thing just to rule out the Alternator as the problem. I had to keep the engine just above idle to keep it from stalling but it did run just fine with the battery out of the car. I agree not recommended, as far as I know I did no damage and the car worked just fine after the new battery install.
07-21-2016, 11:22 AM
... but I do use a green **** on the positive post...
