Interesting. I've always put cutoff on the positive, though I don't really have a reason why, that's just what I've done.
Negative kinda makes sense though, any time I'm working on the electrical system I always pop off the negative cable, not the positive.
I'm not so good with electronics. If a motor could still keep running without being grounded (I assume it would die pretty quick after though, if it has electronic fuel pump?), could you push-start a car that's not grounded?
Nope. As long as the engine is running and the alternator is charging it will never shut off.
You have an older car or truck? If so, go start it up and take the battery cables off while it's running. I bet you it stays running until it runs out of fuel.
NHRA, NASCAR, ect all require it to be wired in to the posititive side for this reason.
All my heavy equipment the shut offs are on the negative side. That way when you run the volatage down you don’t run a bijillion Amps through the switch, instead you just burn the cables off at the starter.
fwiw cat makes a awesome keyed shutoff that holds up forever. I got like 40 of them in service and the only reason I had them fail is the keys rusting in them from the lack of use.
Mine are diesel, so they run without a battery regardless
That makes sense with the alternator, I guess the distributor doesn't need ground to make spark then? I know magneto distributors will spark on their own.
For my current project, I picked up an old porsche cutoff switch, where the handle to the switch comes off when it's shut off. I like it because it looks different than the standard Moroso style switches. The only problem though, is that when you turn it off, the handle/key literally just falls out. So you can't leave it in there if you want to.
Does the CAT key stay retained somehow when it's turned off? or do you have to remove it every time like this one?
Think of the alternator as the positive and the engine as the negative. Everything stays grounded because the positive has a path back via the engine, frame ect.
Cat key will not come out unless off.
In most forms of competitive motorsports the battery switch MUST be tied in to the positive side of the battery and alternator charging wire to meet the rules. As someone stated above, if its tied into the negative side, once the engine is running the battery switch won't do shit to turn off the electrical system. It is installed on the positive side so if there is ever a crash ect and fuel lines get ripped open the pumps and engine will not stay running when the switch it turned off. It's for saftey.
If all your looking to do is add one on to keep a battery from discharging, go on with your bad self and install it on the negative terminal.
I don't get this. Are you saying the rules require the positive battery disconnects and the charging wire disconnects from the positive side? (Meaning they must not be connected together) Otherwise, it will keep running. Is this some kind of double switch?
So I should use the cutoff on the Positive cable , run the output of the alternator back to the switch. I guess the switch should be in some type of container to prevent being shorted by random crap?
I haven't heard of a battery overheating in like, never.... Must be an aviation thing.
What a can of worms. Yes,some sanctioning groups require a pos. located cutoff. It seems a lot of folks say go with a neg. cutoff. I am going to do neg.cutoff at the battery for the simplicity. With luck I will be cutting power for non emergency reasons.
to be honest, that's the only real reason I run a cutoff switch (I don't race), to just turn off all the power when the vehicle is not in use.