07-01-2019, 01:49 AM
It depends a bit on what you want the switch to be used for. If to just isolate the battery when the car isn't used then close to the battery on either positive or negative will work. On my MGB I have a big red key kind on the positive lead mounted to the panel behind the drivers seat (the battery is behind that). Positive lead so I can have a thin, fused wire, to keep the clock and alarm powered. I never actually use the alarm though, instead I just take the big red key with me!
If it is more for safety as in to stop a running car will an ordinary cut off switch do it? Disconnecting the battery alone might not. It won't on an alternator car I think which is why in the US for racing they specify a battery cut off on the positive side but they use special switches with extra terminals that also cut off the alternator (or ignition?).
What happens on an A7 if you turn off the switch with the engine running? It would be like disconnecting a battery lead which I am sure they warn against doing. The generator will still generate voltage so won't the engine keep running? But now you don't have the battery there acting as a ballast so I imagine the voltage will shoot up and possibly damage things? I don't know how the cut off and regulator affect things?
I would always use a decent quality switch. When closed there is a lot of current passing through the contacts when starting using the starter motor and a cheaper one might not handle that reliably over time. Worst case would be the contacts weld together then when you turn off the switch it's not really off. I sometimes inadvertently check mine by forgetting to turn it on and wondering why the fuel pump/ignition aren't working.
Simon
If it is more for safety as in to stop a running car will an ordinary cut off switch do it? Disconnecting the battery alone might not. It won't on an alternator car I think which is why in the US for racing they specify a battery cut off on the positive side but they use special switches with extra terminals that also cut off the alternator (or ignition?).
What happens on an A7 if you turn off the switch with the engine running? It would be like disconnecting a battery lead which I am sure they warn against doing. The generator will still generate voltage so won't the engine keep running? But now you don't have the battery there acting as a ballast so I imagine the voltage will shoot up and possibly damage things? I don't know how the cut off and regulator affect things?
I would always use a decent quality switch. When closed there is a lot of current passing through the contacts when starting using the starter motor and a cheaper one might not handle that reliably over time. Worst case would be the contacts weld together then when you turn off the switch it's not really off. I sometimes inadvertently check mine by forgetting to turn it on and wondering why the fuel pump/ignition aren't working.
Simon