How do I use a switch without current running through it?
All switching circuits will require some current flowing through the switch. It can, however, be kept small so that a miniature switch can control a larger switch rated to connect and disconnect the load.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Simple relay circuits.

Figure 1a shows a simple 12 V relay switching the load. Your switch only has to power the relay coil.

Figure 1b shows how to use a relay to switch multiple power rails simultaneously. In this layout the control circuit is completely isolated from the load power.

Choose the relay coil voltage to suit your control circuit and check that your switch can safely handle the coil current. Select the relay contacts to suit your load voltage and current and make sure that they are DC rated if you are switching DC. Car relays may suit your application as these are common, cheap and switch high current loads (10 A for headlights, for example).