English: Vacuum pump control for an electric vehicle conversion. Image drawn and uploaded by User:Leonard G..

PDV version for printing at :Image:WPEVVacuumControl.pdf

Upper portion of drawing is wiring logic diagram. Lower part is a physical wiring guide. Relay shown is a common automotive relay, but note that some examples of this type of relay may have a different orientation of the mounting tab.

Colors used are for diagram purposes and may not correspond to colors used in vehicle.

This allows the turn-on and turn-off pump settings to be individually adjusted. By adjusting for a wide operating band, numerous short pump cycles are avoided. The third vacuum switch is an optional low vacuum warning that is connected to the vehicle's oil pressure warning light.

Theory of operation.

• At system start up assume no vacuum in the reservoir, all three vacuum switches are closed. Run power from a switch, keyswitch, or start-run latch relay is applied to the run circuit.
• Ignition power is applied to one side the low oil warning light (used for low vacuum), while the other side is grounded via VS3, so the light is iluminated
• Start switch applies power to the coil of relay Ry LL. The contact pulls in and applies power to the coil of vacuum pump power relay Ry VP. This power is also routed through the stop switch to latch Ry LL closed, even after the start switch opens.
• As vacuum increases the warning switch will open and the warning light goes off, then the start switch opens but Ry LL remains closed since its coil is powered by the latch circuit.
• When vacuum reaches the upper set point, the stop switch will open, breaking the latch circuit, Since the start switch is also open, Ry LL will open, removing power from Ry VP, which in turn opens, removing power from the pump.
• When vacuum falls to where the start switch closes, the cycle repeats. Note that the warning switch will not close after initial pump-down if the switch settings are correct.

The vacuum point settings may differ from one vehicle to another. The vacuum pump start point should be sufficient to assist the brakes in a hard stop. If the setting is too low a hard stop will require more than the usual pedal pressure.

Note that when starting from a cold start that it will take a moment to produce effective vacuum. It is a good idea to wait for the warning light to extinguish, ensuring sufficient brake boost vacuum for all normal operations.

Wire sizes. Battery power to Ry VP, pump power from this relay, the pump power ground should be AWG #12, with an appropriate fuse at the twelve volt service battery. Other wires are low current and may be AWG #16 or #18.