1983 Porsche 911 SC Targa

Wednesday, February 1, 2012


The vacuum kit I ordered for the car arrived today.

Most cars on the road have power assisted brakes. When you press the brake pedal, a brake booster increases the pressure in the brake lines in proportion to the force applied at the brake pedal. The brake booster operates on vacuum, which is available from the intake manifold on internal combustion engines. On an electric car, the vacuum must come from another source – a vacuum pump. On some electric cars, the vacuum pump can be the noisiest part of the car. I found a pump kit that has a reputation for quiet operation: VBS-EV-12 . The pump operates from the car's 12 Volt system.  The exhaust of the pump is coupled to an oil filled muffler. This cuts down emitted noise. The pump will be installed with a rubber isolation mount, to keep vibration from transmitting through the structure of the car. If pump noise still proves offensive, then the final contingency is to mount the pump in an acoustic enclosure.

When the vacuum pump is switched on, the pressure in the brake booster drops. Once the proper pressure is achieved, the pressure switch will open and turn the vacuum pump off. Provided there are no leaks, the vacuum level can be passively maintained until the brakes are operated. The check valve prevents the vacuum from leaking through the unpowered pump. After a few cycles of pressing the brake pedal, the pressure will rise, and the vacuum pump will switch on. The purpose of the buffer tank is to store vacuum, and increase the number of times the brakes can be operated before the vacuum pump turns on again.

The electrical circuit will only turn the pump on when the pressure switch measures poor vacuum, and when the ignition switch is in the run position. The main relay is rated for 40 amps. The reason for the second relay is not clear to me. The only thing that comes to mind is that the coil of the main relay must draw a fair bit of current, and the second relay keeps the current drawn from the ignition switch reasonable.


  1. Thanks for the sharing excellent information......
    Mufflers Toowoomba

  2. Great little device, you got the van style pump, which runs faster, thus the high amp rating of something like 28A at 12V with load.
    There is also a piston style version, runs on the same 12V but at 8A, however it runs slower at 51L/min but noise level is lower.
    These are designed in Taiwan where I am from.

  3. Thanks for sharing.

    It draws a lot of current. Is there a way to limit the current flow to the pump?

    1. The pump will only be running when the brakes are used. Sizing a large reservoir tank will reduce the number of pump cycles.

      As Traveleg above mentions, there is a piston pump from the same mannufacturer that only draws 8 amps. I'm not sure about availability. The VBS-EV-12 is very common for electric car conversions. Here is a link a website with details on the lower draw pump: http://www.yutai.tw/English/vpdp.html

      Another option is the 24 Volt version of the pump. At higher voltage, the current is lower. But, 12 Volts is more common on cars.

    2. Hi Joey,

      Thanks for the reply. Yes I agree with you, VBS-EV-12 is more commom and I am also using it. I am afraid that the starter lead acid battery won't last a long time with this pump.

      What did you used for the 12v source?

      I was thinking about applying a DC/DC converter to the battery with +/- 13,8v continuous wile driving.

    3. I haven't put together the 12 volt system yet. I'm thinking of 4 headway cells (15 Ah 40152S) in series.


      I will do a load analysis, and if more capacity is needed I can add additional cells in parallel. I really want a DC-DC converter from Evnetics, the same company that makes my controller, but it is still under development, so I might get a chennic and ungrade later.


      The chennic needs an external diode and inductor to prevent voltage ripple from the controller from destroying the DC-DC converter input caps.

  4. where did you get the pump kit
    am looking at adding one to my car!

    1. I got it from a private party, listed for sale on a forum. The next generation is supposed to be much quieter. I would get if from here (I've purchased other gear from this site in the past): http://evolveelectrics.com/electric-braking-kit/electric-braking-kit/