# Electric Vehicle Vacuum Pump Question



## madderscience (Jun 28, 2008)

The vacuum switch you are using lacks "hysteresis".

Basically what hysteresis means is that the level of vacuum for the switch to turn "on" is different that the level to turn "off". If they were at nearly the same level (like your switch, apparently) then you might find that the sensitivity of the switch is too high and the pump will do things like turn on and off very rapidly.

Did you use a switch that came with the pump, or a different one? was the pump designed for use in a car?

I have the SSBC vacuum pump and I initially used a different relay than the one that came with it. bad idea, as it turns out that the hysteresis function was built into the relay that came with it. The pump buzzed and did other annoying things when turning on and off until I figured that out.

Good Luck.


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## DONEAL (Sep 10, 2008)

>The pump runs for about 20 seconds and then shuts off when the vacuum switch is satisfied. <

This is about the length of time it takes mine to pump the vacuumed for the first time, I have a very slow leak, I think in the booster. Takes about four hours for it to leak down.

>The problem is that right after the pump shuts off, it switches on for about 3 more 1/2 second "pulses" until it finally stays quiet.<

No, I wouldn’t think this is normal, Mine don’t.

>Then, as soon as pressure is applied to the brake pedal the pump switches back on immediately for a few seconds.<

You should get more than one pedal press before the pump kicks back on. I get about 3 to 5 pedals before my pump kicks on.
I used a vacuum gauge to set the on and off cycles of my pump. The amount of times you use the pedal depends on the amount of vacuum and the size of the reservoir tank. Vacuum gauges are not expensive, I think mine was around $17.00 usd. The one I have is called a Gas Saver.


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## Zuglet (Oct 17, 2009)

Thank you to madderscience and DONEAL for sharing your experience on this.

I contacted Electro Automotive (my supplier for the pump and switch) and Mike Brown indicated that they no longer use that switch and sent me a new one right away.

I think that I will also permanently install a vacuum gauge under the hood so that I can monitor the vacuum level at a glance.

Thanks again for the prompt replies to my question.


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