# Vacuum switch.



## poprock (Apr 29, 2010)

bump


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## z_power (Dec 17, 2011)

Inspired by cts_casemod's solution I used generic GM 1 bar MAP sensor with some simple electronics (5V stabilizer, LM211 voltage comparator and N-channel MOSFET) to control VW/Audi pump. It's not been tested in real driving conditions yet because car is not finished; works OK when testing on jackstands. Actually there're two circuits in one box, second one is controlling warning lamp in dash.
Cost of elements was ~$20 including sealed enclosure and used MAP from junkyard. I'm not very talented in electronics so it was nice learning project


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## poprock (Apr 29, 2010)

z_power said:


> Inspired by cts_casemod's solution I used generic GM 1 bar MAP sensor with some simple electronics (5V stabilizer, LM211 voltage comparator and N-channel MOSFET) to control VW/Audi pump. It's not been tested in real driving conditions yet because car is not finished; works OK when testing on jackstands. Actually there're two circuits in one box, second one is controlling warning lamp in dash.
> Cost of elements was ~$20 including sealed enclosure and used MAP from junkyard. I'm not very talented in electronics so it was nice learning project


Thank you for your reply. In Oz we have a saying: " tall dog, short tree ". In other words, what you have said is far beyond my level of skills and has gone straight over my head. Being a mechanic with minimal electrical skills I was thinking in terms of a low vacuum warning switch from the reservoir tank of a Toyota Dyna or similar, which normally activates the low vacuum warning buzzer, hooked into a reservoir tank to activate the relay to the vacuum pump.


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## dedlast (Aug 17, 2013)

poprock1 said:


> Thank you for your reply. In Oz we have a saying: " tall dog, short tree ". In other words, what you have said is far beyond my level of skills and has gone straight over my head. Being a mechanic with minimal electrical skills I was thinking in terms of a low vacuum warning switch from the reservoir tank of a Toyota Dyna or similar, which normally activates the low vacuum warning buzzer, hooked into a reservoir tank to activate the relay to the vacuum pump.


I don't know the specs on the warning switch you are looking at, but it sounds like it could work. I think the thing to be concerned with is if the alert point is too low for what you need for safe braking. I wonder if there is any way to adjust that set point.

Bill


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## poprock (Apr 29, 2010)

I see your point. The only way to use a non-adjustable switch would be to use a matching switch & reservoir. I would think that a smaller reservoir would give a false signal. But then again I suppose it is the reverse of oil pressure : the vacuum should read the same regardless of volume and as the Daihatsu Sirion already has a sizable booster it may work. The only warning given in older cars was a harder pedal.


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## Duncan (Dec 8, 2008)

Hi poprock

Here (NZ) I would need a vacuum switch for the pump and another to warn if vacuum was not available

So I just went unboosted - is that an option for you?
Increase the pedal leverage?
Or just push harder?

Brake boost is a recent thing - in the old days only very big heavy cars had boosters


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## poprock (Apr 29, 2010)

As the Sirion is a 98 model this clause applies: RMS NSW. Vehicle Safety Compliance Certification Scheme 19/11/2012 p19 :-" if the original vehicle was fitted with air brakes,vacuum brakes or p/steer an alternative source must be fitted. The power and capacity of the new source must be of sufficient capacity to provide efficient functioning of the system and meet all the legal capacity requirements " " Vacuum assisted braking systems should be provided with audible or visual low vacuum warning devices ". Yes, life was simpler when I bought my 1949 lowlite Morris Minor in 1962


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## BrownBageV (Nov 10, 2011)

I am using these. A bit cheaper, but adjustable, new, 6 psi hysteresis, NC and NO in same switch, and small. $28.
I used one as the switch and one to wire into the oil pressure gauge (with a resistor).
http://www.viot.us/otherp.php?other=VParts&model=VS


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## dtbaker (Jan 5, 2008)

on the Miata I used a little pressure transducer/switch, SSR, and no res.... works GREAT and is way smaller and lighter than old square D mechanical switch. the pressure transducer and SSR can be found on eBay if you search the electronics section.... the Thomas vac pump pulls about 7 amps at 12v when under load so you need a pretty hefty SSR. You have to use an SSR rather than a cheap 12v Relay because the pressure transducer sends a small signal....

ssr - crydom d1d12, about $22 on ebay
transducer - SMC zse30 about $30-$50 on ebay
diode - in1201a

http://www.envirokarma.org/ev2_mx5e/gallery/121023_vac_done.htm


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## dtbaker (Jan 5, 2008)

BrownBageV said:


> I am using these. A bit cheaper, but adjustable, new, 6 psi hysteresis, NC and NO in same switch, and small. $28.
> I used one as the switch and one to wire into the oil pressure gauge (with a resistor).
> http://www.viot.us/otherp.php?other=VParts&model=VS



wow, nice little combo unit. no readout, but semi-adjustible is nice. I had to 'de-rate' the vacuum level the pump was trying to reach because at my altitude (7000'ft) the Thomas/Gast can't pull down as far as sea level. I de-rated until it runs 5 or so seconds to recover from a full pedal stroke


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## dtbaker (Jan 5, 2008)

poprock1 said:


> " Vacuum assisted braking systems should be provided with audible or visual low vacuum warning devices ".



I think you could sell them that the 'audible' is when you CAN'T hear the pump.


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## poprock (Apr 29, 2010)

The preamble to the regulations states:"must" = compulsory. "Should" = recommended.but not compulsory. "may"= up to you. As the donor car does not have that feature when standard I would assume it comes under the "up to you area


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