Vac switch? I want to turn stuff on.

[TERRA Operative]

Just looking for an easy way to switch a relay at between 8" and 0" vacuum and keep it on through to positive pressure. Any ideas? Googling only seems to reveal industrial switchgear and the like........

[Duk]

Do you have a MAP sensor that you can get a voltage signal from?

[TERRA Operative]

On my engine yea, but I'm looking for something cheap that I can use on any car.

[thechuckster]

what ECU do you intent running? anything half decent will have a programmable output (e.g. when rpm>0 and MAP>80kpa, port X earths).

[TERRA Operative]

It's for a stand alone application. The sensor just has to switch on a relay as the manifold pressure rises above about 8" to 0" of vac. Totally independent of anything else.

[Duk]

Something like this is what I'd use, but it's only applicable to engines that have a variable voltage MAP sensor http://autospeed.com.au/cms/A_110548/article.html

[TERRA Operative]

I could probably use that with a MAP sensor. It needs to work on AFM engines etc, so an independent MAP sensor is required.

I'll have a look into it.

[wilbo666]

Jaycar have a kit that looks to do what you want...

http://www.jaycar.com.au/productView.asp?ID=KC5377


But then again a conparator and a few resistors could do it too (and for cheaper)

LM311 = $1.95... http://www.jaycar.com.au/productView.asp?ID=ZL3311
Resistors / Pot = cheap




http://home.cogeco.ca/~rpaisley4/Comparators.html

I.e.



Cheers
Wilbo

[TERRA Operative]

That looks like it'll do what I want. I might experiment with that.

Thanks.

[wilbo666]

Another option is a "Hobbs Switch"

i.e.
http://www.atpturbo.com/mm5/merchant...de=ATP-BCS-003

http://content.honeywell.com/sensing.../catswitch.asp

Cheers
Wilbo

[thechuckster]

If you go down the Comparator route, you'll need a 5V+ Regulator to provide the 5V+ Ref segnal to the MAP sensor and the circuit Wilbo's listed.

[wilbo666]

If you go down the Comparator route, you'll need a 5V+ Regulator to provide the 5V+ Ref segnal to the MAP sensor and the circuit Wilbo's listed.

Could also acquire from +5V from the ECU... (i.e. TPS)

Cheers
Wilbo

[the_random_hero]

5V regulator can be made for a few bucks, no point in chopping into ECU loom.

[TERRA Operative]

Yea. This could be installed on carburettered cars, so a regulator is no big deal to add in.

Does anyone know of any good cheapish sources of MAP style sensors? Not the wrecker, as I can't guarantee supply (I'll be making a few of these things) and RS Components wants about $50 a pop for just the sensor module. The range only has to go to about 5psi, but it has to withstand at least psi.

[briney]

carburettored early magnas and later sigmas had an adjustable vacuum switch which turned on a light at low vacuum. it could be used to switch on a relay. they fit in your pocket at the wreckers