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FAO electricians. help me brainstorm a relay circut (Read 812 times)
Teribus
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FAO electricians. help me brainstorm a relay circut
23.09.11 at 14:34:24
 
Hey guys.

I hope someone can help me out here. The system i am thinking of applies to a bus but the principles are the same to a car

The system is an electric water pump which boosts water pressure to the demister matrix, which will only work when the demister motor is turned on. However, we dont want the pump to always run when the demister motor is on, what we have is a push-and-release switch which will make the pump start and it will keep running until the demister motor is turned off

I think that this circut is designed with normal four or five pin relays.

Can one of you clever electricians help me figure out how this was done?

On newer stuff it is all done through the computers but wanna try and figure out how it worked with good old fashioned relays etc

-T
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His: 2006 Ford Focus 1.8TDCi Ghia
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midnight oil
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Re: FAO electricians. help me brainstorm a relay circut
Reply #1 - 23.09.11 at 18:21:50
 
so basicly you want the water pump to come on when demister pump is switched on.
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Steve Parker
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Re: FAO electricians. help me brainstorm a relay circut
Reply #2 - 23.09.11 at 20:10:04
 
Here is a basic circuit using a couple of general car relays (or one 12V double pole relay, push switch and one diode.

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Teribus
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Re: FAO electricians. help me brainstorm a relay circut
Reply #3 - 24.09.11 at 19:25:50
 
Steve, thanks I'll try that.

midnight oil - it's not necessarily something I am ACTUALLY trying to set up. It is something that is already in place on some of the vehicles. The circuit must be similar to the circuit set up for the "bus stopping" lights inside the buses - ONLY when the door is closed, a single press of a STOP button inside the bus will ring a bell AND illuminate a lamp saying "bus stopping". The lamp then stays on until the entrance doors are opened.

We have vehicles already that have an electric water boost pump which can be activated when the demister blowers are on. The boost pump does not run all the time, it is only activated when the driver pushes a switch.

It would be an easy circuit if you had a rocker switch, but these have a starter-style switch that springs back once you release it. I've been on a training course last week and we were trying to figure out how these boost pumps were rigged up, but we all got stuck.

-T
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Re: FAO electricians. help me brainstorm a relay circut
Reply #4 - 25.09.11 at 02:40:18
 
Could you do it only using one relay, connecting the switched +ve coming from the relay to the positive coming in to it?

Connecting pins 85 and 87, and missing out the bottom relay  and diode shown in the pic above.  So your momentary switch triggers the relay then its own power out keeps it triggered.  Just realised you couldn't then switch it off.  I'll give it a bit more thought...
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