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  #41 (permalink)  
Old 12-17-2009, 01:44 PM
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A sudden loss of oil pressure under high-power conditions is going to do damage no matter how fast a buzzer or driver reacts. It becomes a true idiot light: "You just blew your engine, idiot!"

A warning would be for the spectrum of lesser conditions where the indicator and the driver react fast enough to prevent damage. It's a "might as well" item.

A system that monitors RPMs and oil pressure and cuts the ignition in case pressure drops away while at speed would prevent damage - but only if the driveline wasn't forcing the engine to speed. It could also be fatally startling to the driver.
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  #42 (permalink)  
Old 12-17-2009, 02:39 PM
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Gunner, I would like to see what you have. The "delay on make relay" was about $30.00. I have been building engines since the 60s and have found when engines go they have damage in varying degrees depending on when they were shut down. It all comes down to sooner warning than later. Gee, there must be some reason planes and expensive boats have low oil pressure warning buzzers. No question during high rpms if you lose pressure there is not much you can do. It comes down to the odds of when it happens.
I think it has merit so I'm putting it in my car.
Wayne
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  #43 (permalink)  
Old 12-17-2009, 04:44 PM
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UPDATED - CORRECTIONS AND ADDITIONS

Okay, let me see if I can make this make sense. I've uploaded a schematic to my gallery:

Danger Danger Will Robinson: electronics ahead!



Any electronics store should have all these components - I have a salvage electronics store down the road that would have all this for about $2.00.

The key is the SCR, which is a sort of double transistor switch that stays off until a small voltage is applied to its gate terminal, when it "fires" and closes like a switch. It will stay closed, conducting electricity, until power is removed.

If you put this in line with a buzzer or lamp, the lamp will stay off until the sensor switch closes. Then the capacitor will slowly charge through the 2.2M resistor until it reaches the voltage to trigger the SCR's gate. The SCR closes and the buzzer or lamp goes off until you kill the power.

If you use an SCR in a TO-3 case (see illustration), you can build this as a "wireframe" circuit with no circuit board and put it in a small tube of some kind.

If the sensor switch connects to ground when it activates (as do most low-pressure switches) use circuit A - run switched 12 volt to the buzzer and put the circuit between the buzzer and ground. If the sensor connects to +12V when it activates, use circuit B - ground the buzzer and run +12V from the sensor to the circuit.

When the sensor closes, the circuit starts charging. If the sensor opens again before about 2 seconds, nothing will happen. Once it goes over the 2 second mark, the circuit will "fire" and the buzzer will sound or lamp will light. The buzzer/lamp will stay on until the sensor switch opens or until you kill switched +12V.

It's best to test it a few times before putting it in a tube or installing it. If the delay is too long, make the 2.2M resistor a little smaller - 1.8M, 1.5M, even 1.0M. If it's too short, increase the resistor in similar steps until you have about a 2 second delay or whatever suits you.

The good: it's cheap and works well. The bad: you do need a tiny bit of electronics assembly ability to build it right.

I've updated the diagram to show where the sensor switch goes in each circuit - the circuit will trigger when the sensor switch closes (typical automotive sensor behavior). I also corrected a small error - I suggest a TO-220 case, not a T)-3 - and added a small diagram showing how to build this circuit "flat" with no circuit board. Once built and tested, you can glue the circuit to a square of plastic and cover it with shrinkwrap, tape or a tube.
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Last edited by Gunner; 12-17-2009 at 06:09 PM.. Reason: Corrections and updated diagram.
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  #44 (permalink)  
Old 12-17-2009, 05:14 PM
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Great information. I am going to have to study this. Mine would be circiut A. I may not have that, "tiny bit of electronics assembly ability to build it right." First I better fully understand it. Thank you for the information.

Wayne
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  #45 (permalink)  
Old 12-17-2009, 05:18 PM
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I can 'splain more if you need it. Also thinking about the other alternative, suppressing the buzzer at startup while permitting an instant warning later. It can be done; just thinking about "simple and reliable."
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  #46 (permalink)  
Old 12-17-2009, 05:57 PM
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how about a cutoff for the ignition instead of the buzzer. use a delay to get the engine started, then if oil pressure goes below a set point it shuts the ignition off. probably good and bad points here.
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Old 12-17-2009, 06:54 PM
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Actually I was talking to Ken at Haywire the other day and he brought that up to. He talked about doing it with a simple relay. Like you say though just having the engine shut down also creates consequences. Then the issue would be do you really know it was shut down for lack of oil pressure or something else. How about shut the engine down and let the buzzer sound until the igniton is shut off?
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  #48 (permalink)  
Old 12-22-2009, 01:56 PM
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I have owned some high performance boats that have been equipped with a large light at eye level on the dash that will come on if you lose oil pressure. because of the noise in an open cockpit boat with 1-2 motors with open headers, there is no way you would hear a buzzer. I would think the same type of system would work well in a cobra, if you don't mind the look of the light on the dash.


Here is a link to the light. You would need a sending unit as well. I was only able to find fuel and water pressure sending units on their site, but I know they make one for oil pressure.

http://teaguecustommarine.com//store...oducts_id=2779

Last edited by SP01715; 12-22-2009 at 02:09 PM..
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  #49 (permalink)  
Old 12-22-2009, 06:18 PM
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Quote:
Originally Posted by vector1 View Post
how about a cutoff for the ignition instead of the buzzer. use a delay to get the engine started, then if oil pressure goes below a set point it shuts the ignition off. probably good and bad points here.
I tried a set up like that on my Formula Atlantic and it really worked, lost oil pressure in a high speed corner, it shut the engine off and I crashed into the berm. I figured the crash did more damage than I saved in engine repair cost
do to loss of oil pressure.
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  #50 (permalink)  
Old 12-22-2009, 07:19 PM
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Anything that suddenly changes the vehicle's driving characteristics is a bad idea, no matter how clever it might seem at first. I've never seen anything but strong negatives against ignition cutoffs, be they actuated by engine warnings, alarm systems, whatever.
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  #51 (permalink)  
Old 01-24-2012, 10:37 AM
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This was an old thread I started a few years back but I realized I never finished the solution on here for what I finally did.

System
The system allows the engine to start without the buzzer going off for a few seconds. If on start there is no pressure the buzzer will go off after a few seconds. The time delay can be changed for the buzzer going off at start by changing a resistor for a buck at Radio Shake.
If loss of oil pressure after start the buzzer goes off right away, and there is no delay.
The system also has a red loss of oil pressure light on the dash in addition to a regular gauge.
The buzzer can be turned off by a switch.

Components
One additional loss of pressure sender. Idiot light type that grounds with low or loss of pressure.
A delay timer, Amperite # 12D.2-20SST1A
A standard automotive relay.
A buzzer. The louder the better.
A red light for the dash.
A simple toggle switch

I started my engine last summer and the system worked really well. Yes the buzzer can be annoying, thatís why I added the switch to turn it off. I can supply a diagram if anyone is interested.

Wayne

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