Low Oil Presure Buzzer

[trularin]

Gary, think about that for a moment. 15 Years isn't that long ago, Are you sure it wasn't 25 years ago? That might have impressed your neighbor. Just a bit of humor.

Wayne, you might want to do a little experiment with the alternator as you could get a loud buzzer for oil and charging failures if you work it right. You do not want it buzzing if you are at low idle.

[patrickt]

Originally Posted by trularin

Wayne, you might want to do a little experiment with the alternator as you could get a loud buzzer for oil and charging failures if you work it right. You do not want it buzzing if you are at low idle.

That $30 3-second 12v relay is starting to look pretty good.

[Wbulk]

Gary, thanks for the update.

Patrickt, you may be right in the end, but I want to pursue this avenue for now. When I read that Susuki patent I realized it really solves a lot of the problems. This may have to wait for awhile as I am still early in my build. Just trying to think ahead.
I would think Cobra owners would want a buzzer as a warning for low oil pressure. A lot of boats and all planes have them because peoples lives are on the line. If an owner ruins an old rare engine and the wife finds out, I would suppose their life may be on the line to. Thanks.
Wayne

[patrickt]

Originally Posted by Wbulk

I would think Cobra owners would want a buzzer as a warning for low oil pressure.

Wayne, to be honest with you, the only thing that would really save me would be an AccuSump (which I don't have) plus buzzer and light. I look at my gauges from time to time while I'm driving, but if all of a sudden I lost oil pressure (maybe some sort of pump failure) I would not see it on the gauge, and I don't think I would hear a buzzer over my pipes -- and if I did, I couldn't think fast enough to do something to save my engine anyway. I know me; if I heard that buzzer go off I would first think "Now what the hell is that? Oh yeah, it's my oil pressure buzzer -- WTF? My oil pressure gauge says zero! I better pull off." By that time my brain connected with my foot and fingers I will have probaby fried my engine.

[RedBarchetta]

Originally Posted by patrickt

I know me; if I heard that buzzer go off I would first think "Now what the hell is that? Oh yeah, it's my oil pressure buzzer -- WTF? My oil pressure gauge says zero! I better pull off." By that time my brain connected with my foot and fingers I will have probaby fried my engine.

The same principle holds true with a radar detector. Half the time I hear an X or K band (very common and usually caused by automatic door openers at shopping centers), I typically find myself looking at the display before thinking about braking. KA band on the highway (CHP)? QUICK BRAKES or it's too late...you have to instinctively react or you're toast. Same holds true with any audible device to warn you about low oil pressure. But I suppose something is better than nothing.

-Dean

[Wbulk]

Good points gentlemen. It really is all about time. I believe the more notice you have the more time to react, which increases the odds of less damage done. I ran a shop rears ago and an employee failed to refill an almost new Crown Vic with oil. He drove it about 1 1/2 miles and burnt up the engine. He never saw the red light on the dash until the engine was making noise.
For me it's about knowing sooner than later. Is the damage just to the rod bearings or is there a rod through the block. The buzzer I have is pretty loud and annoying.
Wayne

[patrickt]

Originally Posted by RedBarchetta

...you have to instinctively react or you're toast.

There are only a few things that I do well instinctively... and reacting to a low pressure oil buzzer ain't one of them.

[Wbulk]

I am wiring my car now so I just wanted to report what I decided. Gas64 (Gary) had a really good idea with hooking the buzzer to the "I" terminal on the voltage regulator but I believe there would be times the buzzer would sound for a just a second or two until oil pressure built up.
I decided to go with a device called a "delay on make timer" by Amperite. You can adjust the time delay from .1-30 seconds and it will flow 2 amps. This will allow me to start the car and give enough time to build oil pressure before the buzzer sounds. Then pressure is built and the oil pressure switch opens (no ground no buzzer). When driving if I lose oil pressure the buzzer will sound after a few seconds. I will then add a switch under the dask to shut the buzzer off if I am working on the car with key on.

[Gunner]

There's no need for an expensive delay relay or anything as complex as a timer circuit. There is a much simpler way to add a delay to a buzzer (or light), needing only a handful of parts costing a few dollars. It would be about the size and shape of an inline fuse holder. If you're not already committed to one of the above solutions, I can post a diagram.

[RedBarchetta]

Originally Posted by Wbulk

When driving if I lose oil pressure the buzzer will sound after a few seconds.

Then what's the point? A few seconds is enough to say sayonara to your bearings. If it's instant-on then it might help you when cornering and oil slosh causes the issue. But any delay, IMHO, defeats the purpose of having a warning system.

-Dean

[Gunner]

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.

[Wbulk]

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

[Gunner]

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.

[Wbulk]

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

[Gunner]

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."