Need help designing an automotive engine run detector.

Hello all,

I am trying to develop a new type of aftermarket product that will connect to a vehicles battery. Ground return will be through the chassis. I desire no other electrical connections. This will help simplify installation for the typical consumer. Do you know many people who can't find their vehicles battery? Well, I'm sure you could name a few. But, the majority of us can. What I want to avoid is telling someone to splice into some signal within their vehicle. This can get difficult. The type and location of such signals will vary from one manufacture to another. Who knows, it may not exist at all in some vehicles...

Oh yeah, one more thing. This product will be mounted in the engine compartment so any electronics specified will need to be available in extended temperature ranges.

When activated this product will draw about 5 amp. I'm trying to devise a way to allow activation of this product only while the engine is running (for obvious reasons). Therefore the product will need to sense engine running. If this criteria is met, it will be allowed to switch in its load. It will also need to detect when the engine has stopped. At this point it will disconnect its load and go into a low power mode. It will sit powerd up indefinitely in low power mode. Therefore, whatever sensing scheme we come up with will need to draw minimal current. Preferably in the neighborhood of 500uA or below. I don't want to drain someones battery!

I have already tried electrical system voltage sensing with no success. One would think that when a vehicle is at rest the battery would sit at approximately 12.6VDC. When the engine is running, system voltage climbs up to charging levels (typically 13.0VDC or greater). However, what I find is that system charging voltages range all over the map from one vehicle manufacture to another. For instance, one vehicle manufacture in the USA typically charges at

14.00VDC. However, they also have a mode that will drop charging voltage down to approximately 10.8VDC in cold weather. Another US manufacture charges at 13.2VDC and also has its own version of low charging voltage mode. Some European vehicles charge at 12.8VDC. Then there is the inconsistancy in rest voltage of a vehicles battery. A fellow co-worker has a brand new vehicle who's battery rests above 13VDC! As you can see, this is all over the map. Where would I set a comparator to allow activation of my circuit?

This got me thinking about alternate options. One thing I do know is that the raw power feed on a vehicle is REAL noisy when the engine is running. Is there a way I can use this to my advantage? Essentailly what i would need is a noise detector. At rest the VBAT power buss is quite. While the engine runs there is all kinds of crud superimposed on it. One interesting nibblet is the pulse generated on the power buss whenever a cylinder fires. Could I detect and latch on in the presence of ignition pulses? A potential problem... The shape and amplitude of these pulses varies from vehicle to vehicle. In one vehicle we tested, pulses were about 600mV high. The highest peak was about 2uS wide. The period between pulses was 50mS with engine at idle. In another vehicle, the pulse was approximatley 1V in amplitude but only a few nanoseconds wide! The period between pulses was about

25mS with engine at idle.

Can you think of a highly reliable way to detect engine noise, or better yet engine running, through sensing of the vehicles battery feed? Something that perhaps would throw a logic signal high in the presence of engine noise and then bring it low when the engine is shut off? This circuit would need to reject random EMI coming from other sources than the vehicle. I don't want someones ipod setting off my product while the car is parked in an airport long term parking lot!

Any help you can offer would be greatly appreciated.

Ge0

Reply to
Gerbermultit00l
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Somewhat confusing on the first reading, but if it's a petrol engine, you could make a capactive sensor around the spark plug lead, that could possibly trigger a monostable/ microprocessor to come out of sleep mode, for diesel, a guess, a current transformer across the fuel injector cable

Martin

Reply to
Martin Griffith

What, do you think I'm a little wordy :)?

I've learned from experience that I need to lay most of my groundwork up front. That way I'm not spending days answering questions. However, there is a fine balance between not enough content, and too much content. I haven't mastered that one yet :).

If I were to run an external sensor, or pickup wire as you suggested, my options would open up considerably. However, in this instance, I'm trying to work out something using only the power and ground feed coming into my product. My intent was to constantly monitor for noise vs. a clean DC signal. This is under the assumption that the DC voltage buss in a vehicle gets real noisy once the engine has started, and is nice and clean when the engine is not running.

Ge0

Reply to
Gerbermultit00l

Yes, a small table, may have been simpler

agreed

yep

What you seem to have proved is that the variables mentioned are extremely variable, I would not trust them. You could however use a motion sensor, to see if the vehicle is moving, say a magnet on a string and a reed relay.

Martin

Reply to
Martin Griffith

Your observations on charging are off base... but...

Use a microphone and *listen* for a running engine.

I'd monitor battery voltage, that will always tell you when the battery is charging, and it is safe to draw a load from it.

Another alternative is an indcutive pickup fastened to the alternator.

Reply to
PeterD

Or a thermocouple on the exhaust downpipe.

Reply to
Jim Stewart

Jim Stewart wrote in news:XOOdnaLh186WXZfanZ2dnUVZ snipped-for-privacy@omsoft.com:

That will tell you its running for an hour after it is off.

Just pick the signal off the distributor (i.e. tachometer signal).

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Reply to
me

Can you AC couple the alternator ripple through a capacitor, rectify, filter, then compare to a reference with a low power comparator?

Reply to
Glen Walpert

If you happen to have a GM alternator where they bring out the "neutral" pin, there's a nice BIG ripple there.

This output is interesting, because its duty cycle and DC offset can pin-point faults in the alternator.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Batteries have a temperature coefficient. Account for it. Also Google for automotive load dump and be prepared to take on some 80V spikes.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

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void _-void-_ in the obvious place

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Reply to
Boris Mohar

snipped-for-privacy@gmail.com hath wroth:

Bad idea. You're bypassing the entire fuse and breaker protection mechanisms in the vehicle. You would need to attach a fuse directly to the positive terminal of the battery, a non-trivial exercise. You're worried about the GUM (great unwashed masses) doing a proper install, yet you don't seem to be worried about the same person is going to get a wrench between the positive terminal and ground, with the resultant smoke, fire, burns, and litigation.

Ground return through the chassis is possible, but be advised that many vehicle bodies are now mostly plastic and fiberglass. Finding a suitable place to handle your 5A of continuous load may be a challenge.

Yep. That's the worst case scenario for electronics. Roughly -40C to

+105C. Don't forget about water proofing and high voltage spikes on the power lines.
75 watts? Where are you going to empty out the heat?

Ignition switch. If that's offensive, try the cancer stick igniter, which only has power when the engine is running or the ACC switch is on.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Reply to
Jeff Liebermann

The High Tech Way... Ever use voice recognition software?.. Last time I used that, I had to talk for 30 minutes to train it to my voice. Similarly, a computer (uC, DSP) may need to be trained to identify the noise off the battery when the engine is running. Your gizmo may need a training mode.

The Low Tech Way Hall effect sensor (current clamp) on ignition coil primary wire..

D from BC

Reply to
D from BC

Nope. In fact, it's refreshing to see such a comprehensive problem statement.

The typical statement reads something like "I'm trying to fix a system that runs all the automation in a factory, but I only read 2.3 volts. Should I change R17?"

Tom

Reply to
Tom2000

Further on the above... you also presented some good real-world information on charging systems that was new to me, and I appreciate it.

Now, on to your problem. I'm thinking that anyone who has the skills and confidence to find some clear sheet metal in the engine compartment for a mounting location, drill the mounting holes, and install the battery cable taps could find the LV ignition wire that would be used as a goof-proof signal to turn your unit on and off.

However, I can appreciate your desire for the simplest installation possible, so I'll add one more idea to the collection. How about little a piezo vibration sensor that the installer would attach to a convenient mounting point on the engine assembly? Valve cover? Wiring loom mounting bracket? Something like that.

Good luck with your endeavour.

Tom

Reply to
Tom2000

On a sunny day (Mon, 08 Oct 2007 13:03:43 -0700) it happened snipped-for-privacy@gmail.com wrote in :

No electical connections? Forget it. Engine sensing I have seen done by taking ignition coil primary, and using that impulse to discharge a capacitor with a transistor. Something like this was in my car that ran on LPG (liquid propane), it closed the valves if engine stoppped:

+12 | R1 from ign. |----------------R --- 0V if engine runs, else 12V coil prim. c |

- R -- C ---b NPN | | e C1 R | | | | | /// /// ///

I know this, because I had to fix it.... Solder joint (can blow you up too). Ooops, homeland security, ban all LPG cars.... LOL ;-)

Reply to
Jan Panteltje

snip

A microphone and detect acoustic noise. I'm aware of one "engine detector" in a product that uses this.

Barry

Reply to
Barry Lennox

Many GM alternators also bring out one phase as well. Frequently used to drive tachometers for example, and to provide a low power AC voltage.

Reply to
PeterD

At first I thought your question was silly and easy but in 2nd thought I see it's more subtle than that. We'll need to 1st define what "engine run" is defined by, off hand I'd say a Power Stroke Combustion, PSC. If so, what's a cheap easy rugged way of confirming PSC? And then do we use one or all cylinders?

I know how to do it, but it ain't cheap. Ken

Reply to
Ken S. Tucker

I did once play with the thought of making an RPM indicator / shift light based on the alternator whine always present on the battery DC. I never built it, but should not be too difficult with some adaptive filtering and a simple cpu. (and some calibrating obviously)

No matter how low the Ri of the battery, the rectified pulses from the alternator are measurable. Car radio manufacturers spend a lot of engineering to get this unwanted sound out.

If only the *presence* of the characteristic whine needs to be detected...., for added securety corellate frequency with DC - delta...hmm.

--
 - René
Reply to
René

How do they do it in standby gensets? They auto-start; there must be some way to detect "engine running" so it knows when to release the "start" button, right?

Good Luck! Rich

Reply to
Rich Grise

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