Need help designing an automotive engine run detector.

[Barry Lennox]

Won't work on an electric or hybrid vehicle when running on battery.

Well, the original spec was not too clear on that point, but maybe it
works perfectly, ie, when the IC engine is not running it won't
record any runtime. ?

 

[[email protected]]

I thought about the cigarette lighter circuit, too. Then I thought
about all the plastic I'd have to remove in my own car to get anywhere
near the cigarette lighter wiring. In many cars, that would be a
major undertaking.

Tom

The whole idea is to keep all connections under the engine
compartment. Installation time and complexity increases significantly
when you pass wiring from the engine compartment into the passenger
compartment through the fire wall. Most people won't do it. I
majority of people who attempt it do it wrong. It takes a mechanic
much more time and costs you more money. We sell another non-related
under hood product. Many major chains (Goodyear, Firestone, Canadian
Tire, others) will not carry our product due to concerns about passing
wires through the fire wall.

I'm not sure you can say in ALL instances that an ignition signal
would be easily accessable under hood. It seems like the obvious
solution but when you really dig into it, may not be....

 

[Tom2000]

The whole idea is to keep all connections under the engine
compartment....

Yeah, that was my point. With all the surgery I'd have to do in the
passenger compartment to get to the cigarette lighter wiring, the
requirement to do so would be a deal breaker for me. So the lighter
circuit is out of the question.

By the way... the Speed channel used to advertise a gizmo that
appeared to be an accelerometer-based performance monitor. I think it
was called a GTech Pro or something like that.

One of its advertised features was shift lights. That would imply
that their engineers had figured out some way of directly or
indirectly measuring engine RPM. Since its only connection was a
cigarette lighter plug, they must have picked up some sort of signal
from the DC feed. Maybe you could look it up and see if you can
figure out how they did it.

Another thought was your installation location. You mentioned that
you're installing your unit very close to the battery. Well, that
battery must be acting like a really great filter that's killing any
signals that might be of use to you. Maybe if you could move your
installation downstream a bit, you'd have enough inductance between
your power pickup point and the battery that you might have more
useful power line noise to work with.

Good luck!

Tom

 

[Gary Tait]

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.

Older Ford alternators also had an AC output to drive the electric choke,
on carburated engines.

 

[Rich Grise]

Excuse my ignorance. What is a standby Genset?

"Genset" is a contraction for "generator set". A "standby" genset is
one that just sits there, not running, until there's a power failure,
at which point it starts itself, and a transfer switch switches from
the (now dead) mains to the generator. They're used a lot at places
that absolutely, positively have to have power, like hospitals.

Hope This Helps!
Rich

 

[[email protected]]

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

Try a scope on the battery and see what you find. you can get rev.
counters
that get the engine speed from the alternator noise in the cigeratte
lighter socket

-Lasse

 

[neon]

Put a keep alive oneshoot across the point as long as there is pulses there it means the engine is running. when it sops the oneshoot times out shuting down your box. you will need some start up logic because when it starts the battery dips into 8 or lower voltage depends on battery health and engine. the heat on the engine is something else depends where you install the box depends whether it will survive. engine stops in 120 degrees outside temperature is the worst case you need some air flow to cool it down. your stand by concerne is immaterial a normal battery will self discharge in 30 days with or without your box.
normal drain on battery while running is 5 7 amps which the generator will supply easy.

 

[Gary Tait]

They use an RPM detector and oil pressure detector, the former from the
generator output, the latter from the engine wiring harness.

 

[Rich Grise]

They use an RPM detector and oil pressure detector, the former from the
generator output, the latter from the engine wiring harness.

That's probably what OP was looking for, but he/she is a google-groupie,
so has probably abandoned the whole thread by now.

Thanks,
Rich

 

[[email protected]]

Try a scope on the battery and see what you find. you can get rev.
counters
that get the engine speed from the alternator noise in the cigeratte
lighter socket

-Lasse- Hide quoted text -

- Show quoted text -

I've done this. The problem I see is signal levels and consistency
from one vehicle to another. For instance, in my vehicle a 300mV
pulse is generated every time a plug fires. The pulse is just over a
nanosecond wide. The noise floor from all kinds of other crud on the
power buss is about 50 to 100mV. Longer wire runs (away from the
battery) only increased signal level marginally.

The REAL kicker, and unltimate downfall to this line of
expreimentation, came when I turned the radio on. The crud generated
by the vehicles audio amplifiers FAR swamped any other signal I was
seeing before. Current drawn from the amps is modulated by the audio
signal. My proposed circuit could trigger off this. Not bad if you
assume everyone listens to their radio while the vehcile is running.
However, I've been tailgating at football games before and have left
the radio on "blairing" sportscasts for an hour at time with the
vehicles engine off. Or, I may run the radio with engine off while i
was my car. I would hate to have the proposed product running during
this time frame.

Ge0

 

[Rich Grise]

.

I've done this. The problem I see is signal levels and consistency
from one vehicle to another. For instance, in my vehicle a 300mV
pulse is generated every time a plug fires. The pulse is just over a
nanosecond wide. The noise floor from all kinds of other crud on the
power buss is about 50 to 100mV. Longer wire runs (away from the
battery) only increased signal level marginally.

Connect it to the oil pressure idiot light.

Good Luck!
Rich

 

[bearchow]

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

Generator auto starts use a connection to an oil pressure sensing
switch to detect engine running. You know, the switch that is closed
when oil pressure drops below 4 psi. I know this because I have
several auto start generators.

A lot of cars use only a gauge type sensor (but be careful, some
gauges, some Ford
and Dodge pickups come to mind, are fake lights where the sensor is a
switch but it closes with pressure, but you could still use that). So
if they only have an analog sensor you'd have to y off and add a
switch type sensor.

Jerry Steele

 

[krw]

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.

If you're going to all that trouble, why not just take the RPM
directly off the flywheel sensor? No need to worry about the battery
state or ratio between the crank and alternator pulleys.

 

[Jim Yanik]

If you're going to all that trouble, why not just take the RPM
directly off the flywheel sensor? No need to worry about the battery
state or ratio between the crank and alternator pulleys.

In the first place,WHY does anyone NEED an "engine run detector"?

doesn't the dashboard give any indication of that?
(besides your ears and seat-of-the-pants)

 

[Jim Thompson]

In the first place,WHY does anyone NEED an "engine run detector"?

doesn't the dashboard give any indication of that?
(besides your ears and seat-of-the-pants)

Remote start/warm-up ???

You know some places in the world get cold ;-)

...Jim Thompson