Engine On/Off Indication From Lead Acid Battery

I'm working on a system using a PIC24FJ256GB106. One task it will be doing
is monitoring the battery level of an industrial engine that charges one
12V or two 12V(24V) batteries with an alternator. These are typical
automotive batteries. The PIC also has to keep track of when the engine
goes from on to off or off to on. 

Is there any way I can get an engine on/off signal just from the level of
the lead acid batteries? Otherwise, I'll have to use another component (oil
pressure switch) to get engine operational status.

On Mon, 17 Aug 2009 19:10:26 -0500, "eeboarder"
<jmeyer@emittechnologies.com> wrote:

>I'm working on a system using a PIC24FJ256GB106. One task it will be doing
>is monitoring the battery level of an industrial engine that charges one
>12V or two 12V(24V) batteries with an alternator. These are typical
>automotive batteries. The PIC also has to keep track of when the engine
>goes from on to off or off to on. 
>
>Is there any way I can get an engine on/off signal just from the level of
>the lead acid batteries? Otherwise, I'll have to use another component (oil
>pressure switch) to get engine operational status.
This is like the 5th time ypu have posted this.  

Pick one of the existing threads, and just use that one.  

The answers are NOT going to change!!!
-- 
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To reply by email, remove the extra stuff from the reply address.

On 2009-08-18, eeboarder <jmeyer@emittechnologies.com> wrote:

> I'm working on a system using a PIC24FJ256GB106.

Yea, we know.  We got it after the first 4 copies of the posting.

-- 
Grant Edwards                   grante             Yow! An INK-LING?  Sure --
                                  at               TAKE one!!  Did you BUY any
                               visi.com            COMMUNIST UNIFORMS??

eeboarder wrote:
> I'm working on a system using a PIC24FJ256GB106. One task it will be doing
> is monitoring the battery level of an industrial engine that charges one
> 12V or two 12V(24V) batteries with an alternator. These are typical
> automotive batteries. The PIC also has to keep track of when the engine
> goes from on to off or off to on. 
> 
> Is there any way I can get an engine on/off signal just from the level of
> the lead acid batteries? Otherwise, I'll have to use another component (oil
> pressure switch) to get engine operational status.

No.  You can't.  It won't work.  Bye...

In article <h6enpi$mo$3@news.eternal-september.org>, 
jstewart@jkmicro.com says...
> 
> eeboarder wrote:
> > I'm working on a system using a PIC24FJ256GB106. One task it will be doing
> > is monitoring the battery level of an industrial engine that charges one
> > 12V or two 12V(24V) batteries with an alternator. These are typical
> > automotive batteries. The PIC also has to keep track of when the engine
> > goes from on to off or off to on. 
> > 
> > Is there any way I can get an engine on/off signal just from the level of
> > the lead acid batteries? Otherwise, I'll have to use another component (oil
> > pressure switch) to get engine operational status.
> 
> No.  You can't.  It won't work.  Bye...

However you could monitor the rotation of the flywheel with an Hall 
effect sensor and that will give you a lot of information.

"Matt" <fleck2001@yahoo.co.uk> wrote in message 
news:MPG.24f531d7f04409639896de@news.eternal-september.org...
> In article <h6enpi$mo$3@news.eternal-september.org>,
> jstewart@jkmicro.com says...
>>
>> eeboarder wrote:
>> > I'm working on a system using a PIC24FJ256GB106. One task it will be 
>> > doing
>> > is monitoring the battery level of an industrial engine that charges 
>> > one
>> > 12V or two 12V(24V) batteries with an alternator. These are typical
>> > automotive batteries. The PIC also has to keep track of when the engine
>> > goes from on to off or off to on.
>> >
>> > Is there any way I can get an engine on/off signal just from the level 
>> > of
>> > the lead acid batteries? Otherwise, I'll have to use another component 
>> > (oil
>> > pressure switch) to get engine operational status.
>>
>> No.  You can't.  It won't work.  Bye...
>
> However you could monitor the rotation of the flywheel with an Hall
> effect sensor and that will give you a lot of information.


Surely if the batteries are being charged it can only be because the voltage 
applied exceeds their internal EMF?

What voltage do you see when the engine is on and off?

I would also imagine that the voltage would vary when the alternator is 
turning (possibly a more or less rectified sine wave).  You could even 
(tongue in cheek) extract a spectrum and work out the engine speed.

Take some measurements.

>"Matt" <fleck2001@yahoo.co.uk> wrote in message 
>news:MPG.24f531d7f04409639896de@news.eternal-september.org...
>> In article <h6enpi$mo$3@news.eternal-september.org>,
>> jstewart@jkmicro.com says...
>>>
>>> eeboarder wrote:
>>> > I'm working on a system using a PIC24FJ256GB106. One task it will be

>>> > doing
>>> > is monitoring the battery level of an industrial engine that charges

>>> > one
>>> > 12V or two 12V(24V) batteries with an alternator. These are typical
>>> > automotive batteries. The PIC also has to keep track of when the
engine
>>> > goes from on to off or off to on.
>>> >
>>> > Is there any way I can get an engine on/off signal just from the
level 
>>> > of
>>> > the lead acid batteries? Otherwise, I'll have to use another
component 
>>> > (oil
>>> > pressure switch) to get engine operational status.
>>>
>>> No.  You can't.  It won't work.  Bye...
>>
>> However you could monitor the rotation of the flywheel with an Hall
>> effect sensor and that will give you a lot of information.
>
>
>Surely if the batteries are being charged it can only be because the
voltage 
>applied exceeds their internal EMF?
>
>What voltage do you see when the engine is on and off?
>
>I would also imagine that the voltage would vary when the alternator is 
>turning (possibly a more or less rectified sine wave).  You could even 
>(tongue in cheek) extract a spectrum and work out the engine speed.
>
>Take some measurements.
>
>
>
>

I'm very sorry this was posted three times. I submitted the original post
last Monday, but they weren't posted until this Saturday. I thought I did
something wrong posted it again. 

It won't happen again.

Also, thank you all very much for your help. 

On Aug 24, 6:06=A0pm, "eeboarder" <jme...@emittechnologies.com> wrote:
> >"Matt" <fleck2...@yahoo.co.uk> wrote in message
> >news:MPG.24f531d7f04409639896de@news.eternal-september.org...
> >> In article <h6enpi$m...@news.eternal-september.org>,
> >> jstew...@jkmicro.com says...
>
> >>> eeboarder wrote:
> >>> > I'm working on a system using a PIC24FJ256GB106. One task it will b=
e
> >>> > doing
> >>> > is monitoring the battery level of an industrial engine that charge=
s
> >>> > one
> >>> > 12V or two 12V(24V) batteries with an alternator. These are typical
> >>> > automotive batteries. The PIC also has to keep track of when the
> engine
> >>> > goes from on to off or off to on.
>
> >>> > Is there any way I can get an engine on/off signal just from the
> level
> >>> > of
> >>> > the lead acid batteries? Otherwise, I'll have to use another
> component
> >>> > (oil
> >>> > pressure switch) to get engine operational status.
>
> >>> No. =A0You can't. =A0It won't work. =A0Bye...
>
> >> However you could monitor the rotation of the flywheel with an Hall
> >> effect sensor and that will give you a lot of information.
>
> >Surely if the batteries are being charged it can only be because the
> voltage
> >applied exceeds their internal EMF?
>
> >What voltage do you see when the engine is on and off?
>
> >I would also imagine that the voltage would vary when the alternator is
> >turning (possibly a more or less rectified sine wave). =A0You could even
> >(tongue in cheek) extract a spectrum and work out the engine speed.
>
> >Take some measurements.
>
> I'm very sorry this was posted three times. I submitted the original post
> last Monday, but they weren't posted until this Saturday. I thought I did
> something wrong posted it again.
>
> It won't happen again.
>
> Also, thank you all very much for your help.

I still think your best hope would be to detect current DIRECTION. The
2 problems is, A. Some vehicles at idle with headlights, heater fan
and other accessories on MAY not be charging the battery - so current
direction would give false indication of engine OFF.
B. There would still be 'noise' and , even with Germanium diodes, SOME
threshold issues to filter or hysterisis to work around.

But, in a general sense, current direction would be a binary indicator.

1 Lucky Texan wrote:

> A. Some vehicles at idle with headlights, heater fan and other
> accessories on MAY not be charging the battery - so current direction
> would give false indication of engine OFF.

Any remotely current car with a on-board electronics worth its salt will 
up the idle revolution frequency sufficiently to avoid that.  Very old 
ones would do it blindly if you switch on the lights, modern ones have 
considerably more sophisticated battery energy management.

But none of that bears much relevance to the actual question.   The 
answer to that is a solid "Don't do that!"  If you want to know if the 
main engine is running, acquire that signal at its source, not at some 
barely related point several massive disturbances away from it. 
Guessing what the voltage at a terminal shared by an alternator, a 
battery, and probably a several active loads might mean is just a 
nightmare waiting to haunt you.

On Aug 26, 8:02=A0am, Hans-Bernhard Br=F6ker <HBBroe...@t-online.de>
wrote:
> 1 Lucky Texan wrote:
> > A. Some vehicles at idle with headlights, heater fan and other
> > accessories on MAY not be charging the battery - so current direction
> > would give false indication of engine OFF.
>
> Any remotely current car with a on-board electronics worth its salt will
> up the idle revolution frequency sufficiently to avoid that. =A0Very old
> ones would do it blindly if you switch on the lights, modern ones have
> considerably more sophisticated battery energy management.
>
> But none of that bears much relevance to the actual question. =A0 The
> answer to that is a solid "Don't do that!" =A0If you want to know if the
> main engine is running, acquire that signal at its source, not at some
> barely related point several massive disturbances away from it.
> Guessing what the voltage at a terminal shared by an alternator, a
> battery, and probably a several active loads might mean is just a
> nightmare waiting to haunt you.

Yes and no. Sometimes allowing a simple retro-fit is worth the effort.
ie We have done battery-voltage decision based systems, for coarse
power saving
decisions - but we did not make mission-critical decisions. .

 The OP should measure  systems (MORE THAN ONE), and look for the DC
and AC (Audio) signatures at the battery.
 eg A properly advanced system could get Tacho info, from the charge
ripple frequency spectrum ;)

 Including temperature improves what it possible, as Lead Acid
batteries have
a clear tempco.
-jg