3 cylinder tach

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Date

05-11-2008

clare at snyder dot ontario do

clare at snyder dot ontario do

Posted by jw on May 12, 2008, 12:49 pm

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> "Karl Townsend"
>
>
>

> > I'm looking for a tach. for my 3 cylinder ford
> > tractor. looking for digital as I need to know
> > whether the engine is running 1200 or 1300
> > rpm. The dial gauges that go to 10,000 rpm
> > just don't have the resolution I need.

> > They don't seem to make a tach for three
> > cylinder engines. here's the best page of
> > digital tachs. I've found:
> >http://tinyurl.com/4lg6ru

> > Is there an easy device to add to a tach set
> > for six cylinders to actually read for a
> > three? Some other idea?

> > Karl

>
> There are a bunch of units out there that use
> sources other than the ignition for tach
> input. Does the tractor have an alternator?
> Alternator tachs are common. Lots
> of engines use a hall effect transducer reading
> a magnet in the flywheel. I've even seen
> one setup that used a proximity sensor reading
> the fins on the generator fan.
>
> What you are looking for seems to be more akin
> to the readout on a stationary power unit.
>
> Give the folks as Isspro in Portland OR a
> call----(888) 447-7776. They are who I've
> used for mobile equipment instrumentation for
> years.
>
> Bill

OK, that brings up a question. How does an alternator tach work? Or
I guess more importantly, how does it know the engine rpm based on the
alternator speed? If I have different pulley ratios than the
calibration for the tach won't it be off? I can easily follow that it
is picking up on the frequency of the AC in the alternator, but never
figured out how it "knew" the correlation to engine speed.

Inquiring minds would like to know...

JW

Posted by BillM on May 12, 2008, 9:24 pm

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>
> OK, that brings up a question. How does an
> alternator tach work? Or
> I guess more importantly, how does it know the
> engine rpm based on the
> alternator speed? If I have different pulley
> ratios than the
> calibration for the tach won't it be off? I
> can easily follow that it
> is picking up on the frequency of the AC in
> the alternator, but never
> figured out how it "knew" the correlation to
> engine speed.
>
> Inquiring minds would like to know...
>
> JW

On the back of the alternator tachs I've used
there is a hole under a plastic cover.
Inside the hole is a row of dip switches. You
figure out the pulley sizes, number of lobes
on the alternator rotor, square root of pi and
the phase of the moon. Plug it all into
a formula and determine the proper dip switch
settings. Well--maybe not all
THAT complicated, can't be too bad if I can
figure it out!

Bill

Posted by jw on May 13, 2008, 10:46 am

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>
>
>
>
>
>

> > OK, that brings up a question. How does an
> > alternator tach work? Or
> > I guess more importantly, how does it know the
> > engine rpm based on the
> > alternator speed? If I have different pulley
> > ratios than the
> > calibration for the tach won't it be off? I
> > can easily follow that it
> > is picking up on the frequency of the AC in
> > the alternator, but never
> > figured out how it "knew" the correlation to
> > engine speed.

> > Inquiring minds would like to know...

> > JW

>
> On the back of the alternator tachs I've used
> there is a hole under a plastic cover.
> Inside the hole is a row of dip switches. You
> figure out the pulley sizes, number of lobes
> on the alternator rotor, square root of pi and
> the phase of the moon. Plug it all into
> a formula and determine the proper dip switch
> settings. Well--maybe not all
> THAT complicated, can't be too bad if I can
> figure it out!
>
> Bill

Makes sense. I will have to check the next time I have one out. I
have several running around, but never took the time to figure that
out. They always seemed "right" so I just left them alone.

JW

Posted by on May 12, 2008, 10:28 pm

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wrote:

>> "Karl Townsend"
>>
>>
>>

>> > I'm looking for a tach. for my 3 cylinder ford
>> > tractor. looking for digital as I need to know
>> > whether the engine is running 1200 or 1300
>> > rpm. The dial gauges that go to 10,000 rpm
>> > just don't have the resolution I need.

>> > They don't seem to make a tach for three
>> > cylinder engines. here's the best page of
>> > digital tachs. I've found:
>> >http://tinyurl.com/4lg6ru

>> > Is there an easy device to add to a tach set
>> > for six cylinders to actually read for a
>> > three? Some other idea?

>> > Karl

>>
>> There are a bunch of units out there that use
>> sources other than the ignition for tach
>> input. Does the tractor have an alternator?
>> Alternator tachs are common. Lots
>> of engines use a hall effect transducer reading
>> a magnet in the flywheel. I've even seen
>> one setup that used a proximity sensor reading
>> the fins on the generator fan.
>>
>> What you are looking for seems to be more akin
>> to the readout on a stationary power unit.
>>
>> Give the folks as Isspro in Portland OR a
>> call----(888) 447-7776. They are who I've
>> used for mobile equipment instrumentation for
>> years.
>>
>> Bill

>
>OK, that brings up a question. How does an alternator tach work? Or
>I guess more importantly, how does it know the engine rpm based on the
>alternator speed? If I have different pulley ratios than the
>calibration for the tach won't it be off? I can easily follow that it
>is picking up on the frequency of the AC in the alternator, but never
>figured out how it "knew" the correlation to engine speed.
>
>Inquiring minds would like to know...
>
>JW

Simple. You tell it. There is a calculation/table and dip switches on
most.
** Posted from http://www.teranews.com **

Posted by Pete C. on May 11, 2008, 10:46 pm

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Karl Townsend wrote:

>
> I'm looking for a tach. for my 3 cylinder ford tractor. looking for digital
> as I need to know whether the engine is running 1200 or 1300 rpm. The dial
> gauges that go to 10,000 rpm just don't have the resolution I need.
>
> They don't seem to make a tach for three cylinder engines. here's the best
> page of digital tachs. I've found: http://tinyurl.com/4lg6ru
>
> Is there an easy device to add to a tach set for six cylinders to actually
> read for a three? Some other idea?
>
> Karl
>

I'm in a similar boat with the 3cyl diesel tractor I just got (used).
Looking at the various commercial offerings I've seen a few that read
off the A/C from the alternator, and another that uses a hall effect
sensor and a magnet you epoxy to something rotating. I'm not real happy
with the prices on them however and am considering just building my own
unit using a hall effect sensor.

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