Listers,
There are basically two types of electric tachometer: current sense tachs, and
voltage sense tachs. The current sense tachs (which is the type used in the
stock Tiger) connects to the (+) side of the coil, through the ballast resistor.
Usually (as on the Tiger) there is a starting circuit which bypasses the ballast
resistor. Then the other side of the coil primary connects to the distributor
points. Since all the current used to drive the ignition is passed through the
sense loop on the tach, this gives a very positive 'firing' signal to the tach.
The tach counts up the pulse rate in some fashion, and the count is used to
drive the pointer around the dial.
A voltage sense tach reads the voltage spikes from the points (distributor) side
of the coil as the points open and close. In this case the coil (+) terminal
connects to the ballast which is connected directly to the ignition switch.
Again there will be a ballast bypass circuit hooked to the 'start' switch
position. The voltage sense tach can be used in amplified ignition systems (such
as MSD or other aftermarket high-energy systems) because its sense circuit
operates in parallel with the coil firing circuit. Most aftermarket tachs
(AutoMeter, etc.) are voltage sense tachs.
Theo Smit
tsmit@novatel.ca
B382002705
> -----Original Message-----
> From: Colley, Chuck [SMTP:Chuck.Colley@wang.com]
> Sent: Tuesday, June 08, 1999 6:52 AM
> To: 'Doug & Rett Leithauser'; Tiger List
> Subject: RE: Tach hookup
>
> Doug,
>
> I'm new to the chat and with a new Tiger 1A . I've have been soooo
> enlightened by the information this media provides. I thank you all. I learn
> quite a bit about my Tiger each day.
>
> If you look at the schematic in the Workshop Manual, it shows the tach
> before the Ballast Resistor, which is before the Coil, which is before the
> Distributor. Seems pretty straight forward to me... Am I missing something?
> Is there another way??? I plan to install a Pertronics Electronic Ignition
> and with Tom Halls most resent Tech Tip (Thanks Tom) modify my tach, so this
> discussion is most timely.
> Thanks for the education.
> All the Best,
> Chuck Colley
> (B382001278)
>
>
> -----Original Message-----
> From: Doug & Rett Leithauser [SMTP:dleit@mintcity.com]
> Sent: Tuesday, June 08, 1999 7:28 AM
> To: Tiger List
> Subject: Tach hookup
>
> My tach (original, working, not fried) is connected to the
> distributor side
> of the coil. I've worked with a lot of different tachs & have never
> heard of
> connecting to the ballast resistor or the power side of the coil, I
> don't
> see how such a hookup could work.
> Doug Leithauser
>
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