Subject: RE: Mike Skaggs-Humanitarian
Author: murp-@aol.com
Date: May 2, 2001, 10:25 PM
Post ID: 1706570923
David,
I have been thinking about your tach hookup, and have some
suggestions.
The following depends largely on the input impedance and sensitivity
of the electronic tach, but will work assuming that its input impedance
is fairly high.
You should be able to use 2 diodes and one resistor. The anodes (+ve
side) of the diodes should be connected together, and a resistor
connected between this point and +12V. You would then connect the same
point (the connection of the 2 anodes and resistor) to the tach (the
other tach connection is to ground). Each cathode (-ve end) of each
diode should be connected to each coil at the connection between the
coil and the points (or electronic ignition). This may sound complex but
it is not.
There are several other considerations. The value of the resistor
depends on the input impedance of the tachometer (I will try to measure
mine tomorrow). If it has a fairly high input impedance (hopefully above
1 Kohm), then you can use something like a 100 ohm, 1W resistor. If it
has a fairly low input impedance, then you will have to use a lower
valued resistor with a higher power rating. For example, if the input
impedance is 100 ohms, then you will need something like a 10 ohm
resistor with a 10W power rating. In this case, It may be better to go
with a more active (transistorized) design, which would take about 4
power transistors.
The other consideration is that with the 1-coil, 2 cam-lobe setup,
the signal to the tach goes to 0V (or ground) potential every time the
points close. In your system, that signal will go to about 0.6V (instead
of ground), corresponding to the voltage drop across one diode when it
is turned on. Again, it is pretty likely that the tach won't mind this.
Here again, a more active transistor design would largely get around
this.
The more complex 4-transistor design would definately work, but would
require some more resitors in the circuit. I think the above should
work. I will try to find the input impedance of the tach to confirm
this.
Brian
'74 Eldo
'78 T3
'80 BSEE
David Washburn wrote:
| I did a trial fit of the K&N's before Mike sent me the Venturis and they fit. The backs touched and they were not perfectly symmetrical but they fit. If it don't work carb sox are next. What about my wiring question? Anybody else running a dyna on a loopframe? I put the tank up on the coffee table this morning and my lovely wife applied the decals. She did a fine job and the V7 sport decals look great on the all black tank. David |