Re: Tachometer Pickup

[jklein <jklein@hpower.com>]

Actually most of the sensors that I have seen are hall effect sensors. The
sensor picks up the magnetic field of the magnet and creates a pulse. This pulse
is then sent to the processor and is counted as a single revolution. My Corvair
has an aftermareket sensor with three wires. MY cruise control has a sensor with
two wires. My bicycle has a 2 wire sensor. The three wire system is "excited" by
low voltage, then the passing feild is the lever that closes the switch, and
sends a pulse to the processor. A three wire system is more stable around other
electrical fields (less electrical noise in the circuit), but for a Tach a two
wire system is fine.
     WARNING : A three wire system MAY NOT OPERATE ON 12 VOLTS. If the connector
is smaller then the standard 1/4 inch SAE blade, it is possible that this is a
low voltage lead (4,6, or 8 volts). You can blow out your sensor AND tach if you
put a full 12 volts through the sensor. If the connectors are smaller then the
standard blade terminal (usually round, but can be 1/8 blade type) check the
donor system to see what voltage it needs to operate.
   A properly prepared surface AND a good epoxy will hold the magnet (make sure
you get the epoxy that will not be harmed by water and temperature).

Joe Klein
Process Technologist
H-Power Corp..

ev stuff wrote:

> In message <v04011701b326b84aecd0@[206.86.222.131]>, Nathaniel Martin
> <nat@lumiere.net> writes
> >Hey EVeryone...
> >
> >I want to have a rev limiter on my car, or a tachometer, so that I don't
> >overrev my Prestolie. However, the tachometer pickups that I have seen are
> >a little plastic collar that is supposed to go around the shaft that sticks
> >out of the back of the motor. My prestolite only has a shaft on the front,
> >not on the back. There is no room to put a collar inside the transmission
> >bell, by the clutch. How else can I put a pickup on it? I don't want to
> >ruin the motor. (and Uve's EV calculater says I can overrev it in 3 gears!)
>
> If you are running a flywheel then it may well be possible to use a
> crank position sensor from a standard electronic fuel injection system
> to sense rpm, I've not had much experience with them but I suspect that
> you will find most of them have 3 wires, well my car and that of 2
> others that I've worked on have. You will most probably have a live
> feed, an independant earth ( seperate to casing to reduce electrical
> noise) and a high/low switched output.
>
> sooty
> --
> ev stuff