Questions about tachometers....

[NMShooter]

I've been hunting a cheap tach for my Force, and since it is a 20 pole motor, they are not as common. I'm wondering about a few things....

1) What effectively does a 20 pole vs 12 pole mean? I suspect that this means that there are 20 pulses per revolution as opposed to 12 per revolution. Can somebody clear this up for me?

2) What is the amplitude of the voltage pulses as delivered to the tach? I'm guessing this comes off of the charging circuit, so the voltage pulses can be fairly high... maybe as much as 20V peak?

3) What are the wiring requirements for the tach? I'm guessing a ground, +12V, lamp, and the tach pulse input. Is this correct?

thanks...

Frank

 

[SweeperForce]

Re: Questions about tachometers....

The only tach I found was from Great Lake Skipper on E-bay at $72.

You are dead on about 20 vs 12 pole.

The voltage coming of the green wires (AC wires) is about 25 volts AC. The ac wires are connected to your stator. Your charging system requires a voltage reulator/ rectifier. This changes that 25 VAC in to 14 volts DC. Pretty simply to hook up.

Your tach signal wire connects directly to one if those ac wires( it does not matter which one). You will a ground and a +12volt coming off your light circuit to operate the lamp. No +12volt is needed for the tach itself. Only 3 wires should be connected.

Here are some pics that may help you out.

 

[NMShooter]

Re: Questions about tachometers....

Cool beans.. Thanks for the help.

I'm putting a slower pitch prop on. Any idea what the max RPMs I should limit the engine?

 

[SweeperForce]

Re: Questions about tachometers....

I think between 5000-6000 rpms.

 

[NYBo]

Re: Questions about tachometers....

I got my tach on eBay for $25 (used).

 

[NMShooter]

Re: Questions about tachometers....

I'll give you $26 for it

 

[Frank Acampora]

Re: Questions about tachometers....

A 20 pole ststor has 20 discrete pole on it HOWEVER, ten poles are used to charge the CD boxes and only ten poles are used to charge the battery---so---a 20 pole tach is a bit of a misnomer.
All 12 poles on an older ignition 12 pole stator charge the battery so those tachs are indeed 12 pole types. AGAIN, HOWEVER, complicating things, most of these older ignitions use the white wire from the CD box to signal the tach.

The signal to the 20 pole tach can be anywhere from 12 to 18 volts depending upon the voltage delivered by the non-regulated stator. Signal from the CD box or stator on older systems will be around 12-14 volts.