Mechanical Hall Effect Tach Transducer
Squeak said:
I have Van?s wiring harness, and the conventional Mag switch with start, and slick mags. The EIS 4000 drawing shows a switch for left and right P mag leads to allow you to choose which mag you use as your tach source. This allows you to select the active mag when performing a Mag Drop Test. Can a Mag Drop Test be done without the switch? If so where do I run the EIS Tach wire (Right Mag..... Left Mag.... or to both?
Squeak
RV-7A
Three ways:
**The easiest typical way is to connect it to one mag (say the LEFT). You get RPM drop when the RIGHT is off, and just listen for the mag drop when you turn the LEFT off. It works. Lets face it you know when the RPM drops or the engine runs rough.
**Extra select switch, as tc1234c said. Throw a switch to manually select mag.
**
Third way and what I did: I bought a "UMA" hall effect tach sensor. It runs mechanically off the back of the engine. The EIS4000 tach is not off the mags, so it does not matter what the mags or electronic ignition is doing.
You can use any hall effect sender. Most put put two pulses per rotation. The TACH drive is 1/2 RPM I recall, so its a EIS setting of (1).
I don't like the looks of the tach sender Van sells. UMA was used because its small and I don't care for Westach. The UMA unit takes a 5 volt input and sends out a nice square wave signal the EIS can handle.
The first choice is NOT a bad one. It is simple, light, cheap and really RPM drop and smoothness is not hard to tell with out a tach. All effect sender is not real cheap, but not too bad either.
You could get fancy with relays and fancy switches but you are adding failure points and I don't like tying the two independent ignition together.
