277 Tacho Wire

by Daniel in 2 Stroke Technical Questions 6 years ago

Hi, I have a Rotax 277 engine with Bosch points ignition. I am trying to build an electronic tachometer sensor that can pick up the pulse signals from the coils and output a 5V digital or analog signal. I found a similar project on this forum, but it is for a Ducati ignition system.
https://www.rotax-owner.com/en/rotax-forum/1-2-stroke-technical-questions/6155-tacho-wire#15952

The second attached diagram shows how to connect the tachometer without and with a rectifier.
Does anyone know the output signal of these wires?
And will the signal differ if it is connected to both of the coils (without rectifier) vs. single coil (with rectifier)?

Thanks a lot, Dan

pointswiring_2017-11-06.gif (You do not have access to download this file.)

pointstachrectifierwiring_2017-11-06.jpg (You do not have access to download this file.)

Re: 277 Tacho Wire

by Nick Axworthy » 6 years ago

Nick Axworthy

16 325 0

Would you not consider one of those Tiny Tach types...very cheap these days...an accurate.

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Re: 277 Tacho Wire

by Daniel » 6 years ago

Daniel

1 2 0

I currently do have a Tiny Tach installed and it does a great job. I just want to build my own sensor with an OLED display to match the others.

So far I know that the SCP2 Bosch Points Ignition System has 3 coils, they all produce AC output and possibly 2 pulses per stroke.

The 30 Watt Lighting Coil which is connected to the SOLID GREEN wire and GREEN WITH BLACK STRIPES wire. The output varies between 18 volts - 50 volts depending on engine RPM and is pulsed so can be used to drive a tachometer. The coil is commonly connected to a rectifier to convert the AC to DC. The 110 Watt Lighting Coil is connected to the SOLID YELLOW wire and YELLOW WITH BLACK STRIPES wire. The output similar to the 30W Lighting Coil varies between 18 volts - 50 volts depending on engine RPM. The output of this coil can be used in its raw AC form or be connected to a rectifier / regulator to convert it to DC. Wires from the 30 Watt Lighting Coil and 110 Watt Lighting Coil can be connected together in parallel (for a combined power output of 140 Watts) as they emerge from the magneto housing and then sent to the regulator / rectifier.

Can anyone confirm the operating voltages and if there is 2 pulses per stoke?

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Re: 277 Tacho Wire

by John Hoxie » 3 years ago

John Hoxie

2 2 4

I have a 277 I bought on an ultralight this year. It apparently has never had a tach hooked up. Do I put my analog tach in series between the SOLID GREEN wire and the GREEN WITH BLACK STRIPE wire?

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277 Tacho Wire

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