The J/109 Class Association Forum

The 3YM30 is normally supplied with a 60 amp or 80 amp alternator. Those who have the upgraded electrical system with the Balmar 110 Amp alternator may find that their tachometer reads high. This was noted on the survey when I purchased hull #266. The Tachometer / Engine Hour meter used in the Yanmar panel is manufactured by VDO. It is digitally programmable so it can be used in a number of gasoline and diesel engines. When it is shipped for the Yanmar engines, it has a pulse calibration setting of 10.29. This is used to convert the pulses off the alternator into an RPM value. The number of pulses is proportional to the engine rpm and is impacted by the pulley ratios and the number of poles in the alternator. The Balmar 110 Amp alternator has different number of pulses than the stock Hitachi alternator. I did some measurements with a hand held tachometer and determined that the correct pulse setting should be 12.45 instead of 10.29.

For those who have the 110 Amp Balmar Alternator, set the 12.45 value in your tachometer using "2. Manual Calibration with a known value (Pulse)" in this procedure