Alternator putting out 17.25 volts

[Noah]

Volt meter: i doubt the volt meter is 27 yrs old. I believe it orignally came with an AMP meter? Has your engine wiring harness been upgraded as per "critical upgrades"??  if so, gauge was probably changed then or later.?

[Clay Greene]

This might be a good time to check the water level in your batteries if they are flooded.  You can also probably check "equalization" off on your list of things to do for the next six months.   

[Stu Jackson]

Stu:  I couldn't find the sense wire on the diagram.  Suggest that diagram be updated with a photo that tgsail1 can provide, also model number if anyone knows it, and labels on the terminals.  I'd be happy to help with that.

It's there in Sketch 1:  purple (ignition), AO, orange (tach goes to brown) and the RED is the sense wire.  No update required.

[mainesail]

Turns out my OEM Motorola alternator does have a voltage sense wire contrary to the owners manual wiring diagram. I connected it to the house battery and voila, start isolation works!  Alternator is putting out 15.0v at the house battery then combines after about 30 seconds with the start battery.
Thanks all for the valuable insight. 

For a fair stretch of time these Motorola alts had regulators limiting voltage to 15V. On short runs this is not bad, and actually be beneficial, unless you have AGM or GEL, but for longer engine runs it can negatively impact the battery.

Leece-Neville now makes an adjustable version of the Motorola regulator called the 8RG2043 (sales # 105-280). The regulator is self excite, using the two yellow AC Tap/Stator tap wires for self excite purpose.

The red wire is regulator power/field/volt sense and the black wire is regulator negative/brush negative. The black & red can be fed direct to a house battery for optimal voltage sensing provided you account for the 5A +/- that circuit will carry when full fielded.


Remove the red and black wires, from the back of the B+ & B- of the alt. Now feed them direct to the house bank, allowing for almost zero voltage drop in that circuit. The wiring should be sized for 5A +/- with less than 1% voltage drop, you will now have an externally sensed Motorola with an adjustable regulator. A fairly inexpensive way to get better charging performance...