1967 Merc 950 SS not charging

[The Bug]

I have a 1967 Merc 950 SS 6 cyl engine (electronic ignition), and just rewired practically everything due to corroded wires (included new Mercury brand pigtail and individual wires). The rewired engine starts and runs great, however, does not appear to be charging; battery voltage is 12v whether engine is running or not (multimeter does not change even when engine is revved), and I would expect 13 - 14v when running. Also engine immediately dies when + cable is disconnected at the battery. I did have to rewire the 2-wire stator due to corroded wires (used crimp sleeves right near the stator to splice), but ohm reading is good (stator coils were well sealed, no rust on any part of it, visually looked good). With stator wires removed at rectifier, AC voltage goes as high as 30vac depending on rpm. I have no idea of amperage, but assume stator is good because of the ohm and voltage tests. I did test the rectifier per on-line instructions and it also looks good (volts only go in one direction at each of the diodes). Plus with the red lead off of the rectifier and using a multimeter on the B terminal to ground, I got up to 20vdc depending on rpm. All engine wiring looks correct per diagrams available on-line. Any ideas why it does not appear to be charging or why the engine dies immediately when disconnected from the battery? I am all out of ideas, except possibly the stator may not be putting out enough amps (not sure what the values should be or how to test it). Thanks

 

[Texasmark]

If you don't get an answer just answer it yourself with the word "Bump". That will put your post back as the top of the list, like my comments here caused to happen, where it can be more clearly seen.

Back in that time line I was an OMC guy and not keen on Merc engineering.

If you are getting up to 20vdc vs rpms your rectifiers are working....big Selenium guys????? What you don't have is regulation that would limit that voltage to 14.5 area. Nowadays the rectifier-regulators are in a potted aluminum module about 2x2" and magnetos are no longer used.. battery voltage and magnetic pickup from the stators and trigger circuit coils under the flywheel.

If your 20 volts you measured was wired to your battery, which apparently it isn't, you'd be down to 16 volts at max rpms. Seems that where you inserted your meter for that measurement isn't wired to your battery + terminal.

In saying that, if you have something besides a magneto ignition, which generates it's own power, you need battery voltage to get your trigger circuits to work. Possibly the wire that's missing, mentioned above, if installed, would back feed battery voltage to your triggers and you wouldn't be having that problem either.

On later engines the input ⅜" stud on the starter solenoid (not the side that goes to the starter) is a junction point for battery cable attachment and a tie point for all-most all power requirement connections....including the charging circuit.

 

[The Bug]

Texasmark, thanks for the reply. What I meant above about the rectifier test is that I removed the red lead from the rectifier only to perform the test mentioned that yielded the 20vdc. However, with that red lead connected as it should be, I am not seeing any increase in voltage when the engine is running. When measured at the battery, I have a solid 12vdc, whether the motor is running or not. I would expect to see 14 or more volts with the engine running. The red lead mentioned that connects to the rectifier (which is the vdc output from the rectifier) does have a direct path back to the battery. This is what is baffling me. Any other thoughts?

 

[DeepCMark58A]

When ever I redo an old motor the charging system is removed, when they fail they make a mess. My boats are garage stored stored so charging is not an issue.

 

[jimmbo]

deleted

 

[Texasmark]

If you have Open Circuit voltage and no in circuit (loaded) voltage, I'd expect high impedance (resistance) in the circuit.

Using a Digital MultiMeter with the engine wiring hooked up like it is supposed to be, get on your AC voltage 20v or higher scale and put your leads across the stator input wiring terminals to the rectifier module......engine running at 1500ish RPMs. Come back with the results.