Evinrude 1971 100Hp charging problem

Hello
I have a 1971 100Hp Evinrude with a charging problem.
i have checked the ac voltage at both legs of the stator and get around 24V AC depending on engine revs. i have 15 to 18 volts at the DC leg of the Rectifier, but the rev counter is not showing that the system is working, and i have no change in battery voltage (12.6 to 12.8 engine stationary) with the engine running at medium to high revs.
An Ampmeter connected into the power supply shows up to 2.8 amps discharge when running.
What is going wrong here?
Hope someone can help me

Handy Harry

Take ohm reading -yellow to yellow wires on the stator.------Take ohm reading from one yellow to ground.---If those are good then likely you need a new rectifier and they are not that much $$

With engine running at idle, using a "AC" voltmeter connected to either yellow stator lead and ground, you should get a reading of about 12 volts.

Ohm tests... Disconnect battery or turn battery switch OFF if so equipped.

Meter set to low ohms, connected between the two yellow stator leads. The 9 ampere stator should read .75 ohms +/- .2 ohms... The 15 ampere stator should read .4 phms +/- .1 ohm. No reading obviously indicates a open stator which requires replacing.

Meter set to high ohms, connected between one yellow stator lead and ground, repeat test on the remaining yellow lead. Any reading indicates the windings are grounded requiring stator replacement.

(Small Rectifier Test)
(J. Reeves)

Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a fourth yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction.

Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other.

Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires.

Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.

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racerone said:

Take ohm reading -yellow to yellow wires on the stator.------Take ohm reading from one yellow to ground.---If those are good then likely you need a new rectifier and they are not that much $$

Click to expand...

I have 1.4 Ohms on one meter and .4 on another. no circuit to ground

I will re-check the rectifier, but i would have thought that 15 to 18 volts at the DC side would show that the rectifier was good??

Check the circuit out as I described. I didn't draw it from memory other than the rectifier test (My Database)... it's directly out of a 1971 100hp OMC manual.

if the rectifier test good i would go back and verify the output of it....if you in fact do have the 15 to 18v dc output then you should also read the same on the battery..you should also be able to flip the meter to ac voltage and have a reading also because the rectifier output is not filtered down to a flat dc...in fact these pulses are what drive the tach..
there are two wires on the terminal block at the rectifier that we are interested in with this problem..one is a grey wire feeding the tach...the other is a red wire that does the charging...so i doubt if you have 2 wires open at the same time..i am assuming the grey wire from the tach goes all the way back to the terminal strip on this motor..i am not familiar with the physical wiring on this motor.. if it dont go all the way back to the strip then you could have a open...
what type battery are you running?did you change batteries in the last year?there is a known problem with a rectifier only charging system and the maintenance free or gel batteries...i have saw failures on good marine batteries but it may take longer to show up.. the problem may show up fairly quick or can take a year or more but you will lose a rectifier sooner or later..there are two indications of a problem developing...the first is a high reading on the charging circuit...above 16v and i have saw it peg a 17v meter...the other is the tach going crazy and reading all over the place..then one outing your meter will show only battery out put and the tach shows nothing...at that point the rectifier is shot...the root cause is that these motors were not designed for the new good batteries of today...