Charging issue

[medicineman]

Thank-you very much boscoe I will not be back to the boat until Memorial Day weekend but I will follow your suggestion then! I do appreciate you sharing your knowledge.

[medicineman]

One question on lightening voltage output. Measure between the two green or between green and ground?

[fairdeal]

is it likely the bad battery would have messed up the coil?

certainly not "likely" - perhaps "highly unlikely"? -

but is it not "at least theoretically possible"?

for two diodes to fail "closed" and allow battery current to run, through two legs of the Wye, to ground?

[fairdeal]

16 volts is a bit high isn't it???

I would think so.

did charge at 16 volts or better consistently.

Seems a flooded battery would be in order - and keep after those electrolyte levels

[boscoe99]

One question on lightening voltage output. Measure between the two green or between green and ground?

Between the two greens. This is an AC circuit. Voltage is being developed solely between the two green wires.

[boscoe99]

certainly not "likely" - perhaps "highly unlikely"? -

but is it not "at least theoretically possible"?

for two diodes to fail "closed" and allow battery current to run, through two legs of the Wye, to ground?

Possible. But highly unlikely. I have modified my comment.

If battery voltage were to be applied to the lighting coil I would suspect the coil would be mostly gone. Smokey. Charred. Do some math. 12.6 volts across a resistance of less than an ohm equals what amount of current?

[boscoe99]

16 volts is a bit high isn't it???

In a number of Yams, yes. In some Yams, no.

The smaller power output R/R's seem to operate at a much higher voltage than the higher output R/R's. Even at 16 volts the current is so low that it won't harm most stuff.

[zenoahphobic]

certainly not "likely" - perhaps "highly unlikely"? -

but is it not "at least theoretically possible"?

for two diodes to fail "closed" and allow battery current to run, through two legs of the Wye, to ground?

If we don't have actual data on how those Yamaha rectifiers that have failed, judging from what I have seen in similar power rectifiers broadly, it is a possibility.

The slow overheating can lead to two diodes going short circuit. The probability is not based on them "failing" exactly at the same time, if one goes short circuit the circuit is still complete so current can still flow through the other one, letting the "situation" lead to its demise.

If power diodes are specified high current, and there is excessive current but limited, as would likely be the case with the outboard in question, diodes tend to slowly melt combining conductive material. However if there is large current available, as there would be from the battery, the diode junctions tend to "blow apart" and go open circuit.

In the OPs case, talking about battery current reversing to damage the coil is the least probable! There is the coil output to consider first.
The OP describes an intermittent open circuit to the battery. So high voltage spikes and short high current switch on, would be occurring seeing the coil output could be quite high at 5000rpm. Those diodes may not have liked working in that environment, failed by shorting sending destructive battery.current, or simply rested with that. Alternatively the coil pulsing output simply was too much for the diodes alone.

[medicineman]

update on charging-----turned out that lighting coil is dead. next trip i will try to replace it. i know i have to pull the flywheel, but forgot to check the size of nut holding it down. Anyone happen to know off hand? can't find it listed in parts list or in repair manual

[boscoe99]

36mm as I recall.

[medicineman]

Thanks. Any adjustment or gapping for new lighting coil or just bolt on

[TownsendsFJR1300]

Thanks. Any adjustment or gapping for new lighting coil or just bolt on

It'd be a bi..h to gap from underneath, I suspect it'll only go on one way (W/O any play, may be an alignment pin)

[99yam40]

getting the nut off is one thing, getting the flywheel of is another.

If Yamaha designed it, there is probably some special tool for setting.
but I have no idea, so service manual probably would help

[medicineman]

I have service manual and it tells how to check but have seen no info on replacing. I know lawn mowers use business card between coil and flywheel

[TownsendsFJR1300]

I have service manual and it tells how to check but have seen no info on replacing. I know lawn mowers use business card between coil and flywheel

Correct but the ignition coil on most mowers / weed eaters, chain saws are accessible OUTSIDE the flywheel. Your Yamaha coil is under the flywheel.