Measuring charge from Outboard

[coveman]

Thank all for your help - now to test it and see what is going on!

 

[VicS]

I presume this is the replacement part if the rectifier is knackered, rather than some form of cure for running the engine disconnected?

I do not believe running the engine with the battery disconnected will harm the rectifier. It might if the rectifier is under spec'd and I suspect Yamaha are covering their backsides by suggesting that running for exceptionally long periods without a battery connected might harm it.

Yes, by replacement part I mean a new one to replace a knackered one

If you have a digital multimeter with a diode test range you can easily test the rectifier. ( You were probably wondering what the diode test range was for )

I assume it looks something like this:

Disconnect the rectifier completely ( after making a note of how it is connected ) Remove it and take it to the workshop bench if more convenient than testing in-situ.

Identify the leads .The positive output, (probably red), the negative / ground ( probably black) and the two AC input wires ( probably yellow, or green ??)

Set the meter to the diode test range and ensure the leads are in the appropriate sockets for diode testing.

Carry out the following tests

1. Connect the meter between the positive output and one of the AC input connections. Note the reading, if any. Reverse the meter leads and note the reading, if any.
2. Repeat test 1 between the positive output and the other AC input
3. Repeat test 1 between the negative output/ ground connection and one of the AC inputs
4. Finally repeat the test between the negative and the other AC input

You should now have 4 pairs of results. Each pair, being the "forward and reverse " readings on one of the four diodes, should consist of a reading ( probably about 700) and a "no reading".
Liken these readings to forward and reverse flow measurements on a non return valve. One way water will flow, the other way it won't.

Any deviation from these confirms the rectifier to be knackered.......... You will probably find one or more pairs are both "no readings" indicating blown diodes.

 

[coveman]

I do not believe running the engine with the battery disconnected will harm the rectifier. It might if the rectifier is under spec'd and I suspect Yamaha are covering their backsides by suggesting that running for exceptionally long periods without a battery connected might harm it.

Yes, by replacement part I mean a new one to replace a knackered one

If you have a digital multimeter with a diode test range you can easily test the rectifier. ( You were probably wondering what the diode test range was for )

I assume it looks something like this:

Disconnect the rectifier completely ( after making a note of how it is connected ) Remove it and take it to the workshop bench if more convenient than testing in-situ.

Identify the leads .The positive output, (probably red), the negative / ground ( probably black) and the two AC input wires ( probably yellow, or green ??)

Set the meter to the diode test range and ensure the leads are in the appropriate sockets for diode testing.

Carry out the following tests

1. Connect the meter between the positive output and one of the AC input connections. Note the reading, if any. Reverse the meter leads and note the reading, if any.
2. Repeat test 1 between the positive output and the other AC input
3. Repeat test 1 between the negative output/ ground connection and one of the AC inputs
4. Finally repeat the test between the negative and the other AC input

You should now have 4 pairs of results. Each pair, being the "forward and reverse " readings on one of the four diodes, should consist of a reading ( probably about 700) and a "no reading".
Liken these readings to forward and reverse flow measurements on a non return valve. One way water will flow, the other way it won't.

Any deviation from these confirms the rectifier to be knackered.......... You will probably find one or more pairs are both "no readings" indicating blown diodes.

Vic,
Many thanks for this clear explanation - very much appreciated

 

[VicS]

Vic,
Many thanks for this clear explanation - very much appreciated

I hope you mange to identify the problem.

One final thing you could check is continuity of the AC generator coil.

while the rectifier is disconnected from it measure the resistance, using your meters lowest ohms range, of the coil winding between the two AC output wires.

Cannot quote a value of hand but should be pretty low.