How does a starter motor change polarity?

[Brandoned]

I always disconnect the negative (only) cable from my battery (boat/outboard motor) when I bring it in. Yesterday, I connected the negative cable back to the post, tried to start and the starter would spin but (after MUCH investigation) I discovered that it was spinning in the wrong direction. I disconnected/reconnected the negative cables and, voila, it started spinning correctly

 

[MVP]

I think I remember years ago changing the polarity of a car dynamo from positive to negative earth by briefly connecting the battery to it directly the wrong way round, i.e the way you finally want it.

Reckon it would be the same for a starter motor, so guess somehow the current was applied incorrectly

 

[VicS]

Unless the starter motor is a permanent magnet motor, or maybe incorrectly assembled, even reversing the connections should not make it spin the wrong way
(reversing the battery connections, even momentarily, will blow your rectifier though!)

Are you really sure that it was spinning the wrong way, not just failing to engage due to a poor (battery) connection.

As far as I know all outboards spin clockwise so the starter motors spin anticlockwise.

Clean and remake all the connections, not forgetting the negatives. A Scotchbrite pot scourer is good for removing corrosion and oxidation from battery posts without removing metal.

 

[[2068]]

I would be checking to see if it was properly grounded.

 

[PaulGooch]

Whatever, i wouldn't be disconnecting/connecting cables every trip. I'd fit an isolator switch in the positive cable.

 

[ccscott49]

I think I remember years ago changing the polarity of a car dynamo from positive to negative earth by briefly connecting the battery to it directly the wrong way round, i.e the way you finally want it.

Reckon it would be the same for a starter motor, so guess somehow the current was applied incorrectly

You are almost there, you "flash" the field connection (disconnecting the woire first) with a wire connected to the positve battery terminal, to make it pos earth or the other way round to make it neg earth, often old stock dynamos needed it done, because the residual magnetism, which decides which polarity it is, and starts the dynamo charging, (self excitation) has ebbed away.
Wow, didnt think I would be able to remember that!!