Battery not charging slow cranking

[jbmarley30]

I took the boat out this weekend and while trying to start it the flywheel spun slow making about a 1/4 of a revolution at a time. It felt way too slow to start the motor. Then it just spun fast enough (out of no where) and started up. (1988 85 hp)

I took it for a spin and shut it down for a few minutes and the same slow cranking occurred when trying to start again. I got it started again by chance. I noticed the battery wasn't charging very good while running. It would stay around 11.7 while trolling and then 12.5 at full throttle. Every time I try to start it the battery alarms goes off and its at about 10.5.

Switched the battery with a newer one (Maxx Marine purchased last year)that was fully charged and got one good start and then the same thing happened as previously mentioned. This problem just started this weekend. Motor would turn over great before.

Checked the cables (that were replaced last year) and they look fine. I'm going to get the batteries tested to see if they're good today. Any other ideas?

Thanks

 

[pnwboat]

Re: Battery not charging slow cranking

Sounds like your charging system is not working. You should see a minimum of 13.5 volts DC when you are running at full throttle. Could be the rectifier or the charging winding in the stator. You should see about 14 - 16 volts AC across the two green wires connected to the rectifier with the motor running. If not, disconnect one of the green wires and measure the resistance across the two green wires (with the motor off). You should measure very low ohms, like .6 - .8 ohms. If this checks out OK, then I would suspect a bad rectifier, or bad ground connection on the rectifier. Rectifiers are available at Radio Shack for much less than marine supply places. 25A bridge rectifier. If you don't read anything when you ohm out the two green wires on the stator, then the charging coil is open. You need to replace the stator.

 

[jbmarley30]

Re: Battery not charging slow cranking

thanks for the reply. i'll check it this week

 

[john from md]

Re: Battery not charging slow cranking

Also, if you want your battery to last a few years, invest in a battery tender. This is a charger that maintains your battery at 13 volts so that the plates don't sulfate.

Also, avoid trying to start an engine when your voltage is low as it also sufates the plates.

John