SailNet Community - View Single Post - Nissan alternator problem
View Single Post
post #1 of Old 12-27-2007 Thread Starter
Join Date: Dec 2007
Posts: 1
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
Nissan alternator problem

I need the help of someone that understands batteries and DC electrical systems.

Here's the deal.

I have a 6hp Nissan long shank outboard in the motor well of my CD25. I had an alternator (read coil with rectifier) installed. When I measure the output of the motor in neutral I get something in the vicinity of 14.4 volts at something less than full throttle. When I put the motor in gear the output falls to about 10 voltsat full throttle. After extensive discussions of this situation with Nissan tech support, I am told that everything is working properly and that at 10 volts the battery is being charged.

Will a battery charge from a source from which the voltage is lower than the current charge in the battery (i.e. will 10 volts charge a battery that is registering 12.4 volts)? It was always my understanding that it wouldn't but, I am not sufficiently certain to argue the point with a professional technician.

I am also told that, due to the size of the boat, the motor is unable to achieve the rpms for which the motor is rated. They suggest switching from an 8 pitch prop to a 6. The idea is that this will let the motor operate at higher rpms and the alternator to put out more power.

The alternator is rated at 6 amps. I realize that this is not much but, on a typical day of sailing I am not using much power on a C25. I typically motor 2-3 hours in a day of sailing. Shouldn't that put at least 12 amp hours into the battery while a handheld gps, listening to a VHF, a depth gauge, and tiller pilot would not draw near that much?

I hope there is someone out there that understands all of this stuff and can explain it until a novice can understand. I definitely need ?DC Systems for Dummies?. I'll certainly appreciate any help anyone can give. I'm "bumfuzzled".

If you have any thoughts, let me know.
hlkaulfman is offline  
Quote Share with Facebook
For the best viewing experience please update your browser to Google Chrome