Starter verses Alternator - SailNet Community
LinkBack Thread Tools
post #1 of 4 Old 10-10-2006 Thread Starter
Senior Member
Join Date: Aug 2006
Location: Nantucket
Posts: 270
Thanks: 1
Thanked 6 Times in 6 Posts
Rep Power: 11
Starter verses Alternator

Attempting to winterize the boat and she wouldn't start. It only started twice after some hesitation. Turn the key for the Yanmar diesel and voltage meter drops from 10 volts to 0 and the engine does not turn over. The starter was hot to touch. The starter selinoid began to smoke.

We charged the batteries and purchased a new No.1 starting battery. We are not sure why the voltage meter is registering 10 volts when it should be 12? A few tests and sounds we are aware of indicate the starter selinoid or starter have failed and need replacement. But how can we be certain it is not the alternator? Any thoughts?
ambianceack is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
post #2 of 4 Old 10-10-2006
Seinor Member
capn_dave's Avatar
Join Date: Feb 2000
Location: Green Cove Springs, FL
Posts: 276
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 18
I doubt it's the alternator

Where are you reading the battery voltage? On your electrical panel or on the instrument panel? Dose the key have to be on to read the voltage? Did the new battery read 10 volts? Did you run the engine and check the voltage while running?
While cranking the voltage will drop, as the alternator is not charging at this point and the starter is drawing allot of current. Most alternators will not start charging until they get to a certain rpm. For sake of argument about 1000 engine rpm then once excited will continue charging even at idle. When the alternator is charging and the engine reved up a bit you should be seeing around 14 volts.

Fair Winds

Cap'n Dave

Last edited by capn_dave; 10-10-2006 at 06:46 AM.
capn_dave is offline  
Quote Quick Reply Share with Facebook
post #3 of 4 Old 10-10-2006
Join Date: Apr 2006
Location: Spokane, WA
Posts: 93
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 12
The starter should be a No smoking zone

The fact that the starter solenoid was smoking is a clue!

Batteries have the ability to produce thousands of amps when shorted. The alternator does not produce any current until the engine is up to speed, definitely not occurring while starting. This makes the alternator nothing but a drag until the engine has started, all the power is coming from the battery.

The 10 volt reading simply meant that you had an excessive load on the battery. The voltage drop could have been in the battery or the battery cables, I “volt” for the battery cables (sorry, I couldn’t help myself).

The alternator is probably fine. Check the battery voltage once the engine is started, if it is up to 14 volts + then it’s OK.

There are two types of fools...

One says this is old, and therefore good..

The other says this is new, and therefore better...
dave.verry is offline  
Quote Quick Reply Share with Facebook
post #4 of 4 Old 10-10-2006
Senior Member
Join Date: Sep 2006
Location: Scotland
Posts: 2,365
Thanks: 0
Thanked 11 Times in 11 Posts
Rep Power: 11
It does sound like the alternator is down. It really should be raising the voltage to about 14 V.
Rockter is offline  
Quote Quick Reply Share with Facebook

Quick Reply

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Similar Threads
Thread Thread Starter Forum Replies Last Post
Bad alternator??? cgha33 Gear & Maintenance 11 10-12-2006 04:56 AM
alternator noise filter no longer useful? TahitiDave Gear & Maintenance 1 10-03-2006 11:58 AM
Yanmar starter kavakava Gear & Maintenance 4 09-14-2006 11:59 PM
Perkins 4-108 Alternator Mount mcain Gear & Maintenance 3 07-23-2003 08:16 AM
Starter Problem pehrst Gear & Maintenance 2 08-29-2002 08:34 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome