'87 Johnson Sailmaster charging circuit - SailNet Community
LinkBack Thread Tools
post #1 of 3 Old 07-14-2013 Thread Starter
Senior Member
bblument's Avatar
Join Date: Oct 2012
Location: Syracuse area, NY
Posts: 390
Thanks: 63
Thanked 38 Times in 30 Posts
Rep Power: 5
'87 Johnson Sailmaster charging circuit

Me again... '72 Pearson 26 from hell... ..

Actually, things are going very well. The new compression posts, mast support crossbeam, and bulkheads are installed, the mast is rewired, and the mast step is sealed and in place. The outboard mentioned in the subject has had its bottom end rebuilt down to the last bushing, bearing and seal, and, after running poorly, just been the recipient of a carburetor rebuild. I haven't learned this much in so short a time since college. I won't tell you when that was.

Anyway.. does anyone have any knowledge about the charging circuit of the aforementioned outboard? I have the shop manual, but it barely mentions the alternator circuit.

Here's the situation. This is a manual start engine. There's two wires coming off the charging circuit of the motor that are connected directly to the battery via the battery master on/off switch and a 1 amp fuse. At idle, the wires output about 4 volts, and the voltage rises to about 16v at full throttle. When connected to the battery that shows a voltage of 12.58 at rest (a new basic deep-cycle battery), the voltage read across the battery terminals increases as the engine is revved but not dangerously so... maybe to 13v... but reads lower than the battery at rest when the engine is idling.

There are no regulators anywhere in the line, other than whatever is under the hood of the outboard.

Is all well? Is something wrong? I'm concerned about the huge swing in voltage output between idle and full throttle... 4v - 16v or more. The 1 amp fuse seems a little low to me, too. The original fuse was blown when I took possession of the boat; I temporarily replaced it w/ a 5 amp just to run a quick test or two. 2 amps, maybe?

Thanks in advance for any insight. This place has helped me more than words can ever say.

Best to all.


Thanks in advance for any input.
bblument is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
post #2 of 3 Old 07-15-2013
Join Date: Jun 2009
Location: Almost Heaven West Virginia
Posts: 239
Thanks: 1
Thanked 17 Times in 15 Posts
Rep Power: 9
Re: '87 Johnson Sailmaster charging circuit

Don't worry about idle voltage. The alternator is too small to overheat the battery. If the charging voltage is somewhere between 12.8 V and 15.5 V you are gaining some but not too much. There is no voltage regulator. I would use a fuse somewhat larger than the rated output of the alternator which is probably about 6 amps.
Riding lawnmowers use a similar system.

Seafarer 29 KCB
Mechsmith is offline  
Quote Quick Reply Share with Facebook
The Following User Says Thank You to Mechsmith For This Useful Post:
bblument (07-15-2013)
post #3 of 3 Old 07-15-2013
Join Date: Jul 2007
Location: Truckee, CA
Posts: 8,867
Thanks: 2
Thanked 117 Times in 115 Posts
Rep Power: 0
Re: '87 Johnson Sailmaster charging circuit

I had about the same output on my Evinrude 35 HP 2 stroke. The charging capacity was pretty wimpy. Agree on the fuse.

Paul T
dabnis 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
Johnson Sailmaster 6 hp throttle 'frozen' Cal28 Gear & Maintenance 1 03-22-2012 10:03 PM
Fuses for the charging circuit rocinante33 Gear & Maintenance 5 06-17-2009 10:16 AM
Adding Fuse to charging circuit rhadsock Electrical Systems 1 06-11-2009 03:42 PM
Johnson Sailmaster 6 vs Me Jonathan316 Gear & Maintenance 8 06-24-2004 08:08 PM

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