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Author Topic:   Yamaha 90-HP: Battery Charging
Rotten posted 11-26-2013 06:24 AM ET (US)   Profile for Rotten   Send Email to Rotten  
Hello, How do I know if my Yamaha 90 has an [alternator] and a battery charging circuit? Does running my 90-HP Yamaha charge my battery? Do I have to charge [my boat battery] when I am done boating for the day? Thanks
PeteB88 posted 11-25-2013 07:23 PM ET (US)     Profile for PeteB88  Send Email to PeteB88     
It probably has an alternator and there should be a gauge on your dash that indicates output of alternator. Mine runs around 14 volts when the motor is running. It's handy to see what battery is putting out when you turn on key - at least I think that's what it does. My boat lives on a trailer and I plug it into to battery maintainer device most of the time. Or make sure it's got full charge prior to use. Is yours a one or two battery system? I've been delaying upgrading to two battery system which I will be doing ASAP - maybe this winter while it's in storage.
jimh posted 11-25-2013 07:50 PM ET (US)     Profile for jimh  Send Email to jimh     
Your outboard engine will charge the battery if

--your outboard engine has a battery charging circuit, and

--the battery is connected to the battery charging circuit.

Of course, this assumes the battery charging circuit is working correctly.

Whether or not at the end of a day of boating the charge on your battery will be at a full charge level has little to do with the engine or its horsepower.

The state of charge of the battery at the end of a day of boating depends on:

--the initial state of charge

--the total current discharge from the battery

--the total charging current supplied to recharge the battery.

For most small boats whose engines have battery charging, the electrical load on the engine charging system and battery will be low enough to create surplus charging current, which will recharge the battery. However, the net charge after a day could be higher or lower, depending on how much load was placed on the battery, how much the engine was run, and at what speed the engine was run.

seahorse posted 11-26-2013 07:07 AM ET (US)     Profile for seahorse  Send Email to seahorse     
If your 90hp has electric start, then it has a battery charging circuit and an under-flywheel alternator on it. You can search this site for articles about outboard motor alternators.

If your engine is not charging the battery, then you may have a wiring problem, bad battery, or likely a regulator that has failed.

What is the engine's model number?

Rotten posted 11-26-2013 07:50 AM ET (US)     Profile for Rotten  Send Email to Rotten     
I just bought the boat. It has an electric start. The outboard engine model number is 90 LTR. It is a 2008. It also says 6H1 L
jimh posted 11-26-2013 10:09 AM ET (US)     Profile for jimh  Send Email to jimh     
It is most likely that your Yamaha 90-HP outboard engine with electric starting has a permanent magnet alternator that creates electrical energy for charging the battery attached to the engine. It is common that the rectifier or rectifier-regulator portion of the battery charging circuit can be damaged. If there is damage to the rectifier, the battery charging output will be affected.

The simplest test to determine if the battery is receiving charging current when the outboard engine is running is accomplished as follows:

--connect a voltmeter with an accuracy of 3-percent and a resolution of 0.05-Volts DC to the terminals of the battery;

--note the battery terminal voltage when the outboard engine is not running. If the battery is at full charge, the terminal voltage should be in the range of 12.6 to 12.8-Volts. If the battery is not at full charge, the terminal voltage will be lower.

--start the outboard engine, run it at a fast idle speed, about 1,200-RPM.

--observe the terminal voltage of the battery.

If the terminal voltage of the battery increases when the engine is running, the engine is supplying charging current to the battery.

jimh posted 11-26-2013 10:33 AM ET (US)     Profile for jimh  Send Email to jimh     
[I have combined two threads on this topic into one.]
Rotten posted 11-26-2013 12:48 PM ET (US)     Profile for Rotten  Send Email to Rotten     
Thank you Jim, I'll have to pick up a Voltmeter. Any recomendations? What is the average price for such?
jimh posted 11-28-2013 02:13 AM ET (US)     Profile for jimh  Send Email to jimh     
I tend to prefer very good test equipment. I figure if you are going to make a decision about a $10,000 device, you should use test equipment that costs more than $10. With digital multi-meters (DMM) there is almost no limit to how much you could spend.

For a DMM that you will be the only one using, you don't plan to drop on the floor repeatedly, won't leave out in the rain, don't plan to use in a highly explosive environment, and do not need calibration traceable to the national bureau of standards, a nice meter can be bought for around $60. See

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