Moderated Discussion Areas
ContinuousWave: Small Boat Electrical
Charging System Problems
|Author||Topic: Charging System Problems|
posted 02-12-2007 12:42 PM ET (US)
I just purchased a poontoon boat with a 1996 Mercury 60-HP Bigfoot motor. The voltmeter on the dash doesn't work. I don't think the charging system is working right. I tested the voltage across the battery with the motor running and without the motor running, and both times it was 12-volts DC. Should the voltage be higher with the motor running to charge the battery? What [are] some of the electrical [components] that I can [check]? I don't think the flywheel was ever pulled. Thanks--Dave
posted 02-12-2007 05:55 PM ET (US)
Sounds like a problem. You should be reading higher than 12V if the battery is fully charged. What are you measuring your voltage with?
Suggest that you remove the battery and have it tested
posted 02-12-2007 08:22 PM ET (US)
When there is current flow into a battery and the battery is being charged, the terminal voltage measured at the battery will appear to rise above the terminal voltage measured when the charging current is not being applied.
The charging system of a typical outboard motor consists of:
--source of alternating current
A source of alternating current is explained in detail and in an extraordinarily clear and concise manner in an article in the REFERENCE section:
and applies to outboards which have the usual under-flywheel alternator arrangement. If you have an automotive style alternator, you can find very detailed explanations of how they work on websites oriented for automobiles.
The rectifier is almost always a solid-state rectifier. Often these are built into custom modules to suit particular mounting and heat sink configurations for particular engines.
The regulator can be either separate or combined with the rectifier. Again, these are often built into custom modules to suit particular mounting and heat sink configurations for particular engines.
My advice on diagnosis of battery operated systems:
--check the battery first
If you have the OEM service manual it will explain the procedures for check the components using resistance and measurement tests, however these procedures often assume use of particular measurement equipment which can influence the results.
posted 02-12-2007 10:08 PM ET (US)
A good battery will have about 12.5-12.7 volts, depending on the motors charging system you should be getting a 13-14 volt reading with the motor running. I would have the battery load tested and check all the connections to eliminate the obvious. If this doesnt work I would bring it to a mechanic to diagnos your problem. It might cost you a few bucks to do this but trial and error can be expensive too. Any electrical parts are non-returnable if you get it wrong you own it.
posted 02-13-2007 09:37 AM ET (US)
Thanks for the replies
I'm planning to get the boat out of storage as soon as the snow melts.
I'm positive the battery was in good condition. I purchased it new last fall.
I'll make an appointment with the local mercury dealer to look at the motor
Thanks again guys
posted 02-13-2007 02:53 PM ET (US)
You didn't specifically say that you stored your boat with the battery in it, I hope that is not the case. If you go through the winter months without charging, unless it is an AGM battery, you will permanently lose some capacity. With cold temperature storage if the battery discharges significantly the electrolyte can freeze and cause mechanical damage to the cells, maybe also rupture the case.
A new battery can also be defective, as others have suggested, testing the battery is a good first step.
posted 02-13-2007 05:11 PM ET (US)
Davej14, I did all my testing with a Fluke 77 multimeter. I don't store the boat or my camper with the batteries in them. I keep all my wet cell batteries in my cellar up off the concrete on wood and rotate float charging them.
I tested the motor running and it was 12 volts dc. While the motor was running I disconnected the battery to see if it was feeding off the battery, the motor kept running. This tells me that the output is enough to supply the motor but not high enough to charge the battery.
This battery is a Wal-Mart Maxx deep cycle.
I'm going to put on deep cycle charger and then test it.
I want to get this problem resolved before the spring rush.
Thanks for the feed back
posted 02-13-2007 05:41 PM ET (US)
Your Fluke meter is indicating a deficient battery unless it doesn't display tenths of volts. You are only reading the surface charge of the battery. A valid test will require applying a load. Any of the major automotive supply stores should be able to test it for you at no charge. I would still start with the battery.
BTW, I would not run the motor without the battery in the circuit because this could damage the charging system.
Let us know how you make out.
posted 02-13-2007 07:38 PM ET (US)
The Fluke 77 is the Boston Whaler Outrage of voltmeters.
Mine displayed two decimal digits (12.61) when I put it across
the battery in my truck just now (engine not running).
If you are getting 12ish volts with the motor running, you
posted 02-14-2007 11:30 PM ET (US)
You need to measure the battery voltage to greater accuracy. See the REFERENCE article on battery state of charge for a conversion between battery terminal voltage and battery level of discharge for a flooded cell lead-acid battery:
posted 02-14-2007 11:43 PM ET (US)
Wouldn't hurt to check it with another meter either.
posted 02-19-2007 08:24 AM ET (US)
I tested my battery and it checked out 12.75 volts dc
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