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Old 02-09-2009, 14:43   #1
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Problems Charging Battery...What Are My Options?

Hello all,

I've had my boat for about a year and I've never had much success charging (or even maintaining) my batteries from the outboard. It's 15 hp 2004 Mercury, with wires that run from the engine for the purpose of charging a DC battery. I tested the wires on a voltmeter and they only generate about 8 or 9 volts of current. I'm not sure about the amperage or anything out. I don't have a manual but I've been told by people at the company that a small outboard really isn't enough to charge a 12v deep cycle battery.

This has never been that big of a problem for me since I have two batteries and I haven't been away from the marina for more than a week at a time... until now...

I'm planning a couple of longer cruises and I'm trying to figure out what my options are for keeping my batteries charged while I'm away from the outlets. I've looked into the portable solar panels, but wouldn't they suffer the same weak voltage flaw as the outboard? The wind generators are a bit expensive for me. Does anyone have advice on this issue? I don't use a lot of power on the boat, mostly running lights and radio and the occasional cabin light. The biggest trip I will be taking is 6 weeks up the Maine coastline (next summer). Does anyone have experiences with using a solar trickle charger? Or should I expect more from my outboard's built-in alternator?

Any advice is much appreciated,

Jack
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Old 02-09-2009, 15:42   #2
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"I tested the wires on a voltmeter and they only generate about 8 or 9 volts of current."

Let's forget about the terminology - you cannot charge a 12 V battery with 9 volts at ANY current. You need more voltage than the battery to push current; typically 13+ volts/
If your outboard isn't producing that voltage, something is obviously wrong with either the outboard power or the wiring, or both.

Check the easy stuff first - the voltage at the terminals to determine if you have a bad cable connection or low voltage from the outboard. The source of your problem and therefore the fix will be apparent after having done that.

For two batteries, you really need more than a small outboard or a solar trickle-charger to maintain the batteries. Presuming you already know the other options as well as your budget, first figure out what your demand is between recharge and size the appropriate charging source accordingly.
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Old 02-09-2009, 16:06   #3
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My last boat was a 23 with a 9.9 yamaha four stroke. It charged at 12 amps and I had a 15 watt solar panel. I never had a flat battery while often taking trips of 30 days and more. Draw was tiller pilot, GPS, VHF and lights. Something is wrong with charging of system of your outboard. Yamaha was making small fourstrokes for mercury. Is yours four stroke? If not I would consider upgrade. You won't be disappointed. If so you should have no problem keeping batteries up with properly working charging system.
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Old 02-09-2009, 16:13   #4
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My motor is a two stroke. I've checked all the connections leading into the alternator and everything looks ok. Any insight into how I could troubleshoot the motor?
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Old 02-09-2009, 17:09   #5
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Hi Jack
To Help we need more information
When you measured the 8 to 9 volt was that with the battery connected or is that the open circuit voltage (i.e. with the battery disconnected).
Is the battery new or old?
How big is the battery (how many amp hours)
Try and borrow a clip-on amp meter and see what current is flowing when the battery is connected.
Martin
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Old 02-09-2009, 22:05   #6
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Hello Martin and others,

I checked the charger with a multimeter and recorded 8 volts with the battery not connected (the positive mulitmeter lead on the positive lead from the motor, negative to negative, no battery involved)... The battery is new. It is a pretty big deep cycle battery, maybe 150 amp hours but I could be wrong on that.

Does my multimeter measure amps as well? I'm not sure how the thing really works but I will give it another shot and report back with more information. Thanks a lot for the help so far....
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Old 02-09-2009, 23:02   #7
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It sounds like you have a faulty rectifier/regulator. I would try and remove it so you can take it to someone for test/repair
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Old 05-09-2009, 08:59   #8
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Depending upon the make, model and horsepower of your 2-stroke outboard, you may just have malfunctioning generator in the outboard motor. First, check your outboard motor manual to see how you are supposed to attach the battery to the motor. If there is a warning to not run the motor without an attached battery - then you might have an alternator in the motor and operating the motor without an attached battery burned out some diodes or something. If the outboard motor manual states that you can operate the outboard motor without a battery attached then you probably just have defective generator system in the outboard motor and it needs to be repaired or replaced.
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Old 05-09-2009, 10:34   #9
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The charging system in small outboards is based on some magnets in the flywheel which whirl past a stator coil. The output of the coil is alternating current, which then goes to a bridge rectifier which converts it into DC. The rectifier is an option on some outboards, and is only included if you get the electric start package.

In the Mercury, you should see two yellow or yellow/red wires from the coil near the flywheel hooked up to a little rectifier box, which also has a red wire and a ground to the chassis. If you are only getting 9 volts DC between the red wire and ground, rev the engine up and see if you get more --you should see like 15-18 volts open circuit. If not, the most likely candidate for replacement would be the rectifier.

Don't expect a lot of charging capacity from this circuit--you could run it for 10 hours and it probably still wouldn't fully recharge a dead 100 amphour battery.

Portable solar trickle charges put out less than 1 amp, and even a 1 amp panel will take more than a week to recharge a 100 amp hour battery. If you have a decent dockpower battery charger, you best option might be a small portable gas genset--the Honda 1000i is the Cadillac, but there are cheaper ones around which will be fine for occaisional use.
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Old 05-09-2009, 11:47   #10
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Originally Posted by marting View Post
Hi Jack
To Help we need more information
When you measured the 8 to 9 volt was that with the battery connected or is that the open circuit voltage (i.e. with the battery disconnected).
Is the battery new or old?
How big is the battery (how many amp hours)
Try and borrow a clip-on amp meter and see what current is flowing when the battery is connected.
Martin
Clip on amp meters will work fine on AC circuits but not for DC. Although you will get a reading in circuits with alternators is just because the diode bridge in not ideal and have an AC component (rise and fall od voltage)

To measure DC current you need to apply ohms law. Amps = Volts divided by ohms. You can get a device known as a shunt which is a low value resistor. or you can use a resistor in the circuit of say .5 ohms or less. Read the voltage across the resistor.and apply the formula. If i had a voltage of .25 volts and a shunt or resitor value of .5 ohes then .25/.5= amps. A cheap and dirt shunt resistor is a lenth of wire . a 16 gage wire has a resitance of about .005 ohms per foot so 10 feet is .05 ohms.(close enugh for a sailer) You can read the resitance value with a milimeter and if you like me cut it to an easy math resitance.
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Old 05-09-2009, 11:52   #11
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Clamp ammeters work fine for measuring both AC and DC current.

http://us.fluke.com/usen/Products/Fl...(FlukeProducts)
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Old 05-09-2009, 12:16   #12
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Thanks for the link . Can you tell me the DC current measurement capability from there spec? I could not find it.
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Old 05-09-2009, 13:14   #13
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Actually, the Fluke 321/322 Clamp Meters to which David linked, only measure AC current. Meters like these operate on the inductive principle.

Clamp-On Ammeters, such as the Fluke 355 and 353, which measure both AC & DC current, operate on the Hall Effect.

Fluke 353 and 355 True-rms 2000 A Clamp Meters
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Old 05-09-2009, 13:29   #14
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Thanks Gordon...my mistake, bad example.
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Old 11-09-2009, 22:30   #15
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U need the BIBLE of boat maintenence, not de utha 1

Orange Crush Mate,

you need Nigel Calder's hefty tome on boat maintenance. It is my bible. There was a new edition out ?2005. So you should be able to get the previous edition 2nd hand cheaply

post#13 at DIY Maintenance / Repair Books?

gives a good list of books on boat maintenance. A good boat library is as important as a good set of the correct tools.

You can probably download a manual for your outboard from the net. A good workshop engine manual is vital to give you confidence to start tinkering.

PS "Orange Crush" as the name of a boat is just asking for trouble IMHO see recent "boat names" thread in general sailing forum
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