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 Catalina/Capri 25/250 Sailor's Forums
 General Sailing Forum
 Outboard overcharging batteries		  New Topic  Topic Locked
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albert
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USA
262 Posts
Initially Posted - 10/30/2004 :  20:48:54  Show Profile  Visit albert's Homepage
With the outboard at half throttle, my voltmeter shows 14.5 volts going into my battery. Is this normal? I would think that a couple of hours of this would boil off the electrolyte. What would cause this? BTW, my battery is fully charged at the time that I checked.
Albert Iturrey
al@comhertz.com
Abacus 1984 C25 #4679
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Waterboy
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USA
204 Posts
Response Posted - 10/30/2004 :  21:13:10  Show Profile  Visit Waterboy's Homepage
I'm not an outboard expert, but the first thing that comes to mind is a faulty voltage regulator on the outboard - it should sense the charge level of the battery and provide current accordingly. Secondly, just because it's at 14.5V doesn't (I think) mean it's overcharging ... if it's 0.002 amps at 14.5V it shouldn't hurt the battery.

12V outboard experts?
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John V.
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559 Posts
Response Posted - 10/30/2004 :  22:11:12  Show Profile  Visit John V.'s Homepage
My Honda 9.9 produces that kind of voltage but never more than an amp or two. At that rate it would take 230 hours to recharge my batteries.
Most light outboards like the ones used by C25's have a small 12 volt output it is not the same as an output from an alternator which can be at many amps. Larger outboards have this higher output in order to recharge the starting battery.
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albert
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262 Posts
Response Posted - 10/31/2004 :  00:45:32  Show Profile  Visit albert's Homepage
The outboard puts out less than 6 amps. Its an older Tohatsu 18hp.
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oldsalt
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USA
578 Posts
Response Posted - 10/31/2004 :  22:42:11  Show Profile
My 2 stroke Johnson 9.9 Sailmaster likewise puts out 14.5 volts to the batteries but only at about 4 amps at the usual throttle speed. This is normally a good voltage to charge your system and at the low amperage it's unlikely that you will supply enough amp hours to cook your cells. Most small 2 stroke outboards don't have regulated alternators.
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Bill Holcomb
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769 Posts
Response Posted - 11/01/2004 :  09:36:52  Show Profile
Hi Albert,

As the other responses have stated, 14.5 volts is normal. The amperage is the key as well as how far down the battery charge has been allowed to go.

But, the answer to whether the alternator can "boil" the electrolyte out is potentially yes.......especially if you are motoring for a considerable period of time and start with a fairly "fully charged" battery. I noticed that the electrolyte in my #1 battery was below the top of the plates after motoring for around 6 hours one nice summer day with no breeze.

Bill Holcomb - C25 Snickerdoodle #4839
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Bruce Baker
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402 Posts
Response Posted - 11/01/2004 :  15:39:17  Show Profile
The previous owner of my outboard (Nissan 8 long shaft) warned me that it has the potential to fry the battery under extended motoring conditions.
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mday
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Response Posted - 11/02/2004 :  00:13:31  Show Profile
Albert,

I'll agree with the others that have answered -- 14.5 volts is normal and good. If you have an ammeter in your car, you will see about the same reading there. As your battery charges, it will tend to draw less current and "boiling off the electrolyte" should not occur.

Max
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.