Moderated Discussion Areas
ContinuousWave: Small Boat Electrical
Maintenance-Free Battery Charging
|Author||Topic: Maintenance-Free Battery Charging|
posted 05-07-2009 07:37 AM ET (US)
My 1989 Johnson 70 (and the attached 15 SuperSport) came with a maintenance-free battery. This is clearly not recommended by the motor manual. However, the battery does seem to be working and holding a charge, and there is no spitting of electrolyte visible on the battery or in the case. My voltmeter does show a clean 18-Volts when running, but on the other hand, it's only 6-Ampere maximum.
Ought I to change out the battery for a non-sealed one? Or wait for this one to fail somehow? Clearly I should change it, but the current battery is paid for. Will the maintenance-free unit fail in some spectacular fashion, and take something else with it? Or just start failing to hold a charge? Will it give me some warning, or just leave me stranded some day?
I'd appreciate any real-world experience on the subject.
posted 05-07-2009 07:52 AM ET (US)
18V when running? That will burn a battery out. The max in general is 15.0 and really should be about 14.2 when running. Have your charging system checked.
posted 05-07-2009 07:54 AM ET (US)
Glen, 18 volts is normal for these older motors that have unregulated power supplies. The charging system is working as designed - it's just an older, less sophisticated design.
posted 05-07-2009 08:56 AM ET (US)
The term "maintenance free" battery is not a precise descriptor of the battery type. I am not sure exactly what type of battery you have. I will assume that your maintenance free battery is really a sealed valve regulated lead-acid battery with conventional flooded cell construction, or an SVRLA battery.
When the charging voltage applied to a lead-acid battery is higher than about 14.5-volts, the chemical reaction that occurs causes hydrogen gas to bubble out of the electrolyte. In a non-sealed battery the gas vents to the atmosphere. In a sealed battery the gas is contained, and materials in the battery try to move the gas back into solution with the electrolyte. This is a recombinant technique. If too much gas is produced, it exceeds the capacity of the recombinant material to handle it, and internal pressure in the sealed case builds up. A relief valve eventually opens to vent the gas to the atmosphere. If enough venting occurs the result will be loss of electrolyte. If enough electrolyte is lost, the battery loses its capacity to hold a charge.
Some "maintenance-free" batteries have caps which are removable, and they provide access to the cells and their electrolyte. If you have a battery of this type you can replenish the electrolyte by adding distilled water to the cells. These caps are not intended for routine service, but can be removed if needed.
If you have a SVRLA battery that is completely sealed and provides no access to the cells, you cannot replace any lost electrolyte. If you overcharge such a battery you will eventually boil off the electrolyte. The battery will slowly lose its capacity as it loses its electrolyte. Also, more of the lead plates will become exposed to air. This may also cause damage.
It is hard to know exactly how much gassing will be produced by your charging situation. If the recombinant feature of the battery can keep up with the gassing, the battery will repair itself. If the charging keeps causing the battery to vent gas, and you cannot replace it, the battery will eventually fail.
I can't offer any first-hand experience with this because I have not tried it.
posted 05-07-2009 09:03 AM ET (US)
Thanks Jim, and thanks for moving this to Small Boat Electrical - I wondered where my question should go, but for some reason this forum never occurred to me.
My battery is completely sealed - no way to add water. I'm really just wondering if I need to replace it, and how soon. I don't want to be left stranded, or have it fail and take out my regulator (such as it is) or have it fail in some other dramatic and dangerous fashion.
posted 05-07-2009 11:41 AM ET (US)
wow...thanks for the education. I did not know that. And that does not fry a battery?
posted 05-07-2009 02:53 PM ET (US)
Check your outboard. Does it have a voltgage regulator or just a rectifier? If just a rectifier then use a larger battery such as a group 27 or group 31. The battery acts as a regulator in these types of charging systems. Do not use a maintenance free or sealed battery.
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.