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Catalina/Capri 25/250 Sailor's Forums

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Overcharging?

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Doug
Captain

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USA
457 Posts

Initially Posted - 07/07/2004 : 09:20:49

My outboard power runs through a switch on the panel that interupts the power running between (To and from)the battery and the outboard. This switch is getting bad, and it also happens to be in a great spot for me to instal a 12 volt outlet.
I can't figure out why I need a switch to turn off power going to the motor (starting) so I assume the purpose of the switch is to stop excess power going to the battery.
Is it possible for my outboard to overcharge my battery? If so, do I need to monitor and turn off the charging when the battery is at capacity? Is there any other reason to keep the switch or can I get rid of it?

Doug - #1913 Noeta

Edited by - on

RoofRoof
Navigator

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USA
186 Posts

Response Posted - 07/07/2004 : 10:38:39

Hopefully someone will verify what I'm about to say....

But, I was under the understanding that the charging cable from the motor must be connected to the battery without any switch. A switch effectively cuts the cable so the charge goes nowhere. I am pretty sure that this is bad for your alternator.

Someone help verify/disprove my thoughts.

Edited by - on

Bill Holcomb
Admiral

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USA
769 Posts

Response Posted - 07/07/2004 : 11:01:25

Hi Doug,

Yes, it is possible for some outboard engines to overcharge the batteries leading to the electrolyte "boiling" out and exposing the plates..... ruining the battery If you are going to motor for a considerable period of time, a switch that opens the circuit will prevent the loss of electrolyte.

It is okay to run the engine with the charging circuit open. It is the same thing as not having the engine hooked to the battary. Just make sure that the switch opens the positive side of the charging circuit...if not both sides.

Also, DO NOT TURN THE SWITCH OFF IF THE ENGINE IS RUNNING! On some engines this can destroy the charging circuit in the engine. Check with your dealer or owners manual.

Bill Holcomb - C25 Snickerdoodle #4839

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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 07/08/2004 : 08:36:22

Doug - you don't specify what model of outboard you have, so we can't do more than guess at the charging output, but most outboards of 5-10 hp size have no more than 5 or 6 amps of charging output. This is not much current, and you would have to run the motor at full speed for several hours to really boil the battery. A few outboards like the Yamaha and Honda 9.9 HT's have 12 to 13 amps of charging output, and this is enough current to overcharge a battery if you ran the motor for a long time. I wonder if these outboards with the 12 amp alternators have a voltage regulator built in to prevent battery damage? Anyone have a Yamaha 9.9 that would know?

I think RoofRoof is incorrect about the cable having to be connected. Small outboard motors have a very simple alternator consisting of a permanent magnet mounted inside the flywheel, that induces current to flow from a stationary coil (or two) mounted on the powerhead. Alternating current from the coil is rectified into DC by a bridge diode array. Since there are no commutator brushes or slip rings involved, there is nothing in the alternator itself that would care if the battery cable is connected or not. The only questionable item is the bridge diode, it might be damaged by excessive voltage, or sudden current spikes caused by plugging or unplugging the cable while the motor is running. I will call our local Yamaha/Honda outboard motor dealer and ask the service tech about this.

Edited by - lcharlot on 07/08/2004 08:38:02

Doug
Captain

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USA
457 Posts

Response Posted - 07/08/2004 : 10:25:22

I have a Yamaha T8. It runs at about 5 amps. I think I'm going to leave the switch in and turn it off on long motoring runs, but not worry about it the rest off the time.

Edited by - Doug on 07/08/2004 10:26:07

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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.