Outboard Charging System

[Salmon Hatchery]

So, excuse me if these questions have been answered previously but, I couldn't find straight answers to these questions.

I have a Honda 75 (7.5hp) outboard on my Cal 25, in which i restored. I am trying to setup a system in which the alternator on the outboard charges the Deep Cycle marine battery i have aboard. I have a few questions about that system:

1) I currently have only 2 things connecting to the battery, the wires from the alternator, and wire from all the peripherals (pumps, lights, electronics, ...). Currently, I have the two positive wires bound together and attached to the positive battery terminal. Similarly, i have the 2 negative wires bound together then attached to the negative terminal. Something seems to rudimentary, to simple for a sailboat, is that assumption valid?

2) Do I attach positive to positive from the alternator to the battery, or negative to positive?

3) I am getting upwards of 20 volts when the motor is at full throttle. Does this voltage imply the need for a voltage regulator? Because i have attached the alternator to the battery in the way i outlined above, and checked the power coming off the battery and the voltage never reached above 13, at about 75% throttle.

4) Should the alternator wires be on some on/off switch? because it seems that if they are not, then the current from the battery could shock someone who plays with the plug that goes into outboard, since the plug is always connected to the battery, and not always connected to the battery.

Any light that can be shed on these 4 questions, or the appropriate resources to find solutions would be amazing. Thanks!

[GordMay]

Greetings and welcome aboard.

Originally Posted by Salmon Hatchery

...
2) Do I attach positive to positive from the alternator to the battery, or negative to positive?
3) I am getting upwards of 20 volts when the motor is at full throttle. Does this voltage imply the need for a voltage regulator? Because i have attached the alternator to the battery in the way i outlined above, and checked the power coming off the battery and the voltage never reached above 13, at about 75% throttle.
4) Should the alternator wires be on some on/off switch? because it seems that if they are not, then the current from the battery could shock someone who plays with the plug that goes into outboard, since the plug is always connected to the battery, and not always connected to the battery.

2. Positive to positive, as described in your 1.

3. I expect you’re right - you appear to have an Un-Regulated power supply, typical on small outboards, intended to operate Nav’ Lites; not to charge batteries.
Your Honda dealer will be able to confirm this.

4. I don’t understand the premise of the question.

[sandy daugherty]

If there is some reason to disconnect the plug to the motor, then it should be tucked away out of reach or hands or saltwater. Were the battery completely charged, the circuits attached would see higher voltages, which could exceed the capacity of the wiring or the units themselves. A regulator can prevent this.

Did I misunderstand your question?

[David M]

It sounds like it could be one of two things.

1. You need a regulator. 20 volts will destroy electronics meant for 12 volts only. Your battery will definitely get destroyed if it gets close to being fully charged and the voltage climbs up to anywhere near 20 volts. Do not connect the outboards magneto (not an alternator) to anything until you get a regulator designed for charging 12 volt batteries.

2. It may be the case that you do have a voltage regulator but the voltage sensor wire is not connected to the 12 volt system or its broken, causing the voltage to go sky high.

Check with the manufacturer of your engine to see if your engine came with a regulator....some outboards do and some don't. The newer ones usually do though.

[GordMay]

David's accurate comments remind me that the output is quite likely AC (or very high ripple DC), which will run lights but little else. In which case, simple regulator won't suffice.

[Cheechako]

I would assume if it's an electric start motor that the alternator is intended to charge the battery....? But you better check with the Honda dealer.... maybe it is unregulated.. Of course it may be putting out next to nothing in terms of charging.... would 20 volts at .1 amp hurt a battery?

[Salmon Hatchery]

Thanks for the replies!
The motor is a pull start. Attached is a picture of the motor, the arrow points to the plug.

So if I'm getting this right, the outlet plug on the outboard is meant not for charging the battery, but for powering lights only when the motor is on? I guess i don't really see the advantage of that, when the battery already powers all the lights.

But to elaborate on the 4th question. There are two wires that run from the battery terminals and then attach to a plug near the transom that I am supposed to plug into the motor (I assumed for to charge the battery). The thing is, the plug can't always be plugged in due to spacial difficulties(which I'll figure out myself). So when the I don't have the plug in the motor then there is essentially a live wires in the cockpit. So wouldn't it be advantageous to add some on/off switch to kill the circuit?

Also, while charging, is it OK to run the electronics, or will they be damaged?
To quote the owners manual:

"The DC receptacle provides a 12 V, 60 W current for 12 V battery charging and lighting. The circuit is protected by a 5 A fuse that is accessible by removing the engine cover. An electrical plug for the DC receptacle is supplied with your motor. Wire your charging or lighting cord to this plug."

The 12 V they speak of is not consistent with the reading i'm getting off the voltage meter.

[roger.waite]

Some pull start outboards came with a minimal generation capability that was just sufficient for nav lights when the engine was running (fraction of an Amp). Remember, many runabouts (their target market) have no batteries.

Had to install extras to bring charge capacity up to 5 or so amps. So you need to check whether you are producing enough juice (vs. your energy consumption) to make it worth wiring up. E.g. check engine manual or ask outboard mechanic.

Strongly advise a cutoff switch (and a fuse) to isolate the battery. I mention fuses becuse you seem to be describing a basic setup, and I have caused a short cutting what I thought was a dead (and fused) circuit ... Cable melting in seconds ... Fire would have started within a minute. Found out later they ran the wire right past a plastic petrol tank.

A much wiser man would have looked carefully at how the electrics were set up when he bought the boat ... but if you live, you learn.

[roger.waite]

Sorry - I did not register your excerpt from the manual re: power output ... the rest of my comment stands ...

[Cheechako]

If you have a good voltmeter, you might try measuring the voltage at your radio, just to see if it shows high voltage also. (engine running) There are small 50 amp circuit breakers that would work well for your disconnect. Or maybe a full size battery switch is just as cheap. Amazon.com: MKR-19 Circut Breaker: Sports & Outdoors

[Salmon Hatchery]

Originally Posted by roger.waite

Some pull start outboards came with a minimal generation capability that was just sufficient for nav lights when the engine was running (fraction of an Amp). Remember, many runabouts (their target market) have no batteries.

That makes perfect sense, i hadn't really even thought about that!

[cal40john]

The OP posted what the charger was designed for from the Honda manual, for charging batteries and running lights. It also states that it has a 5 amp fuse, and it is a 60 W charger, or about 5 amps at 12 volts. Do not hook up an unregulated charger to your boat's electrical system without the battery in the circuit. The battery determines the voltage of the system based on it's state of charge. Some of the old unregulated chargers could hit 90 volts. Good thing our club boats at the time only had light bulbs to replace when someone forgot to hook up the battery.

It would take a lot of motoring to overcharge your battery with that small charger, that's why they didn't go to the expense of putting one on. If you need a plug it in and forget it system, you need a regulator. As far as I know Honda does not make an upgrade for their engines. If you're motoring long distances, look at the battery voltage, if it goes over 14.4 volts, unplug the charger or turn on some lights. If you want to properly charge your expensive AGMs to absolutely maximise their life, you're gonna need a bigger boat with an inboard, alternator and external 3 stage regulator.


Look at a maintenance sized solar panel. You don't need a regulator and you can leave it charging the battery forever. Open circuit voltage on most panels is 17.5 volts, but that's not the voltage you see when it is connected to the battery.


John