Charging one battery with solar panel and outboard alternator on sailboat

rporter · March 2017

I'd like some opinions on the best way to connect these two charging sources to the battery. Is it ok to run the solar panel and outboard alternator into a solar panel controller? Would it be better to have a separate controller for each one? Will a solar controller function correctly with input from an outboard motor alternator?

Thanks.

Estragon · March 2017

You would connect the alternator directly to the battery. It should have its own regulation. Charge controllers aren't normally designed to handle alternator output.

softdown · March 2017

I second Estragons offering.

rporter · March 2017

Its a 6hp outboard with an "alternator" which looks like two coils that fit under the flywheel and there is a rectifier. The only info I can find is that the output is about 5 amps. Do you think the rectifier has capability to regulate the charge rate? I don't want to over-charge the battery if I'm running the engine for 8 hours.

softdown · March 2017

I should think you could measure the output from the alternator and see if it tapers off as the battery approaches full charge. If it is so simple that it does not, I should think (more often really) that one could find a simple gadget that would moderate the output. Bear in mind that I am doing some speculation here.

jonr · March 2017

Perhaps of interest for unregulated alternators:

http://www.boatingmag.com/converting-your-outboards-unregulated-charging-system

You know you are unregulated if the battery voltage goes too high (eventually, with no loads).

Estragon · March 2017

What kind of battery and bank size are you charging? Do you know the voltage on the alternator output?

dennis461 · March 2017

Do you know make, model, year of outboard? From your description it sounds like the rudimentary system used on 1960-1970 vintage two stroke motorcycles. The main source of regulation was the battery itself. The magneto-coil-rectifier setup simply sent pulses of DC to the battery. If the battery lost all it water (like when the dirt bike falls over) the pulses of DC would be high enough to burn out the lights in short order.

oil pan 4 · March 2017

If you have an oversized battery for running lights at night or a secondary electric motor then 5 amps is probably not enough to come close to keeping the battery fully charged.

jonr · March 2017

In theory, a DC-DC converter (as is found in the better solar charge controllers) could take excessive voltage from a simple permanent magnet alternator and convert it into additional current. My understanding is that most small engines use a shunt regulator (briefly shorting out the windings to reduce voltage).

My guess is that one could connect the output of the alternator+rectifier to a solar charge controller. But only if the peak (not rms) open circuit voltage of the alternator was less than the charge controller's max input voltage.

oil pan 4 · March 2017

I have seen simple magneto generators put out up to 24v OCV with the battery removed, with an otherwise functional regulator. Straight off the magneto can produce up to 48VAC at no load.
I'm not saying every single one is like this, but I have seen a few.

jonr · March 2017

So for that generator, maybe 68V peak. OK for some solar charge controllers.

Last summer, I blew an ignition module surge protector/fuse. Apparently because the bad battery wasn't accepting much charge (and the regulator wasn't regulating very well).

rporter · March 2018

Update a year later.

Currently I use the solar panel or the outboard charger separately. I would still like to combine the wiring so the outboard charger runs through the controller. I have posed the question to Morningstar. (Sunsaver 10).

And I just received an answer but no reason given, "do not connect the outboard charger to the the controller".

The outboard charger had a voltage limiting system built in. I have installed a voltage meter reading to two decimal places. The voltage is cut off at about 14.65 volts. My concern is overcharging the battery if the motor is running 8 or 10 hours.

Horsefly · March 2018

As others have said, let the Morningstar controller handle the solar. The alternator should be a separate, parallel charge source. My sister's sailboat has a 100A alternator that does lots of duty charging the house battery. It goes thought a Balmar ARS-5, which turns the alternator power into a three-stage charging source for the AGM batteries. Then you don't need to worry about over-charging from the alternator. When the battery is full, the ARS-5 will lower the regulated output voltage to float.

I think my sister and brother-in-law are not real happy with the Balmar, but it's mainly because it is a challenge to program. I think once it works fine it works fine.

rporter · May 2018

That probably worked well for them but it sounds like it is on a sailboat with a diesel engine with alternator. That Balmar unit is for that type of installation.

I have a 6hp outboard motor on a 22' trailerable sailboat with what is really a generator and a rectifier (even though the manufacturer calls it an alternator). So far I have not found any small, 12v device for controlling the charge. The rectifier does a good job of limiting the voltage but it will keep putting out 5 amps for hours if I motor all day.

mikechro · September 2020

@rporter I have the same configuration (Tohatsu 6HP with 5 amp rectifier) and I want to connect it up to the house battery using the volt meter you discussed. Can you share some info on your system? Battery size, volt meter model, solar panel size and solar controller. I also have a 22' trailerable sailboat (Catalina 22).

wellbuilt · September 2020

It’s been a long time , but my Catalina had a10 horse out board that just charged the battery .

I think I had 2 battery’s but don’t remember where they where .

But I used a 80 watt solar panel mounted off a stainless steel hoop over the rear seat with morning star 20amp controller .

The battery just stayed charged every thing worked together .

Same thing with my C30 and C36 but the 36 had 3 80watt panels .

With a bolmar alternator and a Alt power systems 3 stage regulator
I had the most fun on the C22

Charging one battery with solar panel and outboard alternator on sailboat

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