Can a Solar Charge Controller be used to regulate an outboard ?

[Leeward Rail]

Question for the electrical nerds out here.


My Tohatsu outboard has unregulated output via magneto (12V DC, 5 amps @ wide open throttle)
In most cases people seem to just run the outboard directly to the battery.
The output of the outboard, in real use would be low.

This setup seems a bit lacking. Therefore I'm now wondering...

Can a PWM solar charge controller be used to regulate the output of an outboard, or should I just get a simple regulator for the motor ?

Could I hook the outboard output to the PWM charge controller used for my solar panel ?
That way a single device would manage battery charging.
If so, would you need some type of isolation for the two charging sources running into a single charge controller ?

 

[Chief RA]

Is that a true volt and amp meter readout by you or a quote from the Tohatsu book? The voltage is usually higher than 12 volts and yes you can hook it to your controller with those 2 extra wires that are probably not currently being used on the controller. Be aware that a battery can handle reasonable unregulated current/voltage anyway. I run my Tohatsu directly to my battery bank. Chief

 

[capta]

In over 50 years of messin about on boats, I've never heard of anybody needing to regulate the output power from a small outboard before. What does the manufacturer suggest?

 

[walt]

you may have heard to never disconnect the outboard charging circuit from the battery while its running - it will blow the diodes in the rectifier circuit. A PWM solar controller does exactly that.. disconnect and then connect the solar panel to the battery. I wouldnt try it, good chance of blowing both the outboard charging circuit diodes plus the PWM solar controller.

 

[Ron20324]

IIRC my Honda 8 charging 12v was not intended to charge the battery per se, but to give you something to limp home on. Run the depth, maybe radio.

 

[capta]

you may have heard to never disconnect the outboard charging circuit from the battery while its running - it will blow the diodes in the rectifier circuit. A PWM solar controller does exactly that.. disconnect and then connect the solar panel to the battery. I wouldnt try it, good chance of blowing both the outboard charging circuit diodes plus the PWM solar controller.

Most of the small outboard electrical outputs are primarily to run navigation lights and often never get used at all, so I doubt that disconnecting them from a battery would do any harm.

 

[walt]

Most of the small outboard electrical outputs are primarily to run navigation lights and often never get used at all, so I doubt that disconnecting them from a battery would do any harm.

No problem if the outboard charging system is not connected while the outboard is running. What you should never do is disconnect the charging system WHILE the outboard is running. The current flowing in the charging coil all of a sudden has no where to go when disconnected from the battery and a big voltage spike occurs which can exceed the reverse breakdown voltage of the rectifier diodes - and way exceed the solar controller max input voltage.

 

[Jim 5757]

In any case it sounds like you're trying to INCREASE the voltage output of your outboard. Is this so?
If not then there seems to be no point in trying to control it if it only puts out 5 Amp max. You'd have to run the engine for days to have any effect on the battery.

 

[Chief RA]

Careful Jim, 5a is a lot more than a trickle charger. Chief

 

[Leeward Rail]

Is that a true volt and amp meter readout by you or a quote from the Tohatsu book? The voltage is usually higher than 12 volts and yes you can hook it to your controller with those 2 extra wires that are probably not currently being used on the controller. Be aware that a battery can handle reasonable unregulated current/voltage anyway. I run my Tohatsu directly to my battery bank.

Tohatsu manual data. My new outboard is currently in a truck heading my way.
Good to know.
@Gene Neill also has the exact same motor connected directly to the battery, with a controller only for his Solar panel.

Careful Jim, 5a is a lot more than a trickle charger. Chief

That was my concern.
Once my new motor arrives I'll test to see what it puts out at realistic rpms.
I'm guessing it will actually be so low as to be a non issue.
But "inquiring minds".... etc.

I've never heard of anybody needing to regulate the output power from a small outboard before. What does the manufacturer suggest?

It's my nerd tendencies that were driving my question.
My thinking was... "If i can do it, and it's a better option, without additional cost.... why not ?"
FWIW, I assume Tohatsu simply suggest direct connection to the battery, like usual.
In fact I think it even comes with a pre-made cable.

In any case it sounds like you're trying to INCREASE the voltage output of your outboard. Is this so?
If not then there seems to be no point in trying to control it if it only puts out 5 Amp max. You'd have to run the engine for days to have any effect on the battery.

Nope. Just limit the output based on battery charge state.
Agreed about the actual risk to the battery. See above... It's my nerd side who cares.

you may have heard to never disconnect the outboard charging circuit from the battery while its running - it will blow the diodes in the rectifier circuit. A PWM solar controller does exactly that.. disconnect and then connect the solar panel to the battery.

The current flowing in the charging coil all of a sudden has no where to go when disconnected from the battery and a big voltage spike occurs which can exceed the reverse breakdown voltage of the rectifier diodes - and way exceed the solar controller max input voltage.

VERY GOOD POINT. In the tiny amount of research I've done so far, I assumed a PWM controller didn't simply disconnect/connect.

That settles it I guess. Store this in the bad idea bin.

Edit: I now wonder about a MPPT being safe to use for this.

Thanks VERY much for all the input.

 

[thinwater]

This is not needed. Since you will only run the engine for short bits and probably less than WOT, the actual charging on any day will be a few amp-hours. Typically, it's not even enough to keep the battery up. Plus the other reasons people gave.

 

[Leeward Rail]

This is not needed. Since you will only run the engine for short bits and probably less than WOT, the actual charging on any day will be a few amp-hours.

Agreed.

The nerd in me will make me test to see what the actual real world output will be.
Needed ? no Thought it would be "nice" to have though, since it would have just been a matter of routing/connecting the cable differently.

 

[Johnb]

Agreed.

The nerd in me will make me test to see what the actual real world output will be.
Needed ? no Thought it would be "nice" to have though, since it would have just been a matter of routing/connecting the cable differently.

You better pay attention to what Walt wrote above or your are going to score an own goal

 

[Leeward Rail]

You better pay attention to what Walt wrote above or your are going to score an own goal

Obviously.

 

[John Nantz]

This was a good post and I learned something from it.
My dad had a Mercury 9.9 on his boat and I volunteered to bring it back from another marina to his house. It was a fairly long trip and I started out in the late afternoon but part way it became dusk and I turned on the running lights. When it got dark one could see that the running lights and the interior lights were really bright. This was especially noticeable with the port and starboard running lights. I learned that the output voltage was quite high but never got into what one could to to regulate it so this thread had a lot of new information in it.

 

[walt]

Simply monitoring the battery voltage when the outboard is running is generally about all you need to do. If you have very much battery capacity, almost never an issue with too high of voltage. However, if you start out with a fully charged battery and its maybe a little bit past its prime, you probably could have these small outboard charging systems create too high of voltage. Someone posted on this forum a while back this happening. They were able to purchase some sort of aftermarket regulator intended for this application but I cant remember what it was or where they bought it.

The PWM solar controller idea "could" possibly work if you added a large capacitor in parallel between the outboard and the solar charge controller input. The PWM solar controller regulates charge by "duty cycle" switching (connecting or disconnecting the solar panel input to the battery) at some frequency and the large capacitor "in theory" would provide the energy storage to prevent the damaging large amplitude voltage spikes from occurring.

If someone wanted to mess with the capacitor and PWM solar controller, I would start with maybe 10,000 uf cap something like this https://www.amazon.com/10000uf-Electrolytic-Capacitor-35x51mm-105ºC/dp/B00K87I3PO/ref=sr_1_2?ie=UTF8&qid=1498838407&sr=8-2&keywords=10000+uf+capacitor . The cap would just go across the + and - wires between the outboard and the solar charge controller input. Be careful with the polarity on the cap. this type can literally explode if hooked up backwards.

And before I hooked the PWM solar charge controller up.. I would try this with just the outboard/ capacitor / battery and check how large the voltage spikes were when you disconnect from the battery. You would need an oscilloscope for this measurement. You may need more than 10000 uf. You would also need to check to make sure that when the battery was disconnected, the "open circuit" voltage on the capacitor did not go above the max input voltage spec of the PWM solar controller. Of course.. you risk damaging your outboard rectifier just trying this...

 

[Chief RA]

Walt: That kind of experimentation is not for a layman to do! Chief

 

[Leeward Rail]

great post @walt

Does a MPPT Type controller actually disconnect/connect ?
I'm new to solar charging so I'm still reading up on the details of how the various controllers actually work as opposed to the usual marketing overview

@Chief RA Very true. Good to have that warning voiced

FWIW I'm ok with some experimenting. While I'm not an electronics pro, I spent 3 years in High School electronics, and I do repairs on electronics/wirng in customer's vehicles almost daily. For this season I'll just get the boat's wiring functional enough to be usable, in spite of my "natural tendencies" hehe. Might be a good winter project though.

This whole idea occurred to me, because some of the PWM Controllers I have been looking at, have displays showing battery state, charging in progress etc. So my initial thought was "Would be nice to not only make sure that voltage from the outboard doesn't get too high. While I plan in installing a Volt/Amp meter for monitoring, maybe this can be done with a solar charge controller, to decrease complexity and lower cost"

 

[Ward H]

Someone posted on this forum a while back this happening. They were able to purchase some sort of aftermarket regulator intended for this application but I cant remember what it was or where they bought it.

I think it might have been Brian of SV Four Points. Here is the link I bookmarked to the electrical category of his blog:
http://sailingit.com/blog/category/boat-projects/electrical

I linked to the category because it also contains some related posts that might be interesting. The one on installing an OB regulator is near the bottom of the page.

 

[Han Solo]

This thread is bit old but I don't want to start a new thread. I am asking the same question except I don't have a cranking battery. What I want to know if I can hook up my Yamaha F6 to a solar panel controller to change my lithium batteries?