Outboard charging circuit

[x-man12345]

Hello guys,
I thought I should pass this one on.
Ladybird has a Mariner 6hp outboard with a charging circuit, the also has a 20w solar panel (with Steca controller). These both keep a 33 ahr AGM battery charged.
After a few sunny days (:D) with the battery status at 100%, we motored out for a sail and noticed that the solar panel controller was in fault (battery voltage too high). This returned to normal when the engine was turned off.
I have looked into this and taken some measurements and it seems that this is in fact true. The output from the Mariner and I guess most small outboards is un-regulated 1/2 wave DC. I have measured in excess of 15v DC at the battery with the engine running at 3/4 throttle .
I have now purchased a rectifier/regulator from electrexworld (very helpful) to solve this.
I think it would be Ok with just the outboard but the solar panel is working so well the battery is at full charge most of the time.
Happy sailing
Ian

[Nick Martin]

I've measured over 40 volts (peak) off my Yamaha .. may well bigger spike but not measurable with my meter .. this can can destroy a lot of regulators .. the only one that's survived long term for me is well over rated and designed for a wind generator using a dump resistor .. all 'entirely electronic' ones eventually failing .. will be interesting to see how you get on .. Nick Martin

[x-man12345]

Hello Nick,
Did you measure this open circuit or at the battery terminals?
Any sort of resistance will pull down line voltage.
Thanks
Ian

[Nick Martin]

40 volts was open circuit .. I cannot remember how much I had at the battery when connected - obviously less - but still more than I would have liked .. and still there's the potential for nasty DC / spikes so you need to be sure about where the battery isolation switch is so you don't end up without the battery load .. hope that makes sense .. Nick

[x-man12345]

New regulator/rectifier fitted:) close to battery.
Installed new tinned two core cable from outboard back to battery.
Quick test results -
Battery at 100% SOC (thanks to solar panel).
Engine running at approx.3/4 throttle.
Max voltage across battery terminals 14.4 volts.
Regulator is designed to operate at 14.4 volts, so all seems well.
Happy days.
This Reg/rectifier is a solidly built bit of kit.
Ian

[SimonW]

With a boat in build, I was about to order a Mariner/Merc/Tohatsu 6hp and add the charging circuit and lead. However, because the boat needs a standard(short) shaft, the engine cant be bought as a saildrive as that only comes in Long Shaft. That means adding the charging kit. UNfortunately that in itself adds a whopping £350+ to the price of a small engine, so I am wondering if its worth it. I have the 30 AMH battery going in and wondered if a solar panel would be enough on its own to power the LED lights and instruments. Does anyone have experience of doing it this way?

I also understand that you can attach a solar panel directly up to a certain level, after which you need a diode or some sort of controller.

Any thoughts welcome?

[x-man12345]

Hello Simon,
I bought our Mariner 6hp from the marina where we keep Ladybird, they fitted a sail drive kit (charging coil and high thrust prop) and gave me a good deal.
Would I have a charging coil fitted now? Not sure, depends on price.
Would I have the high thrust prop fitted? Yes, no doubt.
I fitted a good quality solar panel with controller and I believe that this is enough. It all depends on how much you intend using the battery?
How much will you run the engine? You will not be charging the battery when you are sailing.
Then again you need a bit of sunshine to charge a battery from a solar panel.
I ended up paying an extra £70 for a reg/rectifier to control the output voltage of the charging coil as well. The output from the charging coil is pretty crude.
I figured at the time it was worth covering both means of charging. You could add another battery and give yourself a lot more amp hours?
It's a difficult one, isn't it?
I would look at the demand you are going to put on the battery. LED lights and most instruments use very little. I fitted a tiller pilot, that uses a bit more.
Good luck.
Ian

[Ru88ell]

I didn't want to use the engine to charge the battery as I like quiet. I agree with Ian on the high thrust prop though. I have so much more close quarters control now.

[Black Sheep]

Hi,
Definitely a solar panel will do the job when you are only using LED cabin lights and the cigar socket for charging cell phone, ipad, vhf, etc.
In 4 years I never had to charge my battery on shore power (also in winter my battery is in the boat). So I would recommend the solar panel (and the right prop of course.
Best regards,
Black Sheep

[SimonW]

Thank you all. I have actually decided to go with a Yamaha 6, primarily because the UK distributor is very local providing excellent service on my RIB outboard. Rather surprisingly it has also worked out cheaper than a Mariner/Merc and the charging circuit is cheaper.

I will probably get the charging circuit as its only £140, but will definitely get a solar panel - 10 watts seems the right sort of level?

I will also be getting a fine pitch (nee high thrust) prop!