Charging from a Mariner 4hp sailmate

[LewisB]

Hi all,

I was wondering if anyone could help me with how best to connect up my Mariner 4hp sailmate (2-stroke) to my battery for charging.

I've had a look around, and have read that with the alternator kit with AC-DC rectifier attached to the engine (which I have), you can plug the engine straight into the battery without the need for a voltage regulator. This seems odd as the engine seems quite happy to pump out ~35V (depending on revs) which I would have thought would cook my battery (a small 45Ah (I think) car battery). At the end of last season I took my old battery off and it was swollen, however I don't know if this was caused by the engine over-charging. I would obviously like to avoid this happening again, so want to make sure that I have a regulator if it's needed.

Thanks in advance for your help!

Lewis

 

[TSB240]

Are you measuring voltage without it connected to the battery as this seems very high?

Our Tohatsu 6 hp with a charging coil would lift the voltage to up to 14 volts when connected to a battery. You would be lucky to get 6 amps charging at max revs. In my view if you want to charge and maintain your batteries charged you are better off using solar over a week of inactivity and whilst sailing unless you are using your engine all day at a weekend.

 

[VicS]

Hi all,

I was wondering if anyone could help me with how best to connect up my Mariner 4hp sailmate (2-stroke) to my battery for charging.

I've had a look around, and have read that with the alternator kit with AC-DC rectifier attached to the engine (which I have), you can plug the engine straight into the battery without the need for a voltage regulator. This seems odd as the engine seems quite happy to pump out ~35V (depending on revs) which I would have thought would cook my battery (a small 45Ah (I think) car battery). At the end of last season I took my old battery off and it was swollen, however I don't know if this was caused by the engine over-charging. I would obviously like to avoid this happening again, so want to make sure that I have a regulator if it's needed.

Thanks in advance for your help!

Lewis

I guess that's 35 volts open circuit. It does sound rather high but you will find that once you draw some current the volts will fall to a more realistic figure. I assume that is the AC output as you prefix it with the ~ symbol

45Ah is pretty small battery but unless you run your engine for prolonged periods at highish revs you are more likely to find that the output from the outboard falls short of your electrical requirements.

Most people find that they need to supplement the output from an outboard engine with, for example, a solar panel as TSB240 suggests

I used to have to take my battery home periodically for charging until I added a small solar panel. Now I don't have to keep lifting it on and off the boat I have fitted a slightly larger battery.

I suggest you simply monitor the situation initially. An inexpensive digital voltmeter will be adequate. If you really do find an overcharging problem fit an inexpensive regulator. A motor cycle type should be suitable.

 

[LewisB]

Thanks for the replies.

That's the voltage not connected to a battery, so 'open circuit' as you say. I haven't looked at what it is while connected to a battery. The 35V I quoted above is DC; by ~ I meant approx. Sorry for the confusion.

So I'll connect it up to a battery and see if it still pumps out a high voltage. From what you guys say, if it drops down to around 14V when I do that then all should be ok?

I draw very little off the battery; just some LED nav. lights, GPS, and interior light. So it's just to keep it topped up when I am motoring. I do take it off occasionally to charge at home too.

Thanks again!

Lewis

 

[ghostlymoron]

Best thing you can do as suggested, is fit a small solar panel. If you're usually sailing at the weekend, even a 10w panel will recharge in 4/5 days. That's what I had on my engineless boat and never had to take my battery for charging. The battery even lasted for a 2 week cruise but it was reasonable weather so was picking up charge all day under sail.

 

[LewisB]

Thanks for the suggestions. I'll look into a solar panel system. It would be quite nice to have the battery charged each time I step onto the boat rather than have to run the engine.

Lewis

 

[William_H]

Re the charging. You should monitor the battery voltage while using the engine and charger. My guess is that the battery voltage will be around 12.5volts when on charge. This may rise to near 14v after some running in which case you have no problems. Any higher voltage and the battery may be damaged after a lot of charging. More likely it does not rise much at all in which case charger is not much use. I did find with my old Johnson charger that I could get more voltage hence more current by replacing the charger diodes with shotky low volt drop diodes.
Of course really an amp meter showing charge current is the best test. You may be able to use you multimeter in current range between the +ve battery terminal and the connecting wire. Current can give you an idea of what is actually going into the battery. Compare the current and time AHs to the total battery capacity and to what you may have used with lights etc. However and and most others have not bothered with o/b charging just relying on solar battery charging. good luck olewill