charge battery from outboard

[DryDock]

Hi,
I wanted some advice on connecting the 12v 60 watt output from my outboard. I would like to charge the leisure battery and make use of it. It states in the manual that it’s for lights and they should be wired in line.

Is there a gizmo I can get that would regulate the correct output to charge a battery, be good to use the power and keep my battery topped up?

 

[VicS]

It sounds as though your engine is not equipped with a rectifier for charging and just has an AC output for lights

If so you will need to obtain the charging adaptor or make/ improvise a suitable rectifier. A simple two wire AC output can use a suitably rated bridge rectifier. A three wire output will require a six diode rectifier.

Can you explain what you mean by " they should be wired in line."

Its been common practice for small outputs, like 60watts, to be rectified but not regulated. Larger outputs are more likely to be regulated. More modern practice is to regulate the lower powered outputs as well.

What engine?
Make, Hp, model, serial number, year of manufacture?

The amount of power you get for battery charging is very small. Almost to the point of being useless on a sailing boat where the engine running time is short and seldom at high enough revs to generate the full output but on a mobo where you will be running the engine at decent speed for longish periods its worth using.

I do use the output from mine for charging a leisure battery as it has a rectifier fitted a standard equipment. It is not enough so I also have a solar panel.

The previous engine had an AC output and I used an RS bridge rectifier.

 

[DryDock]

Can you explain what you mean by " they should be wired in line."

My mistake it says 'connected in parallel'.

Its a
Volvo penta Archimedes
20 hp
Not sure of year I think they stopped making them in the 80s.
Will dig out number
Boat came with a maplin solar panel. 17.5volts

Cheers

 

[VicS]

Yeah just seen your other post.

Cannot help with the Volvo/Archimedes/Crescent motors. No info on line that I know of. They are well and truly obsolete. ( My old one was, still is in fact, a small VP.

Provided the instructions for wiring lights is just a simple parallel circuit ( mine had a 24 volt output and the lights had to be wired in a series/parallel circuit) a simple bridge rectifier will do the job but you might be lucky and find the charging adapter on ebay

Your best bet is to get a Maplin bridge rectifier unless you strike lucky with the charging adaptor. A 6 amp one will be adequate but a 10 amp one might be more sensible. Also a 50 PIV one should be adequate .
http://www.maplin.co.uk/Module.aspx?ModuleNo=19088

Which ever if you get one with spade terminals then you can use push on connectors. Not sure what case design that is! It might be necessary to mount it on a small heat sink. I made a heat sink that doubled as the mounting bracket.

Connect the AC from the motor to the terminals that are probably marked ~
and the battery to + and - . FIT A FUSE close to the battery in the + connection.

 

[DryDock]

Thats great will have a look at those
what rating fuse do you need for this as i have some small quick blow kicking around.

cheers

 

[VicS]

what rating fuse do you need for this

Ensure you use adequately heavy cable to carry the current. Size the fuse to protect the cable. ie no more than the cable maximum rating but more than the output from the engine.
7.5 amp fuse in a 10 amp cable would do nicely if the cable run is fairly short.
Other wise use 15 amp cable to minimise volts drop, then a 10 amp fuse would be acceptable.

 

[Assassin]

60W is only 5 amps maximum, so i would agree on the cable sizes but not the fuse rating as this is slightly too high, enter the losses from rectification and you would be lucky to see 4 amps usable current for battery charging.

 

[Rivers & creeks]

And that's only from high revs and with a battery that needs plenty of charging. But 4amps will happily run a cool box whilst the engine is on. The other option depending on how big your boat is, would be a £50 genny from B&Q to charge via it's 12v output (usually about 8amps). A 1980's 20hp 2 stroke outboard is going to guzzle fuel so you would never want to be running it just to charge the battery!

 

[VicS]

i would agree on the cable sizes but not the fuse rating as this is slightly too high

The fuse is there, and positioned at the battery end of the wiring to protect the wiring from the high current that could flow from the battery in the event of a short circuit in the wiring.
Subject to not being less than the max output of the engine what matters is that it is less than the safe current capacity of the wiring.

It need not be a big as I have suggested but provided the wiring will carry the current safely its OK.


BTW , Dry Dock

Be absolutely sure you don't ever connect the battery to the rectifier with the polarity reversed. Instant death to the rectifier if you do.
Also do not disconnect the battery while the engine is running. That is likely to blow the rectifier as well.

 

[DryDock]

Thanks for all the advice; I don’t really need much electric to use the boat. The battery is for lights, horn, bilge pump and a radio. So we use hardly any power so far. I was interested just to keep it topped up for now but a cooler box would be a good idea, have to look around

Cheers

 

[Assassin]

It is a subjective issue on fuse sizes, and for good reason sometimes; it is however recommended that the fuse should be as small as possible because its blowing amps are twice the normal working rating. For a 5 amp fuse it would blow at 10 amps, for a 7.5A it blows at 15A, for a 10A fuse it would blow at 20A.