Charging battery from outboard!

[Zagato]

The leisure battery I inherited with the boat can be charged from the 6HP outboard but it appears to be a simple lead from from the engine to the battery terminals unless their is a fuse of something hidden!

I am always concerned with charging sealed batteries due to the risk of it exploding let alone the hydrogen they give off (A few have been known to blow up when charged in kitchens near naked flames!) This scenario should only happen with high powered chargers so am I right in saying that the outboard engine charge is so low it doesn't matter. Do you leave your charging cable connected all the time or have you put something in line to go onto to trickle charge when the battery is fully charged as my charger does for safety?

Can anyone write a more long winded question....need a coffee

 

[BAtoo]

AFAIK the output from these small OBs is itself quite small and probably little more than a trickle charge. Size of battery to be charged is important too. I would expect the charging line to be fused.

 

[JustMelfort]

Well it all depends......

For the effort involved. I'd install an inline fuse somewhere in there. Probably under the engine cowl.

I'm assuming the output is rectified to DC - check.

It depends what size battery is. I have a 190Ah battery with an outboard contributing to its charge (at 5 Amp max, on a very good day) so don't have a regulator. If you are using a very small battery, say from a fire alarm, just to run an echo sounder, then there may be a small risk of overcharge. I would have thought it unlikely that any car size or leisure battery (50-70Ah ish) will be overcharged by an outboard, but its worth checking the voltage across the battery when being charged.

In real use, I have found that my outboard (yamaha 8hp) doesn't produce a high enough voltage to fullly charge the battery, though it helps keep it at 70-80% charge and I need to top up using solar or charger.

I leave it connected all the time as there is no drain when the engine isn't running. Again though, stick a meter across the battery to check.

p.s. My battery is sealed too, but because the charge is low (little chance of over gassing) and the voltage is also 'low' (battery doesn't overcharge) I've never had a concern.

 

[noelex]

The small outboards do vary a lot in their electrical output. I had a 8hp 2 stroke Yamaha and it would put out 4A at crusing revs and raise the voltage up to 19v if allowed, so it did need regulation, with a single 80 AHr battery.
I achieved this by monitoring voltage and turning it off if necessary. There is a thoretical risk of damaging things if you turn them off when running, but in practice it never caused any problems over 2 similar outboards and 15 years of use. The most likely damage is to the bridge rectifier, which is only a few dollars if you get it from an electronics store rather than the Yanmar parts.

 

[VicS]

Install a fuse but NOT as suggested above under the engine cowl but as close as possible to the battery.

Its rating should obviously be high enough to take the maximum output from the engine charging circuits but it should be LESS that the maximum safe current rating of the wiring.

The purpose of the fuse is to protect the wiring from high currents from the battery in the event of a short circuit or other fault.

The output from charging coils of small outboards is pathetically low. You will only get a significant input into your battery if you run the engine at fairly high revs and for fairly long periods. Both of these are things you generally try to avoid with a sailing boat.
Unless you have very small battery, say less than 45 Ah, or do run at high speed for many hours at a time, a regulator is not necessary.

IMHO a permanently mounted solar panel is the way to keep the battery of a small sailing boat charged.

.

 

[Zagato]

Thanks, It is a big enough battery by the sounds of it and I found a fuse close to the battery terminals (was dark in the cabin last night with the cover over it!) so will be OK then.

Will look into a small solar panel charger unless anyone knows of one in particluar...

PS Thanks especially VicS you always seem to come to my numpty aid!!

 

[sparkie]

Install a fuse but NOT as suggested above under the engine cowl but as close as possible to the battery.

Its rating should obviously be high enough to take the maximum output from the engine charging circuits but it should be LESS that the maximum safe current rating of the wiring.

The purpose of the fuse is to protect the wiring from high currents from the battery in the event of a short circuit or other fault.

The output from charging coils of small outboards is pathetically low. You will only get a significant input into your battery if you run the engine at fairly high revs and for fairly long periods. Both of these are things you generally try to avoid with a sailing boat.
Unless you have very small battery, say less than 45 Ah, or do run at high speed for many hours at a time, a regulator is not necessary.

IMHO a permanently mounted solar panel is the way to keep the battery of a small sailing boat charged.

.

Second that- I went to a lot of trouble with my new motor installing coils etc, and the output is useless. Wouldn't bother again. I fitted a small (10w) solar panel and regulator two years ago and haven't had to charge the battery since, even in darkest Wales.

 

[VicS]

Will look into a small solar panel charger unless anyone knows of one in particluar...

My solar panel is a 5watt semiflexible "Spectralite" from Seateach
Not cheap at a few pennies under £70 but there is plenty of cheap stuff about on ebay.

If I had the space I would have fitted a 10 watt one but I dont and the 5 watt one has proved to be adequate for my needs

 

[TSB240]

I recently fitted a charge coil and bridge rectumfriar to a recently purchased 9.8 tohatsu O/B

Was it worth it?

I reckon it is for my circumstances, Quite often we are motoring hard to get to a tidal gate or pushing against a bit of a tide or head wind on the Menai. The measured output at full throttle is 7 amps.

Even at just above tickover I am seeeing 4 amps. I use a high thrust prop which means the engine runs at a higher rev range generally.

On balance I can usually rely on 20 watts of Solar panels to fully recharge the battery between weekends. I do have to be careful of how much I use the hydraulic lift motor for the keel as this pulls about 30 amps but not for long.

Having the OB running when we lift the keel just reduces the shock to the battery.

If you do go solar try to avoid placing under boom as shadow effect considerably reduces their efficiency.

My ob charge kit came with a fuse that is fitted inside the engine cover and is rated to protect the wiring that is used to feed the charge to the battery. I think its only a 10amp fuse. I also have a fuse adjacent to the battery for short circuit protection of the battery.

When the OB is disconected I can safely connect either another 5w solar panel or a battery charger from shore power to the same socket.