Charging a battery from an outboard

seanfoster

seanfoster

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I'm installing a simple electrical system on my boat with a 105 a/hr battery feeding a few nav lights etc.

I have an old Yamaha 8A outboard which has a charging circuit on it, I want to connect it to the battery for topping up from time to time, I've read a few books around the subject and they seem to over complicate things a bit!
Could anyone tell me how I make the connection, do I just connect straight to the battery terminals? Do I need a diode? What size, and cable size?

Any help would be appreciated!
 
From your post, I assume the outboard has it's own battery, but it's the boats aux/leisure battery that you're wanting to charge from the outboard?

I don't think connecting straight across the terminals would work, as the outboard would then effectively be trying to charge two batteries in parallel, and it wont have the juice for that. Simplest way would be to have a switch which swaps the two batteries round. There are far more complicated ways of doing it with automatically switched charging circuits, but if you're just looking for a simple, manual way of upping the charge on your leisure battery, this should do it.

a
 
Hi Sean, yes you can connect direct, but you stand a chance of frying the radio with the higher unregulated voltages.
I suggest an inline rectifier to stabilise the voltage, which I had on my older BF75 Honda. That seemed to work.
Flat out, my outboard would deliver about 4amps, so not really sufficient to recharge batteries, but will keep up with the onboard load whilst it is running.

I bought a cheap 10w solar panel and strapped it on the top of the boom. That kept me trickle charged all season. I think I picked mine up for about 40 quid.

Other than that, if you are only running a couple of instruments, day use only, 105Ah would probably last most of the season anyway.
 
I think that's the way to go, the elctrical system comprises depth & log, LED mast light, 2 led interior lights and a spare cigar socket for odds and ends.

Did you buy the solar panel new for £40?
 
[ QUOTE ]
Did you buy the solar panel new for £40?

[/ QUOTE ]

Yep, got it from the Aussie guy with the bush hat who does all the jumbles. It was a bog standard solid frame, and he gives you a diode to solder on yourself. Very DIY, but they work OK. They dont like shadows though.
 
I have similar power requirements to you. Occasional Nav Lights, Radio, Depth Gauge charging phone etc. week ends aboard.

My mecury 8Hp has a charging coil, no regulator straight on to the battery. It delivers maybe 4 amps when engine at high revs. I also use a 10W solar panel.

Those two provide the power we need for most of the season, might take the battery off and charge it once in October. Gets low if we are on the boat for a week or two. If away from base (Windermere with no shore power) we go into a marina and put a car charger (slightly better than the most basic) on it which soon tops it up.
 
Thanks for your reply David, I'm going to be on Windermere (for the first time this year) so got very similar requirements to yours. Which marina do you go to, I wasn't sure you could use them for visitor berths?
 
You'll be flogging a dead horse ... I tried it and wasted a lot of effort on it.

You need a rectifier box as the supply from the outboard is AC, unless you have a box in the lead fitted inside the engine cover ? Unlikely - but you may.
The box can be bought from any outboard service agent. He'll gladly relieve you of a sum of dosh !

105 A/hr battery .... mm that's gonna need a good charge to maintain. Consider that outboard power is similar to a motorbikes supply to lights..... so don't expect great shakes from it. It will likely fall off quickly as battery comes up as well giving less than satisfactory level of voltage final.

As other says ... maybe better to get hold of a decent value solar panel ...
 
I used to have a Yamaha 8B which charged the battery via a rectifier.

If your frugal with lights it will keep you charged up but I found it couldnt keep up with the demand from Autohelm and lights together.

You definitely need a rectifier between the motors output and the battery as the output is AC .

I have had small boats powered by outboards for a long time.It is worthwhile but you do need to be very frugal with the battery power

.Although you dont get as much output as from an inboards alternator the plus side is you dont waste any of what you do get starting the engine.

Modern outboards are much better in output.My Honda 8hp gives 10AMPS at full revs. The latest one 12 amps.

On our current 25 ft boat the outboard is the only means of charging the battery and does keep it topped up.
 
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I think that's the way to go...

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Definitely - I took the trouble to connect up the charging circuit for a similar vintage Honda outboard on our previous boat - Waste of time. It had to be revving its bits off to generate even an amp of charging current (much faster than was useful for pushing a 22' boat along), and it was never running for long enough, anyway.

Paid £25 for a solar panel from that bloke-with-the-aussie-hat-that-does-the-boat-jumbles (can't remember the wattage, but it was about a foot square in a metal frame). Had this permanently connected to the battery on a flying lead (fused at the battery end). Just left it on the cockpit seat when we were away from the boat and when we went sailing, it went into a cockpit locker. Never any problems with power again /forums/images/graemlins/smile.gif

Andy
 
I had a Yamaha 8hp outboard (about 1988). It would put out 5A at cruising revs. Not a lot but useful. All you need is a cheap bridge rectifier (about $4 ). I also had an 80w solar panel so had to turn the outboard charging off when the battery was full.
 
possible in theory, but unsatisfactory in practice, having tried it I'd advise against attempting it.

Reasons:-
1. The output from small outboards is so minute as to be almost useless.
2. You have to fit a rectifier, to convert the ac from the outboard into DC for the battery, together with a diode to prevent the battery being discharged by the OB when not working. In themselves not particularly expensive.
It's unlikely you'll need a regulator, most OBs won't produce enough current to damage a battery.
3. Any current produced is only close to maximum revs of the engine.
 
[ QUOTE ]

Could anyone tell me how I make the connection, do I just connect straight to the battery terminals? Do I need a diode? What size, and cable size?

Any help would be appreciated!

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You need
A bridge rectifier (say 35A and 400V)
connect the battery + to the + pole of the bridge rectifier, with a 10A fuse and switch in the circuit. Battery negative is the diagonaly opposite pole and the AC from the outboard connects to the 2 remaining poles.
Note a means of reading battery voltage is necessary and you will need to turn the charging of if the voltage climbs too high.
In Australia I would get the rectifier from Jaycar, look up the part and you will be able to get something similar from a local company.
The bridge rectifier is Jaycar part number ZR-1320
 
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I remember his name is Tom. I think

[/ QUOTE ]

I had 'JonJo' in mind, but I think it might be 'TomJo Marine', or maybe 'TomJo Solar'

Geoff??? /forums/images/graemlins/laugh.gif

(Doesn't matter) Point being that any 'cooking grade' 10-20W solar panel knocks spots of outboard charging for what you want. (With possible exceptions for outboards fitted with alternators rather than charging coils).

Andy
 
If your engine has a DC output for charging you do not need an additional rectifier.

If it is only AC then you need either an expensive charging adapter or an inexpensive bridge rectifier from Maplin or the likes. (some outboards have a three wire AC output that requires a special rectifier. AFAIK that's not so with Yamahas)

Include a fuse in the circuit, close to the battery.

Take care, as already pointed out, not to run on-board electronic stuff directly from the engine with no battery connected. Some things will not tolerate the high voltages you can get at low loads. (been there, got the tee shirt)

As said the output is not great unless you run the engine at a decent speed for longish periods.

A regulator would not normally be used, although larger engines with a higher output stator coil do fit a combined rectifier/regulator.

I have a 6hp outboard with 5amps DC output (maximum) and a 5 watt solar panel.
On its own the output from the engine is inadequate but the small solar panel is sufficient to top the battery up between weekend outings
 
By Away from base I meant away from Windermere i.e. trailed somewhere like the Clyde. When on Windermere I if I need to charge I would take the battery home or put in the car and go for a drive. In the summer with plenty of the sun the battery usually just about holds it own. Mine is 80 AH I think.

Marina Village or Windermere Aquatics may allow a short term berth rental if they have one available.
 
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