fitting second battery

[Dave99]

I have been told that it is not possible to fit a second battery to my 1960s Sabb 10hp engine, due to the fact that it has a dynamo and not an alternator. To fit an alternator would not be viable, is there another option to increase power for domestic use (coolbox etc.) The current battery is 110Ahrs, but I am told the dynamo will only actually only charge a 70amp hr battery fully. Is there anything I can do? Thankyou in advance.

 

[Guest]

why no alternator?

 

[Dave99]

Because I was quoted £2K for new alternator and fitting

 

[HaraldS]

That is way too high! You should be able to get a good refurbished alternator at some 200 pound or less. At onboardpower for example you can get a new high output alternator (125A) for under 300. Fitting shouldn't be that difficult if you can replace the old dynamo. (That is if it's not a dynastart). You'll need V-belts, and probably a new trension arm, maybe a bracket. But no way 2k!

I dont know what output your dynamo has but however slow, it should be able to charge two of your batteries. It will just take twice as long. Solar panels, wind generators, are all in a low amp range and do ok aswell, as long as you don't consume more than they deliver, your battery will get charged.
Downside of slow charging could be sulfatation which you could overcome with a pulser, like the Megapulse.


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[pvb]

Options...

I don't see why your dynamo can't charge a bigger battery (or bank of batteries), but it might take a long time. It probably has a fairly low current output, and it might have a mechanical regulator. You can't do much about the output, but it would be possible to fit an electronic regulator which would get the charging voltage up and so increase the charging efficiency.

You say you've been quoted £2000 to fit an alternator. This is ridiculous! You need to talk to some other suppliers. Alternators are cheap and cheerful off-the-shelf items, but you'd probably need to spend a bit on a new bracket to get it secure and properly aligned.

 

[paulrossall]

I would get down a car scrap yard and get an altornator off a decent car, say a VOLVO with an output around 70ah. Not more than £20 around Newark. However I would have to ask one of the clever technical boaters on this site whether I could just bolt it on and where I conect the wires to. Volvos also have a clever adjustment screw on the adjustable arm which prevents the adjustment slipping, which seems to happen when diesel engines vibrate.

 

[halcyon]

We run a Sabb 7.5 HP with Dynostart and alternator.
Previous owner hung a alternator on a bracket on the side of the engine bay, and ran the belt on the flat outside of the fly wheel, the large OD made up for the lack of Sabb revs. Our local LSUK were selling new lucas marine alternators around £60 no exchange last year, or visit the scrap yard.
Yes it does work ok, the previous owner did two trans-Atlantic crossing and a couple of yearcruising while over there.
Fitting two batteries this year, dynostart will charge the engine one, alternator the domestic one.

Brian

 

[snowleopard]

adding another battery won't solve the problem unless you can generate the extra amp hours you will consume. will your dynamo produce what you need without having to rum the engine for extra hours? the arithmetic should look like this (all figures per day):

generated amp hours = consumed amp hours <= 30% battery capacity

(ok you nit-pickers, it's approximate)

 

[sirius]

I don't have the same engine (mine is a VP 2003), so I can't help with advice on the bracket. However, an earlier boat I owned was fitted with a Vire single-cylinder petrol engine which had a Dynostart. I was able to fit an alternator on the other side of the engine by getting some brackets welded by a local workshop for £10. The biggest issue was getting a pulley wheel to run the alternator from. In the end I removed the flywheel from the engine (a big iron wheel about 20inches across), and had a pulley from a Volvo car welded to it.

This may be the biggest issue you will have. If your dynamo runs off a very big pulley, then it will be turning at a completely different speed to that required of an Alternator, so you may need to consider that.

Regarding the alterrnator itself, I recommend the car scrap-yard. If you go and ask for an alternator for a Volvo 760 or V90, you are likely to get one which is rated for all of the fancy bits they have, like Climate Control, Heated seats etc. These alternators have a max output of 120amps, so are a very powerful charging source (normal ones are 55amps). As a cost guide, I replaced the starter motor and alternator on my boat engine with units from the scrap yard next to Halying Yacht Company last March for £25 for each unit.

Simon

 

[jleaworthy]

I fitted an alternator to a Saab 10 GG which had been built in 1967. I got the alternator from the local Lucas agent who even took the old dynamo in part exchange! Cost me £16 (yes 16) in 1984. I made up a bracket from two pieces of angle iron welded edge to edge so making a trough and hacksawed out the necessary clearance for the body of the alternator. I mounted the bracket on the large single stud which originally held the dynamo. I can't remember how I tensioned the belt but it couldn't have been difficult or I would remember. The drive belt I got from a scrap yard having taken along a bit of string of the right length. It worked perfectly from the start charging two batteries through a changeover switch and is still working today almost twenty years later - the boat is now owned by a friend and based in Tollesbury. A job well worth doing.

 

[Dave99]

Re:dynamo or dynastart

Whats the difference??

Thanks very much for all your responses

Dave

 

[HaraldS]

Re:dynamo or dynastart

The difference is that a dynastart is a combination of starter and dynamo. In that case you would need it to start the engine and then you cannot simply replace it with an alternator. If the starter is separate and your dynamo is just that, you can remve it and use the place and pulley for a new alternator.

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[snowleopard]

dynastart...

is a dynamo that also acts as a motor and starts the engine. obviously it's not an option to replace this with an alternator.