engine start battry size

[roger]

I would like to use both the existing 100Ah batteries on my boat to feed services and fit a new small one just to start the engine (Betamarine 3 cyl. BD733 30 hp). The nice people at Beta say I need 450-540 amp cold cranking capacity and 65 -75 hp. That seems a bit large in fact about the same as my Ford Mondeo 1.7 litre diesel.
I do have limited space so the job is only practicable if I can use the minimum battery size. Do any of you have a view as to the minimum reasonable size to use?
Thanks in advance

<hr width=100% size=1>Roger

 

[bedouin]

If you genuinely want small then look at batteries like the Red Flash range - for starting you will get away with one that is a fraction of the size of a conventional multi-purpose battery.

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[Chris_Stannard]

i have a 75 amp hour Tudor for engine start which starts a 53hp Yanmar 4 cylinder without fail. I would think that yours could be smaller than that for your engine

<hr width=100% size=1>Chris Stannard

 

[Heckler]

a 60 amphr battery is more than sufficient for your needs, my bene 351 came with one as std and ive just put another bog std lead acid one on as a replacement with no probs.
stu

<hr width=100% size=1>http://www.beneteau-owners-association.org.uk

 

[vyv_cox]

Last year I replaced the starter battery for my 1.6 litre VW diesel van. On collecting the battery I queried it, thinking they had given me one for a smaller vehicle or the petrol version. They verified that it is the correct one. As far as I remember it is 55Ah.

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[oldharry]

The key figure is the cold cranking capacity, not the AH. If the battery cannot deliver sufficient amps to the starter motor, then it will not turn the engine over quickly enough which may lead to difficult starting, voltage drop may damage the starter motor through overheating, and the battery plates may overheat and be damaged.

The amount of power required by the starter to turn the engine over depends largely on the size of the flywheel and the gearing ratio between the starter and the engine, so that it seems that your 30hp Beta needs as much power as my 90hp Renault to kick it in to life!

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[pvb]

CCA rating...

The CCA test is a bit extreme, being carried out at -18 degrees celsius. In the US, they often use an MCA (Marine Cranking Amps) rating, which is tested at 0 degrees celsius and therefore is more representative of winter temperatures in a boat. The MCA rating is typically 40% more than the CCA rating.

I'd have thought you could manage quite happily with a battery giving around 350 CCA. If you go into a Halfords store, you'll find a huge selection of batteries which all carry the CCA rating. I'd suggest you get a maintenance-free battery, which I think Halfords guarantee for 4 years.

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[pwfl]

I would suggest you obtain specs/catalogue from a supplier such as Barden. You will see that Red Flash batteries (which someone has already mentioned), are absolutely tiny in comparison with standard batteries. Even one with much more CCA than you require.

This is because they provide very high CCA, but hardly any Ah. They are specifically for starting engines.

I would also suggest you get hold of a copy of Nigel Calders Boatowners Mechanical & Electrical Manual (or similar text). If you read the relevant sections, then, unfortunately, you will find that the route you are hoping to go down is a lot less simple than you might have thought.

I wanted to do exactly what you're thinking of, & ended up giving up on it in the end.

It would would seem that there are only 1 or 2 devices, which are capable of splitting the charge to 2 banks of very different types & capacities, without either short or long term damage to one or the other. (none of the standard charge splitters on the market will do it properly, so he claims - feedback anyone??)

The recommended devices turned out to be American, not sold in the UK, & cost about $500 3 years ago (ie ~£500 once you've paid delivery & VAT).

The only other way to do it is if you're not charging both banks from the same alternator. - ie either have 2 alternators, or charge your domestics from wind / solar.



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[roger]

Re: engine start battery size

First - thanks for all your replies.
Second my apologies for a lot of mistakes including spiling.
The engine is of course the BD722 and 20 hp.
According to the guff I have to hand it has swept volume of 60 cubic inches which looks to my surprise like 1 litre. That is a lot more than I would have expected. In fact its not far off a car engine.
The Red Flash batteries look promising - really very small. They are pricey though. and the prices vary
A UK supplier quoted £154 for the 26 hp and a German one £104. In both cases delivery to Sweden, where the boat is laid up will add extra cost.
I will look up the charging implications in Calder. I do have a diode triple splitter and a Sterling charger with 3 outputs so the obvious problems are taken care of - the less obvious ones possibly not.
I also had a look at some batteries in the local shops today.
My feeling is that I dont have room for a conventional battery that will do the job.
Thanks for your thoughts

<hr width=100% size=1>Roger

 

[pvb]

It\'s smaller than a litre...

The BD722 is only a 719cc engine (0.7litre). You could probably start it with a jetski battery, which would typically be about 6" x 4" x 6".

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[pvb]

Feedback...

You asked for feedback, so here goes.

First, don't believe everything that Nigel Calder writes.

Second, you can use a diode splitter to charge 2 banks of batteries without any damage to either bank. You have to buy a diode splitter which will cope with the maximum current your alternator can supply.

There is a voltage drop of about 0.7v inherent in a diode splitter, so the charging voltage at the batteries will be too low unless you modify your alternator.

The simplest modification is to add a remote sensing lead - any alternator specialist will do this for you. The remote sensing lead should be connected to your domestic bank.

A better way of overcoming the voltage drop is to add a "smart regulator" - Adverc, Sterling, etc - which will automatically compensate for the voltage drop in the diode splitter, will give a faster more effective charge, and will also adjust the charging voltage according to temperature.

For best results with either of these routes, use a maintenance-free starting battery. As the charge current is automatically distributed, you can also throw away your 1-2-Both switch and instead just have a simple on-off switch for your domestic batteries, and a second on-off switch for your engine starting battery.

The Americans tend to favour "battery combiners" rather than diode splitters. Combiners are more complex, more expensive and are basically big relays which link both battery banks together once the charge voltage reaches about 13.3v. In extreme cases, where the domestic batteries are very low, this can result in a big current flow from one bank to the other, which I don't think is good for the batteries. By contrast, with a diode splitter, the two banks are always kept separate.



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[JerryHawkins]

But what about...

...the fact that there will be two different battery types (ordinary wet cells for house and the Redflash sealed for engine start); the charger (and alternater regulator if fitted) have different settings for these different types. Vented wet cells can take 15v and gas freely, sealed types must limit voltage to prevent most gassing.

So, for this set up to work you'd need to double-up on all charging methods i.e. two chargers (for shore-power charging) and two alternaters each with smart regulator!

Cheers, Jerry

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[bedouin]

Re: But what about...

This bothered my when I was thinking of fitting a Red Flash for Engine starting (I still might). If you contact the distributors of the Red Flash batteries they will tell you not to worry - that the battery will take as much as you can throw at it, but not all battery experts would agree with that.

What I have been considering, but not implemented, is some way of regulating the voltage to the Starter battery separately, either simply adding another diode to add an additional voltage drop, or some other form of regulation.

That is the main reason I have not yet gone in that direction myself.

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[pvb]

It\'s not a problem...

Mixing battery types isn't a problem. Simply set the charger or smart regulator for the more sensitive type.

You mentioned Red Flash - according to their specifications, these are safe for charging voltages up to 14.7v, more than you'd get from a charger/regulator on a "sealed" setting.

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[Dave_Knowles]

Re: It\'s not a problem...

Can anyone please give me a link to a website where I can find out more about Red Flash batteries.

<hr width=100% size=1>Take care.

Dave

Dave Knowles
Southampton - UK

http://www.MyCleopatra.co.uk

 

[bedouin]

Re: It\'s not a problem...

http://www.dmstech.co.uk/redflash.htm

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[Dave_Knowles]

Re: It\'s not a problem...

Thanks. I have beenm doing internet searches but the search engines have come up with nothing.

<hr width=100% size=1>Take care.

Dave

Dave Knowles
Southampton - UK

http://www.MyCleopatra.co.uk