Engine Start Battery Size

purplerobbie

purplerobbie

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At the moment i have 2x 110amp batteries. One is the start battery and the other is the house.

I'm renewing all the cables and and sorting it all out. I'm going to have the 2 110's as house batteries (I might fit a 3rd if i have the room) and get a dedicated engine battery rather than a leisure battery.

What size cranking battery would i need to fit to start a 25hp 898cc diesel?

Rob
 
I would suggest a CCA of 500A plus, the bigger the better to allow for difficult starting conditions. Your normal peak cranking amps will be in the region of 250-300A. You should allow for a half charge start, cold weather and sustained cranking if the engine is difficult.
 
Haven't found any reason to change the 110 aH battery which starts the engine - and as it's an old 120HP Perkins I would have noticed! Another 110aH serves domestics without problems.

I considered larger simply 'cos there's room in the battery box but local wholesaler can't supply sealed batteries (wot, go back to hygrometers and acid and stuff???), so haven't changed, simply added a third as reserve.
Previous boats had two 110aH batteries with changeover switch, never had a problem. Don't forget they're only guaranteed for a couple of years and any longer is a bonus!

IMHO 110aH will do you fine
 
You might like to look at the Red flash or similar batteries

http://www.dmstech.co.uk/marine/pdf/redflashdata.pdf

Basically they have high CCA with smaller AHr ratings and hence smaller batteries. They can also be mounted any way up.

I fitted one of these (1200 from memory) which starts a 28HP Beta without any trouble. The saved space / flexible orientation let me get another house battery in.
 
[ QUOTE ]
I was told to get the smallest possible for engine start. I got a normal car battery.

[/ QUOTE ]There's no such thing as a normal car battery and CCA is not necessarily directly related to AH rating or physical size. Use of a 4 cylinder diesel car starting battery is probably a good starting point.
 
I didn't quite mean 'normal' but for our 1.5 diesel i went to motor factor and asked for a battery for a 1.9 Audi. The marine electrician reckoned if you put something too big in, it won't charge and discharge at the right rate.
I might be wrong?
 
Local Tyre / Battery discount centre and get a Diesel Duty van battery .. they are basically a Heavy Duty "Car" battery that can thump a diesel over. But in all honesty - a bog standard medium sized Car battery is fine.

IMHO - I would not completely separate all - I would always leave position switch so that domestics could start engine in event of failure ...
 
I have fitted the BEP Marine battery switches with the vsr.
I have a house battery switch a start battery switch and an emergency parallel.

I think a car battery is only about 65 amp?

Rob
 
65 Amp ?

Do you mean 65 A/Hr ? That's middle - to high capacity for a car battery. My Perkins 42HP beast lived last year happily on my temp. 50 A/hr car battery - that battery is now in the boat store ready to be fitted to my smaller weekender.

If all you want is a start battery and not to do any other service - then it's fine.
 
ive got a similar sized engine and have a 100 or 110 amp hour if i replaced it i would not go any bigger and have never had any problems even when i had engine starting problems the battery allowed me to crank for a good long while.
 
I have the same battery setup and I am doing exactly the same with it, apart from the vsr I am staying with the 1/2/both switch.
What I did was to look up the engine on the interweb found the manusl and that told me I needed 45Ah 350CCA its the CCA value that is importnant for starter batteries That equated to a type 105. Having said that the engine is only a beta 10.

What make/model is the engine?
 
One of the biggest deciders on battery size is run time of the engine. If you are a short run out from mooring to stopping engine - then a big battery unless charged from shore as well will be eventually killed by heavy use starting - short recharge time. So then a smaller battery comes into it's own then for being charged to full quickly.

But seeing as you have 2 x 100 A/hr batt's already - then that indicates to me you have reasonable charge regime ie shore connection ?

My boat running plotter, VHF, various stuff additional to nav incl. tillerpilot was happy on standard alternator, a 80 A/hr + a 100 A/hr battery system on the old fashioned change over switch. Nothing fancy. My engine run times were a bit longer than most as I'm a motor sailer - but even so - the system survived days and nights away from shore power well. I had to reduce #2 battery for a while with the 50 A/hr ( my 100 A/hr after many years of service showed it was becoming tired ) ... and I still enjoyed reasonable power availability. I have now replaced with a 100 A/hr truck battery that will give me good service ... hopefully for quite a few years yet !
 
I've got a colleague convincing me of the advantages of getting a tiny Redstart or even Odessy battery for engine starting. The virtue is the thing is it's so small it can be tucked beside the starter motor or somewhere convenient and be mounted any way up. That leaves the space occupied by my current 110 Ah battery to be added to the house bank (now 3 x 110 Ah).

Nigel Calder expands on the virtues of the Odessy batteries in Professional Boat Builder.
 
[ QUOTE ]
a colleague convincing me of the advantages of getting a tiny Redstart

[/ QUOTE ] Redstart?
redstart_male_300_tcm9-142394.jpg
Perhaps he meant Red Flash? /forums/images/graemlins/grin.gif
 
The engine is a beta 25.
I have a 25amp battery charger when on the mains.
I have the alternator and Air-X wind generator which is alleged to be 400 watt and 50 watts of solar panels.

Rob
 
From the Beta handbook
Minimum battery size
65-75 Ah
450-540 CCA
Best to call a decent battery supplier ( I use http://www.shieldbatteries.co.uk ) and give them the spec above and the size of the space you have to put the battery in, they should then be able to recomend a suitable battery.
Mine had to fit in a 5inch gap and the 105 is the only one that is that narrow.
 
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