sailorman
Well-Known Member
18hp is quite small in diesel terms.
any battery that starts a small car will do.
why fit a small battery when a bigger one will give you reserve/emergency capacity
Sizing an Engine Start Battery.
- Thread starter sailorman
- Start date
18hp is quite small in diesel terms.
any battery that starts a small car will do.
why fit a small battery when a bigger one will give you reserve/emergency capacity
DJE
Well-Known Member
I'm intending to fit a dedicated engine starting battery so that the existing two can be paralleled to increase domestic battery capacity. The engine is a Volvo 2002 (18hp) and all I can find in the manuals is that the starter appears to be 1.4kW. Does this mean that I need 1400/12 = 117 Amps from the battery? Is this the required CCA capacity of the battery.
Also any recomendations on type of battery?
Also any recomendations on type of battery?
Refueler
Well-Known Member
Forget all that calcualtion and fluffing around ... you need a bog standard medium sized car battery as fitted to thousands of people-wagons the world over. 50 A/Hr is more than enough ... and if you get down to Quickfit, Halfords or other suitable emporium that loves to part people with money - you can get yourself a battery rated for a small family diesel car.
Or do as I do and make way to breakers yard and pick up a tested second hand similar job for probably a tenner .....
If you leave your battery change-over switch in place on board - you can always in emergency use domestic to start - but in years I've used 2nd hand batterys - have yet to have one fail in short time.
Csail
N/A
Get the smallest possible. Most people (like i used to think) go for the biggest but they don't charge enough.
sailorman
Well-Known Member
mine is 115Ah engine + 3 x 115Ah ( 345Ah domestics) charge up no probs to date.
VicS
Well-Known Member
As refueller says forget those calculations. For a start I think the power of the starter motor is based on a terminal voltage of 9 or 10 volts, not 12.
Even then the power given is when running under normal load so at times the current will exceed the calculated figure.
I think you will find that if you check the manual Volvo specify a maximum battery capacity of 60Ah.
I believe if you use a larger battery there is a risk that under stalled conditions the battery could supply a sufficiently large current to damage the starter motor. By limiting the battery size that possibility is reduced.
CCA is a far more relevant rating than Ah capacity but unfortunately Volvo only give the above Ah capacity recommendation.
Therefore fit a 60Ah starter battery. It should have an adequate CCA rating, but will not be likely to be capable of delivering a current high enough to burn out the starter, at least not quickly. It will have a more than adequate capacity to fulfill the needs of a dedicated starter battery.
Use any spare space to increase the size of the domestic battery bank if you need to.
Even then the power given is when running under normal load so at times the current will exceed the calculated figure.
I think you will find that if you check the manual Volvo specify a maximum battery capacity of 60Ah.
I believe if you use a larger battery there is a risk that under stalled conditions the battery could supply a sufficiently large current to damage the starter motor. By limiting the battery size that possibility is reduced.
CCA is a far more relevant rating than Ah capacity but unfortunately Volvo only give the above Ah capacity recommendation.
Therefore fit a 60Ah starter battery. It should have an adequate CCA rating, but will not be likely to be capable of delivering a current high enough to burn out the starter, at least not quickly. It will have a more than adequate capacity to fulfill the needs of a dedicated starter battery.
Use any spare space to increase the size of the domestic battery bank if you need to.
VicS
Well-Known Member
Congrats to Sailorman for answering the original question 2 minutes before it was asked. 
Such clairvoyance must be useful and profitable at times.
Such clairvoyance must be useful and profitable at times.
sailorman
Well-Known Member
Any Offers on
This weeks Lotto Numbers
Congrats to Sailorman for answering the original question 2 minutes before it was asked.
Such clairvoyance must be useful and profitable at times.
This weeks Lotto Numbers
vyv_cox
Well-Known Member
The CCA of all Yanmar engines up to the 3GM at least, maybe further, is 200 Amps. I am guessing that the figure for the Volvo is not too different.
The Red Flash 900 AGM battery has a CCA twice this figure but is remarkably small. I fitted one last year and it starts my Yanmar 3GM perfectly well.
DJE
Well-Known Member
Thanks all. Space could be a bit tight as the existing battery box is full and I'll have to find a home for the new one under the cockpit floor. I've been looking at AGM batteries and they look promising being small, and tolerant of being mounted in any orientation.
mikehibb
Well-Known Member
We have a 55 amp/hr starter battery. No problems with it so far. Starts the Yanmar 3GM30 OK.
Had the boat two years, and the battery was on boat a few years before we got it.
I work 6 weeks on 2 weeks off, and not had any problems after the six weeks without use.
Had the boat two years, and the battery was on boat a few years before we got it.
I work 6 weeks on 2 weeks off, and not had any problems after the six weeks without use.
BabaYaga
Well-Known Member
Don't know what CCA Volvo would advice for your 1.4 kW starter, but as a comparison: Beta Marine recommends 450 - 540 CCA for their 20 hp and 25 hp engines. The starter capacity of these two engines is in the range of 1.0 - 1.4 kW, according to the manual.
I chose a thin Red Flash 1100 for my Beta 20 (37 Ah and around 500 CCA IIRC). Never had any problems starting the engine, but only four years old.
I chose a thin Red Flash 1100 for my Beta 20 (37 Ah and around 500 CCA IIRC). Never had any problems starting the engine, but only four years old.