dento29
Active Member
Hi all, i have a petrol 200hp 5L mercruiser engine..what size battery should i be using to start her?
Many thanks
Many thanks
what size battery?
- Thread starter dento29
- Start date
VicS
Well-Known Member
You do not give enough info to look it up but read the Engine Specifications in the owners manual. I think you will find a recommendation there. CCA rating as well as capacity.
If you have temporarily mislaid your copy then you can down load one from the "Download Center" tab at http://www.brunswickmarineemea.com/homepage/welcome
If you have temporarily mislaid your copy then you can down load one from the "Download Center" tab at http://www.brunswickmarineemea.com/homepage/welcome
dento29
Active Member
o.k, had a look and says 305-350Ah cold cranking..thats seems alot battery. is that right?
grumpy_o_g
Well-Known Member
Are you sure it doesn't say 305-350 AMPS CCA? It doesn't really make sense for them to quote in Amp-hours. I would expect that amount of current to start a largish V8. Look for a battery that can easily supply at 400 CCA (Cold Cranking Amps I think it stands for) which is basically the amount of current the battery can produce at once if you like. It's normally specified at a particular temperature no make sure you're looking at the CCA at 0C.
As for the Amp-hours (the length of time it can produce a certain amount of current) I was given at least 6 mins as the rule of thumb for battery sizing but that was in the early seventies - don't know if it's changed. The 6 mins means it's a 1/10 of an hour so you can divide the 400 Amps CCA by 10 to get 40 amp-hours. Because a battery shouldn't be discharged below around 40% you need allow for that when sizing it. If 40AH is 40% the 100AH is 100% so I reckon yu need a battery of around 100AH capable of giving 400 CCA.
Do you have a service battery as well (i.e. one for the domestics, lights, etc.). Reason I ask that is that it gives you a back-up if you end up flattening your starting battery on a dodgy engine, which means you can afford to be a bit meaner with your starting battery size. It also means that you won't be nicking any of the starter battery's capacity for anything else so it SHOULD stay fairly well-charged.
If you're worried about size then you can get specialist starter batteries such the Red Flash http://www.dmstech.co.uk/marine/pdf/redflashdata.pdf which are very light and reliable (and pretty expensive).
The difference between a deep cycle and starting battery is that a starting battery is designed to supply high loads for a short time (engine start, electric windlass, etc.) whereas a deep cycle is designed to be more slowly discharged but SHOULD be able to be discharged more fully.
In practice get a decent sized battery and it won't make any odds - get a good fully automatic charger such as CTek or similar and let it get on with it.
As for the Amp-hours (the length of time it can produce a certain amount of current) I was given at least 6 mins as the rule of thumb for battery sizing but that was in the early seventies - don't know if it's changed. The 6 mins means it's a 1/10 of an hour so you can divide the 400 Amps CCA by 10 to get 40 amp-hours. Because a battery shouldn't be discharged below around 40% you need allow for that when sizing it. If 40AH is 40% the 100AH is 100% so I reckon yu need a battery of around 100AH capable of giving 400 CCA.
Do you have a service battery as well (i.e. one for the domestics, lights, etc.). Reason I ask that is that it gives you a back-up if you end up flattening your starting battery on a dodgy engine, which means you can afford to be a bit meaner with your starting battery size. It also means that you won't be nicking any of the starter battery's capacity for anything else so it SHOULD stay fairly well-charged.
If you're worried about size then you can get specialist starter batteries such the Red Flash http://www.dmstech.co.uk/marine/pdf/redflashdata.pdf which are very light and reliable (and pretty expensive).
The difference between a deep cycle and starting battery is that a starting battery is designed to supply high loads for a short time (engine start, electric windlass, etc.) whereas a deep cycle is designed to be more slowly discharged but SHOULD be able to be discharged more fully.
In practice get a decent sized battery and it won't make any odds - get a good fully automatic charger such as CTek or similar and let it get on with it.
Plevier
Well-Known Member
No that means the current in amps, not the Ah capacity. (CCA or cold cranking amps is what a battery in A1 condiion will supply for 30 seconds at -18 deg C down to 7.2 volts at the terminals. Well that's one version of the spec, there are others like 20 seconds to 9 volts etc.) Any conventional battery from about 60Ah up will supply that comfortably. If you use SBS or Odyssey type it could be smaller. It's your choice if you want something bigger to allow for not fully charged, slow to start engine or anything, or if you are going to run anything else from it.
dento29
Active Member
Thank you all so much for your help.