Yanmar 3GM30 Starting Battery Size ?

[endoftheroad]

I just bought a sailboat with a 3GM30.
I am ordering the service manual but in the meantime it would really be helpfull to know the required starting battery size.
Can someone look in their manual for me?

Thanks

[Kettlewell]

I would just fit the biggest 12-volt starting battery you can into the space available. You can never have too much capacity, but a group 24 or 27 should do it, without looking at the manual. A group 27 will start my Perkins 4.236 with no problem. If your engine is in good shape and starts like it should you use almost nothing from the battery.

[endoftheroad]

Thanks but I'm much too prudent to "wing it".

[sabray]

Pretty standard to use a group 27 for starting battery. Not from a manual though

[MechMan]

From the manual... 12V 64 AH or more (type 95D31L or equivalent)

Mine doesn't stress the start battery at all. Starts after one or two revs.

[sck5]

I have a 3gm30 and have a group 27 for a starting battery. No idea what the manual says, though

[bobconnie]

Kettlewell has it on the nose !! always use the Largest Battery you can safely fit into the area you have !! 12 volts is 12 volts but amp hours are what you need !! just my 2 cents Bob and Connie

[Saltyrope]

The engine makers usually specify a minimum size suitable for the engine. For starting batteries the CCA rating is used which is cold cranking current (amperes) The D2/40 Volvo's specify a 700CCA starting battery which is I think a 27 series. On my Volvo 2003 series 28/29 HP I have been using a 24 series which is 680 CCA. The ability of a cranking battery to deliver fast power from its thin pates as opposed to slow power from deep cycle thick plates is the main requirement. I personally like a little up my sleeve to have the battery last a bit longer by emptying it less percentage wise each start and when I replace my 24 series 680 CCA (2007 new) cranking battery I will go up to an 800 or so CCA as modern alternators quickly replace what little is used on starting. And, there may just be that day when for one reason or another, a bit more reserve is needed in the battery. Like now for me, as I change the fuel filter and bleed the injectors via turning the engine over on the starter motor.

[DotDun]

The OM for the 3GM30 suggests a 70AH battery, which equates to a group 24.

IMO, anything larger than that is simply a waste of battery and money.

[DeepFrz]

I don't know why the OM would suggest a 70 ah battery. Starting batteries are rated in CCA (cold cranking amps) or, more importantly for a boat perhaps, MCA (marine cranking amps). A battery rated for a 20 hr rate at 70 ah is meaningless for a starting battery.

[DotDun]

from the manual...

[Saltyrope]

Hi DotDun, Deepfrz is correct when it comes to rating a starting battery and while Yanmar state the Amp Hours that is like saying have a 10 lb pot of jam BUT the big factor is whether it is runny jam or thick stuff as to whether it can empty its contents fast enough get the wheel spinning so to speak. However a 100 amp STARTING battery MAY be 930 CCA as in the Ultra MMF31/930U and a 75 amp MMF24/680u which will deliver 680 CCA. So, Yanmar must of course be talking about STARTING batteries only which can be roughly cross referenced to a CCA... usually. It is when it comes to Hybrids and deep cycle that the A/H relate to CCA differently. Also the colder it is the less performance a battery will give so it can all become a bit of a science but as long as the battery for starting is purely a thin plate starting battery the Yanmar recommendation will give an approximate CCA value and it may be surprising to some just how high a CCA is specified, as per Yanmars recommendations

[DotDun]

Originally Posted by Saltyrope

Hi DotDun, Deepfrz is correct when it comes to rating a starting battery and while Yanmar state the Amp Hours that is like saying have a 10 lb pot of jam BUT the big factor is whether it is runny jam or thick stuff as to whether it can empty its contents fast enough get the wheel spinning so to speak. However a 100 amp STARTING battery MAY be 930 CCA as in the Ultra MMF31/930U and a 75 amp MMF24/680u which will deliver 680 CCA. So, Yanmar must of course be talking about STARTING batteries only which can be roughly cross referenced to a CCA... usually. It is when it comes to Hybrids and deep cycle that the A/H relate to CCA differently. Also the colder it is the less performance a battery will give so it can all become a bit of a science but as long as the battery for starting is purely a thin plate starting battery the Yanmar recommendation will give an approximate CCA value and it may be surprising to some just how high a CCA is specified, as per Yanmars recommendations

I'm not arguing, the OP asked that someone check the manual, that's what I did. Next time I'm on the boat, I'll look in the paperback version.

[DeepFrz]

Perhaps there is a correlation between ah and CCA. Perhaps one could rely on that. I think it is probably a difference in understanding between Japanese and English. In any case it is what it is.

[Saltyrope]

Agreed Deeprfz, but also your original comment about amp hours and CCA not necessarily correlating is also true with the thought that apples must be compared with apples. A 200 A/H (Amp Hour) deep cycle battery may not release enough power quickly enough to turn over an engine fast enough to start it as it is a deep cycle/slow power release battery with for example say 450 CCA's whereas the 100 Amp hour starting battery may release anything in the vicinity of 900 CCA's. Also as you mentioned the release time for that power in the battery sums it up. A huge capacity released over a long period, say at the 20 hour rate measurement, tells us little about its ability to start an engine. I guess for those that are not familiar with deep cycle batteries measured by their release capacity over a given period, in amp hours as their primary function and starting batteries measured by their 'sheer grunt' in power flow of CCA available, a way of understanding it is to imagine a tap or valve on each battery with a little hole to release power from the deep cycle battery and big hole to release power from a starting battery. Obviously one lot of 'power' will flow out a lot quicker. A few attempts at hybrids with a medium sized power release rate is an attempt at having both a deep cycle and starting battery combined. Drains at a medium rate and also fills at a medium rate. Generally a bigger battery than a starting battery would be needed to do the starting only job. Not thick not thin plates. The big advantage of having a starting battery for starting only is that it empties its load quickly but also fills up quickly so short engine runs are not an issue for a recharge whereas deep cycle batteries, even with modern charging regulators still take longer to charge. Cruisers that have told me that they changed to 'truck batteries' because their deep cycle batteries took too long to charge did not have solar panels or wind generators to take advantage of the slower but ongoing ability of a deep cycle battery to continue to accept a charge long after the starting battery has filled up again. And, back to the original Yanmar 70 or 100 amp battery. With that A/H specification It MUST be a thin plate starting battery to be able to release enough grunt. It also says min capacity so if a bigger battery is a waste of time and money I guess that could also be correct. Although, like an anchor, over specified and one (or two) sizes bigger than needed for the size and weight of a vessel. could be a waste of size and money.... unless there is perhaps that odd day when a gale to storm force heads into the anchorage, and the specified sized anchored boats start to drag and there is spray around and the engine takes longer to start than normal because the motion has stirred up water in the bottom of the tank and the battery is used to bleed the engine and, well, those that cruise in more challenging areas will already know the value of having a bit of redundancy built into their systems. The single biggest cause of breakdowns at sea is a flat battery.