Battery systems

[jclays]

Good afternoon.
New to me 1997/350 twin 200hp Volvo’s. Batteries are older. 2017. Going to replace before they fail. Currently 3 12v group 31. One for each engine and the third for the generator. What are you running? Should I do something different.?
Thought of making the generator battery an 8D and moving all the the load to that battery. Would this creat a charging issue since one battery is a different group size?

 

[tiltrider1]

I prefer the generator has its own battery that charges off the generator alternator. I find it is simpler to put two group 31’s in parallel to start each engine rather than having a separate battery for each engine but either way works. You didn’t mention a house bank. I prefer not to combine house duties with starting duties.

 

[koliver]

My last battery replacement was after 11 years on a single 4D start battery.
That battery reliably starts a pair of 200 hp Volvo TAMD41s and a Westerbeke 4kw Generator with glow plugs.

8D is unnecessarily large and far too heavy.

I don't understand your last question "Thought of making the generator battery an 8D and moving all the the load to that battery. Would this creat a charging issue since one battery is a different group size?"
If you move all the load to that battery, where is there a "different group size"?

 

[Comodave]

Good afternoon.
New to me 1997/350 twin 200hp Volvo’s. Batteries are older. 2017. Going to replace before they fail. Currently 3 12v group 31. One for each engine and the third for the generator. What are you running? Should I do something different.?
Thought of making the generator battery an 8D and moving all the the load to that battery. Would this creat a charging issue since one battery is a different group size?

Do you anchor out and have need of a house bank that is capable of deep discharge? If so you don’t have that now and wouldn’t have it with an 8D. Most, if not all, 8Ds are not a true deep cycle batteries. Besides they are extraordinarily heavy. I would do one of several things. Maybe keep one group 31 as a start battery for both engines. Make a separate deep cycle bank out of true deep cycle batteries. And keep a separate start battery for the genset. Or keep both start batteries for the main engines and convert the genset battery to a deep cycle bank and use it to start the genset also. As to the deep cycle house bank 6volt golf cart batteries are good for deep cycle and are reasonably priced. Then all your battery banks would be flooded and could use the same charger. I am going to LiFePO4 batteries for my house bank. They are very pricey but offer lifetime warranty and can be discharged to 20% routinely, something that will kill a flooded battery. The lithium also needs a different charging profile.

 

[Bacchus]

A pair of GP31s is pretty close to the same MCA as an 8D. I would consider combining the 2 GP31s for main eng start and charge w one eng alternator. Use the second eng alt to charge house bank. I prefer to keep a dedicated gen batty that is charged by the gen alternator (assuming it has one) a GP 24, 27 should suffice but if you want to keep things consistent a GP31 is likely more than needed.

 

[jclays]

My last battery replacement was after 11 years on a single 4D start battery.
That battery reliably starts a pair of 200 hp Volvo TAMD41s and a Westerbeke 4kw Generator with glow plugs.

8D is unnecessarily large and far too heavy.

I don't understand your last question "Thought of making the generator battery an 8D and moving all the the load to that battery. Would this creat a charging issue since one battery is a different group size?"
If you move all the load to that battery, where is there a "different group size"?

Each engine has a group 31 to start and each engine/group 31 battery splits the house load.

 

[jclays]

I prefer the generator has its own battery that charges off the generator alternator. I find it is simpler to put two group 31’s in parallel to start each engine rather than having a separate battery for each engine but either way works. You didn’t mention a house bank. I prefer not to combine house duties with starting duties.

The boat has no house bank.
The factory setup was a group31 battery to start each engine with half the house load on each battery.
The gen set battery only starts the generator. This is why I was thinking of unloading the port/starboard engine start batteries and upsize the gen set start battery and place all the house load on that battery. If i killed that battery it is easy enough to jump start if I needed the generator.
Just throwing out ideas to see I there's one out there that will work before I purchase batteries.

 

[jclays]

Do you anchor out and have need of a house bank that is capable of deep discharge? If so you don’t have that now and wouldn’t have it with an 8D. Most, if not all, 8Ds are not a true deep cycle batteries. Besides they are extraordinarily heavy. I would do one of several things. Maybe keep one group 31 as a start battery for both engines. Make a separate deep cycle bank out of true deep cycle batteries. And keep a separate start battery for the genset. Or keep both start batteries for the main engines and convert the genset battery to a deep cycle bank and use it to start the genset also. As to the deep cycle house bank 6volt golf cart batteries are good for deep cycle and are reasonably priced. Then all your battery banks would be flooded and could use the same charger. I am going to LiFePO4 batteries for my house bank. They are very pricey but offer lifetime warranty and can be discharged to 20% routinely, something that will kill a flooded battery. The lithium also needs a different charging profile.

I like your second option. When I had a travel trailer I had 2 Trojan T125 6v golf cart batteries together in series to make a 12v system. I could stay out in the woods for a week.
Would these 2 in series be able to start the generator?

 

[boatpoker]

Would this create a charging issue since one battery is a different group size?

This would create a sore back issue. 8D's are 165lbs.

 

[tiltrider1]

I am assuming that space is an issue. You can have both engines start off the same battery. A group 31 should do the job. Then I would use all the rest of the space for house deep cycle batteries. You can have the generator start off either the house or the start bank.

This is not my ideal set up but it works if you have a space issue. You can add a 1,2,off,all switch so that you can start the engines off either house or start as a back up plan.

Ideally you would run both alternators and your charger to the house bank and then use a Smart ACR between house and start bank to charge the start battery.

I prefer the generator to have its own independent battery as a backup plan should some one change the 1,2,off, all switch accidentally on purpose and drain all the batteries but if you don’t have the space then you compromise.

 

[jclays]

Question
Trojan T125 6v batteries are 240AH. Does placing 2 together in series get me 12v 240AH or 12v 480AH?

 

[boatpoker]

It's hard to make any recommendations without knowing how you intend to use the boat. What are you trying to accomplish ?

 

[Bacchus]

Question
Trojan T125 6v batteries are 240AH. Does placing 2 together in series get me 12v 240AH or 12v 480AH?

Series Add V but A stays the same.
12V 240 AH
Parallel V stays the same AH add.