12V Deka to 6V Trojan - Is this change a good choice

[landonshaw]

I have:

2 - 12V Deka 24M6 Batteries 675 CCA - MCA 820

I need to replace and am looking at replacing with:

2 - 6V Trojan T-105 447 @ 25 amps - 115 @ 75 amps , 5 hr rate AH 185 - 20 hr Rate AH 225

I am unsure as to of how to compare the two batteries. I have a 12Volt system so realize and know how to hook up either system. This is for my engine starting bank. The house is a separate bank of 4 - 6V batteries.

The question is, will I have the same cranking power for my 40HP Volvo Penta with the Trojan as I have with the Deka. I am in Grenada. Can anyone help me with this information? Thanks

[btrayfors]

The two 6-volts would work, but they're not optimum. Deep-cycle batteries are meant to release energy slowly. Start batteries have thinner plates and are designed to release a lot of energy fast -- exactly what you need for starting a diesel.

Remember that while cranking the diesel requires a large current -- upwards of 1,000 amps for a few milliseconds followed by about 150 amps while the engine is actually turning over -- this is only for a few seconds. Normally, starting a diesel requires a total of 0.5 amp-hours. Yes, less than a single AH.

You just need one healthy start battery (not a deep-cycle battery). I'd put in a single Group 27 or, better, Group 31 start battery.

Bill

[landonshaw]

On the island it looks like the best starting battery would be a Exide XXHD-M-24 1000 MCA & 115 MRC. The XXHD-M-27 will not fit in my engine battery bank compartment. I am going to check the owners manual before purchasing. Thanks for your comments. The other batteries have a lower MCA as compared to this one.

[Maine Sail]

Originally Posted by landonshaw

I have:

2 - 12V Deka 24M6 Batteries 675 CCA - MCA 820

I need to replace and am looking at replacing with:

2 - 6V Trojan T-105 447 @ 25 amps - 115 @ 75 amps , 5 hr rate AH 185 - 20 hr Rate AH 225

I am unsure as to of how to compare the two batteries. I have a 12Volt system so realize and know how to hook up either system. This is for my engine starting bank. The house is a separate bank of 4 - 6V batteries.

The question is, will I have the same cranking power for my 40HP Volvo Penta with the Trojan as I have with the Deka. I am in Grenada. Can anyone help me with this information? Thanks

Your Deka's are a thin plate starting battery and you don't need two of them (1350 CCA) to start a 40HP Volvo.

The Trojan's will give you about 800CCA give or take and will start your motor with ease. My question is why do you want to spend that kind of money on this when a single $70.00 battery will do what you need...?

Unless you want the Trojans to serve as a "reserve" bank should there be an issue with the house a simple $70.00 start battery will do all you need...

BTW I used to start the large turbo Cummins in my down east style boat in February with T105's so a 40HP sailboat aux is cake walk..

[landonshaw]

We have very little choice on the Island. In fact they cost $165 ea. That is a GOOD price down here.

I am actually looking at the 1000 MCA M24 from Exide, $190US ea. And yes thye would offer me a backup to my house if I needed it.

Are you saying that if I get 2 - 12volt 1000 MCA batteries from Exide, that would be like having 2000 MCA to start the engine? And no cold weather here.

[Maine Sail]

Originally Posted by landonshaw

We have very little choice on the Island. In fact they cost $165 ea. That is a GOOD price down here.

Ouch!!!

Originally Posted by landonshaw

I am actually looking at the 1000 MCA M24 from Exide, $190US ea. And yes thye would offer me a backup to my house if I needed it.

Are you saying that if I get 2 - 12volt 1000 MCA batteries from Exide, that would be like having 2000 MCA to start the engine? And no cold weather here.

With two batteries in parallel you combine the amperage.

CCA is at 0F (cold cranking amps)
MCA is at 32F (marine cranking amps)

At 70F - 80F you can add at least 30% to the MCA figure.. If I had to shoot from the hip two of those batts should easily give you over 2500CA at the temps you are using them at...

[landonshaw]

I see you are in ME Maine Sail. We still have an old home, 1797, in Alfred that we go to for a few weeks every year. Beautiful even in the winter.

[Caribsailors]

[QUOTE=Maine Sail;1068998]Ouch!!!



But he doesn't own a snow shovel, or snow tires, or three other seasons of clothes...life on an island mon....

And that is a good price! I saw 55AH Optima Blue Tops in Cayman for $400 CI
what's that in USD?

400 x 1.2 = $480 USD EACH

[landonshaw]

We did get caught in St Pierre, Martinique for 5 days without any electric over Christmas last year. I left the house electric on without running the engine. Kept hoping for enough sun to charge the batteries, never did. Finally had to sail out to Rodney Bay. We had to survive on fresh food but did run into town each day for ice for the drinks. Got a wind generator and am now getting new engine batteries. And yes, if I run the refrig to long I will have the same experience again.