Ading Batteries/Starting from Deep Cycle

[witzgall]

Hi all:

OUr current battery setup is a Trojan 1275 house battery, 150ah 12v wet. Starter battery is a Grp 24 Optima battery.

They were both put into service in May. I now want to add another 1275 to the house bank. I know mixing older and newer batteries is not a good idea, but since it was put into service recently, will this be ok? The existing battery spent about two months being charged from engine only, light loads, and then I installed a Iota 45 AMp charger which it has been on since.

Secondly, The Optima is physically in the spot where the second Trojan need to go. So my first step would be to drop the Trojan in, and then relocate the Optima behind the engine, a Volvo 2002 18hp diesel. If I don't get the Optima relocated for a bit, is it ok to start the engine from the combined bank of the two Trojans? I imagine this would be for maybe 10-15 starts max.

Chris

[Pblais]

Given how new the first one is I think it is safe to mix the brand new one. Yes, you could start the engine just fine with the two house batteries. The optima would be the better battery for starting power but you'll be able to start with even just one of the Troan's.

When you connect up all the batteries make sure you pay attention to the distances and gage of wire required. You really do want as short as possible runs using quality cable and properly made connectors. With this much power you can make a lot of sparks, heat, and trouble if you don't get things right. Cables and fuses can get expensive so don't just go smaller to save money when the job requires larger. It's flat out dangerous.

[witzgall]

Paul;

Yes, big cables will be used. The runs to the switch are only a few feet.

You bring up something else I have to think about - there is currently no fuse in the system, only a off-1-2-both selector switch. I assume I should have a large fuse in-line on the cable coming off of the battery going to the switch? What size?

[Pblais]

A shielded fuse block located as close to the battery as possible would be best. The class T blocks are super fast response. If you think about the whole battery bank short circuiting that is one heck of a bang. I'm not sure what the right size would be for your setup.

I also prefer a thermal resettable fuse on the windlass power near the battery too. If it locks up it can pull 75 amps and that can start fires in very short order with a nice long line to the bow glowing red hot. After seeing a windlass burn up I don't mind resetting the breaker when it jams.

[witzgall]

Windlass? What Windlass? That is what my wife is for!

Chris