The Official Dual Battery Thread

[djhuff]

Diesel, I'm running the relay. Do you see any problem with energizing the relay with the "accessory" lead rather than the "run" lead from the ignition. Reason being, If the stereo battery is low and I try to start... the batteries will be in parrallel. Wouldn't this cause the starting battery to discharge into the stereo battery at the same time it is trying to start? I was thinking that if I use the accessory lead, when I turn the key to "start", the relay will be open, and the starting battery will be isolated while starting, but switched back to parrallel once the engine is running. I have nothing hooked up to the accessory switch right now (radio is solely hooked up to second battery with manual off/on switch). Thanks

[Diesel]

Diesel, I'm running the relay. Do you see any problem with energizing the relay with the "accessory" lead rather than the "run" lead from the ignition. Reason being, If the stereo battery is low and I try to start... the batteries will be in parrallel. Wouldn't this cause the starting battery to discharge into the stereo battery at the same time it is trying to start? I was thinking that if I use the accessory lead, when I turn the key to "start", the relay will be open, and the starting battery will be isolated while starting, but switched back to parallel once the engine is running. I have nothing hooked up to the accessory switch right now (radio is solely hooked up to second battery with manual off/on switch). Thanks

I don't think the accessory lead on a boat works like an auto where it is not energized during start up?? When in the run or start position I think the accessory is still energized. I think the accessory and "run" are all the same when the key is to the right.

Actually now that I think about it you might be on to something here. I will have to get my fluke out to see what is going on in the ignition switch.

If I am wrong this is a very good way to alleviate the concern regarding large flows of current at start up.

[Matt L.]

Huh???

Okay, now my head is spinning from reading this stuff!!!

here is what I've got to work with.

Perko Switch, Optima Blue top starting batt, Deka AGM deep cycle.

I just want a system that will automatically disable the starting batt when the ignition is off, enable the deep cycle when the ignition is off, and charge both properly when running.

Is that too much to ask???!!!

Perko is under a seat (where kids/babies always end up falling asleep) and is a real PITA to remember to switch around.

I've got a boat and crew to manage (wife and 3 boys), I don't need to worry about the batteries too!!!

Thanks,

Matt

[Diesel]

Okay, now my head is spinning from reading this stuff!!!

I just want a system that will automatically disable the starting batt when the ignition is off, enable the deep cycle when the ignition is off, and charge both properly when running.

Is that too much to ask???!!!

Buy the relay and wire it according to the first post and forget about it.

[djhuff]

Let me know what you find Diesel. I've got til Saturday to get this figured out before I christen the boat.

[Matt L.]

Buy the relay and wire it according to the first post and forget about it.

Dooh! I mean, Sweet!!! Sounds pretty simple then.

So when the relay is energized by the ignition switch I get both the starting batt and the deep cycle in parallel with both the starting and charging systems?

When the ignition system is off the relay opens between the starting and deep cycle batteries, leaving just the deepcycle batt exposed to discharge.

If that is all right then my only concern is for the deepcycle. Will it be exposed to the sudden and deep draw of the starter motor?!? If so, won't this damage the deep cycle?

I spent big bucks on these big AGM batteries and I don't want to ruin them. The boss....er wife will kill me if I have to explain why that $150+ deepcycle was ruined by adding the relay.

Could I add a second relay in the same manner as the first, but energizes to cut the deepcycle out when the starter motor circuit is energized?

Thanks,

Matt

[Diesel]

Dooh! I mean, Sweet!!! Sounds pretty simple then.

So when the relay is energized by the ignition switch I get both the starting batt and the deep cycle in parallel with both the starting and charging systems? Yes

When the ignition system is off the relay opens between the starting and deep cycle batteries, leaving just the deepcycle batt exposed to discharge. Exactly

If that is all right then my only concern is for the deepcycle. Will it be exposed to the sudden and deep draw of the starter motor?!? If so, won't this damage the deep cycle? Not enough to matter. Your deep cycles will be fine.

I spent big bucks on these big AGM batteries and I don't want to ruin them. The boss....er wife will kill me if I have to explain why that $150+ deepcycle was ruined by adding the relay.

Could I add a second relay in the same manner as the first, but energizes to cut the deepcycle out when the starter motor circuit is energized? Not quite following you here but either way it is not necessary.

Thanks,

Matt

Response in blue above......

[kalanic]

Finally finished my battery install between our crappy weather....hope it works!

[Diesel]

Great looking install!!

I love those billet Optima trays and wish I had room to use a pair.

[kalanic]

Thanks Diesel! Im gonna get another next year. I will see how the factory battery performs with the Optima supporting my high power amp. You think I will need to fabricate a cover for the Isolator?? Will water screw it up if it gets wet?

[Leroy]

Diesel;

I think what Matt is concerned about and I think could be a concern, you run the deep discharge battery dead, then when you start not only is the current from your good battery starting the boat, but is surging into the dead battery. If you could delay the relay connection until the motor started there would only be one load at a time on the good battery.

Could I add a second relay in the same manner as the first, but energizes to cut the deepcycle out when the starter motor circuit is energized? Not quite following you here but either way it is not necessary.

[Diesel]

Thanks Diesel! Im gonna get another next year. I will see how the factory battery performs with the Optima supporting my high power amp. You think I will need to fabricate a cover for the Isolator?? Will water screw it up if it gets wet?

No it is sealed. I would make sure that compartment is left open after a day on the water to help prevent terminal corrosion.

[kalanic]

Right on Diesel...Thanks!

[Diesel]

Diesel;

I think what Matt is concerned about and I think could be a concern, you run the deep discharge battery dead, then when you start not only is the current from your good battery starting the boat, but is surging into the dead battery. If you could delay the relay connection until the motor started there would only be one load at a time on the good battery.

Could I add a second relay in the same manner as the first, but energizes to cut the deepcycle out when the starter motor circuit is energized? Not quite following you here but either way it is not necessary.

If it is a concern just wire the DPDT switch in the dash and then you can manually engage the relay once the motor has started. I have a hard time remembering to hit the switch and have never had a problem with extreme current flow so I like the ease of wiring it to the ignition................fully automatic, i never have to think about it, and no matter who drives my boat (wife, friend, dad, etc.) I don't have to worry about explaining how to work the "Battery" switch.

Off the top of my head I can think of a couple a dozen set ups I have done that have never had any problem. In fact I have taken my aux battery in my Jeep to beyond dead with the winch and was still able to start the LT1 multiple times with no problem. I don't believe it is an issue.

[BrianS]

Diesel;

I think what Matt is concerned about and I think could be a concern, you run the deep discharge battery dead, then when you start not only is the current from your good battery starting the boat, but is surging into the dead battery. If you could delay the relay connection until the motor started there would only be one load at a time on the good battery. [/color]

I was concerned with the same thing. I used this instead of the relay. This combiner doesn't put the batteries in parallel until the motor is running, ie the alternator is charging the system. No chance of killing your starting battery with a drained aux battery. No switches needed, totally automatic and very simple to wire in.