Dual Battery Set up

[Smiderman]

G'day

just looking for some guidance / diagrams on a dual battery set up for the boat.

usual story one for the motor and the other for lights sounder radio etc.

[roverfj1200]

How fancy you want it..

Mine is simple One on the motor and a second AGM for the electrics. No isolators or solenoids I just put the battrey charger on the night before I go fishing. The 120ah AGM will easily run all lights and shit for a week away. I let the motor take care of the starter battery..

Cheers.

[daveylad]

Mine is similar to the bottom picture both batteries can be charged at once when motoring or switch to one battery for night time or electrics. Available at Whitworths $59"00

[Smiderman]

[attachment=35265]batteryswith.jpg[/attachment]

[attachment=35264]84425_7650_BlueSea_DualCircSys.jpg[/attachment]

Mine is similar to the bottom picture both batteries can be charged at once when motoring or switch to one battery for night time or electrics. Available at Whitworths $59"00

Daveylad what is the purpose of the module on the bottom and does $59 cover the switch or both whole thing?

[Smiderman]

How fancy you want it..

Mine is simple One on the motor and a second AGM for the electrics. No isolators or solenoids I just put the battrey charger on the night before I go fishing. The 120ah AGM will easily run all lights and shit for a week away. I let the motor take care of the starter battery..

Cheers.

As I understand it, unless the batteries have exactly the same state of charge, the combined voltage to the two batteries in parallel will sag to a voltage somewhat lower than the highest battery's terminal voltage. Current from the higher voltage battery will flow into the lower voltage battery and begin charging it. As long as the state of charge in one battery is higher than the other, the lower battery is more of a load than a source of power. Eventually, the batteries will reach an equilibrium, and they will both have the same terminal voltage. At that point they will both tend to supply current to loads that are attached to them, and they will both receive charging current furnished by the engine.

If the batteries are significantly different in their age, their type of construction, and their state of charge, this unequal distribution of current can be more significant. To describe the situation in the simplest of terms, when two batteries are connected in parallel, they will probably tend to behave more like the weakest battery of the two than the strongest.

If one battery is fully charged and the other is totally discharged, connecting them in parallel can cause very high currents to flow between the batteries. Extreme heat can be generated by the sudden charging of the discharged battery. Use caution in this situation. It is better to recondition a discharged battery by slowly re-charging it with an AC-operated battery charger.

thats why I asked!!!!!!!!!!!!

[daveylad]

Smiderman,

The pics were reversed when they were posted the bottom one was supposed to be at the top.The diagram was just to show you a dual battery battery system which I thought you asked for in your post!!!!! The top pic is the one I have the swithch is about $50 at Whitworths. I have 2 diff batteries one cranking (starting)and one a deep cycle Glass(AGM),120amphrs which will also do for starting if needed. I use the 2battery mode when the boat is underway and after I have been using the deep cycle battery so that it will recharge. I then switch to the deep cycle for electronic uses or nighttime. I know if there is a problem and the cranking battery becomes too low I can bank them together to start up the boat then switch them over again to single battery.

your last post suggests that having different age and type of batteries is not good, I cant understand that because most boats have more than one battery some up to 4 all in parrarel and for different purposes ie, cranking and deep cycle. The boats then have a selector switch like the one in the pic (2) I should think that at any time none of the batteries would be equal in charge so what you are saying is that its not a good thing to bank batteries together unless they are all equal in type and charge. I realise that one may sap on the other to recharge it but this comes into being responsible and knowledge of your own battery system and battery use. Also making sure the batteries are properly charged before putting out, I have a C-Tec Marine charger that uses an 8 stage trickle charge this seems to keep them under good maintanance.

Reading your last post you seem to know a a good deal about batteries and there systems cant understand whith your knowledge why you would want a diagram if you want to keep them isolated for seperate jobs a simple switch will do that :pinch: !!!!!!or you can save yourself $50 bucks and physically do it yourself!!!!!!

/>http://www.outbackmarine.com.au/shop/Battery-Switch.44?gclid=COOPsKmmnakCFc2DpAodIWPhsw

best diagrams on the subject here,

[Smiderman]

Thanks For your help Daveylad. The info above is what I researched off the the net after creating the post.

this is the site where the info came from;

http://continuouswave.com/whaler/reference/dualBattery.html

[Surfingant]

I would lean towards using a fully automatic isolator. Might cost a bit more initially but more than makes up for it when your manual isolator corrodes and doesn't do the job anymore or you get lazy/forget to switch it over. A simple VSR from an auto shop will do it and there is no need to worry about different size and age batteries as it will not connect unless the crank battery is fully charged, and will disconnect when the second battery drops below a preset voltage.

[roverfj1200]

How fancy you want it..

Mine is simple One on the motor and a second AGM for the electrics. No isolators or solenoids I just put the battrey charger on the night before I go fishing. The 120ah AGM will easily run all lights and shit for a week away. I let the motor take care of the starter battery..

Cheers.

As I understand it, unless the batteries have exactly the same state of charge, the combined voltage to the two batteries in parallel will sag to a voltage somewhat lower than the highest battery's terminal voltage. Current from the higher voltage battery will flow into the lower voltage battery and begin charging it. As long as the state of charge in one battery is higher than the other, the lower battery is more of a load than a source of power. Eventually, the batteries will reach an equilibrium, and they will both have the same terminal voltage. At that point they will both tend to supply current to loads that are attached to them, and they will both receive charging current furnished by the engine.

If the batteries are significantly different in their age, their type of construction, and their state of charge, this unequal distribution of current can be more significant. To describe the situation in the simplest of terms, when two batteries are connected in parallel, they will probably tend to behave more like the weakest battery of the two than the strongest.

If one battery is fully charged and the other is totally discharged, connecting them in parallel can cause very high currents to flow between the batteries. Extreme heat can be generated by the sudden charging of the discharged battery. Use caution in this situation. It is better to recondition a discharged battery by slowly re-charging it with an AC-operated battery charger.

thats why I asked!!!!!!!!!!!!

All the above is true.. But the house battery in my setup is not connected to the start battery. Being a AGM it can be run flat many times with no or little damage. The house is charge at home. But for a week away it will run everything with out the need to be charge..As I said simple..Nothing fancy to corroded.

Cheers