Spare Battery Setup

[Tazy]

Being electronically challenged I was hoping for some advice.
Can I connect another battery to the one I already have by connecting + to + and - to - with a cutout switch on the negative wire turned off and if the main battery goes flat could I turn the switch on to use the other battery.
As its a 4 stroke motor could I let it run with both batteries connected this way to help them both charge or should I turn turn the switch off once the motor has started and let the main battery charge.
Could the electronics be damaged if this is done.

Any advice greatly appreciated as I'm heading off on a fishing adventure, and although never having had battery trouble before I thought a spare might be handy.

[FrankFWM]

Hi Tazy,

You don't actualy disconnect the negative through a battery switch. The battery Switch actualy disconnects the positive of the battery you are "switching off".

You normaly connect the negative of both batteries together.

The positive terminal of the starting battery runs to a battery one pole on a battery switch and the second battery positive runs to the battery two pole on the switch.

The positive from your accessories and engine harness runs to a "common" pole on the battery switch.

This is the basic setup that is usualy used.

Never have the battery switch in the "Off" position when the engine is running. This will in most cases damage the diodes in your alternator and the electronics on board. Always have the swich on either "battery 1", "battery two" or "both". Only use the "Off" position when the boat is at home and out of the water in storage to prevent anything draining the battery.

You battery acts like a power filter and helps supply "clean" power.

Charging them is another subject... if they are different battery types - then make sure you charge them when you get home seperately to top them up.

Frank

[Hamish73]

Tazy, switching the -ve will work, but isn't ideal as you wont be able to:
Isolate all batteries for storage purposes
or
Select only battery 2 if battery 1 fails.
I good quality 1,2,both,off switch is only about $50 and well worth it.
The perfect system would also include a voltage sensative relay between battery 1 and 2.
With this system you would leave switch set to battery 1.
This would automatically charge battery 2 when the engine is running, but isolate battery 2 when the engine is off. If you were to accidently drain battery 1 whilst fishing, simply turn the switch to battery 2 (or both) and start your engine

Permanantly parelleling 2 batteries (-ve to -ve and +ve to +ve) isnt a good idea as if one battery fails it will flattern the other.

[Tazy]

Thanks boys,

The first drawing is what i want to do, if batt 1 goes flat, will I be able to turn the switch on and have enough power to start and run for at least an hour?

The second is how i understand your comments.

The engine is a Merc 60hp 4 stroke EFI. People have told me that 4's have a better charging system than two strokes, does anyone know if that is true.

Thanks again for your help,
Tazy

[driveon]

Hi Tazy, your first drawing is actually fine.

There is no real reason why you can't put the switch in the negative cable but for simplicity sake, use the same drawing but put the switch in the positive cable and only use a two position ON / OFF marine battery switch instead of a 4 position switch.

Leave your existing cranking battery wired as it is and just run a cable from the cranking battery’s negative terminal to your new battery’s negative terminal.

Then a cable from your cranking battery’s positive terminal to one side of the ON / OFF switch and then run a cable from the other side of the ON / OFF switch to your new battery’s positive terminal.

Job done.

[dnej]

This may also help,it uses two isolation switches.
David

[dnej]

http://www.ausfish.com.au/vforum/sho...529#post688529

Previous posting may also help you.
David

[Kleyny]

You could also try running one isolator switch on the second Bat (pos. terminal)
then run a smaller wire say 6-8mm with a diode in it so it will still charge with the isolator in the off position but not loose charge through the other battery.

I'm sure I'll be corrected if I'm wrong but you need to keep neg connected to get charge into the battery. IMO if you don't have the neg connected, its like turning your hose on but forgetting to open the nozzle.

neil

[Millby]

buy a basic twin battery cable setup (100 bucks) from a marine shop or 4x4 shop, and run accessories off the second battery to give it a bit of use. Carry a jumper lead if you need to use the second battery to start off and use that in emergencies, just like in your landcruiser.....

battery system isolates the second battery from use, but still lets it get charge. jumper lead is the easiest and best switch for when you need it to start your engine.

[mike wallace]

Tazy, switching the -ve will work, but isn't ideal as you wont be able to:
Isolate all batteries for storage purposes
or
Select only battery 2 if battery 1 fails.
I good quality 1,2,both,off switch is only about $50 and well worth it.
The perfect system would also include a voltage sensative relay between battery 1 and 2.
With this system you would leave switch set to battery 1.
This would automatically charge battery 2 when the engine is running, but isolate battery 2 when the engine is off. If you were to accidently drain battery 1 whilst fishing, simply turn the switch to battery 2 (or both) and start your engine

Permanantly parelleling 2 batteries (-ve to -ve and +ve to +ve) isnt a good idea as if one battery fails it will flattern the other.

Hamish, Where do you buy a "voltage sensite relay" & what are the specifications for a couple of deep cycle batterys currently switched as 1,2 or Both for emergencies ?
Mike Wallace

[ozbee]

4 stroke electricity what next? must be from the guy with the left handle screwdriver

[Hamish73]

Hamish, Where do you buy a "voltage sensite relay" & what are the specifications for a couple of deep cycle batterys currently switched as 1,2 or Both for emergencies ?
Mike Wallace

You can get voltage sensative relays from BIAS, Springers etc or any marine acessory outlet.
Not sure what you mean by the 2nd part of your question
I'd run boat on 1
With VRS connected, battery 2 would automatically get charged whilst running.
If you flattern 1, switch to 'both' start engine and it will recharge flat 1 as well as top up 2. When all is good again, return switch to '1'
A VSR will sense of one battery (the master) and connect the second battery when the voltage is high enough. This doesnt work in reverse (brand dependant I would imagine) In other words. If battery 1 was flat and you were running on '2', it wouldnt charge battery 1 because it is sensing off 1. If 2 was flat and you were running off 1, as soon as 1 reached 13v, it would connect battery 2 and charge both batteries.