Charging 2 batteries at the same time???

[JP_R]

Hello Guys,

I have two batteries on my boat and I was wondering if there are any consequences on having the battery switch on "both" so the two batteries receive charge at the same time while the engine is running.

Is there something I should be worried about? Right now on the "common" terminal I have the (+) to the trim pump, the (+) to the ignition, and well the (+) going to the stater.

the (+) to the ignition I thought should be wired to the fuse box but this is the way the boat came when I bought it.

Thanks,

 

[Boatist]

Re: Charging 2 batteries at the same time???

Main thing with a switch is never turn the switch thru off with the motor running.
Also if your switch is not a make before break type then do not turn with the motor running.

With a 5.0 MPI you are going to have a big alternator, 60 to 100 amps so charging in the both position is fine.

Problem with the both postion is with a very small charging system or when the motor is shut off.
When the motor is shut off and switch is in the both postion several bad things can happen.
If you leave it in this postion then both battery will be discharged by any thing still turned on like a big stereo.
Also if one battery is weaker than the other the stronger battery will try and charge the weaker battery and both batteries get run down.

Personal I like charging both batteries thru a battery isolator if you have a 3 wire alternator.
If you have a 1 wire alternator or a smaller outboard then a VSR or ACR would be better.
Any of these will charge both batteries while the engine is running but stop battery 2 from discharging battery 1 when stopped if the switch is not in both.

 

[JP_R]

Re: Charging 2 batteries at the same time???

Main thing with a switch is never turn the switch thru off with the motor running.

This I knew but thanks for reminding me..

Also if your switch is not a make before break type then do not turn with the motor running.

Is this a make before break type???? I don't know what you meant by this..

The main concearn I have is having 24 volts running to the trim pump and the ignition switch when the switch is in BOTH. Do you think this could damage or burn any fuses/wires??

 

[q5ka]

Re: Charging 2 batteries at the same time???

Switching to both should not be making the system from 12V to 24V. It should be still 12V with twice (in theory) the capacity. To get 24V, you would have two batteries but battery 1 sends hot out and its negative is hooked directly to hot on second battery and negative of second battery is hooked to ground (series). Your setup is probably hot hooked to hot hooked to power out and negative hooked to negative hooked to ground. That still gives 12V. Also as mentioned, if you get an isolator, then both batteries will charge even though the switch is switched to 1. That way you are not draining your start battery and get stranded in the middle of a lake of cove.

 

[JP_R]

Re: Charging 2 batteries at the same time???

Switching to both should not be making the system from 12V to 24V. It should be still 12V with twice (in theory) the capacity. To get 24V, you would have two batteries but battery 1 sends hot out and its negative is hooked directly to hot on second battery and negative of second battery is hooked to ground (series). Your setup is probably hot hooked to hot hooked to power out and negative hooked to negative hooked to ground. That still gives 12V. Also as mentioned, if you get an isolator, then both batteries will charge even though the switch is switched to 1. That way you are not draining your start battery and get stranded in the middle of a lake of cove.

Thanks for the explanation. The way I have my batteries hooked up is:

Negative for batteries 1 and 2 have a jumper cable and then to the engine block and then positive of battery 1 to slot 1 on switch and battery 2 to slot 2 on switch.

Thanks again.

 

[Silvertip]

Re: Charging 2 batteries at the same time???

You indeed have a 12 volt system in which you can supply power to accessories AND charge the batteries in any combination. BAT 1 = ONLY BAT 1 supplies power and will be charged when the engine is running. BAT 2 = same as BAT 1 except for BAT 2. BOTH = Both batteries power the loads and BOTH will be charged with the engine running. Both batteries will NOT die if you leave the switch in the BOTH position without the engine running. The weaker battery will draw down the stronger battery until both are equal. The only way both batteries die if you suck them both dry by having the switch in the BOTH position while you have something turned on (like a killer stereo system) when the engine is not running.

 

[JP_R]

Re: Charging 2 batteries at the same time???

Thank you very much for the help everybody.

From now on what I'll do is that I'll run the engine with the switch on BOTH and when I get to the sand bar I'll switch it just to battery 1 which is the main battery for the stereo. That way I have plenty of power in battery 2 to turn on the engine.