Charging 2 Deepcycle batteries at once.

[stuee]

Hi.
Im not sure if this is possible and hope it is.
I have 2x 12v battery setup on my boat, the first is direct to the motor and charges via alternator and an Anderson plug which i plug into my battery charger at home,.
the second ive just added at the front is not connected to the motor and only used for internal electronics.

Now 2 questions.

1st, I have an ARB battery isolator solenoid hooked to my ignition on the motor, when I turn the key on it open the solenoid for charge but also lets the cranking use both the batteries. if i put a diode on on both + & - 8ga from the starting battery to the accessories battery would that allow charge when ignition is on but stop the cranking battery also draw from the accessories battery. If so what diods should i use?


2nd is it possible to hook both the batteries to the Anderson plug and diode them both between the battery and Anderson so I can plug in the Anderson to my battery charger and it will charge both at the same time?

thanks in advance

 

[ClydeCrashKop]

This is a good document on battery isolators.
https://www.marinco.com/files/support/product/manuals/HOW%20TO%20CONNECT%20BATTERY%20ISOLATORS.pdf
It uses one diode per battery from the alternator output. (None on ground)

 

[MikeMl]

Post a wiring diagram of how the batteries are hooked up. I cant understand your hook up.

What kind of solenoid?

 

[stuee]

hopefully this makes sense, the dotted wire is wha ti want to put in so i can charge both battaries at the same time when i plug in the anderson.

 

[tcmtech]

There are two ways you can do this.

One way is with using the two battery isolator diodes coming right off your alternators output and connecting your anderson connector to to the alternators output lead ahead of the isolator diodes as well.

Or you have to use two more isolator diodes coming off of your anderson connector with one going to each battery.

Either way works just one will let you get away without needing a second set of diodes for the anderson connector feed.

 

[dr pepper]

There are marine battery management units for doing this, such as adverc or sterling.
If you connect 2 batteries together you run the risk of very large currents flowing, this will ruin a leisure battery, or even a lead acid.
You can also buy fairly cheaply a diode module for doing the same thing, they use high current diodes, the only issue with this is that the battery voltage drops by 0.6v, which for a lead acid makes a big difference.

 

[stuee]

As it is setup at the moment i the solenoid activates when the ignition is turned on so it ends up using both batteries to crank but in also when the motor is running it charges both batteries. I dont want it to use both batteries though for starting only the cranking battery. For this can i add a diode to the line from the battery to the solenoid so it only lets power 1 way?

Also so for the charging.. if i hook the dotted line to the already hooked up anderson so they both are on the same plug and then add a diode on the + on both batteries to allow power to them only and not return does this mean i can charge both at the same time?
If that works how would the standard battery charger know when they are full it its getting no power feed back from the battery?

I dont want to spend $100's on a battery management system as its only a 21ft fishing boat but trying to simplify my setup so I'm not disconnecting and reconnecting things all the time.

thanks
Stuart

 

[dr pepper]

What you says makes sense.

Your diode idea will work, however like I allready said battery voltage will be reduced, if your charger is a simple device that doesnt measure the voltage then it probably wont make any difference having the diodes.
It becomes more apparent when the engine alternator is charging the battery, it thinks that the battery is at 13.8v because that is what is present on the alty o/p terminals, but the battery(s) will actually be that -0.6v=13.2v (diode forward voltage) , whch for a lead acid is a significant difference, if your boat is used occasionally it'll still probably work well enough, for a house boat though battery life would be significantly reduced, in which case the expense of a charge controller is justified.

 

[stuee]

i wouldnt put a diode between the alt and crank battery, just one between the crank battery and accessories. its mainly so when the motor is running its just putting a little charge back into the accessories batt. as its a fishing boat its only running for 15 mins max then prob 5 mins each time we move around.

What diodes would i use for the charging side of thigs from the anderson where the normal battery charger plugs in?
Also what would i use between the crank battery and access battery

 

[ClydeCrashKop]

If you only put a diode between crank battery and accessories battery, the accessories battery can drain and crank battery.
If the alternator senses voltage from the ignition circuit, it will put out an extra 0.6 volts. Battery isolators are used all the time. Don't worry about .6 volts.
Check Digikey for stud diodes, at least 100A.
I can't see your battery-setup picture.
Disregard if I am missing something.