Hello Kevin,

My marine electrical system currently includes one maintenance free starting battery (Group 24) and one AGM maintenance free deep cycle battery (also Group 24). I have the Guest 2611A battery charger attached to these two batteries for charging at the dock.

I was considering putting in a second deep cycle battery to provide more accessory time while out on the water and my plan would be to configure the boat wiring to connect it to the other deep cycle battery ‘in parallel’.

Would my 2611A charger be capable to charging these three batteries?

Thank-you
John

Hi John,

YES, but it will take a very long time to completely recharge.

The 2611 only puts out five amps max on each leg. Two dead batteries connected to one of the legs will take close to 2 days to recharge. Guest makes excellent products, but you may want to consider one of their larger units for your marine electrical system.

Kevin

Kevin,

Thank you for your response.

Generally when our charger is on it has a couple of days between uses so I’m not as concerned about the time it would take to recharge. And I would think that making the 5-6 mile run back to the marina with the Switch in the “All” setting would give the batteries a bit of a charge from the alternator as well.

I just wanted to make sure there were no safety issues. So if I put a third battery (a deep cycle) in the boat and connect its positive to the other deep cycle’s positive with a jumper and similarly connect up their negative terminals – when I put the switch on “2” the accessories would pull from both deep cycles and, in theory, I would get more accessory time?

I guess I just want to see if I can get by with my current switch and charger or do I need a more robust switch and charger to have three batteries.

Thanks again (and I will make a contribution via PayPal)

John

Hi John,

Adding a third battery in parallel to your second is a very common boat wiring practice.

When you do this, make sure that you use cables that are at least as large as the largest cables that are currently used on the battery switch system.

Kevin

Kevin,

Thanks again.

I was hoping to get the cables this week and won’t have access to the boat before then so I may have to guess. Do you think four AWG would be safe for a basic speedboat (24’ Malibu Wakesetter)?

John

John,

It’s really funny that you should ask that!

I’m just finishing a downloadable Battery Cable Calculator. I’ll post it in the next day or two for all of our readers.

Kevin

Hello,

First off…..Let me say, that I have enjoyed reading through a ton of posts on your site. You perform a great service, and knowledge is power.

I am going to be adding a trolling motor soon to my 191 CC Mako. The trolling motor is a 24 volt model. I would like to add two Group 31 deep cycle batteries for the trolling motor, and have one dual purpose battery to crank with. Three batteries total.

I would also like to pull 12 volt power leg out of my 24 volt series to power accessories and act as a house battery when I am not using the trolling motor, and an emergency crank battery.

I have included a wiring diagram that I drew up. Please take a look at it for me.

What concerns me most is the 12 volt ground coming off one of the batteries in series. Have I done this right? I thought this problem might be a good one to discuss on Easy Ac/Dc.

I have found no answer to this on the internet yet. I would be happy to update this diagram per your recommendations and give you the corrected one in the end, if you would like it.

Thanks,

David

Hi David,

Very nice schematic.

I would suggest some minor changes.

I would use battery A instead of battery B as your paralleling battery. Basically you would be paralleling to your 0 to 12 volt battery instead of your 12 to 24 volt battery. This will create a common ground in your boat wiring and help reduce stray current corrosion and accidental mis-connected grounds.

After you switch your paralleling switch to be connected to battery A, pay close attention to 12 volt devices that you may connect only to Battery B. If their ground wire comes in contact with any other ground wire in the system, it will create a dead shore across Battery A. You may want to consider installing circuit protection in the ground wire of any 12 volt item that you connect only to battery B.

Your bilge pump “manual on” switch needs to draw power from the same fuse as your bilge pump “auto” switch. You should only have a single source of power for any device. I would keep the switch at the helm, but run a wire from the auto bilge fuse (load side) to the line side of your bilge pump switch.

Make sure your wire sizes are appropriate. When your cranking battery switch is in the parallel or trolling motor battery position, the cranking circuit will include the wire from the switch to Battery A. Battery A to your Ground buss. Ground buss to Battery C. These wires should be at least the same size as the main engine battery cables.

Let me know if you have any other questions,

Kevin

Hi Kevin,

I need information on the alternator for my boat wiring project.

I have a 1988 Sea Ray 340 Sundancer with twin 350HP Crusader engines. I want to replace the 55 amp, three-wire alternator with a new single-wire type. The boat has two battery switches and an marine electrical isolator.

Can I do this, or do I need the original three-wire alternator?

Thanks.

Walter

Hi Walter,

Your batteries will not fully charge when you use an isolator with single-wire alternators.

The alternator needs an external sense wire that is connected to the starter (usually through the key). With an external sense alternator, the battery charges to 14.4 volts with an alternator output of closer to 15.1 volts. If you use a single wire alternator, the batteries will only charge to 13.7 volts instead of 14.4 volts. This 0.7 volt difference is caused by the voltage drop induced by the diode inside the battery isolator.

Hope this helps,

Kevin

Kevin,

Thank you for your quick response.

Is there a way to wire this by running a second wire?

Walter

Walter,

On some single-wire alternators, there is an internal jumper that connects the output post to the sense post. If you remove this jumper and run a wire from it to your engine battery, you will be sensing the battery voltage below the isolator and your battery will charge completely.

Good luck,

Kevin

Kevin

I have a 27’ boat with shore power, a Heart Freedom 1500 inverter charger, two group 31 AGM Lifeline batteries and a battery switch that has four settings.

The battery switch settings are Off, Battery 1 , Both, and Battery 2. The Battery 1 portion of the switch has the wire from the Charger portion of the Freedom unit connected to the lug.

When I leave the boat hooked up to shore power the Freedom unit is operating and supposed to charge the batteries. The remote panel indicates it is working and the batteries condition shows green or “float” on the remote.

Since I have owned the boat I have gone through three batteries hooked up to the Battery 1 position.

My questions are as follows.

• What position should I leave the battery switch when hooked to shore power and I am away from the boat?
• Is the Freedom unit defective and burning up the #1 battery by overcharging it?
• What is the correct wire routing for the system especially the connection from the Freedom charger portion to the four way battery switch?
• What is the most likely cause of battery #1 going dead ?

Thanks John

Hi John,

In my opinion, the best way to connect a battery charger is at the battery switch on the battery posts of the battery switch instead of the common post. When you connect the charger to the battery side of the switch it doesn’t matter what position the switch is in. The charger will always charge the battery.

Boiled batteries are usually caused by the charger staying in the bulk stage of charging. Large draw devices can trick the charger into thinking the battery still needs more charge. Refrigerators are notorious for this. They draw 5-10 amps when it is warm out. The battery charger never shuts off. Most new chargers have a timer on the bulk stage to prevent this from happening.

If no devices are connected to the battery and the inverter is still boiling the batteries, I would replace the charger/inverter.

Hope this helps,

Kevin