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

Kevin,

I was reading up on adding shore power and came across your site and thought I’d consult someone who knows what they are doing. I want to add AC power to my boat and plan on running one, possibly two AC GFI outlets and a battery charger.

I want to be able to run the DC power on the boat (Stereo, cabin lights) while not draining the battery.

I plan on installing a proper 30 amp shore power inlet and connecting that directly to an AC distribution panel with three breakers. One breaker will go to the outlet. One will go to the battery charger. One will remain open or will be connected to the second outlet.

My questions are:

• Is my thinking correct?
• Is my wiring scheme proper?
• If I have the battery charger connected will I be able to run the DC on the boat without draining the battery?

No one at the marine shops I go to seem to be willing to offer an opinion. Maybe that is out of ignorance or maybe out of fear of liability. What do you think?

Garrell

Hi Garrell,

You thoughts are correct, but the number of breakers that you are planning on may be overkill.

If you are only running outlets and a battery charger, you could easily use an AC panel with just a single 20 amp main breaker with outlets connected through it.

When your shore power is connected, the battery charger will be on and your outlets will be live. The charger will draw a maximum of 5 amps leaving 15 amps (1800 watts) to run everything else.

The simplest system that I have seen for your application is from our partners at EzAcDc.

They have a new marine shore power kit that gives all of the components that you are looking for. The panel has a main breaker rated at 20 amps. There is a GFCI on the panel. This system also comes with a remote outlet kit that plugs directly into the back of the panel. The wire on this remote kit is 10′ long. The AC panel has an outlet on the back. This outlet is ideal for built in battery charger applications. It provides a handy location to connect to AC power and allows for the built in look.

All outlets in the panel are protected by the GFCI. All components are rated at 20 amps.

The kit also includes the power on light, reverse polarity light, and AC to DC grounding wire required by the US Coast Guard.

Installation is simple and safe.

Please let me know if you have any 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

Hi Kevin,

First of all, thank you for all of the time and effort that you put into your website. The boat wiring information that you share is invaluable.

So tell me Mr. Marine Electrical, do my ambitions exceed my abilities?

My wife and I have a small sailboat that we’ve enjoyed for many years. It’s a perfect size for the two of us and can’t imagine anything that would make the boat more fun…with one exception. We find that we are very jealous of our marina neighbors who have shore power. Whether they are using a television, a drink mixer, a vacuum, a toaster, or even a simple battery charger, we start down the “if only” path.

How tough a project is it to add AC power to an older boat? I’m reasonably comfortable with simple household wiring jobs, but have been told that marine AC can be an incredibly complicated and – if not done correctly – incredibly dangerous.

Any suggestions?

Thanks.

Matt

Hi Matt,

No project is too big, not project is too small when “Mr. Marine Electrical” is on the scene!

Seriously, there is a great new product from our partners at EzAcDc that will fit your needs. They have a complete marine shore power system that follows their snap-together philosophy of simplifying boat wiring jobs.

Installation of the new marine shore power system is easy.

The panel is pre-wired and comes with a remote outlet with 10′ of boat cable that simply plugs into a “snap together” plug on the back. The kit is also pre-wired with 10′ of Marine grade boat cable that runs from the boat AC panel to the included shore power inlet.

Best of all, any complex electrical connections are already made inside the powdercoated aluminum box.

All outlets are GFCI protected. And, for additional safety, the AC panel has a dual pole breaker to protect the boater if the dock outlet is wired backwards.

The panel also includes a power “on” indicator light and a reverse polarity light. It also comes with the AC to DC grounding wire that is required by the US Coast Guard. This wire runs from the back of the panel to your DC negative buss, engine ground, or battery negative and provides an additional safety path to ground if you have an AC fault on your boat. Even though required, this wire is redundant on this well-designed system since the GFCI also protects everything.

Additionally, there is a single outlet on the back of the shore power panel to allow a built in AC device to be connected. This is ideal for a battery charger or refrigerator that comes with a standard 15 A household plug. Simply plug it into the back of the panel before installing.

It comes with the industry standard 30 amp Marinco inlet. You can choose between the standard square plastic inlet or upgrade to the stainless steel version. Both will connect to an 30 amp marine cordset or adaptor.

Please let me know how your project turns out. I always like pictures.

Kevin