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,

My family and I are planning on a multi-year sailing trip. I have an Perkin-Sabre M65 engine in my 44′ sailboat. I want to upgrade the existing alternator with a high output Balmar alternator. I am interested in one that works with an external regulator and has the highest amp rating without jeapardizing the water pump bearings. Probably one of the 70-Series 3.15” Dual Foot alternators?

I am also interested in a second alternator.The Perkins-Sabre rep advised:

“The challenge with running a high output alternator in place of the stock 65 A is that you are limited to about 90 A on a single belt. If you require a high output at a lower rpm the belt tension is critical which is extremely hard on the water pump bearings. I have a friend that went through 3 water pumps in one cruising season. The bullet proof way to run large cruising alternators is to run them off the front end, inline with the crank shaft using a coupling and a jack shaft with 2 bearings. This way the engine has no side load on the crank shaft.

The second best would be to have some pulleys made to a specified size for proper alternator speed and side mount the alternators, 1 on each side. This would allow you to drive with double belts as well. Alternators can be a bit of a science project. In a perfect installation the alternator mounting brackets would bolt to the engine allowing everything to operate on the same plane. This does throw you into one more consideration if you choose heavy large frame alternators……front motor mounts. The extra weight may sag the mounts causing alignment problems. The other way is just like the second ,only mounting the alternators to the stringers, one on each side and hope for the best counting on the belts to take up any shock.
There are no brackets available. Anything you do will be custom if you go above 90 A………maybe 100A if you don’t try to pull full output at low rpms.”

I have found no reference to any alternator that operates inline. Can you help me?

Jim

Hi Jim

I have little experience with customer alternator installations.

I would recommend checking with Scott Fracter. Last year, Scott generously allowed us to publish his “Adding a second alternator” article, which is a comprehensive overview of the whole process. He is truly an expert in this area.

If Scott doesn’t have the parts you need, he may be able to make them, or send you in the right direction.

Enjoy your trip.

Please send photos,

Kevin

Dear Kevin,

I am currently beginning my first boat wiring project, a total rewire of a small Owens cruiser from the late ’60s.

Here’s my problem:

The old wiring runs behind the original paneling and headliner. I could try dismantling everything to remove and replace the wires, but am concerned about damaging any of the woodwork. It’s old. It’s gorgeous. It would be a bitch to replace.

I don’t mind leaving the old wiring in place and just running a new harness, but that still leaves the problem of installing the new wires without causing any damage.

Any ideas?

RP

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Kevin.

Hi Kevin,

I’m an airplane guy who’s redoing the boat wiring on my brother-in-law’s 1972 22’ Reinell.

I have a couple of questions.

We ordered a boat horn and a Smart Battery Switch from EzAcDc yesterday. However, we only ordered the VSR thinking it was all we need but after looking closer I’m not sure.

The boat has two batteries and a manual 1/both/2 switch. Should I change our order to the complete Smart Battery Switch System?

This boat has an original one-wire Delco alternator. I want the following but I’m not sure how to achieve it:

• The ability to disconnect the alternator from the battery when the alternator fails (if this is not important than I’ll forget about it)
• The ability to turn on a warning light when the alternator fails (we removed the original ammeter but the 3 in 1 gauge we installed does have a volt meter)

Do you have any suggestions i.e relays or any other components I can use to achieve the above results? I wouldn’t mind upgrading to a more modern alternator if that solves the problem.

Any direction you can give would be greatly appreciated.

Kevin

Hi Kevin,

A VSR works best when you have a dedicated engine battery and a dedicated house battery. The VSR makes the connection between the two systems.

A conventional battery selector (Off, 1, 2, Both) controls which battery the engine is connected to but does not control which battery the house is connected to.

The key to our partner’s complete Smart Battery Switch System is the dual pole On/Off battery switch. This acts like two on/off battery switches combined into one body.

• When the switch is Off, only emergency devices are connected to the house battery.
• When the switch is On, the engine is connected to the engine battery and the house is connected to the house battery.
• When the engine is running, the alternator first charges the engine battery. When the engine battery hits 13.7 volts, the VSR connects the engine battery and house battery together and begins charging the house battery.
• When the engine is off, the VSR keeps the batteries connected until the battery voltage hits 12.6 volts. When it drops below 12.6 volts, the VSR breaks the connection and allows for enough reserve in the engine battery to start again.

I would not worry too much about a way of disconnecting the alternator if it fails.

In the event of an alternator failure, your system voltage would begin to drop. With the complete VSR system, once 12.6 volts is reached, the VSR will open the connection between the engine and house batteries. Your engine will continue to run until the battery voltage is below 10 volts. When the engine dies due to low voltage, you can turn the battery switch to the COMBINE position. This will manually parallel the batteries and allow you to start your engine and continue running until your battery voltage is to low to run the ignition system.

You will probably run out of gas before you completely drain two batteries running only a simple ignition system on a single stern drive.

Thanks

Kevin