Archive for the ‘Corrosion’ Category

Ac/Dc connection

July 12th, 2010 by Kevin Hannula

Kevin,

Why are ac and dc ground buses tied together in boat wiring? It would seem to be a possible source of electrolysis.

George

Hi George,

You are correct.

When you tie the AC and DC ground buses together, you definitely create the path for stray current corrosion through your shore power connection.

BUT

The wire provides a ground path in the event of an AC fault to the DC system in your boat wiring. Without it, your AC breaker will not trip. The path to ground would be through the boat’s DC system, through the engine, and through the water. There is too much resistance in the water to cause the breaker to trip. All DC devices would become energized at 115V AC.

It is probably better to corrode a drive than kill a friend. I always recommend keeping the ground buses tied together. So does the US Coast Guard and the American Boat and Yacht Council.

Kevin

Posted in AC Wiring, Boat Wiring, Circuit Protection, Corrosion, Cruisers, Marine Electrical, Shore Power | Comments Off

12 Volt Accessories – 24 Volt System

May 17th, 2010 by Kevin Hannula

Kevin,

On my boat wiring, I have a 12 volt battery for starting my motor and a 24 volt house battery setup for running my trolling motor and accessories.EzAcDc offers Smart Battery Switch Systems to make your boat wiring project easy.

I would like to have my electronics, which are all 12 volt except for the trolling motor, run off my house batteries, and use my starting battery for starting the engine only.

The boat manufacturer had the house batteries rigged up in 24 volt, but has the accessories connected in 12-volts across only one of the house batteries. Although this works, one of my batteries drains well before the other. Also, something tells me that boat wiring like this might not be a good idea.

Is there a better way to do this? Should I try to balance the load across both house batteries, or should I use a DC/DC converter to step down the 24 volts to 12 volts in order to run the accessories properly? Also, can I use a Smart Battery Switch VSR to charge my 24 volt system from my motor once the starting battery is charged up?

Thanks,

Scott

Hi Scott,

Your boat wiring  has been engineered in a safe, conservative way.

You run into potential problems when you start running two, separate, 12 volts systems with their grounds 12 volts apart.

  1. Stray current corrosion.

    The engine is connected to one battery ground, while the hull is connected to second battery ground – engine corrodes away to protect hull

  2. Fires caused by crossing grounds.

    Gauges and navigation lights have same ground to complete circuit. Your engine harness grounds the gauges and your boat harness grounds the navigation lights. If you connect the engine ground to battery 1 ground and the boat accessory harness to battery 2 ground, the 24 volt jumper wire for your trolling motor completes the dead short from Battery 1 positive to Battery 2 negative.

    The short circuit path is the Accessory harness ground which is connected to battery 2 negative (battery 1 positive), to navigation light switch ground, to gauge ground, to engine harness ground, and back battery 1 ground.

    There is no circuit protection in this circuit so the smallest wire burns. This is usually the small ground jumper wire that connects your gauges.

If you are going to separate circuits to both batteries, install circuit protection in both the negative and positive wires and pay close attention. Label all battery connections because swapping a ground at the battery will cause a fire.

Best of luck,

Kevin

Posted in Boat Wiring, Circuit Protection, Corrosion, Cruisers, Navigation Lights, Pontoons, Runabouts | Comments Off
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