It’s when we’re away from the dock that the boat’s electrical system either proves itself, or proves itself in need of upgrading.

A little knowledge can be a dangerous thing--DC voltage can zap and AC voltage can kill, so before you go pulling on thick cables of wire in the recesses of the bilge to see what will happen, at some point we’ll have to remind you to acknowledge your own skill set and any limitations when it comes to dealing with on board electrical systems. If you’re not familiar with the nuances of a voltmeter, it’s best to leave such tinkering to professionals. With that caveat in mind, we turn to our biggest assets, our readers, for tips, tricks, and techniques to get the most out of sailing. If your do know your volts from your amps and have more than just wiring a light bulb under your belt, read on. There’s more than one way to skin a cat afterall…--Ed.

Having read two pieces on SAILjazz.com about electrical systems written by Norm Berstein: Our Sailors Write--Batteries and Electrical Systems Strategies, Part One and Part Two I’d like to offer insight on what I believe is the correct method of designing and installing a battery system on a boat.

Designing an electrical system on a boat takes in a variety of factors, including, but not limited to the following:

1. How big is the boat?
   
2. What is the boat’s intended function? Day sailing, occasional overnights, vacation cruising or long term cruising will all bring with them different electrical system demands and require different approaches.
   
3. What are the daily loads on the intended battery system?
   
4. Does the owner want to be in charge of making sure the correct switch is thrown to charge the correct battery?
   
5. Money is usually a factor in any boat project--how much of an investment does the owner want to make in the boat?
   
6. And is the owner comfortable with available newer technology?

On a small boat used for occasional weekend trips where the owner does not really want to spend any money, I would recommend a similar system that Mr. Berstein recommends.

However, as soon as a 12-volt refrigerator is added, and the boat is used for more that the occasion weekend campout, the parameters of such a system need to be expanded. I would recommend a much different system--one designed as an integrated system that can be installed in stages.

A Link meter (upper right) monitors the state of charge of the batteries and the power consumption at any given time and gives info on what solar panels or the wind generator adds to the battery bank.

The first thing I would recommend is adding is battery system monitor, such as one made by Link or Ample Power. Either of these will let you accurately know what your system is doing and if there is a problem with voltage or charging as well as how full or empty the battery banks are.

The next step is developing a list of the energy consumers (lights, autopilot, fridge, etc.) that currently are or will be connected to your system. (Two good places to start addressing these issues are Don Casey’s Calculating Onboard Electrical Demands and Sizing your battery bank and charging capacity

If you are planning to use an inverter, you need to also factor in the electrical draw required to use that device. After calculating the amount of amp hours, quadruple it. This figure will allow the batteries to be only discharged to about the 50% level and which will also give you an estimate of the size of battery bank required. On a typical 30-footer with a fridge and normal loads, but without any AC loads the daily load requirements are about 100-to-120 amp hours per day.

That would translate into a battery bank of approximately 400 amp hours. With this size of a battery bank and the above load estimate the batteries will be operated between the 100% and 50% discharge range. And with the battery monitor instrument, you will know where in the range your system is, giving longer life to the batteries.

I’m a firm believer in a single house bank with a separate starting battery. I prefer 6-volt golf cart batteries and currently have six of them. I connected these together in pairs to form 12-volt units and then connected the three pairs in parallel for a battery bank of 650 amp hours. Whichever type of deep cycle batteries you prefer, connect them in parallel for the desired amp hour capacity. Do not include the starting battery in this yet.

Six-volt golf cart batteries connected in pairs--one of the most rugged approaches to a battery bank.

With the batteries into one house bank, the 1-BOTH-2 master switch can be replaced with individual ON/OFF switches for the house bank and the starting battery. I also put in an ON/OFF switch to allow me to connect the house bank to the starter in an emergency.

Now that you have batteries connected together you need to decide how to keep the charged. A high output alternator/three stage regulator (such as Balmar or Ample Power) and a shore power charger (Heart/Xantrex, etc) with three stage charging is next. The three stage charge cycle will ensure proper charging and lprolong battery life.

The starting battery should get wired up to the system using a device such as the Echo Charge from Heart/Xantrex. This system looks at the voltage of the starting battery and determines if it needs to be charged. The unit "taps" a bit of the current charging the house bank to recharge the starting batter. When this battery is topped off, the Echo Charge then switches all the current back to the house bank.

Once the battery voltage monitor, separate ON/OFF switches are installed, and the charging device is wired up for the starter battery, you should have a battery system that is almost bullet proof and fairly automatic. Depending on the type of batteries (wet cell, gel or AGM) you will still have to pay attention to how deep they have been discharged and if the wet cell need topping off. The next logical path for this type of system is to add passive charging such as solar panels and a wind generator.

And finally, I also have an inverter on my boat. Other than occasionally running the microwave, I find it useful for charging my cordless tools so I can use them without being tied up to a marina. A boat’s electrical system can be totally self sufficient and perhaps is most appreciated when it provides ice and cold drinks to the skipper after he has spent a long day working on it with cordless tools, all while away from the umbilical cord of the marina.