Fast Tips…by Dana Sims…Battery Charging

FAST Tip – – Battery Charging – – Dana Sims (FT15-04)

Last week’s FAST Tip was on why boats have a battery switch and how to use it.
This week’s FAST Tip is on the charging systems used to keep the batteries in shape.

A battery charger is a device used to put energy into a rechargeable battery by forcing an electric current through it. In simplistic terms, this is accomplished by providing a voltage to the battery that is higher than the normal battery voltage. On a boat, there are two systems: a battery charger for use at the dock; and the engine driven alternator while at sea.

How can I tell if the batteries are being charged properly?

• When connected to shore-power the battery charger charges the batteries – – both batteries – – whether the battery selector switch is in the 1 – 2 – ALL – or OFF position. However, the “battery charger breaker switch” on the electrical panel must be in the ON position for this to happen.

• Our boats have an analog battery voltage test meter on the main electrical panel. After you have connected the boat to shore-power, push the test switch to battery one, the analog meter should read between 13.5 volts to 14.1 volts. Now try battery two, you should have the same result. This voltage level indicates the batteries are being charged. If the meter reads 12.1 to 12.3, the charger is not supplying voltage to the batteries.

Check the following:
1. Is the “battery charger switch” on the electrical panel in the ON position?

2. Is there 110 VAC power to the charger, check for LED light at the charger? If not, check the 110 VAC Duplex GFI outlet, reset, if required.

2. Power cord properly connected?

3. Is the dock breaker ON?

When the engine is running – –
• When the engine is running the engine mounted alternator is charging the batteries, but only the one(s) selected by the battery selector switch, 1 – 2 – ALL.
• When you are running the engine you can use the battery voltage test meter in the same way as described above.
• If you have the battery selector switch on battery one, test battery one with the meter – – your reading should be as indicated above, 13.5 to 14.1. Test battery two, it should only read 12.1 to 12.3 volts in this instance, since you are only charging battery one from the alternator.
• If the test meter is reading less than 13 volts on the selected battery (1 -2 -ALL) then the alternator is not supplying a strong enough charge. This could be due to a slipping alternator (v-belt). This is why it is important that you check the v-belt tension at each engine check (daily). If the belt is loose, stop the engine and tighten it, then re-check the voltage charge level at the meter. If it is still low notify the Boat Captain, as this may be a voltage regulator problem.
• If the battery test meter indicates the alternator is charging the battery(s) at a high voltage of 15 volts or more then there is a problem and you need to contact the Boat Captain as soon as possible. Charging a wet cell battery (the kind we have) at a high voltage will cause the battery water to boil and dissipate, leaving the battery cells dry and causing irreparable damage to the batteries. This damage could happen within 6 hours of high rate voltage charging. If you are in the North Channel,use only one battery, and only when you must have the engine on. Take the boat to Boyle’s or another full service location/port, to have it checked out – sail as much as possible so you do not have to use the engine. Contact your Boat Captain or Maintenance Director.

Member Battery Maintenance at JBM When the engine is running – –
• Departing the slip – – after starting the engine and once you are clear of the marina entrance/exit, you need to motor out onto the lake at approximately 1800 to 2000 RPM (or around 4 knots) as far as the North Buoy or South Buoy.
• If you raise the sails and stop the engine just outside the marina, you have not given the engine enough time to recharge the batteries at an acceptable engine speed.
• If you had some difficulty starting the engine, multiple tries, then you need to motor past the North or South Buoy for at least another 15 to 20 minutes to keep the batteries healthy.

When back at the JBM dock – –
Before you leave the boat at the dock, make sure that the batteries are being charged by the battery charger (check the voltage test meter).

If you are unsure of how the battery switch operates or just a little “fuzzy” on how this all works, ask your Boat Captain, when you come out to work on the boat’s for spring launch, for a quick tutorial on shore-power connection, the battery charger on/off switch, battery charger location, battery voltage test meter location and functions, battery selector switch, and where the batteries are located.

Since we launch the Interlakes on May 2, next week’s FAST Tip will be Interlake Reminders.

Thank you to Jack Townsend for input on this topic.

Any question, comments, or suggested topics can be sent to

“FAST (For A Safer Trip) Tips are written by ASI members for the ASI membership, and apply to the operation of ASI vessels. While the contributing members may not be experts in a particular sailing field they are experienced members who have developed some “best practices” and wish to share them with their fellow members

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