Power & Battery Management

Using Power & Battery Management

Inverters

One of the most useful items to put on a boat would be an inverter. Inverters make 110 volt AC power from 12 volt battery system. Put simply, for every 100 watts of AC power that inverter is producing, it needs to draw about 10 amps from the 12 volt battery system - (for inverters rated at 90% efficiency, the number is closer to 9.25 amps per 100 watts).

Appliance // Watts // Use Time // Watt Hours // Amp Hours

Sat Receiver // 20 // say 6 hrs. // 120 // 12

Computer // 70 // say 6 hrs. // 420 // 6

12 V lights // 6A* // say 3 hrs. // 18 // 6

IDEAS
Install a small digital panel meter and permanently connect it to batteries?
Change lighting to LEDs?
Solar panels?

RULES
Start out with fully charged batteries.
Turn off lights when not need them. (Pay attention to those things that draw power and shut them down when not actually using them).
Watch the battery meter and get a feel for how healthy the batteries are.
If possible, recharge batteries before they get down to 50% of capacity, as this will extend their life.
Pay attention to the batteries.
Maintenance and proper selection pay off in long life.
Provide for adequate charging and monitoring.
Don't just "plug it in and forget it".


Battery Management:

Unplugged from shore power every amp that systems take out of the battery bank is going to have to be put back somehow, sometime. This is especially true on a small yacht like SY Cryptic. Weight and space restrictions dictated a battery bank of two "Domestics" and one for the "Starter Motor".

A. Power consumption of Cryptic's electrical items:

- Speed/Distance log
- Echo-sounder
- Navigation lights (having LEDs fitted*)
- Anchor lights (having LEDs fitted*)
* can switch between the two.
- Interior lights,
- Sat Nav. (Garmin)
- Auto Tiller

(Key is how many Watts (or Amps) each consumed (in the appliance or in its Handbook ... or get a figure for Amps, and multiply this by 12 volts, to convert it to Watts). Useful formulae

. Watts = Amps x Volts
. Amps = Watts / Volts
. Volts = Watts / Amps

For example, if an item consumes 2.4 watts per hour and is rated 12V it consumes 2.4/12 - or 0.2 amps per hour (0.2Ah).

(B) Battery management

Marine batteries are apparently designed for deep discharge cycles, - i.e. be repeatedly discharged and recharged over quite a long lifespan. However most commentators say that there is a limit, though, beyond which draining a deep discharge battery is unhealthy for it - say discharging below 50% of nominal capacity will shorten the life of a marine battery to an extent, and going below 70% is "no-no".

If the 50% limit is followed a modern marine battery should be able to withstand several thousand cycles of discharge and recharging. Go for the largest capacity battery (re. 50% of its capacity before needing to recharge it), then at the discharge rates described above could likely survive a good deal more than six hours, day or night, without bothering to recharge.

(C) Recharging

Leave the marine with a full battery – so fit decent shore power link and a good battery charger. Charging out at sea - engine only. Remember too, that at night the drain will be far worse so need to run the engine for some hours by dusk to build up any kind of reserve to get through the night.

Some facts and useful information about Batteries

1. Batteries are never 100% efficient - energy is lost (heat as well as chemical reaction) in both charging and discharging. Use 1,000 watts from a battery, it might take 1,200 watts or more to fully recharge it.

2. Slower charging and discharging rates are more efficient.

3. The starting battery needs a very large starting current for a very short time - so have a large number of thin plates for maximum surface area. The plates are composed of a lead "sponge", similar in appearance to a very fine foam sponge. This gives a very large surface area, but if deep cycled, this sponge will quickly be damaged and will fall to the bottom of the cells.

4. Deep cycle batteries are designed to be discharged down as much as 80% repeatedly, and have much thicker plates often solid Lead plates.

5. Marine batteries are actually "hybrid", and fall between the starting and deep-cycle batteries, while a few are true deep cycle. In the hybrid, the plates may be composed of Lead sponge, but it is coarser and heavier than that used in starting batteries. It is often hard to tell what you are getting in a "marine" battery, but most are a hybrid. "Hybrid" types should not be discharged more than 50%.

6. A battery's capacity for storing energy is rated in a number of ways but most often in Amp/Hours.

7. Amp/Hour rating of battery capacity is calculated by multiplying the current (in amperes) by time (in hours) the current is drawn. For example: A battery which can deliver 4 amperes for 20 hours before being discharged would have a 80 amp-hour battery rating (4 X 20= 80).

8. Selecting the correct batteries is all about lifespan.... the correct ones will last a lot longer, - but the lifespan will vary considerably with how the battery is used, // maintained and charged, as well as temperature, and other things ... typically Marine: will last 1-6 years.

Remember

Reversing the polarity of the battery when connecting it may severely damage or destroy some parts of electrical system.

Actions

1. Mark the cables so which is which is obvious.

2. When replacing batteries, remove the negative cable first because this will minimize the possibility of shorting the battery when removing the other cable.

3. Next remove the positive cable and then the hold-down bracket or clamp. If the hold down bracket is severely corroded, replace it.

4. Dispose the old battery by exchanging it when buying the new one.

5. Be sure that the battery tray and cable terminals or connectors are clean.

6. Thinly coat the terminals and terminal clamps with Vaseline to prevent corrosion.

7. Replace the hold-down brackets or straps to secure the batteries in place.

8. Reconnect the cables in reverse order, i.e., attach the positive cable first and then the negative cable last.

9. Before using the batteries check the electrolyte levels and state-of-charge & refill or recharge as required.

Cautions:

- Make sure the battery compartment is vented for batteries.
- Never place batteries where electrical sparks or other ignition sources may exist - for example a simple 12 volt light with a switch on it is an excellent source of ignition spark!
- Secure batteries with straps or brackets to prevent movement
- Most premature failures are caused by low electrolyte levels.
- Electrolyte is is lost whenever the batteries are charged OR discharged heavily.
- Keep the electrolyte level above the plates at all times - adding only distilled water
- In summer, check the electrolyte levels more frequently.
- Check the tightening of belts and also the hold-down clamps and terminals.

Extend the battery's life by keeping it charged properly and avoiding deep discharges. A battery "cycle" is one complete discharge and recharge cycle. It is usually considered to be discharging from 100% to some point not lower than 20%, and then charging back up to 100%. Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to only 50% each cycle, it will last about twice as long as if it is cycled to 20%. Running the battery down totally flat will have a very negative effect on the lifespan of the battery. Avoid discharging the battery below the 40% level whenever possible. If the battery has been charging, then it's important to let the battery set for 2 to 3 hours without a load or charger connected to stabilize before testing. Otherwise, the reading will be high, caused by a phenomenon called "surface charge."

It is also necessary to invest in a good digital voltmeter.... it's the only meter that will offer the necessary accuracy to properly test your battery system.

Most ratings assume that the battery is at room temperature: 21 degrees C. As the temperature of the battery drops, so will the fully-charged voltage reading - it seems to be safe to say that for each 4 degrees C drop in temperature expect to see the voltage drop about a tenth of a volt. (.10 volt) That means that a battery at 0 degrees C d with a no-load voltage reading of 12.35 volts is fully charged. Battery capacity (how many amp-hours it can hold) is reduced as temperature goes down, and increased as temperature goes up. This is why a car battery dies on a cold winter morning, even though it worked fine the previous afternoon. At freezing, the battery's capacity is reduced by 20%. At approximately -27 C battery AH capacity drops to 50%. Capacity is increased at higher temperatures - at 122 degrees F, battery capacity would be about 12% higher. But - even though battery capacity at high temperatures is higher, battery life is shortened. Battery capacity is reduced by 50% at -27 degrees C - but battery LIFE increases by about 60%. Recharge a deep cycle battery as soon as possible after each use. It is very hard on a deep cycle battery to sit for extended periods in a partially charged state.

Charging batteriesMost flooded batteries should be charged at no more than the "C/10" rate for any sustained period. "C/10" is the battery capacity in amp/hours divided by 10. For a 220 AH battery, this would equal 22 Amps. Charging at 15.5 volts will give you a 100% charge on Lead-Acid batteries. Note that flooded batteries MUST bubble (gas) somewhat to ensure a full charge, and to mix the electrolyte. Float voltage for Lead-Acid batteries should be about 2.15 to 2.23 volts per cell, or about 12.9-13.4 volts for a 12 volt battery. Flooded battery life can be extended if an equalizing charge is applied every 10 to 40 days. This is a charge that is about 10% higher than normal full charge voltage, and is applied for about 2 to 16 hours. This makes sure that all the cells are equally charged, and the gas bubbles mix the electrolyte. If the liquid in standard wet cells is not mixed, the electrolyte becomes "stratified". You can have very strong solution at the top, and very weak at the bottom of the cell.

"What does all that mean?" It means that battery charging is a little more complicated than most people think. It's not really safe to assume that running the engine will keep batteries up to par, or that plugging in to A/C power and letting the converter run will do it; (in fact this is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging).

Converters vs. real battery chargersAs stated above, the converter isn't designed to be a decent battery charger. It's main purpose in life is to provide 12 volt power while you are plugged in to an A/C outlet. Since the converter is designed to not exceed a voltage of about 13.5 volts, it will never fully charge batteries. Also, after it has succeeded in partially charging it will then commence to boil off electrolyte, as the "float" voltage is too high. If the boat is plugged into A/C power for months at a time, MUST keep a close eye on battery's electrolyte level. It is very common for a converter to boil a battery dry in a month or two.

It is a big help to unplug the converter or switch it off when the boat is not in use // attached to A/C power. Just run the converter overnight once a month or so and it will be much easier on the batteries. Another significant disadvantage to the converter is that most units aren't capable of delivering their rated amperage to the batteries to charge them. Older converters will only manage about 10 or 15 amps and will put out significantly less when powered by a generator. A much better choice is to replace the converter with a modern 3 stage battery charger. These units are fully automatic and can be left plugged in continuously without damaging the batteries. They provide much higher charging current than a converter and will fully charge the batteries in short order, even on generator power.

Testing the batteries

1. Visually inspect for obvious problems.... for example; damaged cases, corroded terminals or cables, loose hold-down clamps or cable terminals, or low electrolyte.

2. To insure accurate readings, you must eliminate any surface charge before testing. Use one of the following methods;

1. Allow the battery to sit for six hours with no load or charger connected, or...
2. Apply a 25 amp load for three minutes and wait five minutes, or...
3. With a battery load tester, apply a 150 amp load for 10-15 seconds.

3. The battery under test must be disconnected from any load or charger when testing. This is referred to as "Open Circuit".

Check both the specific gravity in each cell with a external hydrometer AND the battery terminal voltage with a digital voltmeter without the engine or converter/charger running. If the state-of-charge is BELOW 75% using either the specific gravity or voltage test then the battery needs to be recharged BEFORE proceeding.

Replace the battery, if one or more of the following conditions occur:

If there is a .050 or more difference in the specific gravity reading between the highest and lowest cell, you have a weak or dead cell(s),
If the battery will not recharge to a 75% or more state-of-charge level.
If digital voltmeter connected to the battery terminals indicates 0 volts, you have an open cell, or if the digital voltmeter indicates
10.45 to 10.65 volts (5.2 to 5.35 volts for a 6 volt battery), you have a shorted cell. [A shorted cell is caused by plates touching, sediment build-up or "treeing" between plates.

Winter Storage - Most boats should be stored in the winter months on the hard. This storage can be very tough on batteries. Batteries in storage self-discharge over time. This is a natural phenomenon and will cause batteries to slowly go flat. Deep discharges drastically shortens battery life. Extremely cold temperatures can cause batteries to freeze if they aren't adequately charged. Some charging current will have to be applied to the batteries periodically during the storage period. To keep batteries safe through the winter storage period, consider removing the batteries and storing then in a warmer place, like a garage. Check the voltage once a month and do an overnight recharge if the voltage falls to the 80% state-of-charge point. If removing the batteries just isn't possible, then there are several things that should be done as the boat goes into storage.

Ensure that ALL electrical loads are disconnected from the batteries. There are lots of things that might put a tiny load on the batteries even though everything is "off". Most smoke, CO and Propane detectors all are tiny drains on the batteries. Even if the current draw is only a few Milli-amps, over time these "phantom loads" will run your batteries flat! Best bet is to identify which 12 volt fuses protect these units and remove them. It is a real good idea to check at the battery with an ammeter to ensure that there is no current drain.

Provide for some sort of charging to offset the batteries tendency to self-discharge. This can be provided by a small solar panel or trickle charger, or the converter or 3 stage charger in your RV. It is best to let the batteries discharge slightly over a few weeks or a month and then do a full recharge overnight. Trickle chargers and unregulated solar panels can slowly boil off electrolyte, or worse, fail to maintain the charge, allowing your batteries to become deeply discharged. If your RV has a standard converter, do not leave it plugged in constantly to keep your batteries up! That converter will boil your batteries DRY in a big hurry!

If a boat is plugged into A/C power over the storage period, make sure to either unplug the converter or switch it off at the breaker. It's far better to run the converter overnight every 3 or 4 weeks or so as needed to charge the batteries. Another possibility would be to put the converter or the whole boat on a simple plug in timer and set it to be "on" for about 1 hour a day. If you have a smart 3 stage charger, it may be safe to leave it plugged in at all times, but pay very close attention to the electrolyte level in the batteries just in case. Boiling a battery down to where the plates are exposed to air will cause permanent damage to the battery. Don't let this happen to you!

Check on the batteries from time to time during the storage period. Stop by at least once a month and check battery voltage and electrolyte levels. Don't walk away from the batteries in November and expect them to still be ready to go in May.

The bottom line....
Pay attention to safety when working with or near batteries.
Buy only good quality Deep Cycle batteries for your boat.
Keep up with battery maintenance... check electrolyte levels regularly and pay attention to charging and discharging protocols to increase lifespan.
Invest in a good digital voltmeter and use it.
Consider replacing an old converter for a better quality 3 stage charger.
Take care of batteries during extended storage periods.