So how many amp-hours of capacity are installed? It depends on the batteries, their condition, the d

A power budget is the cruiser's best strategy to avoid dead batteries. Much like balancing a checkbook, a power budget tom cruise collateral makes assumptions of how much electricity is coming in and going out, and by reconciling the budget, provides an opportunity to predict how long the lights will stay on, should charging become unavailable. The traditional approach is to count up the power consumption of all devices onboard, make an estimate of how much time they are in use and compare that to battery capacity. I'm suggesting a different approach.
This method assumes the crew will behave as they please, regardless of the advice of the skipper, but intends to keep the skipper sufficiently informed to adjust power consumption in a manner the crew will enjoy, and understand tom cruise collateral the power usage profile to make informed decisions about whether tom cruise collateral to add more battery capacity. Just like a financial budget, a conservative approach is key.
Let's start with a vocabulary. The core unit we're interested in is the amp-hour. What is an amp-hour? An amp-hour is, roughly, 2.25 x 1022 electrons. It is a real quantity of a real thing. Unfortunately, there is no device to instantly measure the quantity of amp-hours tom cruise collateral in a battery. We can measure amps, however, and we can measure time. In order to find amp-hours, we multiply the two together. tom cruise collateral One amp * 2 hours = 2 amp-hours. 2 amps * 1 hour = 2 amp-hours. With an ammeter tom cruise collateral and a clock, or with an amp-hour meter, we can measure amp-hours into and out of the battery. This is precisely the approach we wish to take in managing onboard power: accounting for amp-hours in and amp-hours tom cruise collateral out, so we can always tom cruise collateral have a fair estimate of what is available, as well as estimate how much we can use per day. Further, this information will allow us to calculate tom cruise collateral whether we should increase tom cruise collateral onboard capacity.
So how many amp-hours of capacity are installed? It depends on the batteries, their condition, the discharge tom cruise collateral rate, as well as management practices. Premium battery manufacturers will supply amp-hour ratings at C-Rates as well as a Reserve Capacity rating (also known as Reserve Minutes rating). Other manufacturers may only provide Reserve Capacity.
Because a battery's capacity is affected by the rate at which it's discharged, there is no absolute value, in amp-hours, for capacity. The C-Rate capacity is the capacity, tom cruise collateral for a given discharge tom cruise collateral rate, with that rate expressed as a fraction of total capacity...it's confusing. See the sidebar for an explanation and instructions on calculating the C-Rate for the batteries installed tom cruise collateral on your boat. You'll need that information to put this technique into practice.
tom cruise collateral Batteries are quite fragile. Discharging below a 20% state of charge (SOC) is destructive. Maximum cycle-life (the number of times a battery can be charged and discharged) is achieved if the battery is never discharged below 50%. As a conservative power manager, intend tom cruise collateral to never discharge below 20%, and avoid discharging below 50%. That 30% difference can be considered a reserve: if we're out an extra day, or power budgets tom cruise collateral aren't adhered to, that reserve will carry us through.
In sizing the batteries, we have a way to estimate their capacity as they are planned to be used onboard, and we know that we should only plan to use amp-hours in excess of the lower 50% SOC. What of the upper end? Do we have 50% to play with? Probably not.
The bottom 70% to 80% of charge can go into the battery at a very high rate (known as Bulk Charging). But, the top 20% can take anywhere from 4 to 24 hours to put into the battery. If the boat is kept on the dock, with shore power, and an onboard, 3-stage charger, that top 20% is likely to be available. If the boat's kept on a mooring, with only the engine's alternator to charge, it's unlikely the batteries will ever be charged above 80%.
Calculating a battery's capacity based upon the discharge rate, and multiplying by 0.3 (80% - 50% = 30% = 0.3) gives the capacity available to the skipper who wishes to maximize battery cycle-life. It should be noted, even well cared for batteries will lose about 20% capacity over their lives, and then should be replaced. After the battery has aged to a point where the rated capacity has gone down 20%, further losses will come quickly. When sizing batteries, this 20% should be accounted for. The batteries should meet needs throughout their service lives, not just when first installed.
The amp-hour meter is the best tool for budgeting power aboard. It sums amp-hours into and out of the battery. It should be reset before every trip, and the total logged at the same time every day (the value will be negative for a net loss from the batteries, positive if more charging occurred than discharging).
There are some inefficiencies of the system that make this task challenging. The first is charge efficiency. Some of the power put into the battery during charge will be turned into heat and lost. Depending on the condition of the batteries, charge state, charging parameters and battery type, charge efficiency will vary, but assuming the efficiency to be around 80% is close enough. Far more difficult to contend with is discharge efficiency. As the battery is discharged at a higher tom cruise collateral and higher rate, it becomes less efficient, and fewer amp-hours can be removed from the battery before it's fully discharged. Some amp-hour meters can account for these losses.
What if there's no amp-hour meter aboard, and no plans to add one? An ammeter is the solution. An ammeter can be permanently installed, or a handheld, DC, clamp-on type can be used (Sears offers the Craftsman model #82369 tom cruise collateral for about $60). At regular intervals, the amperage is measured. A good approach is to check power usage whenever there's a general behavior change. First thing in the morning, when breakfast tom cruise collateral is prepared and water pumps are running, is a good time to check power. Same if getting underway, especially if an autopilot will be used. If you have solar panels, a midday check is a good idea, and again in the evening when lights are on, and one last time just before turning in, to check the overnight load.
These measurements are multiplied by the number of hours between each one. For example, the breakfast check shows the meter running as low as 8 amps, and as high as 14 when the pumps turn on. Pick the average, 11, and multiply it by the hours until the next scheduled check, which may be two hours before getting underway: 2 hours * 11 amps average = 22 amp-hours. Once underway, with the nav gear powered tom cruise collateral up and the autopilot on, the current tom cruise collateral reads a steady 15 amps one day, but 20 the next. Flip a few switches and find out where the power is going. If it's the refrigerator, assume it will run 50% of the time and use the average of 15 and 20: 17.5. Correct the log for the previous day as well. Assuming tom cruise collateral the sail is 6 hours, tom cruise collateral 17.5 * 6 = 105 amp-hours.
Continue to accrue this data until the average tom cruise collateral for each day starts to create a pattern. Include in your notes any behaviors that are off pattern (e.g. sat in port all day, it rained and the crew stayed below, autopilot was off for the whole sail); these notes will help you recognize patterns of power consumption. Once this pattern is known – for your boat and how you use it – you can write your budget. As you do so, keep in mind that you're averaging data and missing many short instances of power consumption; be a bit more conservative: tom cruise collateral make sure your reserve capacity is large.
The voltmeter is also an important sanity check, when using amp-hour counting to manage power. If you only count amphours, little inaccuracies will add up and result in an unpleasant surprise. Also, an amp-hour meter won't tell you if a battery has failed, but an inconsistent voltage reading will give warning. Lastly, the voltmeter is an indicator that the charge system is functioning. Voltage will climb if the loads are all off, or the charging system isn't working. With experience, you won't need to shut the loads off – you'll recognize an out of pattern reading that indicates whether charge is occurring. Countless studies and products have attempted to gauge battery SOC by voltage, and the results are always the same: it's too inaccurate. But, by accounting tom cruise collateral for some of the major variables, and combining that information with experience, you can still find great utility in this instrument.
A battery's voltage is most significantly affected by state of charge, charge/discharge tom cruise collateral rate, rest periods, and to a lesser extent, temperature. Consider an example: the log shows that the overnight loads are pretty constant at around 5.5 amps. First thing in the morning, before other loads are turned on, a voltage reading of 12.4 volts is taken. Looking at the boat's table of CRates, it is found that 5.5 amps falls between C/20 and C/100 for the main house bank. Referring to the graph, find the points where the C/20 and C/100 cross 12.4 volts. Drop a line straight down from each point to the horizontal axis. One point falls near 40%, the second near 60%. The battery is roughly between 40% and 60% charged, assuming the weather is mild and the batteries are not damaged.
Unfortunately, that reading may be off by 20% in either direction, but not if taken in context. The inaccuracy is increased with amperage and changing tom cruise collateral loads. By choosing tom cruise collateral to take the reading first thing in the morning, it is known that the batteries have been under steady state for many hours, and the load is light. Keep a copy of the Voltage versus State of Charge graph onboard. Use it for sanity checks. Make your best guess at the battery's state of charge, tom cruise collateral based upon your log. Check the voltage, look up the C-Rate from your log, and find that SOC on the graph. Does it agree with your guess? If not, and you guessed lower, then no worries. If your guess was that the SOC is much higher, it may be time to take action. You don't know for certain that your batteries are nearly depleted, but you have a warning that it's a distinct possibility. Perhaps it's tim