DC System
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Research
- DC = Direct Current
- 12-vol direct current (DC) electrical systems….simply inadequate to give you a dangerous shock….Current overloads can generate enough heat to start a fire….Sulfuric acid inside the batteries can cause blindness if you get it in your eyes. (This Old Boat, p. 260)
Monitoring
- Battery voltage is about the closest you will come to having the equivalent of a gas gauge for the charge level of your house bank. If the battery is being discharged…it will register lower than true voltage. If it is being charged, the voltage reading will be higher. Even if neither is occurring at the moment, batteries “recover” for several hours after discharge. For an accurate assessment of charge level based on battery voltage, the batteries should have rested for 24 hours. In practice, you will get a fairly accurate reading of battery condition after a couple of hours of rest. A good time to check battery voltage on a cruising boat is just before sunrise. (This Old Boat, p. 270)
- Between fully charged and 50% discharged, battery voltage declines by less than .5 volt, so assessing the charge state of the batteries based on voltage requires a digital voltmeter. A voltage reading about 12.6 suggests that a 12 volt battery is nearly 100% charged. When 25% discharged, battery voltage will have declined to around 12.4 volts. A reading of 12.2 volts corresponds to the 50% discharge level. (This Old Boat, p. 270)
- Nothing is more convenient than a hardwired monitor for keeping track of condition of your house back on a day-to-day basis. The ageless Link 10 or some other smart battery monitor will keep you informed of the real-time voltage as well as the current level of load or input. This not only tells you the charge level, it allows you to instantly assess the true draw of a particular appliance, determine how much current your alternator is actually delivering, and maximize the output from solar panel positioning. No boat that stays away from the dock for more than a few days should be without a hardwired battery monitor. The voltmeter and ammeter functions will prove most valuable. A reading of 13.9 volts tells you your alternator is charging (and switching to the amps function will tell you the rate of charge). A voltage reading of 11.9 tells you that you are overdue for recharging. A daily early-morning check of voltage after the batteries have rested overnight lets you conveniently track charge status. The amp function reassures you that running a fan all night will have little impact on your batteries. It can also warn you of a current leak or a failing appliance. What you should not put great faith in is the amp-hour function of a batter monitor…the rate of discharge needs to be taken into account. Monitors have a microcomputer that tries to do this, but over time the inaccuracy accumulates. (This Old Boat, p. 270)
- When using a high-output alternator and multistep voltage regulator, it can be a very thin line that separates force-feeding the batteries from doing damage. To walk this line, as well as too manage the DC system to best advantage, precise monitoring and control of the system is needed, which is accomplished in the fine-tuning of the regulator. Although it is no strictly necessary, for those of us who like to keep an eye on these things thereafter, it helps to have an accurate systems-monitoring device onboard. This is best bought as an integrated package from the voltage-regulator manufacturer. My favorites are those from Aple Technologies (The Energy Monitor) and Xantrex/Heart Interface (the E-Meter for simple systems or two E-Meters for more complicated systems) (Cruising Handbook, p. 166)
- Get an “amp meter” (Bluesea product – reasonably priced at Columbia Marine Exchange. Shows voltage and current, whether battery is charging, or outputting), Xantrex charge monitor
- To save engine running time, many boaters charge their batteries to only 80-85% of capacity. But you can maintain a better, balanced energy system aboard your boat and prolong battery life by installing an amp-hour meter or percentage meter. (The meter will tell you how much battery capacity you have discharged. If you follow the experts’ advice and never discharge below 50% of capacity, the amp-hour meter will let you know when it’s time to begin charging. When the battery is fully charged, the amp-hour meter will read “0.” Your charging time will be more efficient, and you’ll rest assured you have enough power to start your engine. An amp-hour meter will also let you monitor your charging so you can decide how much time you want to spend in the absorption phase to gain how much battery capacity. A good rule of thumb for achieving adequate, but less than full charge in a reasonable amount of time is to bring your battery quickly through the bulk stage to the absorption phase, and then let the amperage decline to about 10% of your battery capacity; i.e., charge a 200-Ah battery until it accepts about 20 amps at 14.4 volts (14.2 for gel cells.) If you don’t usually recharge to full capacity, remember to top off your batteries to full charge periodically to prolong their life, and to “zero”, or reset, your amp-hour meter when your battery is fully charged. (http://www.boatus.com/boattech/battchg.htm)
- About Battery Shunts – A shunt is necessary in order to measure amps and amp-hours with battery monitors. A shunt is a very low resistance accurate resistor which is placed “in line” with the wire carrying the current to be measured. Because there are frequently several taps driving power in and out of the positive battery post it is best to place the shunt on the common negative lead so that all charging and discharging current must pass through the shunt. The shunt must be placed near the battery array because these wires carry very high currents the wires from the batteries must be kept short to minimize electrical losses. (http://www.enviroharvest.ca/battery_monitors.htm)
- How a battery shunt works – As current flows through the shunt, a small voltage is developed across the shunt which is proportional to the current flow. The battery monitor measures this very low voltage and converts it to the Ampere reading on the meter. A shunt is rated by the maximum current that can safely flow through it. The higher the current that flows through it the greater the temperature rise of the shunt. Using too small a shunt will cause permanent damage by changing the resistance properties of the shunt or even fire if the current is excessive. (http://www.enviroharvest.ca/battery_monitors.htm)
- Keep in mind that nothing, nada, zilch can connect to the battery ahead of the shunt. If it does it will not be read. It should go;Battery post (with NOTHING else on it but the gnd jumper), ground wire jumper, shunt, system groundsInstalling grounds ahead of the shunt is perhaps the #1 reason for a batt monitor not working properly. Where does your panel ground go to and where is it currently connected? (http://forums.sbo.sailboatowners.com/showthread.php?t=122035)
- OK here’s the gotcha we talked about. Nearly every instance of trouble shooting battery monitors I’ve come across can be lead directly to where you have connected your DC negative wires. A shunt reads the loads on the system as measured across the shunt. This shunt is a 500 amp 50 millivolt shunt. This means that at 500 amps there will be a 50 mV drop across the shunt. Knowing this the monitor manufacturer can make the display correspond to any load from 0 to 500 amps or 0 to 50 Mv..If any load, such as a bilge pump ground, is wired ahead of the shunt or on the -BATTERY side of it, it will NEVER be seen or measured by the monitor. All DC loads on-board should be read by the battery monitor. inverters, battery chargers, solar, wind, alternator, distribution panel, LPG detectors etc., etc., on and on.Keep in mind that many marine alternators are case grounded and thus the system ground, which on most boats is the engine block, is the ground path for the alternator. While I much prefer an isolated ground for alternators most boats just do not have them. Due to this the ships main ground connection should be connected to the -LOAD side of the shunt and NOT ahead of it or on the -BATTERY side. (http://www.sailnet.com/forums/electrical-systems/71197-wiring-installing-battery-monitor.html)
- If you look at the shunt (yellow lines / ignore red for now) you can see that out of the top stud it simply goes to the battery with a single jumper cable. NOTHING else connects to my batteries ground in between the shunt and battery post just like the drawing above. ALL GROUNDS MUST PASS THROUGH THE SHUNT.ALL grounds come out the bottom of the shunt (load side) and are connected to the ground buss bar which is connected to the bottom side of the shunt so that the shunt can measure the loads. If you were to connect ANYTHING to the top stud or the battery you would by-pass the shunt and it would never be seen or measured. Below is a photo of my battery compartment distribution panel: (http://forums.sbo.sailboatowners.com/showthread.php?t=122035)
- A fully charged battery will show a voltage of about 12.8 after being rested for 24 hours. A battery with a 50% state of charge will exhibit a voltage of about 12.2. These values are general and do vary somewhat from manufacturer to manufacturer.With only 0.6 Volts between a fully charged battery and one 50%discharged, it should be apparent that inexpensive analog volt meters are not accurate enough to be meaningful. (Ample Power Primer, p. 2)
Plugs
- Hardwiring is the best way of supplying power to most boat appliances, but for a few items – such as spotlights, vacuum cleaners, and chargers for electronic equipment – plug connectors are appropriate. Unfortunately the plug standard that has evolved is the automotive cigarette lighter socket….the center contact of a cigarette lighter plug is always positive, the perimeter contact negative. (This Old Boat, p. 277)
- For supplying power to appliances used on deck, you will need something better. I have gotten excellent service from Dri-plugs…uses an O-ring to seal moisture out quite effectively. (This Old Boat, p. 278)
Stereo & Speakers
- Magnet type, 2-way/3-way system & frequencies are the most important things to look for and understand when buying speakers. After that, you just want to maximize power capacity (wattage) on the speakers and deck. Perhaps you could look at 3-way systems which have the lowest hz response that you can find. I’ll just summarize what I’ve learned, it might help you when you look more: (www.shawnkilmer.com)
- Magnet type: neodymium (rare earth magnet) vs ferrite or other material: the neo magnets are more powerful and smaller than ferrite magnet speakers, so while this doesn’t necessarily mean a change in audio quality, it means you can have much lighter more compact designed speakers in neodymium that are equal with way heavier larger ferrite magnets. snobs all seem to agree that neodymium mag is superior sound too but its unproveable
- 2-way/3-way systems: theres a little circuit board that filters the audio signal into 2 separate bandwidths or 3. they direct the sub frequencies to a speaker thats built to handle sub frequencies, and send the high frequencies to the mid or tweeter that was designed to handle highs. so, you definitely don’t want a 1-way system, it will sound weak and muddy with one speaker trying to play all frequencies. 3 way would be best, a woofer, mid, and tweeter. they usually come as preassembled 3-way speakers all in one unit, but there are many models available too that are three separate physical components– little tweeters, mids and woofers. however, if you have really well-paired high quality 2-way speakers, they could potentially sound better than a 3 way system of crappy components.
- Frequencies: the frequencies of the speakers you linked me says 60hz-20khz. 60hz is the highest number of hertz that we would really call more “bass” sounding tones. if you had a subwoofer in your car, 60hz would be right around the range that it would be hitting at. the limit of human hearing goes down to about 20hz or so, and all your sweet rap music beats take place between 25hz-60hz. if you run speakers that only do 60hz, you would not hear some basslines entirely on really heavily engineered club music that has basslines in the 30hz’s. it should be acceptable, but those speakers will not “bump”.
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