We haven’t actually finished the task of installing the new battery. When we removed the old battery we also had to remove the vented enclosure it was in. Hydrogen and oxygen gases are generated during charging, particularly so during the equalization process. These two gases are not only highly explosive, they cause electrical components to corrode. Thus we have one task remaining, that being the reconstruction of the battery enclosure.
Now to the series of electrical equipment hanging on the wall:
* The first device (rectangular in shape, mounted horizontally and painted white) is a Xantrex 4024 inverter, which obviously inverts the D.C. power from the batteries to 120 volt alternating current. It can also accept an A.C. feed which can charge the batteries and run household loads at the same time, and is also capable of “Grid Tie” application. The nearest grid power to us is a mile away so that is a feature we care little about. That as an aside, the unit provides 4000 watts constantly with a surge capacity (momentary start-up for heavy loads such as electric motors, etc.) to 6,500 watts.
* The second unit is a “D.C. Disconnect” (mounted vertically and painted white) and is basically a D.C. breaker box. The 2/0 cables from the battery go into this unit and feed into and out of the breaker and then into the inverter.
* The third unit is an “Inverter By-Pass” switch, painted gray, and is mounted directly under the aforementioned D.C. Disconnect. I installed it so in case of inverter failure I could still run power to the house from a generator while the inverter was being serviced.
* The fourth and fifth units are mounted parallel to the D.C. Disconnect and are D.C. breakers that are interfaced on the cables which carry the generated power from the hydroelectric units to the battery. Since the units require some level of maintenance, it is a good idea not to have back-feed from the battery there to kill you while you work, thus the obvious need for the breakers. Worse yet, sometimes in the course of some aspects of maintenance on the units such as the occasional cleaning of nozzles, the floor gets a bit wet. Does the phrase “well grounded” come to mind? Voltage hurts, but it is the amps that kill, and there’s a whole lot of amps going on here.
* The last two units aren’t there for decoration. Even though small in size, they are critical to proper function of the system. The first is also painted white, and is a Xantrex C-40 Charge Controller. Wired to it and immediately to its right is an Enermaxer 900 watt “Diversion Load” that works in sync with the C-40. What? Why? Since this system is nominally a 24 volt system, I’ll use related figures to explain the necessity of these two units. As mentioned, a reading of 25.6 volts is considered a “full state of charge” in a 24 volt battery, even though that isn’t necessarily true. If one imagines a battery more like one of those “water towers” that dominates the landscape of mid-western towns, that 25.6 reading is reached when the water is about halfway up the bubble that sits at the top of the column. It’s “charged”, but not “fully charged.” A true state of “full charge” is around 27.4 volts, somewhat higher up in that visualized bubble.
One will also note when visualizing the circumstance this way that one can see that as the charge level is at 25.6 and points lower, the bubble shrinks in size as it heads down towards the column, thus discharge occurs more rapidly because the volume of water decreases in mass. Electricity in a battery behaves no differently than water does in one of those water columns. To a measurable point, more is better. Lead-Acid batteries begin to “gas” at certain voltages, and in the case of a 24 volt battery this occurs at around 28 volts. The higher above that figure the state-of-charge goes, the more the battery gases. In case you didn’t know, this is not a good thing to have happen under normal circumstances.
The only time you want this to happen is during a “controlled overcharge”, i.e., during the process referred to earlier known as “cell equalization.”
Note the word “controlled.” When engaged in a “controlled overcharge”, one checks that the cells are adequately watered before the process begins and after doing so, runs the battery up to around 30.5 volts for about 8 hours to de-sulfate the cells. After this has been done, you refill the cells with distilled water to the proper level. This is the proper way to conduct a controlled overcharge. The hydroelectric units themselves have no method of determining the battery state-of-charge. They will continue output regardless of what is occurring down-current. Without a method to burn off excess power, they will cause the batteries to reach a state of overcharge.
Battery state of overcharge causes gassing first and then eventually overheating, the latter then causing a fire. Obviously, both of these circumstances need to be prevented, thus the need for the charge controller. The C-40 is wired (though fused) directly to the batteries and “recognizes” when the battery state-of-charge hits 28.5 volts. Upon this recognition it then activates the output side of the unit which diverts the excess power to the Enermaxer, the latter effectively being a 900 watt heat sink. Inside the C-40 are two “set points”, one the installer sets system voltage at (12, 24, or 48 volts) and the second set point is the voltage of the desired “Float Charge.” This is the voltage point just below the point where the battery gasses and varies with the nominal system voltage. In the case of a 24 volt system, the set point is 27.4 volts.
Using the analogy of the water tower again, this is the level just below where the water flows out the top. One should ask the following question: If you are producing 2,304 watts constantly, why do you only have a 900 watt diversion load installed? Answer: The house is always consuming some level of produced energy, thus given electrical production and predictable use, a 900 watt diversion load is adequate. Volts X Amps = Watts. What do the refrigerator and freezers use 24/7? Look on the U.L. label. The pumps and valves for the heating system. The well pump and how often does it cycle? Electric clocks. All the devices that are going to use electricity no matter what, and their use can be determined by employing that that formula above. In effect, they are diversion loads as well as is the Enermaxer. It is only activated when the “Fail Safe” point is reached.
The proper exercise of alternative power is making the entire system work in as close to a state of equilibrium as one can get. What one wants to achieve is a circumstance of “never too little and rarely too much.”
*As an aside, we haven’t actually finished the task of installing the new battery. When we removed the old battery we also had to remove the vented enclosure it was in. Hydrogen and oxygen gases are generated during charging, particularly so during the equalization process. These two gases are not only highly explosive, they cause electrical components to corrode. Thus we have one task remaining, that being the reconstruction of the battery enclosure. We already have a existing vent to the outside of the building for the gases to escape, so later today or tomorrow we shall construct the new enclosure for the reasons cited above.