| 1) RV / Marine / Golf Cart : RV or Marine type deep cycle batteries are basically for boats & campers and are suitable for only very small systems. They can be used but do not really have the capacity for continous service with many charge/discharge cycles for many years. Regular or Car type batteries should not be used at all because they cannot be discharged very much without internal damage. A very popular battery for small systems is the Golf Cart battery. They are somewhat more expensive than deep cycle recreational batteries but are probably the least expensive choice for a small system on a budget. |
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| Industrial strength : Flooded, Gel, and AGM sealed batteries |
| The next 3 types are the heavier industrial type batteries. They are all also considered Deep Cycle and are usually Lead Acid types with much thicker internal plates that can withstand many deep discharge cycles. These next 3 are all designed for alternative energy systems. |
| 2) Flooded types : These are Lead acid batteries that have caps to add water. Many manufacturers make these types for Solar Energy use. Trojan, Surrette, and Deka are probably the most well known. They are reasonably priced and work well for many years. All flooded batteries release gas when charged and should not be used indoors. If installed in an enclosure, a venting system should be used to vent out the gases which can be explosive. |
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| 3) Gel : Not to be confused with maintenance free batteries, sealed gel batteries have no vents and will not release gas during the charging process like flooded batteries do. Venting is therefore not required and they can be used indoors. This is a big advantage because it allows the batteries to maintain a more constant temperature and perform better. |
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| 4) AGM : Absorbed Glass Mat batteries are in my opinion the best available for Solar Power use. A woven glass mat is used between the plates to hold the electrolyte. They are leak/spill proof, do not out gas when charging, and have superior performance. They have all the advantages of the sealed gel types and are higher quality, maintain voltage better, self discharge slower, and last longer. The Sun Xtender series by Concorde Battery is an excellent example of AGM batteries. They are more expensive, but you usually get what you pay for. You will find this type of battery used in airplanes, hospitals, and remote telephone/cell tower installations. |
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| Care and Feeding |
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As a technician, I used to say that if you are not comfortable, then neither is your equipment. I was mostly referring to temperature and humidity. In fact battery capacity ratings are usually specified at 77 degrees F. As batteries get colder their voltage drops and performance suffers. This is one major reason I prefer AGM batteries because they can be stored indoors where the temperatures vary less. |
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| Another important thing to consider is how deeply you discharge your batteries. This is known as the DOD (depth of discharge). In other words, how low you let the voltage drop before the next charge cycle. Most battery ratings talk about 50% or so, but they will last longer if you keep them as charged as possible. I like the 70% range. Lead acid batteries like to be fully charged. They will last much longer if you do not discharge them too deeply. This is known as shallow cycling and greatly extends their life. However, they can withstand discharges down to 20% or so, but I wouldn't do it too often. |
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| How to determine how charged your batteries are |
| Determining the percentage of battery charge from meter readings is discussed in more detail under Meters And monitoring. A common voltmeter and this voltage chart will give you a good idea of the SOC (state of charge) of your batteries. |
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Wiring diagrams for multiple batteries
| Battery wiring diagrams |
| The following diagrams illustrate how to get increased current (more power) by using parallel wiring and how to increase voltage levels by using series wiring. You can do both using series and parallel wiring in combinations. |
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| Use parallel wiring to increase current (power). |
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This diagram shows a simple parallel circuit to increase current or power. Assume that we are using 12 volt batteries. The power of all 3 batteries add to give us the effect of a battery 3 times as powerful but the voltage stays the same at 12 volts. Parallel wiring increases current but the voltage does not change. This is the wiring used when jump starting a car for example. |
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| Use series wiring to increase voltage |
| This diagram shows a simple series circuit to increase the battery voltage level. Assume that we are using really big 4 volt industrial batteries. |
| The voltage of all 3 batteries add to give us the effect of a battery 3 times the voltage or in this case a very large 12 volt battery. In this circuit the current is the same as the current in just 1 of the batteries. But since the 4 volt industrial batteries are very large, we have in effect created a huge 12 volt battery. |
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| Use series & parallel wiring in combination |
| This diagram shows a combination series and parallel circuit to increase both the battery current and voltage level at the same time. Assume this time we are using 12 volt batteries. |
| The left to right series connection add the two 12 volt batteries to make 24 volts. And, since we did this 3 times and then connected each group of 2 (now 24 volts) in parallel we end up with one very large 24 volt battery. It has twice the voltage of a single 12 volt battery and 3 times the current or power because all 3 groups are wired in parallel. |
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| DISCLAIMER : Alway make sure that all of your equipment is properly fused and grounded for safety. Also, be sure to read and follow the advice and instructions that come with your equipment. While projects have actually been constructed and tested under actual operating conditions, we do not guarantee that they will meet all electrical codes in all locales. Nor do we suggest that our advice supercedes the recommendations of a licensed electrician. Hey, we're just trying to help!
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