Charging Systems for DC storage battery banks.

Charging one cell or a bank of cells to a 100% charge will allow your storage system to work more efficiently.


On the previous pages regarding capacity and batteries we know now that a battery is a set of cells in series hookup. This is called a bank of cells and generically called a battery bank. The battery has the same characteristics as a water tank, an air tank, a fuel tank and so on. The capacity can be easily viewed by the physical size of the tanks as in the size of a cell. The larger physical dimension a cell has the more capacity (volume) of electrical energy can be stored inside it. The cell unlike a hollow tank can be internally damaged by excessive heating but could be compared to a water tank or air tank with a tiny hole in it. Even though you fill the water tank or air tank a tiny hole can allow the volume of water or air to leak, the bigger the hole the more it leaks and you need to fill it up more often to get the same work out of it and compared to when there was no leaking hole. Each cell is like one individual tank but when they are in series together in a battery like 6, or 12 Vdc one cell can take a system down if someone tries to keep charging the battery.



When a good cell is charged is gains heat, the more charge volume going into a cell the more heat will build up inside the cell. When charging cells or a battery of cells first the state of charge should be documented on paper for each cell using a hydrometer. The acid and water must stay balanced. On the lead acid cell the electrolyte poured into a new cell is a specific mixture of water and acid and is the baseline to battery life. Technically once the battery is filled and put into service acid should never be added, only water to make up the difference in level. Adding acid will unbalance the electrolyte and severely damage the battery plates.



When a battery remains in a lower state of charge the plates absorb the water from the electrolyte and the specific gravity changes. The more water absorbed in each plate of the cell the less capacity the battery will have. The more heat applied to the battery over 115 degrees f the more softer the cell plates will get and absorb more water from the electrolyte. Needing to add water to your battery is a sure sign of battery plates overheating due to over charging and using to much current from each cell at one time. That is why your system needs to be designed around the 1/10th Amp hour formulation.



On all conventional battery chargers there are knobs and gauges that indicate Ampere's of charge or charge rate. That charge rate is simply dependent on applied voltage to the battery so the only thing you change when turning the charge rate Amp knob is the applied voltage to the battery charge terminals. That is the reason why the charge rate indicated on the knob plate usually never can be viewed on the Amp meter as indicated by the charge rate knob.



For example prior to charging a conventional 12 Vdc lead acid battery use your volt meter to find out how many volts are present and let's just say our meter reads 11.85 Vdc. When you install it on a regular charger and the knob indicates a 2 Amp charge then you turn on the charger hooked up to the battery terminals the voltage will go to 13.2 and above slightly. Turning the knob to 10 Amps and the meter will read slightly higher and around 14.5 volts DC, turn the charger knob to 50 Amps and the voltage rises to 16 Vdc, 100 Amps to 18 Vdc and quick start 220 Amps you will read voltages up to 20 Vdc.



Total current in Amps is forced into batteries by voltage differential and current in Amps results on a meter. If the charger only goes to 12 volts the battery would never get a charge once it is at 12 Vdc and we now know that each cell has the potential to be fully charged @ 2.2 to 2.3 volts DC so the charging system must be able to produce at the minimum 2.2 to 2.3 volts DC for the slowest of charges @ 2 Amps or less. Charge current from a charging system to batteries is directly proportional to voltages applied. Like two water tanks setting side by side and connected with a pipe on the bottom, one tank has 12 inches of water level and the other has 20 inches of water level. I doesn't matter how large each tank is in volume or size what matters is the level of water in each and can be compared to the battery charging system. When the water in the one tank has a maximum high water level @ 13.2 inches like a battery voltage the other tank at a higher level will continue forcing the water into the tank until they are of equal height. In the case of the battery if you are applying higher voltages than the 13.2 heat will develop quickly inside the battery. High charge is good for a few minutes and until the battery becomes uncomfortable to touch then the charger voltage must be turned back to somewhere closer to the maximum full charged 12 volt battery @13.2 Vdc.



As a system is being fully charged each cell has it's own independent temperature that can be measured by taking off the water fill caps and using an infrared temp gun targeting the water in each cell. When you have cells running at a temperature like an average of 100 degrees a bad cell will be colder or hotter depending how it was damaged but the temperature can indicate cells not performing in balance. When the cells are unbalanced due to over heating or setting around in a low state of charge the remaining cells can be damaged or ruined as well as the charge process is taking place. Balance is the key to battery life and total useable capacity in the bank of cells.




In a lead acid electrical storage system (battery cells in multiple) the electron is considered the flowing element. In physics the electron is known as a particle, part of an atom. This particle flowing within a electrical conductive wire is known as electrical current flow (I). Each electron has a specific amount of electrical charge and that is a negative electrical charge, e-. So the electron is attracted to the more positive electrical charge which is anything above the negative charge carried by the electron. So positive does not flow to the negative, it is the negative which flows towards the more positive charges. In the case of the battery cell there is an electron tank and the size of this case tank is directly proportional to the amount of electrons that can be stored. Stored is the key word here the battery does not produce electrons it stores them just like the water tank, the air tank or any other element of physical properties. What you use in electrical volume must be put back into the battery or it will soon fail.



Watts are a specific volume of electrons in clumps that will produce a specific amount of work in appliances. The watt is what you pay for in electrical billing situations. Watts are the sum of voltage potential times the amount of Amps flowing ( Vdc or Vac X Amps = Watts).



For example a 100 Amp hour battery will physically burn out by heat if 100 Amps at one time is drawn from the battery, it will last about 15 seconds and then has to be shut off and charged again. Most lead acid batteries today that are used in the mobile machinery industry for smaller things are rated in Cold Crank Amps (CCA). This number rating only applies for a 15 second period in time. A 1000 CCA battery has the capability of flowing 1000 Amps for 15 seconds before the voltage drops below 9 Vdc. The CCA rating is useless and is only valid when you are calculating using the current for 15 seconds, at that rate the battery needs re charged after the 15 seconds of usage and is only a modern way to make numbers sound like your getting more. Drawing off a charge @1000 Amps would heat the battery quickly and most starters in the average mobile equipment today operate on a 12 Vdc system and draw around 85 to 100 Amps at best. The gear reduction starters average 50 to 75 Amps current draw when starting the engine.



One of the most important things I wanted people to understand is that temperature is the key factor when deciding what your charge rate is supposed to be. You will never go wrong by charging the batteries and making sure the temperature does not exceed the 115 degree farenheight upper limit. It is good for the batteries to get heated up when charging and a good medium charge rate should be targeted to maintain a temperature of 100 degrees f. Quicker charges can be accomplished but the optimum method is 1/10 the Amp hour rating of the battery being charged. Example a 100 Amp hour battery will live long if it is charged regularly @10 Amps for 10 hours.