Basic Technical Terminolgy
Here are some or the terms and abbreviation meanings you might run into in your dealing with batteries and the system they are being used in.
What is a VOLT? A Volt is the unit of measure for electrical potential.
What is OHM’S Law? OHM’S Law expresses the relationship between volts (V) and amperes (A) in an electrical circuit with resistance (R). It can be expressed as follows: V= IR Volts (V) = Amperes (I) x Ohms (R). If any two of the three values are known, the third value can be calculated using the above equation.
What is the Reserve Capacity rating (RC)? The reserve capacity of a battery is defined as the number of minutes that it can support a 25 ampere load at 80°F until its terminal voltage drops to 1.75 volts per cell or 10.50 volts for a 12V battery. Thus a 12V battery that has a reserve capacity rating of 100 signifies that it can be discharged at 25 amps for 100 minutes at 80°F before its voltage drops to 10.75 volts.
What is the CCA rating? The cold cranking ampere (CCA) rating refers to the number of amperes a battery can support for 30 seconds at a temperature of 0°F until the battery voltage drops to 1.20 volts per cell, or 7.20 volts for a 12V battery. Thus, a 12V battery that carries a rating of 600 CCA tells us that the battery will provide 600 amperes for 30 seconds at 0°F before the voltage falls to 7.20V.
What is the marine cranking rating (MCA)? The marine cranking ampere (MCA) rating refers to the number of amperes a battery can support for 30 seconds at a temperature of 32°F until the battery voltage drops to 1.20 volts per cell, or 7.20 volts for a 12V battery. Thus, a 12V battery that carries a MCA rating of 600 CCA tells us that the battery will provide 600 amperes for 30 seconds at 32°F before the voltage falls to 7.20V. Note that the MCA is sometimes referred to as the cranking amperes or CA.
What is the difference between MCA and CCA? The marine cranking ampere (MCA) rating of a battery is very similar to the CCA rating; the only difference is that while the CCA is measured at a temperature of 0°F, the MCA is measured at 32°F. All other requirements are the same — the ampere draw is for 30 seconds and the end of discharge voltage in both cases is 1.20 volts per cell.
What is the pulse cranking amp rating (PCA)? Unlike CCA and MCA the pulse cranking ampere (PCA) rating does not have an “official” definition; however, we believe that for true engine start purposes, a 30 second discharge is unrealistic. With that in mind, the PCA is a very short duration (typically about 3 seconds) high rate discharge. Because the discharge is for such a short time, it is more like a pulse.
What is the Amp Hour (Ah) rating? An amp-hour is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. It is amps X hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) X .333 (hours), or 6.67 AH. The accepted AH rating time period for batteries used in solar electric and backup power systems (and for nearly all deep cycle batteries) is the “20 hour rate”. This means that it is discharged down to 10.5 volts over a 20 hour period while the total actual amp-hours it supplies is measured. Sometimes ratings at the 6 hour rate and 100 hour rate are also given for comparison and for different applications. The 6-hour rate is often used for industrial batteries, as that is a typical daily duty cycle. Sometimes the 100 hour rate is given just to make the battery look better than it really is, but it is also useful for figuring battery capacity for long-term backup amp-hour requirements.
What is a MilliAmp Hour (MAH)? MilliAmp Hour means how much current a battery will discharge over a period of one hour. Higher numbers here reflect a long battery runtime and or higher storage capacity. Higher MAH ratings do not necessarily reflect on speed but more on runtime. For example a 2000 mAh pack will sustain a 2000 milli amp (2 amp) draw for one hour before dropping to a voltage level that is considered discharged. A 1700 will sustain a 1700 mAh (1.7 amp) draw for one hour. 1000 mAH is equal to a 1 Amp Hour (AH) rating.
The battery capacity is the measure of the energy the battery can store and deliver to a load. It is determined by how much current any given battery can deliver over a stipulated period of time. The energy rating is expressed in Ampere Hours (AH). As a bench mark, the battery industry rates batteries at 20 hour rate i.e. how many Amperes of current the battery can deliver for 20 hours at 80 ° F till the voltage drops to 10.5 Volts for 12 V battery and 21 V for 24 V battery. For example, a 100 AH battery will deliver 5 Amperes for 20 hours. Battery capacity is also expressed as Reserve Capacity (RC) in minutes. Reserve capacity is the time in minutes for which the battery can deliver 25 Amperes at 80 ° F till the voltage drops to 10.5 Volts for 12 V battery and 21 V for 24 V battery. Approximate relationship between the two units is as follows: Capacity in AH = Reserve Capacity in RC minutes x 0.6