Let’s demonstrate that Wh and Joule (the SI unit of energy) are equivalents: One is a unit of energy (Wh), and the other is a unit of charge (Ah). Therefore, Wh and Ah are not the same units. Notice that the voltage is the difference between the last equation and the equation for charge capacity (Charge capacity = current x time). If we replace power for its definition in the equation for energy, we get that:Įnergy (Wh) = current (A) x voltage (V) x time (h) Let’s check the equations for energy and power:Įnergy (Wh) = power (W) x time (h) and Power (W) = current (A) x voltage (V) The voltage (the “pressure” with which the current flows through the circuit) is considered with Wh. It indicates the amount of current this battery can store/provide and the amount of energy (a product of power and time). When a battery’s capacity is expressed in Wh, what is actually being expressed is the battery’s e nergy capacity. For this, we use watt-hour.Īs previously mentioned, watt-hour is a measurement of energy. To know the amount of energy a battery can store/deliver, you need to consider both the voltage at which the current flows through the system and the amount of current during a certain period. It has no relation to the amount of energy that this battery can provide. In other words, it tells you the current that can be provided for a certain amount of time (in hours).Ĭharge capacity (Ah) = current (A) x time (h) So when you see Ah being used to express battery capacity, you’ll know that this number indicates the charge capacity of this battery. Therefore, we’ve confirmed that an amp hour is a unit of charge. The only “difference” is that one uses seconds, and the other uses hours to measure time. = x (current times time) and = x (current times time) If we do a dimensional analysis, we’ll see that amp hours is equivalent to coulomb (C): You’ve seen that the unit of charge is the coulomb (C), which can be defined as the charge delivered by an electric current of one ampere (1A) in one second. As previously mentioned, amp hour is a measurement of charge.
Note that amp hour is not a measurement of electrical energy. Similarly, if you deliver 10 amps continuously to charge this 100Ah battery, you would take 10h to fully charge it (10A x 10h = 100Ah). If you draw 20 amps continuously, how many hours will it take you to discharge this 100Ah battery fully? You guessed it right, 5 hours. Drawing 50 amps, you’ll deplete it in two hours. If you continuously draw 100 amps from this battery, you’ll completely deplete it in one hour. Let’s take a 100Ah battery as an example. It tells you the current (in amps) that can be drawn/delivered for a certain amount of time (measured in hours). With these definitions in mind, we can move to a more detailed explanation of the differences between Ah and Wh.Īmp-hour is commonly used to express battery capacity. This provides the right amount of power that the lamp requires to illuminate the room (electrical energy is converted into radiant energy/light). When you plug a lamp in a wall outlet, a potential difference (voltage) forces electrons to flow through the circuit (creating a current).
It can be positive (protons) or negative (electrons). Electric charge: a physical property that causes matter to experience a force within an electromagnetic field. A watt has the same dimensions as energy divided by time.ĥ.
The unit for power is expressed in watts (W). Power: the amount of energy transferred or converted per unit of time. Wh is equivalent to Joule, as we’ll explain shortly.Ĥ. The unit for electrical energy is Watt-hours (Wh). However, there are other units of energy. In the realm of electricity, energy results from the movement of electrically charged particles, like electrons, for instance. In short, energy is the capacity for doing work. Energy: energy exists in various forms: thermal, chemical, nuclear, mechanical, electrical, etc. This provides electrical energy, which can perform work, like drying your hair when you use a hairdryer. Voltage: voltage is the pressure in which the current moves through an electrical system. Current: the rate at which electrons flow through a point in an electrical circuit. To better understand the differences between Ah and Wh, let’s first review a few relevant concepts:ġ. In other words, it expresses the amount of energy a battery can store or deliver. It describes the energy capacity of a battery. Meanwhile, Watt-hour is a unit of electrical energy. It describes the charge capacity of a battery, meaning the amount of current drawn/delivered for a certain amount of time. Notice that the capacity is also expressed in Wh.Īmp-hour - short for Ampere hour - is a unit of electric charge.
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