# DC Power and Battery Life: Understanding Capacity (mAh) for Your Field Recorder If you work with portable gear like field recorders or cameras, you deal with **DC** (Direct Current) power and batteries. This is where the confusion often lies: 3.5 Amps seems like a lot, but in battery terms, the Amp figure describes **capacity**, not instantaneous draw. ## Amps, Amps, and Amp-Hours (Ah) |Term|Symbol|What it Measures|AC vs. DC Context| |---|---|---|---| |**Current**|I(Amps)|Instantaneous flow rate of electricity.|**AC:** Draw from the wall (e.g., 6.0 A for speakers). **DC:** Current being consumed by the device at any moment (e.g., 0.35 A for a recorder).| |**Capacity**|Ah / mAh|Total charge stored in a battery.|**DC Only:** How long the battery will last.| ### Clarifying 3500 mAh When you see a battery rated at 3500 mAh (or 3.5 Ah), it means the battery **contains** enough energy to theoretically supply 3500 milliamps (3.5 Amps) for one hour. It is a measure of the battery's total fuel tank size. Capacity=Current×Time ## Calculating Battery Runtime The primary goal with DC power is figuring out how long your gear will run. To do this, you need two things: 1. **Battery Capacity (**mAh**):** The rating printed on the battery. 2. **Device Current Draw (**mA**):** How much current the device consumes. This is often listed in the product manual's specifications (usually in the 200 to 500 mA range for recorders). The formula for approximate runtime is: Runtime (Hours)=Device Current Draw (mA)Battery Capacity (mAh)​ ## Practical Example: The Zoom H6n Recorder Let's calculate the expected life of a set of rechargeable NiMH batteries in your Zoom H6n, which uses 4 AA batteries. ### Step 1: Determine Battery Capacity We'll use a common rating for high-capacity rechargeable AA batteries. - **Capacity:** 2500 mAh ### Step 2: Determine Device Current Draw We need the consumption for the H6n under a typical recording load (e.g., using two mic inputs with phantom power off). We'll use a realistic average based on manufacturer specs. - **Current Draw:** 350 mA (or 0.35 A) ### Step 3: Calculate the Runtime Now we apply the formula: Runtime=350 mA2500 mAh​≈7.14 Hours The runtime is approximately 7 **hours and** 8 **minutes** on that set of batteries. ## Deep Dive: DC Power in Analog Synthesizers Your question about analog synths brings up a perfect distinction between **power supply** and **control signal** in DC systems: - **Fixed DC Supply Voltage:** The main power supply for the synth's internal circuits (often ±12 V or ±15 V) is a **constant pressure**. This voltage **does not change** and is used to power the chips and transistors. It is analogous to the fixed AC wall voltage (120 V). - **Variable DC Control Voltage (**CV**):** This is a small, variable DC voltage (typically 0 V to 5 V or 0 V to 10 V) that acts as the signal to modulate sound parameters. - **Implication:** When you play a different note or change a filter cutoff, the CV **voltage is intentionally changing** to control that parameter. The current flow used by this control signal is negligible compared to the total power draw of the synth. ## The Oscilloscope and Measurement When you look at a signal on an **oscilloscope**, you are observing **Voltage** (V) over time. You are seeing the waveform (the sound or the CV control signal) displayed as a measure of electrical potential. While current (I) is always present, it is the changing voltage that defines the audio signal's shape, amplitude, and frequency. ## Key Takeaways for DC Power - **Capacity (**Ah/mAh**):** This is the **size of the fuel tank**, not the fuel flow rate. - **Current Draw (**A/mA**):** This is the **flow rate** consumed by the device. - **DC voltage is very low** (e.g., 1.5 V per AA cell). That's why even a small current draw like 350 mA can last for many hours.