DC Power Consumption Calculator

Every ham radio station has a power budget — the accounting of how many watts each device draws and how long it runs each day. Whether you are planning a shack from scratch, justifying the switch to solar, sizing a UPS for contest operating, or building an emergency communications go-kit, the DC power consumption calculation is the starting point. It translates device specifications into daily watt-hours, monthly kilowatt-hours, and annual electricity cost in one consolidated view.

The relationship between power, voltage, and current in DC circuits is described by Ohm's law: P = V × I. At the standard amateur radio station supply voltage of 13.8V, a 100 W transceiver in transmit draws approximately 200W from the AC mains (accounting for power supply efficiency), or about 14–22 A directly from a 13.8V DC source, depending on DC-to-RF efficiency. Knowing this current draw is essential for selecting the correct wire gauge and fuse rating — undersized wire causes voltage drop and heat, and an undersized fuse will not protect the wiring in a fault condition.

Ham radio stations commonly run multiple devices simultaneously: the transceiver, a logging computer, an amplifier, an antenna tuner with a motor drive, LED lighting, a keyer, and various chargers. Each device has its own power draw and operating schedule. The aggregate daily energy (Wh = watts × hours) determines how large your battery or solar system needs to be, while the peak simultaneous power (all devices TX at once) determines the rating of your main fuse, circuit breaker, and power supply or inverter. Both figures are needed for a properly engineered station.

Fuse sizing follows the NEC (National Electrical Code) 125% rule for continuous loads: the fuse or breaker must be rated at no less than 125% of the maximum continuous current. A transceiver drawing 20 A at full TX output requires a minimum 25 A fuse: 20 × 1.25 = 25 A. The fuse should be placed as close as possible to the power source (battery terminals or power supply output) — specifically within 18 inches of the battery per ARRL and ARES wiring guidelines. Anderson Powerpole connectors in the standard ARES/RACES red-black 30 A configuration are rated for 15–45 A depending on contact size and are the most common DC interconnect system in portable ham radio.

When measuring actual power consumption, use a watt meter between the power supply and the radio rather than relying on manufacturer current specifications. The Powerwerx Watt Meter and the West Mountain Radio PWRcheck are popular low-cost instruments for ham shacks. They display instantaneous wattage, peak wattage, amp-hours consumed, and watt-hours consumed — all the data you need to populate this calculator with accurate device figures. Measure separately during receive, SSB transmit, and digital mode transmit to capture the full range.

For Anderson Powerpole wiring, the ARRL/ARES standard uses red (positive) on top and black (negative) on bottom when the tongue opens to the right. The 30 A (15 AWG minimum, 12 AWG recommended) Powerpole is the most common size; the 45 A contact fits the same housing and handles heavier loads such as amplifier power cables. Always install a fuse on the positive lead within 18 inches of the battery terminals, never at the equipment end alone — a fault in the middle of an unfused cable can start a fire even if the device has its own fuse.

The $0.13/kWh default electricity rate is the US national average as of 2024, but rates vary from $0.08/kWh in some southeastern states to over $0.30/kWh in Hawaii and parts of New England. Check your utility bill for the effective rate (total bill divided by total kWh) rather than using the base rate, which excludes distribution charges, taxes, and fees. The true all-in rate is typically 20–40% higher than the advertised base energy rate.