Model Train Power Supply Calculator
Calculate the right power supply wattage and amperage for your model train layout based on scale, locomotives, and accessories.
Sizing a power supply for model trains
Model train layouts need enough power to run locomotives, light accessories, and operate turnout (switch) motors simultaneously. An undersized power supply causes locomotives to slow down when accessories activate, or stalls trains on grades.
Basic formula:
Total current (amps) = Locomotive current + Accessory current
Power (watts) = Total current × Track voltage
Current draw by scale and system:
| Scale | Track Voltage (DCC) | Track Voltage (DC) | Locomotive Current |
|---|---|---|---|
| Z (1:220) | 12V | 0–10V | 0.2–0.3 A |
| N (1:160) | 12V | 0–12V | 0.3–0.5 A |
| HO (1:87) | 14–16V | 0–14V | 0.5–1.0 A |
| S (1:64) | 14–18V | 0–16V | 0.7–1.2 A |
| O (1:48) | 18V | 0–18V | 1.0–2.0 A |
| G (1:22.5) | 18–24V | 0–22V | 1.5–3.0 A |
Sound-equipped locomotives draw more: A locomotive with DCC sound typically draws 0.2–0.5 A more than a silent decoder due to the speaker amplifier.
Accessory current draw:
| Accessory | Current Draw |
|---|---|
| Locomotive LED headlights | 0.02–0.05 A |
| Interior car lighting (per car) | 0.02–0.04 A |
| Turnout motor (stall type) | 0.2–0.5 A (continuous) |
| Turnout motor (solenoid) | 1–3 A (momentary, 0.5 sec) |
| Building lighting (per structure) | 0.02–0.1 A |
| Signal (per signal) | 0.02–0.05 A |
| Smoke generator | 0.3–0.8 A |
Worked example — medium HO DCC layout:
3 locomotives running simultaneously (2 with sound):
- 2 sound locos × 1.0 A = 2.0 A
- 1 silent loco × 0.6 A = 0.6 A
Accessories:
- 10 turnout motors (stall type) × 0.3 A = 3.0 A (worst case, all activated)
- 8 lit buildings × 0.05 A = 0.4 A
- 20 lit passenger cars × 0.03 A = 0.6 A
- 4 signals × 0.03 A = 0.12 A
Total: 2.6 + 4.12 = 6.72 A With 20% headroom: 6.72 × 1.2 = 8.06 A
At 15V DCC: 8.06 × 15 = 121 W
Recommended: An 8A DCC booster (like Digitrax DB210) or a 10A power supply.
DCC vs. DC power supplies:
DC layouts use variable-voltage transformers. The maximum current rating matters most — typically 1–2 A for a single-train layout, 3–5 A for multi-train.
DCC layouts need a fixed-voltage power supply feeding a DCC command station/booster. The command station then generates the DCC signal on the track. Common DCC boosters: 5A (small layouts), 8A (medium), 10A (large).
Power districts: For larger layouts, divide the track into separate power districts, each fed by its own booster. This prevents a short circuit in one area from shutting down the whole layout. A typical district covers 15–25 m (50–80 ft) of track.
Wire gauge for bus wires: Use at least 14 AWG for main bus wires and 22 AWG for track feeder wires. Run feeders every 1–2 m (3–6 ft) to prevent voltage drop.