A high-current actuator does not care how neat the wiring diagram looks. If the relay, driver, fuse, wire, or power supply cannot handle the actuator current, the system will fail. Size the electrical path around the actuator’s real current draw, not just the voltage printed on the label.
Wiring and protection matter as much as force. An actuator is only as reliable as the smallest current-rated part in its power path.
What is a high-current actuator relay?
A high-current actuator relay switches power to a DC linear actuator without forcing the small control switch to carry motor current. The switch tells the relay what to do. The relay or driver carries the load.
What is the simple explanation?
A relay works like a remote-controlled heavy switch. Your button handles a small signal, and the relay handles the actuator power.
Use the formula below to estimate electrical power.
Watts = volts × amps
What should the calculator inputs be?
Use this as a first-pass sizing tool. Then confirm the final choice against the actual FIRGELLI product page, the wiring diagram, and your real mounting geometry.
How do you use this calculator?
- Enter the real project values, not guesses from a different mechanism.
- Use measured current, load, stroke, voltage, or signal values where you can.
- Add margin for real brackets, wiring, friction, and installation conditions.
- Click Calculate to see your result.
How should you wire high-current actuator control?
Keep the high-current path short and simple. Put the fuse close to the battery or power supply (per SAE J1128 wiring practices for automotive low-voltage circuits), then feed the relay or motor driver, then the actuator.
Do not use a tiny panel switch as the main current path unless its rating truly exceeds the actuator current. The switch should normally trigger the relay, not carry the motor load.
What is a simple example?
A 12V actuator pulls 10A running and may see 25A peak. Running power = 12 × 10 = 120W. Peak load = 12 × 25 = 300W.
With 1.25x supply margin, target supply current = 25 × 1.25 = 31.3A. That points toward a 12V supply and control hardware sized above the peak current, not just the running current.
"Wiring fails at peak current, not running current. A 10-amp actuator that stalls at 25 amps will cook a 15-amp circuit even though the running number looked safe. Size the fuse, the wire, and the driver around what the system actually sees on a bad day, not what the spec sheet shows on a good one."
— Robbie Dickson, FIRGELLI Automations founder and former Rolls-Royce, BMW, and Ford engineer
Recommended FIRGELLI setup
Which FIRGELLI products fit this job?
Choose control hardware from actuator current, not from the shape of the switch.
High Current DC Motor Drive
Use this when the actuator current needs a dedicated high-current DC motor driver instead of a small switch carrying the load.
View High Current DC Motor Drive
12V SPDT Relay 20A
Use SPDT relays when you are building relay logic for actuator direction control and the current rating fits the job.
View 12V SPDT Relay
12V DPDT Relay
Use a DPDT relay when you need polarity reversal in a compact relay setup and the current rating matches the actuator.
View 12V DPDT RelayFor simple manual control, use a verified DPDT toggle switch only when its rating fits the actuator. For full actuator selection, start with the linear actuators collection.
Where does high-current actuator wiring matter most?
RV slide-outs and lift systems often run 20A to 40A peak per actuator, so the fuse and wire run from the battery deserve the same attention as the actuator itself. Marine hatch and seat lifts share the same problem with added corrosion risk on terminals. Industrial automation panels typically have proper breakers but undersized control wiring to remote actuators. Automotive applications like tonneau covers, tailgates, and trunk lifts draw heavy current from a tight wiring loom, so fuse placement near the battery is critical. In every case, the wiring path matters more than the actuator label.
What are common mistakes when using this calculator?
- Sizing from running current and ignoring peak or stall current. The wiring and fuse have to survive the worst case, not the average case.
- Treating the control switch as the main current path. A 5A rocker switch in front of a 25A actuator will fail at the contacts, not the actuator. Use the switch to trigger a relay or driver.
- Putting the fuse at the actuator end of the wire run instead of near the battery or power supply. A fault upstream of the fuse is not protected.
- Ignoring voltage drop on long wire runs. The calculator gives you a current target, but a long undersized cable will still drop voltage and make the actuator slow and hot.
- Reusing the supply current target as the fuse rating without checking inrush. Some actuators briefly spike above stall current at startup, and a fuse sized exactly to peak will nuisance-trip.
How can you verify the calculator output is reasonable?
- Compare the running current input against the actuator's product page or datasheet — if they disagree by more than 20%, recheck the model number and voltage.
- Clamp-meter the actuator under real load. The measured running current should fall between the no-load and rated-load numbers on the spec sheet (see NEC Chapter 9 Table 8 for conductor resistance and ampacity reference when checking wire size).
- Measure voltage at the actuator terminals while running, not at the battery. If it drops more than 10% below the supply voltage, the wire is undersized for the run length.
- Cycle the actuator under full load and watch the fuse. A correctly sized fuse should not warm noticeably or trip during normal cycles.
- If the calculator recommends a 30A supply but the only available supply is 20A, the system is undersized — do not assume the actuator will only briefly pull peak current.
