A Transcutaneous Electrical Nerve Stimulation (TENS) unit manages pain by delivering low-voltage electrical currents through electrodes placed on the skin. These impulses disrupt pain signals and encourage the release of natural pain-relieving chemicals. When the unit powers down mid-session, it interrupts therapy and causes frustration. Unexpected shutdowns are usually not a sign of a broken device, but rather a reaction to a detected electrical issue or a pre-programmed safety feature. Understanding the cause allows for quick troubleshooting and a return to effective pain management.
Power Supply Problems
The simplest and most frequent cause of a TENS unit abruptly turning off relates directly to its energy source, whether battery or wall power. If your unit relies on disposable alkaline batteries, they must be completely fresh, as partially depleted cells cannot deliver the consistent voltage required for stable operation. For models using rechargeable batteries, the unit may cut power when the voltage output drops below a safe threshold, often before a low-charge warning triggers.
Checking the battery compartment is necessary. Incorrect polarity will prevent the unit from powering up consistently. Corrosion on the metal contact springs or terminals can create an intermittent connection, causing the unit to flicker off. This residue acts as a resistive barrier that disrupts the flow of electricity.
If the unit uses an AC adapter for charging or running, inspect the cable for kinks or damage. Confirm the connection to both the unit and the wall socket is secure.
Circuit Integrity and Connection Issues
A TENS unit must maintain a complete, low-resistance electrical circuit through the body to operate safely. A shutdown often signals a break in this path. The device constantly monitors the impedance, or resistance, of the circuit and automatically stops if resistance becomes too high. This safety mechanism ensures the user does not receive a painful, high-intensity shock if the connection is suddenly lost and then restored.
The lead wires connecting the unit to the electrode pads are a common point of failure. Frequent bending and pulling can cause internal breaks or fraying at the connector points. These microscopic fractures may briefly open the circuit, causing an immediate shutdown.
Electrode pads lose conductivity over time because the hydrogel that facilitates the electrical current begins to dry out. When the hydrogel is too dry or dirty, the resistance across the skin increases significantly. The TENS unit interprets this as a poor or dangerous connection, triggering its fail-safe shutoff.
Proper skin preparation is crucial for maintaining circuit integrity. Oily skin, lotions, or excessive hair can prevent the pads from adhering firmly. If a pad peels even slightly, the current density increases dramatically at the remaining points of contact, which raises the local impedance and can cause a safety shutdown. To troubleshoot this, users can try gently dampening the pad’s surface with a small amount of water to temporarily reactivate the hydrogel’s conductivity.
Safety Features and Device Logic
Many TENS units are designed with internal logic that dictates when a session must end, leading to an intentional shutdown. The most common reason for a planned power-off is the expiration of the automatic treatment timer. Most programs are preset to run for a specific duration, typically 15, 30, or 60 minutes. Users should check their current program settings to see if the unexpected shutdown aligns with a pre-set session length.
Some TENS models are equipped with a pause or intensity lock feature, which can be accidentally activated. When this lock is engaged, the unit appears to have shut off, but it is merely holding its current state until the user deliberately unlocks or resumes the session.
Another programmed safeguard is the automatic intensity reset, which occurs if the unit detects a sudden, dangerous change in resistance. If a pad completely falls off, the unit’s logic will instantly cut the current or reset the intensity to zero to prevent the user from experiencing a painful surge upon re-connection.
If all external components—power supply, wires, and pads—are confirmed to be working correctly, the issue may stem from an internal logic error or a temporary software glitch. Performing a hard reset, which often involves removing the power source for a few minutes, can clear the device’s internal memory and restore normal function. If the unit continues to shut off unexpectedly after all troubleshooting, contact the manufacturer for specific repair or replacement advice.