Sep. 03, 2025
The following conclusions use device A, which draws 12V at 5A, and device B, which draws 12V at 2.5A, as examples:
Sharing a power supply with device A isolated and device B non-isolated presents three risks: 1. Risk of electrical interference 2. Risk of leakage 3. Risk of device damage
Total Power Consumption Calculation
Calculation basis: Based on the power formula P = UI (P = power, U = voltage, and I = current).
Device A has a voltage of U₁ = 12V and a current of I₁ = 5A. Therefore, device A's power P₁ = U₁ × I₁ = 12V × 5A = 60W.
Device B has a voltage of U₂ = 12V and a current of I₂ = 2.5A. Therefore, device B's power P₂ = U₂ × I₂ = 12V × 2.5A = 30W. Total power consumption: When two devices share a power supply, the total power consumption Ptotal = P₁ + P₂ = 60W + 30W = 90W
Note that at this time, devices A and B require a total of 90W of power to operate (the current of the two devices is 7.5 amps). The current of device B will be equal to the current of device A. At this time, device B will have an overcurrent. If device B does not have current limiting protection, the electronic components of device B (mostly moss tubes) will be burned out. The greater the total power consumption of devices A and B, the greater the current.
Power isolation definition: Isolating power input and output electrically through isolation components to improve safety and reduce electrical interference.
Common isolation methods: transformer isolation and optocoupler isolation.
If a shared battery power supply is connected to both devices A and B, and device A has an isolation module but device B does not, the negative terminal of device A is disconnected from the device ground, while the negative terminal of device B is connected to the outer casing. This will cause devices A and B to share the same negative terminal as the battery. Touching the devices will result in an electric shock (real-time battery voltage). Devices A and B should not be installed in a shared ground environment, as this will cause cross-current and render the isolated power supply on device A ineffective.
Some high-demand devices use isolated power supplies, while low-demand devices do not.
Risk Analysis - Electrical Interference Risk
Sources of Interference: Device B interferes with device A, and device A interferes with device B.
Impact of Interference: Degraded device performance, and in severe cases, a freeze or reboot.
Risk - Leakage Risk
Leakage Hazard: Electric shock hazard, device short circuit damage.
Overvoltage and Overcurrent Risk: During power fluctuations, the overvoltage saturation point of device A is higher than that of device B, causing device B to burn out first.
Long-term Impact: Electrical interference and leakage accelerate component aging.
Conclusion: While connecting two devices using a shared battery power source, with device A having power isolation and device B not, while not guaranteed to damage the devices, does pose risks such as electrical interference, leakage, and damage, necessitating careful consideration in practical applications.
Recommendation: Add protective measures: Add overvoltage and overcurrent protection circuits to device B to reduce the risk of damage. For example, you can add protective components such as fuses and varistors to the power input of device B.
Add isolation circuits: Add an isolated power supply module to device B to provide the same power isolation functionality as device A. An isolated power supply module effectively blocks interference and fault currents from the power supply side, protecting device B. For example, you can choose an isolated DC-DC power supply module with a 12V input and a 12V output and install it at the power input of device B. This electrically isolates device B from the battery power source, reducing the risk of interference and faults.
Use independent power supplies: If possible, provide independent power supplies for devices A and B to completely eliminate the risks associated with a shared power source.
