Part of our Getting On The Air guide.
A DMR hotspot is a small, low-power device, and it is tempting to assume any old USB charger will power it fine. In practice, a genuinely inadequate power supply is one of the most common causes of hotspot instability, random reboots, and connection dropouts.
Why Current Rating Matters More Than You’d Expect
A Raspberry Pi based hotspot, running Pi-Star or WPSD, needs a stable current supply that can handle peak draw during active transmission, not just idle operation. A generic phone charger rated for a lower current than the Pi actually needs under load can cause voltage sag exactly when the hotspot is working hardest, leading to instability that looks like a software problem but is actually a power problem.
Use the Manufacturer-Recommended Rating
Check the current rating your specific Raspberry Pi model actually recommends, since this has increased across different Pi generations, and buy a power supply that meets or exceeds it. A supply rated exactly at the minimum leaves no headroom for peak draw, while a supply with genuine margin above the minimum tends to run more reliably over time.
Cable Quality Matters Too
A high-quality power supply paired with a thin, cheap USB cable can still deliver inadequate voltage to the Pi due to voltage drop across the cable itself. Use a short, quality cable rated for the current your setup actually needs, rather than whatever cable happened to be in a drawer.
Signs Your Power Supply Is the Problem
- A lightning bolt icon or undervoltage warning appears in the Pi’s system logs or display output.
- Random reboots or freezes, particularly during active hotspot transmission rather than idle periods.
- Instability that appears only under load but seems fine when the hotspot is sitting idle.
The Fix Is Usually Cheap
A proper official or well-reviewed third-party power supply rated correctly for your specific Pi model costs relatively little, and swapping to one is often the fastest fix for a hotspot that has been mysteriously flaky despite otherwise correct software configuration.
Still deciding on hotspot software? See Pi-Star vs. WPSD for how the two compare.