Why does my Sirius radio power adapter blow the fuse when I plug/unplug it?

Thread Starter


Joined Jun 28, 2018
Hey all,

I drive a truck and like to listen to my Sirius radio. However, the radio isn't built into my truck and I share the truck with another driver, so I have to plug/unplug the radio every time I use the truck.

I've noticed that if I have the radio on and plug/unplug the power adapter from the truck's cigarette lighter I often get a spark that blows the circuit's fuse.
Obviously, I'm getting a high current draw when I have the radio on and plug/unplug it, but I'm wondering from more of a physics standpoint why this is occurring?

I've noticed that when I plug in other devices (like my phone) I don't get sparking or blown fuses. Also most other power adapters that I use don't result in sparking either. Could the design of the Sirius adapter be not that great?


Joined Aug 21, 2008
If the radio is "on" (circuits engaged through maybe not enough current to play the thing) the input capacitors to the power supply and in this case the (AC?) adapter are likely "empty". When plugged in empty there will be a large inrush of current to charge up the capacitors quickly unless provisions are made to slow down the initial charge, like a positive temperature coefficient thermistor on the simple end and a transistors switch at the other end of the complexity scale.


Joined Jan 23, 2018
Since it is a truck, not a house, I am guessing that you are plugging in to a 12 volt accessory power outlet. And I am guessing that what you are plugging in is a switching regulator type of power supply, (power adapter). If it is a "big truck" the lighter might be 24 volts, that could be a problem.
Very often switch-mode power supplies do have a high input current inrush if the load is already connected when they are first powered. So the plan would be to always have the receiver always disconnected when plugging in the adapter.
And one more suggestion is to check that the fuse is the correct size for that circuit. Many times a smaller size fuse will be installed because the correct size is not handy.