I hope this does not come under the Automotive Guidelines.

I want to plug a device into a cigarette lighter socket / automotive accessory socket. Using a 12V (nom.) car and the device is rated from 10V - 18V and it draws at most 3 amps. It's a battery charger for LiPo batteries.

I already have a connector for the socket, with a built in 15A fuse. However, the battery voltage is barely a fixed 11V - 14.4V. It can have high voltage spikes on it and brief undervoltage moments. Both of these would potentially damage or interrupt the device. So I want to protect against them.

What are my options?

I was thinking of a TVS device rated at 16V with a pi filter to reduce ripple and another TVS on the output. The capacitors would be sized for a 50ms dead time, providing sufficient power to the charger during brief under voltage. A 5A auto fuse would also be used and an LED might be used to indicate power.

 

Hello,
Yes, you are right. a TVS at input and LC filter would do. You don"t need a TVS at output, since output capacitor sees a inductor to charge. Be sure about the energy of the pulses that you are expecting at line. Also a reverse polarity protection, otherwise TVS would blow!