Geoff,
The X6100 has well documented overheating issues, and many have concluded that reducing the power supply to 9 volts, give or take, is the best strategy. I have operated mine as a mobile rig and have encountered several overheating lockups at 13.8V. Keep in mind the guidance to turn charging off. Still, mine will get stuck in transmit mode until I take it apart and disconnect the battery. It happened again last week. I operate 5W CW exclusively, so I am definitely not overdriving it.?
This rig operates natively from a pair of 3.7V cells, so it appears 8-9V will be more than adequate. Others have taken temperature and current measurements that confirm the 9V figure. Any additional voltage will merely generate heat.
I am prepping a buck/boost board to limit the power in the car. For now, my QCX20 is the mobile rig until I get an enclosure and associated wiring done for the board.?
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73 de K9NUD
K9NUD-Steve