Hi Paul,
I needed to get the 4S 5Ah LIPO batteries I had down to 13.8v at up to 5 Amps to power my Xiegu X108G rig.
After trying several buck-boost converters - inverters that reduce the voltage efficiently - I got RF interference again and again. So that was not a good idea! I am told there are some of these units who don’t wipe out 20m or 40m with hash, I never managed to find one though.
My next option was to use high current diodes (6 of them if I remember correctly) in both the plus and minus leads of my 4S 16.4v charged LIPO battery. The diodes each drop a fraction of a volt. This solution actually worked fine, and I used it for several months however it did have one small problem. The diodes get VERY hot. So hot that on one activation the solder between two of the diodes actually melted! The diodes and battery were fine just this “automatic fuse” took me off the air. I didn’t give up though and rather than soldering the diodes together I then mounted them in high current terminal block. This solution then worked fine for several more months until I decided to change it.
Of course all that heat was energy from the battery being wasted and not an ideal solution as I had to be careful not to leave something on top of the diodes in the battery box.
My current solution is to go back to how one would approach this in a normal radio circuit using a LM338 5A adjustable voltage regulator semiconductor mounted on a small heatsink and with resistors to give the required output voltage. This circuit does not get hot at all and creates no RF interference.
I basically went with this circuit but substituted a fixed resistor for the variable.
73 Ed.