The Shack – The Back Room – The Antenna Farm – 12V Power Distribution
Last Updated on 1/27/2026
My 12V power distribution has undergone plenty of changes over the years. Most of what I’ve done was inspired by the overlanding and van life communities in 2020 and 2021 when my wife and I needed to travel from Virginia to California (and back) while much of the United States was locked-down. My first step included installing a refrigerator since many restaurants were closed and we needed to carry our own food. The project eventually grew to support my ham radio endeavors, which can sometimes be remote enough that bringing a microwave oven is handy! This photo alone should hint that I’ve gone over the top for a passenger car setup, especially in a small car like the GTI.
My first step was to run a 4-gauge oxygen-free cable (OFC) from the starter battery, through a 70-amp circuit breaker, and to a 200-amp relay that’s beneath the rear seat delete door on the driver’s side. The relay is triggered by a voltage controlled switch, known as the APO3. The relay passes power so long as its supply voltage is above 13.1V; basically any time the engine is running and for about twenty minutes after shutdown. The APO3 assures good battery health and no dead battery surprises (been there, done that). From the relay, alternator voltage travels to a trailer lighting module and a DC-DC charger for my auxiliary battery.
An auxiliary battery? Yes! I knew that I wanted more battery power when I started traveling with a refrigerator/freezer and operating my ham radios more frequently. I started with a 100-Ah Lithium Iron Phosphate (LiFePo4) battery in 2021, then switched the larger 314Ah LiFePo4 battery shown here in 2026. I charge the battery at up to 50 amps (700W) with an Orion-XS 12|12-50A DC-DC charger. A 314Ah/4kWh battery can power my transceivers at high power for hours on end; or it can run the refrigerator/freezer for about 5-7 days depending on weather. The battery also powers a 3000-watt voltage inverter (self-limited to 2000W in my application), cellular signal booster, 20V power supply, beam antenna rotator, amplifiers, some 12V outlets, and even the car’s OEM infotainment system. The starter battery is almost completely unburdened when the car is parked.
I think the 20V power supply requires some explanation: I use an Orion Tr Smart 12|24-15 DC-DC charger to supply 20V to key equipment in my setup. VHF contest rovers often employ beam antenna rotators in their stations. The vast majority of rotators operate with 115VAC household power. It’s easy to install a 12V inverter that’ll power a rotator; however, most inverters generate radio frequency interference (RFI) of some sort on at least one amateur radio band. Using Green Heron’s RT-21DC, which accepts between 13.8-24VDC, is a cleaner solution. My rotator motor drives with 20VDC. Not only is 20V perfect for my rotator setup, it also powers my laptop without the need for RF-noisy 12V adapters.
I find myself needing to charge the aux battery at home from time to time, either to support heavy weekend operations or because I’m balancing the cells. I eventually installed a NOCO GCP1E to provide a clean way to get household power into the car. I mounted mine onto my existing antenna cable pass-thru in the drivers side rear window. Once inside, household power routes to the basement under my refrigerator where it powers a Blue Smart IP67 Charger by Victron Energy. See more photos in the album at the bottom of this page.
As you can imagine, having all of this equipment in such a tight space can trap a lot of heat! I’ve never had a component overheat, but I still decided to add ventilation when I opted to make my “rear seat delete” a permanent change. This “delete” article describes how I implemented the ventilation and its basic function. In short, I have six 3-inch Noctua fans that can force air through the equipment space at my discretion. The fans have proven to be very effective at holding the equipment space at 110°F/43°C on even the hottest days.
I have a combination of fuses, circuit breakers, and cut-out switches that allow me to isolate faults or completely secure power from any voltage source. All component ground leads are tied to a copper grounding bar that is connected to a seat belt anchor point by 2/0-gauge OFC. I removed my ANL fuse holders since their covers were prone to vibrating loose and replaced them with marine rated battery fuse (MRBF) blocks by Blue Sea Systems. MRBFs are compact and more responsive than ANLs, especially when considering their power handling capabilities! Their only drawback is a lack of retail availability; so, I carry plenty of spares.
This 12-volt wiring system is overkill for my application, but it should never be the weak link in my setup. Read more about my communications system to see the bulk of what this supports. See a video about my distribution system here (old setup; new video coming soon) and a write-up about the battery here.
More Complex Than Required,
Scott
