How to power up yard art with auto headlamps

atwosheds · Sep 10, 2021

Years ago, I cut off the front end of my 1970 Pontiac Catalina before I drove it to the junkyard. I created a bracket and mounted it to my garage wall and successfully hooked up the four headlights and side marker lamps to a power supply that converted my 110 household AC current to the 12 volt DC that the bulbs required. It was a total success. (see picture below) However, this year I moved into a new home and I am converting my masterpiece into yard art. I have created a small outdoor bar (see picture below) with a roof which is far away from any household circuit and I would now like to power the auto car lights from a battery with the intention of adding a trickle solar panel charge to it making it completely off-the-grid. I purchased an ExpertPower SLA battery (12v 7Ah/20 HR) and hooked it into the car wiring. All of the lights lit up just fine but I quickly noticed one problem. When I touched some of the wiring it was quite hot. I quickly disconnected the circuit. After a little research, I realized my wiring was way undersized. The skinny 18 gauge wiring was just fine with the converter. It seems I should replace all of the wiring with 10 gauge and add fuses to each device. The four lamps are 60 watt each and I guess the two side lamps are 3-5 watts each. My question is will the thicker wiring by itself solve my overheating problem? Do I need a smaller battery, and if so, what specification? Or do I need an additional device to dial down the power to the lamps? I do not want to convert the lamps to LED. I am desiring to keep the lamps authentic. Thanks for any help.

Pontiac Front End formerly mounted on garage wall using a 12v power converter:

[ElectriciansForums.net] How to power up yard art with auto headlamps

Outside project (work in progress):

pc1966 · Sep 10, 2021

The problem is the cables to the lights need to be thicker. Each 60W lamp will take 5A at 12V, though you could possibly get LED replacements if you don't mind the change in light colour and modern nature of it.

If you used 18 AWG for each light (so 4 wires in parallel all back to the battery) then it would be fine. But for any that carry the full 20A load you would need something like #12 or #10 gauge.

On the charger supply side at from 120V (and assuming perfect conversion efficiency) it would be only 2A, though in practice you would be looking at closer to 3A and possibly a bit more if also charging as well as running the lamps.

A final consideration is voltage drop - that has a big effect on brightness for filament lamps and is really significant when you are down at 12V automotive applications. That is dependent also on the length of the conductor, so if you have a long run on the 12V side (for example to keep voltages safe and low outside) you may have to go up a couple of sizes to keep a sensible voltage at the lamps.

telectrix · Sep 10, 2021

your 18g wire was OK on the 240V side as the current is low at tha t voltage.once yougo down to 12V, the currentis 20x as much for the same power requirement. i.e at 12V a 60 watt lamp will pull 5A as opposed to 0.25A at 240V (ohm's law).
like the art btw.