So i have a 7 bulb led flashlight that runs on 3 -3.7 volt 26650 batteries. I attempted to remove the head of the flashlight and wire it through a pvc tube to place the battery tube (powersource) further away. About 3.5 ft away from the flashlight head. I used thick 12 guage wire and it appears i fried the circuit board. Any ideas on what i did wrong and how to correctly determine the proper wire size needed?

 

 

there are many things to pay attention in this movie

• good scene lighting
• good scene selection camera work
• good picture quality
• . . . ok
• he uses quite a thick wire (drains off a lot heat from iron) still he manages a quick preparation of wire ends -- likely due right solder and paste and heat applied (notice the guy pre heats stuff to get them best temperature for following operations)
• he cleans off old solder and prepares contacts before making a permanent connections
• he does not keep contacts heated up for long periods (also solders by heating diode side ((with higher temperature tolerance)) not electrolythic cap side ((with lower one)) )

 

Any ideas on what i did wrong

Obviously you wired something wrong. Without pictures of your handy work, how can we tell you more??

how to correctly determine the proper wire size needed?

Determine the maximum current required and consult a wire gauge table that includes current carrying capacity. Power transmission rating would be ultra conservative; you can use the chassis wiring ratings.