Wiring 12v to truck bed

[mtnbike28]

I want to run 12v to my truck's (02 Tacoma) bed for my cooler (cheap Coleman one) - My plan:

1. 10 gauge wire direct to battery with 30 amp fuse at the battery
2. run wire into cab for 0n/off switch - this needs a short ground wire
3. continue 10 gauge wire to rear of truck and attach 12v outdoor connection with another 25 amp in line fuse and short ground wire

Questions- 1. is the 30/25 amp fuse too much? I would rather blow a fuse than melt something. How do I determine the needs of the cooler? I also have a invertor that may once in a while be used there.
2. Is 10 guage too big? what is the draw back to bigger wire?
3. Should I bother with the switch and instead just unplug the fridge whenever leaving the truck more than 30 mins?

thanks

Jay

 

[Bob_Garrett]

I wouldn't go any smaller than 10 gauge. It will keep your voltage loss to a minimum. 10 gauge can handle up to 50 amps, so a 25-30 amp fuse should be ok. One fuse at the battery is all you need.

The Coleman is probably a thermoelectric cooler. Typical current draw is around 4-5 amps. Depending on the amp-hour rating of your battery, you should be able to run it for 2-4 hours and still have sufficient reserve for starting. You can get low voltage cutoff relays for $20-30, that will shut off when battery voltage drops below a preset level (high enough to allow the vehicle to start). It's a good setup for occasional use, however standard starting batteries tend to not like frequent deep discharging.

I would also install a relay in the circuit and use the switch to control the relay. That way you avoid having to route 10 gauge into the cab (relay requires minimal current allowing use of smaller wire) and the switch only needs to handle the relay current instead of the full circuit load.