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Discussion Starter · #1 · (Edited)
I have a 2020 tundra. Looking in the fuse box I see my towing related fuses are all 30amp. Does this mean my trailer will have 30amps available to use when connected to my truck with the 7 pin connector and with ignition on?

if not how many amps should I expect from my tundra?

From what I have gathered it is not typical to have that many amps available using a 7 pin connector in general for most vehicles.

Looking to install DC to DC charger in my camper and want to size it right
 

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IIRC, the 30 amp fuses are for three reasons: first, the electric brake system can consume a lot of juice with three brake axles and sustained downhill braking or a panic stop. Second is trailer marker, brake, and backup lighting. Big trailers can have lots of bulbs that consume electricity - rarely 30 amps worth, but better more than enough than not. Third is the auxiliary power system for charging trailer batteries while in motion - both the breakaway switch battery and auxiliary batteries on camp trailers and such - and for temporary trailer lighting (like interior lights on an enclosed cargo trailer while inspecting cargo at a stop).

It is important to note, however, that the auxiliary power circuit is a keyed circuit, meaning it only works when the tow vehicle is switched to on. This protects the tow vehicle battery from being drained over night if you leave the lights on inside the trailer, or from a bad battery on the trailer. If you plan on any sort of power draw in the trailer, it is always advised to install an stand alone power/battery system on the trailer itself and to not rely on the tow vehicles electrical system.
 

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Discussion Starter · #3 ·
Can I expect to have 30amps of usable 12v power to charge my trailer batteries while driving down the road?

thanks!
 

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UP TO 30 amps... not a constant 30 amp push, if that makes sense. The alternator regulates amperage push to the batteries; when the truck is running, your vehicle doesn’t run on the battery - all of the electrical parts and accessories get power coming directly from the 14.4v alternator rather than the 12vcar battery. The battery just makes a reserve and, of course, the ability to crank over the engine.
Anyways, your trailer battery won’t pull as much current if it is close to fully charged.
 

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Discussion Starter · #6 ·
Thanks for the replies. I’ll probably get around lesser amp charger to install on my trailer.
 
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