Forum Discussion

wopachop's avatar
wopachop
Explorer
Aug 03, 2021

Talk about voltage drop (12v)

Have the trailer in boondocking mode. Some old batteries and 150w of solar. The batteries are showing 13v. I have a little 300w inverter to charge my laptop and things. 14 gauge wire is feeding the little inverter and the USB panel.

Doesnt that seem weird its dropping below 12v and only pulling 3amps?



  • I'm seeing voltage drop along the wire correct? Not battery sag? The test is during the day with solar hooked up. Only drawing 3amps.

    Why dont I see similar voltage drop while on shore power? Pretend the Led display read 14v. When I apply the same 3a load why doesnt the display show 12-13 volts?

    I understand that higher voltage sags less. But we are only talking the difference of 12v boondocking to 14v on shore power.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    300 watts is about 30 amps at the battery 14GA is good for half that at 120 volt and even less at 12 volt due to voltage drop.

    Plus there is a voltage drop INTERNAL to the batteries (I do not know how much)

    The key to battery/inverter is three fold
    One, Keep the leads as short as you can but do not mount the inverter inside the same space as the batteries

    Two HEAVY cable for a 300 watt Starter cable works very well and is low cost up to around 750 watts it works well. long about 1000 it might be a bit...er.. anemic

    3: for as much of the run tape or wire loom the cables like this ============
    Side by side. This is more important on larger inverters.

    AND MORE battery never hurts..

    DEEP CYCLE batteries work best for House use.
    (As opposed to MARINE/deep cycle) note how I use case on those)
  • #10 wire would be much better. I would expect 7.5% voltage drop with 15 feet of #14 and the loads.
  • The meter and LEDs add to the load. There is losses within the unit that draws power.
  • #14 and 300 watts... is that the fuse? Or is that by design so the inverter will drop out before the fire ensues?
  • What brand is that panel meter ?

    Some inexpensive meters are known to be off by 10%.
  • Should mention the circuit is roughly 15 feet long and i believe 14 gauge wire feeds it. I tapped in and added another couple feet of 14 gauge wire up to the USB panel.

    Its been a couple years but im pretty sure im on a dedicated circuit. I might have tapped into the electric awning. Point being i dont think there is any other load besides the 3amps.

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