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Old 04-03-2018, 01:40 PM   #1
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12v or 120v USB outlets

Someone help me with understanding this

I want to install USB ports next to each bed (for phone/tablet charging) and also in the living area for the same reasons.

Now I can purchase 12VDC ports for a boat or car and install those. They have 2x 2.1 amp USB ports.

My other option is to just install some USB/120 volt outlets. They also have 2x 2.1 amp USB ports.

The farthest ports are about 20í from the main distribution DC fuse panel. Iím wondering if due to the distance and amperage (possibly 4.2 amps at each outlet) if itís just wiser to incorporate the USB outlets into my AC circuits for each area?

Only reason I was considering it was to reduce DC to AC conversion loss just to convert it again to DC.




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Old 04-03-2018, 01:48 PM   #2
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I am planning on keeping as much DC as possible because of conversion loss. I think the inverter is only 80%??? efficient, or something like that.
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Old 04-03-2018, 01:50 PM   #3
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Yeah thatís what I figured

Iím running a AIMs 2000 watt pure sine wave inverter

It just seems like such a waste converting 12VDC to 120 vac then to 5vdc for the USB port


I wonder what gauge wire I need to safely run 12 vdc to a USB port about 15-20í from the fuse panel?


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Old 04-03-2018, 02:11 PM   #4
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Someone smarter than me help me out with this electrical math

So a two port usb can put out a maximum of 4.5-5 amps at 5vdc output

Thatís about 25 Watts


25 Watts on the 12 vdc circuit is only 2 amps?

So if a dual port usb is hooked up directly to a 12 vdc circuit is it only putting about 2-3 amps of load on the circuit even though itís outputting 4-5 amps to two usb devices?


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Old 04-03-2018, 02:12 PM   #5
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If always connected to shore power, it doesn't really matter. If you plan to be boondocking and running your inverter as little as possible, go 12 VDC.

Many of the 12 VDC USB converters have two sockets, a 2.1 and 1.1 amp (@ 5 VDC). Assuming that's the direction you're going. You'll be pulling something under 2 amps @ 12 VDC when maxed out. Lots of voltage drop charts online but 16 GA keeps you under 3% voltage drop for a 20' distance. 18GA is only 4% drop.
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Old 04-03-2018, 02:16 PM   #6
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Quote:
Originally Posted by Mgulley82 View Post
Yeah thatís what I figured

Iím running a AIMs 2000 watt pure sine wave inverter

It just seems like such a waste converting 12VDC to 120 vac then to 5vdc for the USB port


I wonder what gauge wire I need to safely run 12 vdc to a USB port about 15-20í from the fuse panel?


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I'm running the same inverter. I ran 14ga speaker wire to my USB charger and LED strip lights. That's probably overkill, since the leads on both the lights and charging station look to be about 20ga.

Blue Sea has a nice quick reference chart on their site. I believe there's also a calculator for more detailed information.
https://www.bluesea.com/resources/1437
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Old 04-03-2018, 02:16 PM   #7
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So if a dual port usb is hooked up directly to a 12 vdc circuit is it only putting about 2-3 amps of load on the circuit even though itís outputting 4-5 amps to two usb devices?
Remember that voltage is critical. An amp means nothing without the voltage.
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Old 04-03-2018, 02:17 PM   #8
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If always connected to shore power, it doesn't really matter. If you plan to be boondocking and running your inverter as little as possible, go 12 VDC.

Many of the 12 VDC USB converters have two sockets, a 2.1 and 1.1 amp (@ 5 VDC). Assuming that's the direction you're going. You'll be pulling something under 2 amps @ 12 VDC when maxed out. Lots of voltage drop charts online but 16 GA keeps you under 3% voltage drop for a 20' distance. 18GA is only 4% drop.




Thanks so my math was correct that itís minimal amperage on the actual 12VDC circuit

Thatís good

We will be off and on shore power depending on where we go.

Biggest thing is we are powering a small 120v refrigerator off the inverter.

So I canít ever really turn the inverter off completely.


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Old 04-03-2018, 02:56 PM   #9
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Quote:
Originally Posted by Mgulley82 View Post
Yeah thatís what I figured

Iím running a AIMs 2000 watt pure sine wave inverter

It just seems like such a waste converting 12VDC to 120 vac then to 5vdc for the USB port


I wonder what gauge wire I need to safely run 12 vdc to a USB port about 15-20í from the fuse panel?


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Stay with the DCV system; run 14gage wire...should be fine...and avoids conversion steps...as they say...eliminate the middle man

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Old 04-03-2018, 04:55 PM   #10
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Quote:
Originally Posted by Drew Bru View Post
I'm running the same inverter. I ran 14ga speaker wire to my USB charger and LED strip lights. That's probably overkill, since the leads on both the lights and charging station look to be about 20ga.

Blue Sea has a nice quick reference chart on their site. I believe there's also a calculator for more detailed information.
https://www.bluesea.com/resources/1437
I'm not really sure how I feel about this.

Speaker wire insulation isn't rated for any kind of heat or voltage capacity. I don't think it's actually supposed to be used to carry any kind of current or electricity, it's mainly just to power speakers. I'm not sure how much power you're running through it, but I'd definitely look into it and whether or not what you're doing is a good idea.
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