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04-03-2018, 01:40 PM
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#1
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Skoolie
Join Date: Feb 2018
Location: Tennessee
Posts: 171
Year: 2004
Coachwork: Thomas
Chassis: 40' Saf-T-Liner MVP ER
Engine: CAT 3126 7.2L
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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 20’ from the main distribution DC fuse panel. I’m wondering if due to the distance and amperage (possibly 4.2 amps at each outlet) if it’s 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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04-03-2018, 01:48 PM
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#2
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Mini-Skoolie
Join Date: Jun 2017
Location: Central Florida
Posts: 66
Year: 1999
Coachwork: Thomas Built
Chassis: Saf-T-Liner MVP
Engine: Cummins
Rated Cap: 84
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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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04-03-2018, 01:50 PM
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#3
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Skoolie
Join Date: Feb 2018
Location: Tennessee
Posts: 171
Year: 2004
Coachwork: Thomas
Chassis: 40' Saf-T-Liner MVP ER
Engine: CAT 3126 7.2L
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Yeah that’s what I figured
I’m 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 15-20’ from the fuse panel?
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04-03-2018, 02:11 PM
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#4
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Skoolie
Join Date: Feb 2018
Location: Tennessee
Posts: 171
Year: 2004
Coachwork: Thomas
Chassis: 40' Saf-T-Liner MVP ER
Engine: CAT 3126 7.2L
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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
That’s 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 it’s outputting 4-5 amps to two usb devices?
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04-03-2018, 02:12 PM
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#5
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Bus Crazy
Join Date: Feb 2017
Location: The West
Posts: 1,210
Year: 1998
Coachwork: MCI
Chassis: 102 EL3
Engine: DD 60
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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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04-03-2018, 02:16 PM
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#6
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Bus Crazy
Join Date: May 2016
Location: Grayson County, VA
Posts: 1,428
Year: 1996
Coachwork: Amtran
Chassis: International
Engine: DT466
Rated Cap: 65
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Quote:
Originally Posted by Mgulley82
Yeah that’s what I figured
I’m 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 15-20’ from the fuse panel?
Sent from my iPhone using Tapatalk
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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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04-03-2018, 02:16 PM
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#7
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Bus Crazy
Join Date: Feb 2017
Location: The West
Posts: 1,210
Year: 1998
Coachwork: MCI
Chassis: 102 EL3
Engine: DD 60
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Quote:
Originally Posted by Mgulley82
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 it’s outputting 4-5 amps to two usb devices?
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Remember that voltage is critical. An amp means nothing without the voltage.
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04-03-2018, 02:17 PM
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#8
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Skoolie
Join Date: Feb 2018
Location: Tennessee
Posts: 171
Year: 2004
Coachwork: Thomas
Chassis: 40' Saf-T-Liner MVP ER
Engine: CAT 3126 7.2L
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Quote:
Originally Posted by JDOnTheGo
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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Thanks so my math was correct that it’s minimal amperage on the actual 12VDC circuit
That’s 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 can’t ever really turn the inverter off completely.
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04-03-2018, 02:56 PM
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#9
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Bus Nut
Join Date: Dec 2017
Posts: 973
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Quote:
Originally Posted by Mgulley82
Yeah that’s what I figured
I’m 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 15-20’ from the fuse panel?
Sent from my iPhone using Tapatalk
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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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04-03-2018, 04:55 PM
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#10
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Bus Geek
Join Date: May 2014
Location: West Ohio
Posts: 3,709
Year: 1984
Coachwork: Bluebird
Chassis: International 1753
Engine: 6.9 International
Rated Cap: 65
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Quote:
Originally Posted by Drew Bru
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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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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04-03-2018, 04:56 PM
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#11
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Skoolie
Join Date: Feb 2018
Location: Tennessee
Posts: 171
Year: 2004
Coachwork: Thomas
Chassis: 40' Saf-T-Liner MVP ER
Engine: CAT 3126 7.2L
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Good news is this
I have TONS of 10 and 12 gauge wire from stripping the bus of all unnecessary light wiring
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04-03-2018, 05:02 PM
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#12
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Bus Crazy
Join Date: Nov 2015
Location: Billings, MT
Posts: 1,269
Year: 2003
Coachwork: Thomas
Chassis: HDX
Engine: Cat C7
Rated Cap: 84 passenger
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I purchased an insert with dual USB ports for the panel to the driver's left from SUPERBRIGHTLEDS. Fills in one (or more) of the holes that the school bus company left wide open (Brunhilde was a hangar queen for her last year with them.) Big plus: it's right above the distribution panels, so the wire run is minimal.
The only electrical have back in the bedroom is for the LED light strip. I will run 120VAC back there for my BiPAP machine, but not for additional lighting.
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04-03-2018, 06:42 PM
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#13
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Bus Crazy
Join Date: May 2016
Location: Grayson County, VA
Posts: 1,428
Year: 1996
Coachwork: Amtran
Chassis: International
Engine: DT466
Rated Cap: 65
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Quote:
Originally Posted by Booyah45828
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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Thanks for the heads up. I'll look into it again.
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