Installing USB port and volt meter display

Discussion in 'Wiring' started by sidneyhop, Jan 11, 2020.

  1. sidneyhop

    sidneyhop New Member

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    I want to install a USB port and a voltmeter display. Can I do this running off of the exterior light wires or should I run separate wires directly back to the inverter?
    Thanks
     
  2. Anthony Hitchings

    Anthony Hitchings Active Member

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    its better to give it a new branch circuit back to your 12V power source, and make the new circuit fused (use a self-indicating fuse). Then if it craps out its easy to diagnose and isolate.
     
  3. Grandpa Don

    Grandpa Don Active Member

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    I connected a cigarette lighter socket wires to the battery + and the battery - at the converter. Then I bought a small plugin off the Internet and plugged it in there. This device shows me the battery voltage at all times and gives me three USB ports to use and additional 12vdc sources.

    https://www.amazon.com/Upgraded-Cigarette-CHGeek-Voltmeter-Charger-Black/dp/B07WC3397Y/ref=sr_1_4?crid=NE9WLE4FPWB3&keywords=12+volt+adapter+plug+for+car+cigarette+lighter&qid=1578770132&sprefix=12+volt+adapter,aps,234&sr=8-4
     
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  4. bheff

    bheff Well-Known Member

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    Funny story about the self indicating fuses. This summer, everything worked on 120V but had trouble with just 12v. Looked everywhere. Started at the battery and worked backwards. First fuse a foot away from had a red light lit up. I figured that meant it was good to go...continued my search and quickly found I had no power. Worked backwards and finally pulled the fuse, it had power on both sides of the fuse holder. Then I Ohm'd the fuse and winner winner chicken dinner!
     
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  5. sidneyhop

    sidneyhop New Member

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    This is a dumb question, but what amp fuse should I use?
     
  6. tombiasi

    tombiasi Well-Known Member

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    What size is the smallest wire in your circuit?
     
  7. generok

    generok Well-Known Member

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    20190504_200804.jpg If it's a USB charging port, it's only going to draw like 3 amps max, right? I put one in my rig and I just tapped in to the nearest 12V source, which was the light for the bathroom. Works good, lasts a long time and I didn't need to fish wires all over the place. It came with an inline fuse IIRC.
     
  8. Grousetales

    Grousetales New Member

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    I installed a volt meter next to my door and just tapped into the yard light wiring that was inside the same cabinet. I put a push on/off switch next to it so I can turn it off when not needed. It's not a USB charger, but same concept for wiring. The draw is low so I didn't run a separate fuse or circuit. It's fused off the same circuit as the yard light. On a side note, this works really well for quickly checking the voltage of the battery occasionally when parked at home. It also makes a nice night light near the door. I plan to add a USB charger nearby. 2017-04-09 19.11.13.jpg
     
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  9. Grandpa Don

    Grandpa Don Active Member

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    There are several things to consider. What are you trying to protect, and what size (gauge) wire is in the circuit?
     
  10. Anthony Hitchings

    Anthony Hitchings Active Member

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    its not so much about protecting wiring as having the rest of the circuit still work. Lets say I tap the USB into the lights - but the USB item starts smoking because its got a problem but its on an incandescent trailer light circuit - so the fuse is maybe 10A and not blowing (yet). I would need to pull the fuse - which also disables the lights. In order to restore the lights I would have to dig around the USB tap-in and cut or or open it up - bit of a nuisance. Having a fuse on each branch makes trouble shooting and control much better.
     
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  11. tombiasi

    tombiasi Well-Known Member

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    If you fuse the USB appropriately the 10 amp. fuse won't blow.
     
  12. Wrenchgear

    Wrenchgear Near Elmira, Southern Ontario

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    I put a momentary push button switch on mine so that its not lit up the whole camping trip. There's no need for it to be on all the time, and I don't need it acting as a nightlight all night long. I just tapped into whatever wiring was behind it there, I might have used the gas detector wiring there, I can't remember, it's been too long since I wired it up.

    My Voltmeter #2.JPG

    My Voltmeter #3.JPG
     
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  13. NavarWynn

    NavarWynn Member

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    IDK, I think it depends on your planned capacity, and access points. As others have pointed out, both are such low draw that they could draw off the light circuit, without likely problems. If you are planning a significant draw, like say 6x 5v/3.0A (which is our plan) - max of 6x5x3/0.8 = 112W /12v= (9.375A) => 10A draw @12v => 15A fuse , then you should DEFINITELY put it on a separate circuit. If, OTOH, all you want is 1/2x 2.1A (5V) (as generok has done), you have about a 2A (12v) draw, which could piggyback on virtually any circuit without a problem. Of course our planned infrastructure is to support 4 kids and two adults, with 8+ devices peak. With 1/2 adults OTOH, the demand is a fraction of that, and so something like generoks setup would likely be ideal. I would say your planning totally depends on your projected power demand (at peak).
     
  14. davido

    davido Active Member

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    Just one little piece of advice.... well, really one observation:

    Cigarette lighter / auxiliary 12v power outlets have been around in essentially their current form factor since about 1960, or a little before. They continue to find their way into vehicles, and can easily be added to RVs. There are countless accessories designed to be used with them. One class of accessory is USB chargers, which come in the USB-A and USB-C form factors.

    USB-A ports that provided sufficient power to charge a basic cell phone in the late 2000s will be underpowered for charging modern cell phones and tablets. There have been several updates to how much power can be delivered through USB-A, and there are often compatibility issues to deal with for optimal charging rates. USB-C has also emerged as a newer standard that is finding its way into modern smartphones, higher-end tablets, and many modern laptops.

    The crux of it is that a 12v port installed in 1960 will still be viable for power delivery to a 12v to USB adapter in 2020. But a USB port installed as recently as two or three years ago may not provide the correct power output to optimally charge your current set of devices. And if your devices use USB-C, you need an adapter to charge with USB-A... and then you're still going to be getting a lower-speed charge.

    I installed dual-USB charging ports in my trailer a few years ago. The dual-port module provides one 1.0A and one 2.1A outlet. But it's been several years since those output levels were well suited to a phone I own. My previous phone would have been better with a more modern IQ charging device, and more recently both my laptop and my smart phone charge from USB-C, which is *not* one of the ports on my installed module.

    If I were doing it over again (which I certainly will be this year) I would just put 12V plugs in, and buy whatever 12v to USB adapters are most appropriate for my devices. Leaving a USB adapter plugged into a 12v plug is really no less svelte than having a USB module installed permanently, and yet it's a more flexible and easier to upgrade option.
     
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  15. roybraddy

    roybraddy Well-Known Member

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    One of my secondary reasons for getting a VOLTMETER installed was to use it as a nite light as well... Didn't work out as it was way too bright haha I had to install an ON/OFF switch for it...

    Roy Ken
     
  16. sidneyhop

    sidneyhop New Member

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    Thanks for everyones input. Versatility is optimal IMO. Even just having the single, separate fused wire to tap whatever comes down the pike into down the road.
     
  17. davekro

    davekro Active Member

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    A while back I purchased a small panel with 12v display, cig. lighter, USB & an on/off switch. I 'was' going to mount it in the cabinet wall near the converter (is also near the bed we sleep in). But now I see mounting it in the cabinet next to the door is much better for our needs because 1) the great idea that it can be a night light for the door -AND- that cabinet top is a better place for phones, etc. to be placed while charging than the dinette seat (table is outside) above the other location. 2) Quick easy voltage check & easier access for turning on/off (and not forgetting to turn it off!) the 12v indicator being LED should not draw any significant voltage over a 3 day trip, so OK to easily leave on all night (or even 24 hrs?) right?
    Thanks guys.
     
  18. Anthony Hitchings

    Anthony Hitchings Active Member

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    I installed two switched USB/12V outlets - one either end of the "kitchen" cabinets. Both have voltmeters.

    The cheapo voltmeters included are within 0.2V, maybe better. But not of the same quality control on voltage level readings as a good DVM (VOM)
     
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  19. CampingFamily1

    CampingFamily1 Active Member

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    Here's a link to a thread on my USB Charger/Voltmeter setup
     
  20. NavarWynn

    NavarWynn Member

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    Another benefit to wiring and using 12v accessory sockets wired into a separate circuit (cause, let's be real here, you are NOT going to tap off the light circuit for a couple of 12v accessory sockets) is that when your 12V USB 2+ high-power-output charger with a built in voltmeter dies an inglorious death, it's utter simplicity to replace. IME, these guys die on a regular basis. Either their power output dies to a trickle, or you get nothing (I've had both happen numerous times). Usually there is no fire or smoke involved. Still not a fan of leaving them plugged in / powered up (even in 'standby') while unattended, because 'usually' is NOT 'never'...
     

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