Installing 12v USB outlets

[JackP]

I've decided to install two 12v USB outlets to our '72 Overlander. I have available slots in my DC distribution box and will run new wiring from the outlets to the DC distribution box.

My question is, should I run the ground all the way back to the ground bus on the DC distribution box or ground the outlet to the chassis near the installation location of the USB outlets?

Thanks.

Jack

[Wayne&Sam]

I pulled the power for mine off a reading light. They are low draw so I think you can ground them anywhere that's easy.

[Tincampers]

Ground is ground, I'd pick the closest or easiest place. Which plugs are you going to use?

[Wayne&Sam]

I find that the adapters die fairly often, so I put in 12v cigarette jacks and plug in usb adapters. It makes it easier to change when the die.

[HowieE]

I have never heard of grounding a 12 circuit. The return path, equal to the neutral on an AC circuit, of a 12 volt circuit is the chassis.

I would just pickup any close by 12 Supply. The current you are looking at is nothing and can be added to any circuit.

[Wayne&Sam]

Originally Posted by HowieE

I have never heard of grounding a 12 circuit. The return path, equal to the neutral on an AC circuit, of a 12 volt circuit is the chassis.

Well if you mount a device in wooden cabinetry you need to get a ground somewhere.

[TG Twinkie]

The negative side of the DC circuit(s) in an RV has been labelled incorrectly for years. It comes from the auto industry.
The proper term for this side of the circuit(s) is "COMMON". Since it is common to all or most 12 volt devices. Rarely is it switched. In most cases the return path is completed by using the vehicle chassis.

[martin300662]

Be sure you actually need USB outlets before going to the effort.

True USB only has +5v, but many devices that plug into cigarette lighter outlets need +12v input so although they may have a micro/mini USB plug on their cigarette lighter adapters, the adapter is not stepping down to 5v.

I have at least 2 devices that have mini USB inputs, but it is 12v that is being delivered on the mini USB live pin from their adapter, and they simply don't charge/run using a true USB outlet/separate mini USB cable, as the voltage is not correct for them.

[Pahaska]

You will find 12v pairs in all sorts of places in an Airstream. Just look for a colored/white pair of wires and tap in using crimp connectors. The white wire is the negative or common wire. The draw of a USB outlet is so small that you can safely add one to any circuit.

Most 12v add-ins will have a colored and a black wire. The black wire attachesto the white wire of the trailer. I have added 4 cigarette-lighter-type outlets in my trailer so that I can use my fan pretty much anywhere without tripping over wires. One outlet is patched in to the wire feeds to the wardrobe light which was easy to access and one is under the microwave cabinet. I also added a 12v outlet in my exterior refrigerator compartment so that I can use my 12v compresor outside.

[John Geisen]

You can now purchase 110V outlets that have two USB ports on the faceplate. Why not consider doing something like that. Clean easy installation. Simply replace your outlet. Just a thought unless I've missed something.

[cazual6]

Originally Posted by mrprez

Ground is ground, I'd pick the closest or easiest place. Which plugs are you going to use?

Not to be mean or technical here, but don't say ground is ground beyond this discussion.

Ground is not ground, there can be a potential difference in ground, that is why it is always best, to ground all the same spot especially for highly technical devices.

[lewster]

Many DC electrical problems can often be traced to ' a bad ground' or negative lead, which is an essential part of any 12 VDC circuit.

For this reason, I rarely (if ever) use the chassis or frame for a negative (ground) connection in a DC circuit, preferring to 'home run' all of my DC cables to a single point ( bus bar, binding post or terminal block) for both positive and negative cables.

Far easier to troubleshoot if there ever is a problem and provides a single place to look for them.


Lew Farber
RVIA/RVDA Nationally Certified Master Tech
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Master Tech Energy Systems, Inc.
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541-490-6357

[vito98103]

USB is 5 volts DC - not 12.

[Pahaska]

Originally Posted by vito98103

USB is 5 volts DC - not 12.

Yes, but USP outlets for Rvs hook to 12v and reduce the voltage internally to 4v.

[Tincampers]

Originally Posted by cazual6

Not to be mean or technical here, but don't say ground is ground beyond this discussion.

Ground is not ground, there can be a potential difference in ground, that is why it is always best, to ground all the same spot especially for highly technical devices.

You are right. In this application, I would also run a pair of wires to any device I was installing a tie into a common point such as bus bars.

[Wayne&Sam]

I hope someone from England chimes in using the term "earth" just to add to the semantics discussion.

[Burnside Bob]

FWIW, I did extensive rewiring in our 2009 FC. From this I can tell you that Airstream direct wires all 12V DC devices back to the ground bus. They also install a ground post on each major section of the body to which they run a 10 gauge 12V ground wire (white insulation).

So I would follow Lewster's advice above and ground thru wiring. Yes, the frame and its sub components are grounded but Airstream, over the years, has found it cheaper, in fielding customer warranty claims, to invest in ground wires instead of relying on chassis grounds.

[rmatkovich]

Originally Posted by JackP

I've decided to install two 12v USB outlets to our '72 Overlander. I have available slots in my DC distribution box and will run new wiring from the outlets to the DC distribution box.

My question is, should I run the ground all the way back to the ground bus on the DC distribution box or ground the outlet to the chassis near the installation location of the USB outlets?

Thanks.

Jack

All grounds go the the chassis so U can do the same and or the body.

[Trnpk Crsr]

[QUOTE=John Geisen;1801223]You can now purchase 110V outlets that have two USB ports on the faceplate. Why not consider doing something like that. Clean easy installation. Simply replace your outlet. Just a thought unless I've missed something.[/QUOT

USB ports that are part of AC outlets convert the AC to DC to power the USB ports. This is ok when hooked up to shore power. But if you are not on shore power, it is a very inefficient use of your inverter. Using 12 volts DC that is reduced to 5 volts DC is a much more efficient use of power.

[gator.bigfoot]

Originally Posted by cazual6

Not to be mean or technical here, but don't say ground is ground beyond this discussion.

Ground is not ground, there can be a potential difference in ground, that is why it is always best, to ground all the same spot especially for highly technical devices.

Never assume ground is ground. I'm glad others see the value of actually running a complete circuit. I get even more anal by insisting upon a star configuration for ground and only with stranded wire.

I spent years trying to teach people this. It gets even more fun when you see 4000 volt spikes between ground and common. Good thing trailers only have 12 volts.

The value of good electrical practices should never be under estimated.