Which wire is negative on usb car charger?

[sifan]

I bought this usb car charger from Amazon nine months ago: https://www.amazon.com/gp/product/B00HHT9FL2/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Now the plug kept popping out of the cigarette lighter socket; I had to push it hard and hold it in order to make full contact. I twisted open one end of the plug hoping to fix the contact. When I put it back, the plug no longer makes contact even I push it hard into the socket.

I plan to use the following replacement cigarette lighter plug from Amazon which has two wires clearly marked negative and positive: https://www.amazon.com/gp/product/B0016L...=A2GCYGV3A67LXH

However, the original plug has two black wires (see the picture on the first web link) and I can not tell which one is negative. Could someone help me how to distinguish which is the negative wire because I don't want to make a mistake here and short out my charger?

Thanks.

 

[Vikas]

 

[Vikas]

I am assuming you have a multi-meter to check the connectivity. You need to trace the wire coming from the shiny silver inner shells of the two port charger that you have. That will be negative.

 

[supton]

First, you won't short out the charger; you'll just apply reverse voltage and possibly (probably) smoke it. No shorts involved.

Secondly, very often the neg wire will have a raised line on it.

Third, failing that, very carefully cut just one wire. Strip back the end of that wire on the charger side. Install the plug, and then find a metal item in the car to short the now stripped charger side wire. If the charger comes alive, then you've found the neg wire. If not, then you've found the hot wire. Regardless, label the wire (on the charger side!) and snip the remaining wire.

Fourth, you could always break apart the faulty cig cord. Usually they come apart; if not, a small sledge will solve that, with some a hit or two on a seam. Once apart you should be able to trace out the wires. Ring is GND, tip (or center) is hot.

 

[Kamele0N]

google usb wiring...and click on pictures

 

[supton]

Err, I see now that it's not working. So ignore suggestion #3.

 

[sifan]

I have have a multi-meter. Lets say I cut the plug off the usb charger. To find the negative wire I put the red probe on one wire and black on the other. If there is current flowing, then the wire corresponding to the black probe is negative; otherwise, the other wire is the negative. Am I right?

Thanks.

 

[supton]

Not really.

Do this: set the meter to the continuity range, the one where it beeps at you when you short the leads together. If it doesn't do that, look for the ohm range, and select the lowest one. In this range, shorting the leads together will read something less than 2 on the display (may be as low as 0).

now, cut just one wire on the cord. Strip back the wire on the plug side. Hold one lead onto that wire. Put the lead onto the GND (or outer) contact of the plug. If it goes to zero, then you know you cut the negative wire. Double check on the tip. Or if failed to read zero, then go to the tip.

At this point you should know which wire you snipped. Label the wire on the charger side, then snip the other.

Edit: it won't matter which lead you use, red or black, not in this continuity (or ohm) range. Also, don't plug the plug into the cig lighter.

 

[HerrStig]

Cut and strip the woies from the plug. With the meter on ohms see which wire is connected to the tip of th eplug. That's +

 

[sifan]

As I cut both wires (one wire at a time), the other ends of both wires from the plug end also fell out. The negative wire's soldering was not attached to the metal piece. Is the negative wire supposed to be soldered to the metal piece in the first place? Anyway I was able to tell which wire was the negative. Thanks to all.

 

[supton]

Good for you.

Likely it was crimped, which is a completely acceptable method of attaching wires--presuming it was properly crimped. Sounds in this case that it wasn't (or something pulled very hard on the wire).

 

[sifan]

I think I broke the soldered connections on both + and - wires inside the plug as I twisted it open. The original plug is really cheaply made. I just ordered a different replacement plug from Amazon that cost almost as much as the usb charger itself.

Thanks.

 

[Johnny2Bad]

On the Cigarette Lighter socket, the tip is hot (+) 12V and the "wings" are ground (-) 12V.

With your Digital Multimeter (DMM) set for continuity (or ohms) place one lead on the tip and probe the USB connector. That will indicate the positive 12V lead on the USB jack. Do the same with one lead on the side connector and probe the USB connector a second time, with the indication now showing you the negative (-) lead on the USB jack.

Having said the above, I wonder why you are putting so much effort into this. Why not just buy another USB charger? They are cheap even at full retail and if you are a true cheapscate, they can be found for like a buck if you are willing to wait for the mail to deliver them.

 

[eljefino]

Originally Posted By: Johnny2Bad

Having said the above, I wonder why you are putting so much effort into this. Why not just buy another USB charger? They are cheap even at full retail and if you are a true cheapscate, they can be found for like a buck if you are willing to wait for the mail to deliver them.


Dollar tree has these; can confirm.

 

[sifan]

I have used this particular usb car charger on numerous trips while using one socket to charge my Garmin GPS and two usb ports to charge my iPad 3 and iPhone 6. It has been proven and fits my needs well. Besides, I just feel bad about throwing things away when they can be salvaged. My daughter's iPhone 5S was damaged by a charging cable from Amazon which cost $70.00 to repair by Apple. She just mailed the phone to Apple and is waiting for its return. I am skeptical on untested cheap usb chargers that may cause damages to my devices. I just don't want to go through the hassles of repairing my devices just to save few bucks on a cheap charger. I always read as many owners' feedback on a product on Amazon as possible before ordering it.