Converting Power Input of USB-C Car Charger

The first introduction of USB-C into my life was my Nexus 5X cell phone. Intrigued by the promise of faster charging possible with USB-C, I bought a few additional chargers including this car charger sold by Monoprice.

MP USBC conversion 00 user end

This particular model is no longer carried by Monoprice, probably because there’s a flaw in the design. After several months, it became difficult for it to make good electrical contact with the standard car power socket that originally started as a cigarette lighter.

MP USBC conversion 01 plug end

My hypothesis is that there’s poor electrical conduction in the system, causing energy to be lost as heat that started melting the surrounding plastic. Eventually seizing up the spring-loaded mechanism so it is stuck.

MP USBC conversion 02 melty closeup

I first tried cutting the metal free from melted plastic and had no luck. This plastic is extremely durable.

MP USBC conversion 03 tough to cut

I then tried attacking the problem from the other end, and felt sheepish because the face plate is only held by friction and popped off easily.

MP USBC conversion 04 faceplate pops open

Looking inside, I could see two screws for further disassembly.

MP USBC conversion 05 two screws visible

Once they were removed, it was easy to pull the guts and lay them out.

MP USBC conversion 06 components laid out

There is a thin spring behind the contact showed heat darkening, consistent with hypothesis of too much power carried within that thin metal causing heating. My experiment of the day would be to replace that connector system, and the easiest type on hand is a commodity JST-RCY connector which is good for at least 3 amps and very commonly handling peak power higher than 3A in remote-control aircraft.

MP USBC conversion 07 JST-RCY soldered on

The first soldering effort was bad. The positive wire easily soldered to where the spring used to be, but the original ground contact is a huge piece of metal my soldering iron could not bring up to proper temperature for a good solder joint. For the second attempt I found another ground on the PCB to solder to, keeping the two wires tight enough so I could thread it through the partially melted hole where the spring-loaded positive contact used to be.

MP USBC conversion 08 JST-RCY threaded through

I reassembled the device without the original spring or its contact. I won’t be able to use it with a car power socket anymore but I should be able to keep using it to charge USB-C devices from other ~12V DC power sources.

MP USBC conversion 09 reassembled

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