PCB female jack and power supply male melted

Question

I've been working in my thesis project which consist on a PID controler to mantain a certain temperature in a case. The heater module is made of two 40W-12V 3D printer resistors and one 15W-10 Ohm wirewound resistor. In addition to these, I have an Arduino Uno, a 20x4 LCD screen, two temperature sensors and two PC coolers (2W each) which all sum up in 5W (rounding up). I'm using a 12V-10A switching power supply.

When the PID is at 100% the tension in the resistor (Rparallel= 1.5 Ohm) is supposed to be 12V, but due to the cables and transistor (IRF540N) drop, the maximum tension is 10V. So, all in all, in maximum behaviour I would be drawing 66.6 W + 5W= 71.6W.

The PID circuit is as follows:

The female jack that is soldered to the PCB is:

which is located near decoupling capacitors in the PCB:

The problem:

I've been doing some test to set up the PID's parameters for over a month (more than 40 hours of tests) without any problems. Suddenly last week while doing a test I smelled like something was melting and found this:

The power supply still works well so I wouldn't say there was an overdraw of current. My best guess would be that the PCB jack couldn't handle that much power but then, why did it resist more than 40 hours of testing? Something had to go wrong this time?

I need to know the cause of the problem so I can continue with the tests. Obviously I will replace both conectors and try to find a more robust one for the PCB but if the problem comes from the power supply or the PCB circuit itself i will face the same issue again. What would you say the problem was? Could the power supply suffered an overdraw and still be working? Is there a way to determine which component overheated first (the PCB jack or the power supply conector)? Would you recommend to solder the power supply directly to the PCB?

Answer 1

My guess is that when you used it over the past month you were using current that was under the maximum specified for that female power jack. The reason why your power supply is fine is because it can handle the power. Unfortunately it seems that the female power jack is probably not rated for 10A or anything slightly below it. If you truly plan to use high current like in 5A or up to 10A you should use some power connectors. For example MOLEX power connectors like shown below. You’d split up your positive pin into 3 wires and negative pin into 3 wires so they share the current.

Answer 2

You converted the power jack into a melting pot and just had your 1st failure to read max current specs and heat rise calculations.

1st rule is to make a power loss budget.

• lookup max current rating on power connectors (3A?) Use HDD MOLEX 4 pin ganged ( actual scpecs range from 2.5A min to 3.5 to 4A for best quality)
• compute temp rise from RthJA = 62 °C/W (say Pd=0.5W with no sink)
• determine max RdsOn . R=V²/P= 12²/100W= 1.44Ω and Pd/P * R = 0.5/100W 1.44Ω = 72 mΩ so the IRF540 is OK with Vgs> 10V

But your choice of BARREL POWER CONN is a HUGE NO-NO for 8 Amps. Try 3A max.

Use this instead.

Answer 3

Barrel power connectors like you show cannot handle as much current as you are trying to pass through it. If the center pin of the jack is the 2.1mm style they are typically rated at just 2A current. Barrel jacks with the 2.5mm style center pin are rated a bit more, sometimes as much as 3A. (This is one reason you see 2.5mm jacks used on powered USB hubs).

The voltage of the supply has little to do with the connector capabilities that we are discussing here. The connector contacts have a certain resistance and it is the I²R power level that causes the connector temperature to rise. In your case till it rose enough to melt the plastic of the connector.

When designing things you should check the data sheets of all parts that you use to assure that your use of all components is within specifications.