Simple wire question - Page 1
Forum section: electronics / beginners

author: edy
author_rank: Super Contributor
timestamp: January 15, 2013, 02:40:11 am
content: Hi folks,I have a power supply MPS-65-12 (Mean Well) which is a medical-grade 12V power supply board, which is powering a monitor. The monitor is rated 12V/5A. See attached photos.The monitor stopped turning on, so I checked it on another power supply and the monitor was OK. So then I went to check the power-supply and noted there was a burn mark on the wire connecting the supply to the monitor (See photos).So I figured the power-supply was dead, but when I checked it... it was fine. There is an LED on the board which was still working so all seemed ok, and volt-meter confirmed 12 V output on the 6 pin-header (3 on left are ground, 3 on right are +12V). All the pins worked as intended.So.... the big questions are....1. Why did the connector to the monitor burn up?The plastic must have melted or charred the connector and that basically insulated it, so it couldn't drive the monitor anymore. Kind of silly I think to put both wires so close together on the plug when they could have been spaced at the far extremes? No?2. Will this replacement do...Now I want to replace the connector and found some computer wiring going to a 6-pin header (just like the one in the photo below) and the wiring on it has writing as follows:AWM 1007 E117721 VW-1 80-deg C 300 V 18AWG SUPERCOM CSA LL62402 TYPE TR-64 90-degAWM 1007 VW-1 CSA TYPE T1 FT1So I assume this should be good enough as a replacement. I don't want anything melting. Are these rated enough to handle 12V at 5A if the monitor draws full power?

author: Skimask
author_rank: Super Contributor
timestamp: January 15, 2013, 03:32:48 am
content: Poor connection, dirty contacts...creates resistance, which creates heat. No resistance, no heat generated, no burns. If that pin was a bit recessed, maybe it didn't have as much contact area as the rest of the pins and all that current was forced to go thru a smaller contact area than the rest of the pins.If the monitor was actually drawing 12v @ 5amps as you say, that's 60 watts. Even a little bit of resistance can make heat over time.In short, I would venture to guess that it wasn't an issue with the connector, or the pins, or the wiring, but more of a mechanical issue with the pin contact itself.

author: digsys
author_rank: Unknown
timestamp: January 15, 2013, 03:33:06 am
content: The MOST likely scenario is that the wire was poorly crimped and simply over-heated. Not common, but it happens enough.Especially if you're sure the PS is OK. IF it was an overload, there'd be a return wire overheated as well.Those pins will take at least 16A, maybe more depending on the spring force of the F/Male.IF you really want to be certain, put a 5A resistive load on that pin and see.

author: Skimask
author_rank: Super Contributor
timestamp: January 15, 2013, 03:44:11 am
content: I was just about to say "I want to see that 60W resistor!!!"...Then I remembered the lowly incandescent household light bulb that has served me well for a load device in years past...

author: UPI
author_rank: Regular Contributor
timestamp: January 15, 2013, 03:47:46 am
content: I agree with all of the above.You will want to replace both the cable and PCB connectors since they were overheated and the plating was damaged.This should get you in the ballpark:http://www.mouser.com/Molex/Connectors/Rectangular-Connectors/Headers-Wire-Housings/KK-Series/_/N-7auntZscv7?P=1z0wxp7Z1yzmt7xZ1z0zlewZ1z0wxoc&FS=TrueCheck your pin spacing and figure out which ones you need.

author: edy
author_rank: Super Contributor
timestamp: January 15, 2013, 04:49:53 am
content: Thanks for the advice. The power supply doesn't look damaged at all. The middle 2 pins are a bit darker with the slightly burned plastic but the outer pins look clean. The "female" plug on the other hand looks completely burned through.I did notice the plastic was dry and brittle, so it could have been running hot all those years. It is 3 years old installation. The heat slowly degraded/aged the plastic.In contrast, the plastic connector on the AC side going to the mains was still soft and bendable.I am going to have trouble removing the power cable going from the supply to the monitor. It is sealed inside this bundle of audio/video cable inside a flexible sliding armature mount holding the monitor that is very long and almost impossible to get into.I will try my luck and just cut the end off the cable (the burned plug) and connect up another plug and hopefully that was the only part of the cable that was affected.

author: edy
author_rank: Super Contributor
timestamp: January 16, 2013, 02:19:59 am
content: Thanks, problem was fixed. I replaced the connector. Here is a photo of the one that burnt up. Ran for 3 years no problem, all of a sudden no power and I find this. I wonder how it happened. Monitor is still fine and so is the power supply (at least on the surface they still work). None of the fuses tripped or burned, everything looks unscathed except for this connector. Odd indeed.