Resistance heating of electrical connectors?

[PVH]

Does anyone know where to find some good information and data on the phenomena of resistance heating of electrical connections. I have an appliance product that is getting repeated overheating failures at its two pin power connection. The connection is often disconnected and reconnected. The device only draw 2 amps but we are still seing signinifacnt heating after several cycles of use of the connector. Also any leads on manufacturers that supply haevy use connectors would be appreciated. I am hoping to find connectors that would be similar in size to those used to connected notebook computer power supplies. Thanks,

Phil

 

[itsmoked]

You realize all connectors have a cycle life related to them?

It often relates to the scrubbing of the surface material caused by plugging and unplugging.

Sometimes you change materials, coatings, or thicknesses to fix the problem.

A picture would certainly be useful in helping the discussion as I can think of hundreds of different "connectors".

Also since every connection incurs a resistance which will heat up based on:

Power = Current(squared) x Resistance

there will always be some heating at a connector. Remember too that all chemical reactions double their rates for every 10 degree rise in temperature. This means some part that is 20 degrees hotter then the rest of the stuff will oxidize and fail 4 times faster then the cooler stuff nearby.

The solution is often providing the design with heat sinking for the connectors. For example connectors that might work great in the air may overheat if buried in some plastic molded housing. One solution would be to attach wires substantially larger to one or both sides of the connector to assist in conducting the connection power away to areas that have more heat rejection ability.

 

[PVH]

Its basically a D-Type Sleeve Connector Pin Socket. I guess you could say it is similar to a grounding pin socket on a polarized plug adapter. I'm not sure where I can post a photo for this. I'll see if I can find a link to the vendor or an online image of it. thanks,

Phil

 

[sreid]

I like Positronic Industries line of power connectors.

http://www.connectpositronic.com/Power/

 

[itsmoked]

You can post pics in here.

See the FAQ:
faq238-1161

or link to a vendor picture. Your app if strange/unique would benefit, probably from an actual picture.

 

[jraef]

Another thing to consider is the quality of your connector. 2 amps is not a lot, but if you are not getting good cantact it can cause heating for sure. A QC iissue we ran into a few years ago had to do with plating. Our purchasing dept. decided to send our spec on a particular connector out for competitive bids when a supply cntract expired. Without consultation, they chose the cheapest. As it turned out (from months of failures and investigations), the cheap supplier used a very thin plating on the connectors. They tested OK on intake, but the plating wore through after only 3 or 4 plug/unplug cycles, which caused immediate corrosion and resistance, then failure.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[PVH]

Here are some links to photos of the sockets and damaged connectors:

http://tinypic.com/ke98nq.jpg

http://tinypic.com/ke99hz.jpg

http://tinypic.com/ke9bex.jpg

http://tinypic.com/ke9c7a.jpg

 

[itsmoked]

Ugh, yeah, not good...

I would study the problem.. Gut the tool so you have just the connectors mounted normally. Then using a scope monitor the current across a small resistor as you wiggly the connector. You may find that it makes really bad contact in certain cases. This would indicate the spring aspect of your connector is weak/bad or highly directional.

You can also do a plug/unplug test. Do a graph showing the contact resistance as a function of insertion number. Use an ohmmeter that goes sub-ohms. You may find that the gold scuffs off in a few dozen insertions. (jraefs example)

Rarely is gold ever used in charger connectors as it is so soft it always wears away quickly. Hence a connector may have a very low contact resistance initially but quickly loses this with wear, whereas a silver contact may have a higher initial contact resistance but it never increases appreciably with use. Keep in mind that if the user is plugging in a power supply that is on it may arc the gold off very quickly.

 

[PVH]

Would a heavily used connector design normally call for a socket with perhaps 3 internal prongs and/or prongs with greater potential spring travel? This D shaped socket barrel appears at first glance to be very sucepticble to over bending and thus loosening of the contact. Furthermore would a heavy use connector socket normally call for a solid material contact such as copper rather than a plated connector? I plan on doing some metallurgical cross section mounts of the connector to get a microscopic view of the plating. Also the cycling/ohm test looks like a good idea. I may need to get a better ohmmeter for that. I was contemplating doing this on a data aquisition system measureing current via a precision shunt and then back calculating resistance change from that. Thanks for the tips.

 

[ScottI2R]

PVH,
I read this that it keeps happening. Silly question, but, you are replcing the plug (male) as well as the recepticle (female) aren't you? And they are physically the correct size for each other, right?

Scott

In a hundred years, it isn't going to matter anyway.

 

[PVH]

Scott,

We will probably replace the pin and sockets as a set. Right now we are trying to understand the exact cause of failure and select a new pin/socket product for future units so that know we won't get this problem again, thanks again,

Phil

 

[itsmoked]

PVH; the shunt method is a great method that will let you use more conventional measuring. Go for it!

A problem with non-concentric connectors is auto alignment.. It is easy to have this happen with parallel conductors especially if the pins get banged.

I look at Mouser and Digikey and they have quite a few co-axial power connectors rated up to 3 amps.

Straight copper can have some issues too. That's why power connectors are generally plated (see the ones mentioned above) or... they are solid brass.

 

[pennpoint]

PVH
Your last two picture are not congruent. You show a male plug corroded, burnt and melted from heat but the mating female component is bright and clean and no heat stress. Whats Up?
or did I miss a pic...

pennpoint

Best regards
pennpoint

 

[itsmoked]

I don't think they were related in time and space..

He has a pic of each sex that is fried.

 

[sreid]

I think we need to know the manufacturer of the pin and socket and a part number so we can see what the electrical rating is, what the construction is, what the base material is, what the plating is and how thick the plating is.

Also, do you do the rubber/plastic over- molding of the connectors and at what temperature?

 

[PVH]

Thanks for all the tips so far. We have the connector and sockets work vended out. I will see if I can get more specs on the sockets and pins and some more info on the molding process. Do you think the molding temperature is causing some socket shape distortion or the parrallenes of the fional cooled mold?

Phil