If the positive and negative terminals of certain DC supplies are brought together under certain conditions, the wires will "stick together" with a slight force, feeling almost like they are magnetically attracted. The force is perhaps only slightly stronger than the weight of a paper clip, but it's obvious if the two wires are hanging freely when they are pulled apart.
This effect can be easily reproduced with a bench supply. 12V and a current limit of about 2A will do. I get good results with alligator or banana clips. Even 12V with a current limit of 100mA seems to be enough. The issue here is the response time of the supply, which is another variable. Perhaps 100mA is meaningless in this case, because upon contact, a much larger current has already passed? If I try 3V and 4A, the effect seems weaker.
I assume this is the same phenomenon that causes broken filaments in incandescent bulbs to re-stick once contact is made. When conventional car headlights "burn out", often the filament is left dangling and can be temporarily restored by banging on the headlight or slamming the hood. The headlight may then work until car shuts off, or even days after.
I also assume this is the same phenomenon that damages relays that close under high loads.
What is the mechanism behind this?
I am doubting magnetism. My guess is micro-arcing (welding).
- Once the two wires are connected, they are essentially one wire. I'm not keeping them running along each other in parallel. They are making a large, 1 meter circular loop to the supply. Keep in mind that the wires themselves do not appear to attract or repulse, it's just the ends.
- If I make contact and then move the wires along each other (while keeping contact), I no longer notice an attractive force when separating them.