Electricity is not we think?

Electroenthusiast

Active Member
Many years ago at school, the professor who dealt with explaining how a semiconductor doping works said me a thing. It was that no one knows how things work, the ones which are being explained are just theoretical, and the practicality is not better known.

Today, i was using a LED table lamp powered by a USB cable. I thought of running the cable to the other side of the cable, but the cable with which it came was not long enough. I used a cheap USB extension cable for that length and it seems to be working little creepily.

The LED lamp works for few seconds and then switches it self off after couple of seconds, this happens everytime i switch the lamp. But, it works perfectly fine when the extension cable is removed, and when only connected to the PS with the cable it came with. Whats wrong with the USB extension cable? Why is it working like this when it is just conductive wire inside?
 
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Resistance.

Every form of electrical conductor has resistance, (other than "superconductors").

Most general USB cables have extremely thin wires and cause significant voltage drop with anything that draws much current.

I have a few USB devices that need quite a bit of power, such as a USB scope, device programmers & audio interface etc.
The only cables that work are either the ones the makers supplied with them, or some I've had for 20 years or so.

NONE of the cables (A to B type) I've bought in the last ten years will run those, even supposedly "heavy duty" ones - they use as little copper as possible, or possibly coated aluminium wire, that has lot higher resistance than the old cables, and the voltage drop is just too much, the devices will not power up properly. The continuously cycle, trying to start.
 
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I had a sat nav that didn't like a high-resistance cable, but was fine with the one it came with.

WIth a high-resistance cable, the sat nav would start charging, find that the voltage had dropped and stop charging. This would cycle continually with about 1/2 second of charging and 10 seconds of not. That resulted in a message on screen saying that it had started charging every 10 seconds or so.

Your lamp seems to turn off and stay off, but it's almost certainly the same issue.
 
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Thanks for the replies. Now, i need to buy a copper core cable to make it work, which would possibly more than the cost of the lamp by itself. I still don't know how these people used high quality cores for their cables or lamp. Just saying.

So, i did try with a USB PSU, it didn't light either with the extension cable. What can be done to get rid of the issue as long as i use the same extension cable?
 
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tepalia02 said:
Sir, how can we identify a good extension cable before buying? Is there any testing method?
Click to expand...
the easy way is to buy a cable from a reputable company. A company that makes high quality consumer electronic devices (Apple, Samsung, ...) or a company that one of those consumer electronics manufacturers endorses.

Otherwise, looking for cords that appear to be heavy is not necessarily a good method because the heavy cord is a toy just insulation - not conductor. You my. Find a cable that appears to specific the wire thickness (wire gauge) and hope they are truthful. Beyond that, you'll have to use a conductivity meter which is more than a simple ohm meter and test them for yourself.
 
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Completely undeserved rant mode - ON:

My high school physics textbook's chapter on electricity said something similar, that no one knows exactly what electricity is. Both the book and your instructor were completely wrong. That is not true, it is not correct, it is the wrong thing to say to a student, and you should forget it.

In 1965, Richard Feynman won the Nobel Prize in Physics for - and this is a direct quote from Time Magazine - "figuring out the electron." From the 17th, 18th, and 19th century geniuses, including Fourier, through Tesla and Heavyside, to Feynman, "we" (certainly not me) know *exactly* how these things work.

OK, I feel much better now.

ak
 
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Should we assume "Completely undeserved rant mode" automatically turned off or will it carry over to future posts or even other threads?
 
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I wonder if all USB power sources behave the same way with this lamp. It is unwise to make conclusions without evidence or at least several comparative tests. There is always a reason why power shuts down.
 
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Pommie I have for now used it direct with a USB PSU directly with the cable the LED Lamp came with.
I for now, don't have the requirement of using an AC extension cable. I know that it would work, since i am anyway using a spike buster from AC mains to turn the Lamp on.
 
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