Positive vs Negative DC Amperage - Page 1
Forum section: electronics / beginners

author: frambois
author_rank: Newbie
timestamp: September 24, 2021, 07:33:04 am
content: From a 14.4 Volt battery, powering a digital camera. Using an 'amp clamp', I'm reading 9.8 Amps on the negative lead, but only 2.4 Amps on the positive lead. 9.8 A seems about right. What I'm wondering is what that 2.4 A means? Anything else I've ever read with a 'clamp' reads the same amperage whether it's on the positive or negative lead. Can anyone offer an explanation for this? What the proper reading really is? What I'm missing? (there are only two wires)

author: mikerj
author_rank: Super Contributor
timestamp: September 24, 2021, 07:41:24 am
content: Is your amp clamp correctly zeroed? If you change the direction of the wire in the clamp do you get the same current magnitude with the opposite sign e.g. +9.8A and -9.8A?

author: frambois
author_rank: Newbie
timestamp: September 24, 2021, 05:29:19 pm
content: Yes, properly zeroed. And, yes, with the same wire it reads opposite sign with direction changed. Checked it with a Fluke, an Extec, and an Amprobe meter, and I get the same results from all of them. I just tested all three meters-the whole system against my power supply. I used a 25 ohm resistor, set 25VDC. The power supply read 1 A, all three meters read 1 A on either lead, then clipped the meters straight onto the camera power and got the same 'different' readings between + and - leads. So I tested the camera power cable on the power supply with the resistor, got the expected 1A readings. Tested another camera power cable, with the same results.Amprobe LH41A, Fluke 325, Extec EX613, Vishay Dale 25Ω 25W 1% wirewound, Sony Venice camera (with several attached accessories). Anton Bauer VCLX battery (NIMH). Power cable is 14AWG wire for both wires-essentially lamp cord, that I split apart to get the clamp around the individual wires.It should read the same amperage whether on positive or negative, right? Or is that wrong? The people who lent the other meters are electricians, and did their own readings with their own meters.

author: Manul
author_rank: Super Contributor
timestamp: September 24, 2021, 05:53:38 pm
content: Quote from: frambois on September 24, 2021, 05:29:19 pmYes, of course same, no question about it. It is hard to say what is the problem, because we were not there with you doing the measurements. Could you post pictures of the measurement in progress, whole setup, wires?

author: james_s
author_rank: Super Contributor
timestamp: September 24, 2021, 06:02:55 pm
content: Kirchoff's law says that the current on the positive and negative wire must be identical, there is no way around this. It has to be an error in your technique.

author: frambois
author_rank: Newbie
timestamp: September 24, 2021, 07:19:42 pm
content: Quote from: james_s on September 24, 2021, 06:02:55 pmThat's the answer I needed. Certainly what I expected. It was a surprise to get a low reading when I first tested it. (figured I set something wrong-checked it-which is how I came about testing both leads-which I wouldn't normally do). It's now obvious that Sony is breaking the law. No doubt we'll see the physics police rolling up any minute now.Interesting that three different people with three different meters all got the same 'wrong' results. I'll experiment some more as I have time. We're done with the camera today. I'll try to photo the setup.thanks all.

author: TimFox
author_rank: Super Contributor
timestamp: September 24, 2021, 07:32:21 pm
content: The only way that makes sense is if there is a third conductor somewhere in the circuit (possibly a ground somewhere?). Even if the DC meter is being thrown off by strong pulsing or AC component to the current, it should be equally bad on the two wires.

author: james_s
author_rank: Super Contributor
timestamp: September 24, 2021, 07:35:08 pm
content: Perhaps it would help to tell us a bit more about the equipment being used. This is a clamp probe? Is there a chance that it's defective? Is the battery low? Shouldn't behave like this but something is going on. Make sure you zero it between clamping it over the wire to measure.

author: timenutgoblin
author_rank: Regular Contributor
timestamp: September 25, 2021, 02:53:14 am
content: Quote from: frambois on September 24, 2021, 07:33:04 amOne possible explanation is that the current consumption is NOT steady i.e., it fluctuates over time depending on what the camera is doing at any instant. Try measuring the current over a 5 minute period while using it (eg., start recording then stop recording) and check for any fluctuations. I don't use a clamp meter nor do I have one. One other possibility is that the clamp/sensor is suffering the consequences of residual magnetism which might be introducing errors in your measurements.Read the article below, it mentions residual magnetism.https://prc.keysight.com/Content/PDF_Files/5989-7529EN.pdfDo you have another clamp meter? If so, try measuring the positive and negative power leads simultaneously.

author: bdunham7
author_rank: Super Contributor
timestamp: September 25, 2021, 02:59:35 am
content: What do you get if you put the whole lamp cord (both wires) in the current clamp? That should be pretty close to zero and if it isn't, you clearly have an alternate route for current somewhere.

author: timenutgoblin
author_rank: Regular Contributor
timestamp: September 25, 2021, 10:43:21 am
content: I didn't read this before I postedQuote from: frambois on September 24, 2021, 05:29:19 pmAre you only measuring the current in the positive wire flowing into the digital camera? What about the current flowing into the accessories? If everything is powered from the same battery then you have a parallel circuit. The sum of the currents flowing into everything should be equal to the current returning to the negative wire.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 25, 2021, 11:24:32 am
content: If the positive wire is pulling current out of the the battery (pushing negatively charged electrons in), but the current on the other lead is different, then the battery itself starts acting as a capacitor to ground and will accumulate a very high voltage differential (many millions of volts) quickly. And this is obviously not happening. as soon as that capacitor is "charged" to the battery voltage the current would stop.A possible but far fetched explanation could be that the outside of the battery itself has become resistive (maybe a combination of leaked acid and dirt?)Kirchshoff's laws hold true. Current runs in circles, and the sum of voltages over separate parts of the circle is zero.---------A possible problem lies in what definition of "current" you use. A common way of explaining current, is that it are the electrons moving through a wire, but as of yet, nobody has ever seen an electron. Also, current can flow through a capacitor, while there are no electrons passing the isolation barrier in the capacitor, and at some point the analogy of visualizing current as electrons moving through a wire falls apart. A more accurate description of current is that it is the electromagnetic field surrounding the electrons that do the actual work, and even though an electron can not pass the isolation barrier in a capacitor, the electromagnetic field can if you put enough effort into it (which result in the voltage over a charged capacitor). The analogy of electrons moving though a wire is also not adequate for explaining skin effect and phenomena observed with high frequency electronics where the electromagnetic field surrounding conductors has much more importance.

author: TimFox
author_rank: Super Contributor
timestamp: September 25, 2021, 02:02:19 pm
content: Although Prof Millikan at the University of Chicago never "saw" an electron with his own eyes, his "Oil-drop Experiment" in 1909 did demonstrate the discrete charge of the electron (although there was a slight calibration error in his original experiment which was the source of confusion for a while). In 1971, I had the "pleasure" of performing this experiment in a teaching lab using his original equipment.

author: ledtester
author_rank: Super Contributor
timestamp: September 25, 2021, 02:21:51 pm
content: "Electron filmed for first time ever"https://phys.org/news/2008-02-electron.html