Wikipedia:Reference desk/Archives/Science/2019 March 19

= March 19 =

Electrical arc generation - transformer specifications
I want to make some low-power electrical arcs (as is every American's birthright) so I'm looking at cheap transformers on AliExpress and I think my BS-detector has found a listing positive for BS. Can someone confirm? The following are the specifications.

5.Input Voltage:DC 3.7-6V

6.Input Current:2A-3A

8.High Voltage Form:pulse DC type

9.Output Voltage:50kV

10.Output Current:0.05A

It says that with two orders of magnitude drop in current you get a four orders of magnitude increase in voltage? Is that correct? I though P = VI. I guess it could be true if it takes time to build up the required voltage before it sparks. I also notice that the spark length of "1-2 cm" is the same claim made for a 400 KV transformer. I'd expect the park to be longer for 400 KV than 50 KV. There's a 15 KV module that claims its spark gap is 1.5 cm.

FYI I know that high voltages are dangerous and do solemnly swear not to apply a high voltage across my own or anyone else's heart or even to touch the outputs with one hand while energised. 79.69.203.233 (talk) 13:24, 19 March 2019 (UTC)


 * 6 volts times 4 amperes equals 18 watts


 * (We can ignore the difference between volt-amperes and watts for the moment to make it easier to think about).


 * 50,000 volts times 0.05 amperes equals 2500 watts.


 * I can think of the following theories.


 * The fine folks at AliExpress are lying to you about the specs. Like maybe saying 0.05A when they mean 0.05mA?


 * The fine folks at AliExpress are lying to you about it being a transformer and it is actually some sort of HV power supply. Do the specs actually say AC output?


 * It only puts out 50KV at a much lower output current, and only puts out 0.05A at a much lower output voltage.


 * They have a tiny nuclear reactor and generator inside to provide the missing watts.


 * Amazon has a 3KV power supply for $12.99 and a 10KV for $36.99


 * But I have a way cooler project for you, and it is cheap to build. Check out these links:


 * https://www.youtube.com/watch?v=o6eCkS77rsk


 * https://www.youtube.com/watch?v=lPiel_jUow4


 * https://www.youtube.com/watch?v=ep3D_LC2UzU


 * Cockcroft–Walton generator


 * https://www.youtube.com/watch?v=KKYGzqI_Ygw (jump ahead to 4:40)


 * --Guy Macon (talk) 15:35, 19 March 2019 (UTC)


 * The most important specification listed above is this bit: "pulse DC type." This is another (somewhat sloppy) way of saying either "pulse width modulation" or "pulsed DC."  The peak voltage and peak current occur at some maximum duty cycle (let's say, 1%); this gives you 2500 watts for 1% of the time, and zero watts for the other 99% of the time, yielding an average power of about 25 watts, which is "approximately equal" to the input power of about 20 watts, to within the realistic margin of measurement error.  Of course we know the output must be less than the input; so where does this discrepancy most probably arise?
 * Throw in some rounded numbers, and it's easy to make sure you're correctly conserving energy; you absolutely cannot get more power out than you put in, but unless you've got really nice lab equipment, you probably can't measure a very short pulse at 50,000 volts with the kind of accuracy to give you even one significant figure, so there's a lot of fudge factor in the math. Maybe you've actually got a 38,000 volt pulse with a variable current pulse whose peak current of 0.10 amps is always occurring a few microseconds after the voltage drops.  So maybe the 38,000 volts occurs at an instant when the current is a few nanoamps, and the 0.10 amps occurs at a different, later instant when the voltage is under a hundred volts, due to the power factor from parasitic inductance or capacitance... but the label on the side of the box isn't exactly as detailed as a comprehensive data sheet.  So treat all the listed values as "approximate."
 * If you want to measure these things on your own, you'll need an accurate and fast high-voltage oscilloscope, or you need to know enough about theoretical electrical engineering to build an effective measurement probe for a fast and high-voltage pulse that you can then couple into an accurate low-voltage oscilloscope - without reintroducing even more power-factor altering parasitics; and then you can collect time-varying data and do some simple integral calculus to compute the total energy in the pulse... otherwise, you probably can't actually measure these things to accuracies of even 10%. And these are slow, low-power signals compared to a state-of-the-art switch mode power supply!  Electronics theory is hard stuff - that's why people spend years to get advanced degrees in it!
 * Use caution when playing with electricity, even if the power levels are "low."
 * Nimur (talk) 18:35, 19 March 2019 (UTC)

L-carnitine and propionylcarnitine
I'm learning about methylmalonic acidaemia (acidemia for Americans). I know that L-carnitine is used in the treatment of the condition. According to my understanding, L-carnitine converts the toxic substance propionyl coenzyme A into propionylcarnitine, but I've been unable to find out the fate of propionylcarnitine (in humans)... is it excreted in the urine, used in the krebs cycle...? A bit of searching hasn't come up with any answers for me. Note this is not a request for medical advice! Many thanks to anyone who can help. RichYPE (talk) 17:49, 19 March 2019 (UTC)


 * I don't see anything useful in KEGG about this:  Searching PubMed gets hits like, which suggests that in normal mice the propionylcarnitine is simply hydrolyzed, but whether that holds in humans or mice with this condition is another matter.  I didn't trouble Sci-Hub with the latter request, so I'm not sure what I missed. Wnt (talk) 01:55, 20 March 2019 (UTC)


 * The latter request, you mean you can't read the paper you linked? The key finding with respect to metabolism of propionylcarnitine is that mice fed the stuff excrete vastly greater-than-normal amounts of carnitine in their urine, similar to what they would exhibit if fed carnitine itself. They don't mention alternative metabolic possibilities, but directly conclude that the one compound is being converted into the other. Someguy1221 (talk) 03:25, 20 March 2019 (UTC)

Stratospheric water content
Is it known how much water (by mass, not by concentration) there is in the stratosphere? The only sources I can find are this and this old one. Jo-Jo Eumerus (talk, contributions) 19:55, 19 March 2019 (UTC)


 * You might start looking through the background review articles on the SAGE series of experiments.
 * Here's The Stratospheric Aerosol and Gas Experiment (SAGE III) on the International Space Station (ISS) Mission, (2014), via SPIE.
 * I have a feeling that you aren't going to find a concise summary answer; you'll have to ramp up on stratospheric models and various data collection experiments, and then conduct some original research to tailor those models to meet your need.
 * Nimur (talk) 20:17, 19 March 2019 (UTC)