Method to create a high current and low voltage

  • #26
jim hardy
Science Advisor
Gold Member
2019 Award
Dearly Missed
9,839
4,880
FWIW

Our main generator armature current was around 20 kiloamps. The armature conductors were made of square strands stacked together and insulated from one another so magnetic effects wouldn't push all the current out to the periphery by 'skin effect'. They left lengthwise internal passages through which hydrogen gas flows for cooling.

Haven't found a picture yet.

old jim
 
  • #27
1,701
1,030
Haven't found a picture yet.
A bit of an advertising (sorry), but the main point can be seen here.
 
  • Like
Likes jim hardy
  • #29
779
526
Me too. Great for car wiring - trailer lights, repairs,
and if you replace the tip with a coil of #12 solid you have a demagnetizer for hand tools tape heads and the like. . Worked great when an unshielded subwoofer underneath my Sony Triniton turned that corner of the screen purple. (today's flatscreens seem unaffected )

Will pick one up for you.

old jim
Another useful repurposing is to supply the soldering gun with a variac, add an ammeter, and use it as an adjustable high current source to check whether motor starter thermal overload relays trip at their rated values. It can also be used to check the calibration of, and set up AC current to 4-20 ma/0-10V signal conditioners.
 
  • Like
Likes dlgoff, Tom.G, jim hardy and 1 other person
  • #30
47
23
Current density is the limiting factor.

For more reasonable currents in a household experimental environment ,
buy a secondhand soldering gun to take apart and play with.

View attachment 228778

low voltage high current out of those two stubs.

Junk shops are full of them, around here they go for five bucks..
Waitaminnit .... how did my soldering gun end up into that junk shop?
 
  • #31
657
292
Another interesting way to make large currents at low voltage and DC is a homopolar generator, bonus you get mechanical energy storage in the form of a fly wheel.

I've read about people making spot welders and other high current things with by re winding micro wave transformers, single turn secondary type thing.
 
  • #32
657
292
A bit of an advertising (sorry), but the main point can be seen here.
Big boy stator!

It always impresses me seeing larger than life versions of things, whether its power plant e machines where you can walk around inside the stator or ship diesel engines where the ratchet to remove the cylinder head bolts is hydraulically powered and has its own crane.
 
  • #33
.Scott
Homework Helper
2,656
977
DC high current capability, 200 million amps, research study
Let's do total cross-sectional current:
I'll build a toroid of 10 gauge magnet wire; inside diameter 2 feet; outside diameter 6 feet; thickness 1 foot.
So the windings will have 2 square feet of cross section. For 10-gauge magnet wire, that's about 15000 turns.
Each turn will average 4pi feet - so 188,500 feet. For that quantity, I think I could get the wire at $0.40 per foot. So $75,400.
The resistance across this toroid will be very close to 188.5 ohms.

If I was to do this with a single toroid, the current would need to be 200Mamps/15000 = 13,333 amps.
But my budget is $250K, so I can stack three of these. Getting the current in each to 4,444 amps. So I will need 838KVolts at 13,333 Amps for 180msec to power this. 11.2GW for 180msec = 2G joules. (560 KWhours)

The copper is 14grams/foot. So total weight of all three toroids would be 3*14*188,500 grams = 7.92Mg.

Taking the thermal mass (or density) of copper at 38.46J/gC. We have a temperature rise of 2GJ/(38.46J/gC * 7.92Mg) = 6.6 degrees Centigrade.
So we won't met the toroids.

Average price for electricity in the US is $0.12. So the energy cost is $67.

I still have $25000 left in my budget to find a way to go from AC to 838KVDC.

When I worked in Ayer, MA, there was an AC/DC power converter next door for electricity coming in from Canada. It was basically a 5-acre electric circuit.
He needs to borrow that for 180msec.
 
  • Like
Likes Asymptotic and Fisherman199
  • #34
144
4
I have to try and look it up again, but years ago I was aware of a 3-set of laminated composite flywheels, these being series-connected homopolar generators which were wound up to speed, either from grid energy, or from diesel generator sets. Then, the high current pulse was made by switching the generators into the load, all in an effort to make an extremely strong pulse magnetic field for research. The storage flywheels weighed tons, supported on air bearings. 1.6 million amperes is a number that I remember.

Today there exists the remains of a 500 MegaJoules homopolar generator used along with a 7.7 MegaElectronVolts cyclotron operated at the Australian National University College of Physical and Mathematical Sciences back in the 1950's. It never completed the original mission, but was used for many other research projects.

At a more modest level, I have a PDF describing use of a homopolar generator to weld railway line, and yes .. it is old, from 1970's 1980's era. At 4.1MB, it is too large to upload, but it can be found at ..
https://repositories.lib.utexas.edu/bitstream/handle/2152/33237/PN_095_Aanstoos.pdf;sequence=1
Apparently 575kA pulse for 3.2s
 
  • #35
52
15
When they were running the Tokamak fusion reactor at Princeton University, they had two 100 ton (not sure about the weight) flywheels in the floor that were brought up to speed and then unloaded through the reactor. Their current creation was enormous (again, don't know the exact number), but was told by the tour guide that without the flywheels, the load would have blacked out Northern NJ.

Here's a description of the motor/generator set that produces the power. It seems very large, but I'm not really able to figure our what the amperage would be on discharge. Perhaps, one of our esteemed readers can decipher it. It gives power, and frequency, but I don't see the output voltage which I believe you'd need to figure amps.

"This paper provides a general description of 475 MVA pulsed motor generators for TFTR (Tokamak Fusion Test Reactor) at Princeton Plasma Physics Laboratory. Two identical generators operating in parallel are capable of supplying 950 MVA for an equivalent square pulse of 6.77 sec and 4,500 MJ at 0.7 power factor to provide the energy for the pulsed electrical coils and heating system for TFTR. The description includes the operational features of the 15,000 HP wound rotor motors driving each generator with its starting equipment and cycloconverter for controlling speed, power factor, and regulating line voltage during load pulsing where the generator speed changes from 87.5 to 60 Hz frequency variation to provide the 4,500 MJ or energy. The special design characteristics such as fatigue stress calculations for 1,000,000 cycles of operation, forcing factor on exciter to provide regulation, and low generator impedance are reviewed."

I have a resistance soldering system that produces up to 100 amps at 3 volts.
 
  • #36
coolul007
Gold Member
265
7
homopolar generator
 
  • #37
berkeman
Mentor
58,373
8,449
When they were running the Tokamak fusion reactor at Princeton University, they had two 100 ton (not sure about the weight) flywheels in the floor that were brought up to speed and then unloaded through the reactor. Their current creation was enormous (again, don't know the exact number), but was told by the tour guide that without the flywheels, the load would have blacked out Northern NJ.
It's been a fun thread with lots of interesting posts, despite the OP going AWOL. It's probably time to tie off the thread, though. Thanks for the posts. :smile:
 
  • Like
Likes Klystron and jim hardy

Related Threads on Method to create a high current and low voltage

  • Last Post
Replies
22
Views
30K
  • Last Post
Replies
3
Views
32K
  • Last Post
Replies
16
Views
19K
Replies
11
Views
6K
  • Last Post
Replies
5
Views
891
Replies
2
Views
3K
Replies
2
Views
1K
Replies
53
Views
7K
Replies
6
Views
4K
Replies
2
Views
2K
Top