Author Topic: Current transformer for narrow spaces  (Read 740 times)

Offline klugesmith

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Current transformer for narrow spaces
« on: September 13, 2020, 06:22:07 AM »
I want to measure the current in electric soldering guns, as part of a bigger project.  (Show the serious mismatch between copper replacement tips for low-V designs, and ferrous tips for less-low-V designs).

Traditional clip-on current probes are too big to fit through most soldering tips.   Picture shows an exception. 
Current starts at 225 amps. It becomes less as the element heats up & wants to damage the insulation on probe core.


Let's make a current transformer with extra-narrow core, out of a little control transformer from some MWO.  Don't want to take apart the interleaved E's and I's, so new primary conductors will need to be fished through the unbroken core.

I chose to remove the higher voltage winding, which occupied more than half of the core window.

Said a bad word after sawing one stroke too far, and breaking the low voltage winding. 
That was before I made the measurement with commercial probe in first picture.
Later I found another MWO body part with a similar transformer, and cut it more carefully. First measured the normal secondary voltage: 12 V with a tap at the 3V / 9V point.

Here is first-round test, using a wire loop bigger than original soldering iron element.  Soldering gun is plugged into a variac, and kluge transformer winding is connected to a multimeter on AC 400 mA or AC 10 A range.

CT secondary current went up linearly with indicated loop current, with ratio close to 250 (50 A : 200 mA).

Easy so far, with the current loop under test going around the thick center leg of transformer core.  When it's moved to an outside leg, to fit the Subject of this post, we get about half as much secondary current, and I don't trust the flux division to be linear.

We could stop most of the leakage flux in third leg by cutting through the core, or putting the laminations in a different configuration.  First I tried encircling the third leg with a shorted turn.  First length of bare stranded wire ran out after 20 turns, and restored the secondary current to 93% of original. 10 more turns filled the core window but didn't appreciably change the CT ratio, now 1:262.  It's practically linear up to (briefly) 120 A, and not sensitive to where the test current wire passes through the core window.  A quick test with the "real" soldering tip, on a different gun than we see in top picture, indicated 240 A dropping to 205 A.
« Last Edit: September 13, 2020, 07:21:09 AM by klugesmith »

Offline Weston

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Re: Current transformer for narrow spaces
« Reply #1 on: September 14, 2020, 11:18:14 AM »
Interesting to see the impact of shorting out one leg of the E core with a bunch of turns! I wonder how that compares to cutting an air gap in the unused leg of the core.

60Hz is pretty low frequency, which might make designing an integrator without low enough noise (given the small signal), but this seems like an application where a rogowski coil might be useful.

Offline klugesmith

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Re: Current transformer for narrow spaces
« Reply #2 on: September 15, 2020, 05:33:39 PM »
I'm planning to carry on the experiments, including some actual transformer design calculations.

One thing that leaped out is heating of CT secondary.  When measuring a current of 200 A, there will be nearly 200 ampere turns in the secondary (no matter how many turns of any gauge wire).  For a conservative loading of 4 A/mm^2, the secondary winding would need to fill 50 square mm. 

That won't happen with existing windings on little control transformers, though it tips us toward keeping the bigger winding.  We can go above 4 A/mm^2 because the transformer is small (good surface to volume ratio). And farther still if we limit the duty cycle; an exercise is to figure the adiabatic heating rate of copper at 10 or 20 A/mm^2.

Offline klugesmith

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Re: Current transformer for narrow spaces
« Reply #3 on: September 20, 2020, 05:31:25 PM »
More progress toward DIY current transformer, for 200+ amps, 60 Hz, able to link soldering gun tips. Among the most challenging are the early Wen units, which work best but are hard to find parts for. Ferrous metal tip needs more volts ( still < 1 ) and fewer amps than all-copper ones.

First a digression.  How about a coreless sensor, inspired by Weston's "little bee" probe? https://highvoltageforum.net/index.php?topic=1154.msg8316#msg8316  When there's 200 A in a straight wire, the magnetic field 1 cm away is about 40 gausses (RMS), eh? OK for inexpensive B-field sensor chips. But what about the B field from other parts of the soldering gun tip?  How about a gapped core, linked with soldering gun loop, with a sensor IC placed in the gap? Might need to be an uncommonly high-range sensor.

Current transformers have the benefit of being passive, insensitive to temperature, and naturally linear. They are sort of "closed loop", magnetically comparing the primary and secondary ampere-turn values; only the small difference goes into core magnetization and phase-shifted voltage drop.

Anyway, previous report ended with a thick shorted turn linking one window of E-I core. How thick must it be, and how does it compare with an air gap in the third leg of core?   I set up an 80 ampere-turn source and measured the CT ratio while progressively removing conductance from the shorted turn. 
Baseline is about 320 mA in secondary (250:1 current ratio), according to this set of instruments, with short practically filling one window.  Down to 312 with window half full and 300 at 1/6 full (five wraps of bare copper stranded 14 or 16 AWG wire). Then dropped rapidly to 160 mA with zero or one wrap.  Sawing a small air gap brought secondary current back up to 313 mA.
Observed that disconnecting the secondary burden (mA meter) made primary current drop. That's because CT core goes into saturation, inducing back EMF that's significant in the very low voltage primary circuit.

Moved on to another transformer from some wallplug battery charger, opened with a rubber mallet resulting in damage to bobbin.
 
Winding R's about 650 and 15.
Voltage ratio 8:1 in normal direction and 1:7.5 driven backwards, indicating turns ratio of 7.75 with 97% coupling.
The E's and I's are not interleaved, so we can cut the core open and arrange to clamp it back with only one loop for flux.  Will monitor core reluctance via the magnetizing current in HV winding. Originally 3.17 mA at 1/2 voltage and 11.44 mA at nominal voltage.  This is important because it produces a nonlinear CT error term, and secondary circuit resistance can be no less than the winding R.
« Last Edit: September 20, 2020, 06:29:33 PM by klugesmith »

Offline klugesmith

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Re: Current transformer for narrow spaces
« Reply #4 on: September 23, 2020, 11:20:53 PM »
Before finishing the work with red-coil transformer, I ordered some commercial CT's rated for 100 A.
Looks like the core will fit through any of my soldering guns, if enough blue plastic is removed.

Won't be hard to characterize its performance details.
If it gets nonlinear before we reach 200 A,  soldering irons under test can be operated at reduced voltage.
The induced EMF in primary circuit may be significant in this application, and unavoidable, but we will know its magnitude.

I also looked into commercial flexible Rogowski coils, many specified with 60 Hz accuracy good enough for "revenue" metering.
Found none that would thread through my tightest soldering gun. 

Might try winding flexible Rogowski coil for the purpose.  Sensitivity is proportional to small-loop area and winding density (turns per mm), regardless of coil length. I predict on the order of 10 mV output for 200 A input at 60 Hz.   No need for electronic integration if we are looking at sinusoids of known frequency.  Maybe electric field coupling to unshielded coil will be significant.  Can find out by mechanically reversing the link to current under test, while triggering scope on "AC line".

How do you wind coils to tolerate bending?  Suppose we wind 34 AWG magnet wire on a tubular former with OD of 1/4 inch (6 mm).
Then bend that into an incomplete toroid that would fit around a broom handle.  How will the wire bunch up on inside edge of the big loop?  Or will it resist compression, so the neutral axis of the bent former is close to inside edge?
« Last Edit: September 23, 2020, 11:48:48 PM by klugesmith »

Offline klugesmith

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Re: Current transformer for narrow spaces
« Reply #5 on: October 06, 2020, 12:03:07 AM »
New CT's (100 A : 50 mA) arrived, each with a 3.5 mm miniature phone plug on the end of a short cable,
Secondary winding has 2000 turns (ideally) and resistance close to 100 ohms.

Time to characterize these CT's and learn about their performance limitations, including any that come from being small.  At what current, and why, do they go nonlinear?  How much do they burden the primary circuit?

Instrumentation was primitive for first tests, I think mainly because of questionable old clip-on meter.
Measured primary current threaded the transformer 3 times (green wire shown before) and then 7 times.


For current measurement, the secondary was burdened with a multimeter on 400 mA AC range.  Transformer seemed to match its nameplate pretty well up to 100 A, and lose some gain between there and 200 A.   (Jumps in the chart correspond to switching ranges in the clip on meter).   
The unburdened (open circuit) secondary voltage was leveling off well below 9 volts, when primary ampere-turns reached 18.


Is the secondary voltage limit caused by an internal protective device (e.g. TVS), or by core saturation?  An oscilloscope view could answer that question immediately.  But let's do some figuring. 
CT core is very close 1/4 inch (6.35 mm) square.  RMS flux of 1 T would induce 15 mV/turn, 30 V in whole winding.
Core has no visible laminations, and picture from catalog shows chamfered corners, so I bet it's ferrite.  Would be well along road to saturation to get 8 volts RMS.

Saturation might explain the response rounding off above 100 A.   At nominal full scale operating point, there must be 5 volts induced in secondary just to overcome the winding resistance, even if external burden were zero ohms.  Could be mitigated by using bigger core (for more volts at saturation).  Or lower resistance secondary winding, I think necessarily larger (not simply same volume with fewer turns of thicker wire).  Or, uh, core of steel.  :)

With 7-turn primary it's easy to see the effect of back EMF on the primary circuit.
Set variac to get 42 mA in secondary.  Primary current (times 7) is 83 A.
Unclip the CT and let the core open up a little.  Feel and hear vibration.  Now 12 mA in secondary, while primary current increased to 102 A.  With CT completely removed, primary current reached 105 A without touching the variac.
« Last Edit: October 06, 2020, 12:59:12 AM by klugesmith »

Offline klugesmith

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Re: Current transformer for narrow spaces
« Reply #6 on: October 11, 2020, 08:15:01 AM »
Not sure I'm reading this correctly, but I think we might be seeing saturation _and_ an overvoltage protection device like a TVS.

Internet shows us a standard way that current transformers are characterized for saturation.  We excite the secondary winding with a variable AC voltage or current, and find the knee of the curve.  Traditionally that's defined as point where the slope is 45% in a log-log chart.  I wonder how the curve differs if we force sinusoidal voltage or force sinusoidal current, since the one not forced will have lots of harmonic distortion when core is saturating.
https://www.researchgate.net/post/What_would_be_a_good_way_to_read_Current_Transformer_saturation_curve


I went and did that with one of the blue 100A:50mA transformers, this time using proper true-RMS meters for voltage AND current.   Excitation source was a 12V transformer on a variac.  Here's the log-log chart (blue curve).

Orange curve is the characteristic of a 100 ohm resistor, which would match the CT secondary winding.  It's automatically got a 45 degrees slope on log-log chart.   I'm having a bit of trouble understanding how, for a given current in secondary, the terminal voltage could ever be less than the I*R drop in the winding.
[edit]
Went and made a DC measurement, added as green curve, which clearly shows a voltage limiting shunt device kicking in before 10 volts.  Forgot to do DC measurement with opposite polarity, but it's too late for that tonight.  Another area for exploration, before breaking out the oscilloscope: AC measurement with a big gap between the two halves of core.
« Last Edit: October 11, 2020, 08:59:20 AM by klugesmith »

Offline klugesmith

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Re: Current transformer for narrow spaces
« Reply #7 on: October 11, 2020, 06:39:10 PM »
DC voltage/current characteristic is practically identical for both polarities.

But that pesky TVS won't normally conduct, even if primary current were 200 amps, because it's shunting the low resistance of external burden.
So this CT could still be pretty linear up to 200 amps (for 100 mA out), if the frequency is high enough to avoid saturation.
Need enough magnetic dF/dt to induce 10 volts RMS in the secondary winding, to overcome wire resistance.
1 watt heats the winding, and is taken from the primary circuit which sees 5 mV drop from the CT.

For this core area, if flux and voltage are to be sinusoidal at 60 Hz, we'd need Bmax of 0.4652 T.
Not going to happen in ferrite.  At 120 Hz, Bmax would be only 0.2326 T.
« Last Edit: October 11, 2020, 10:18:18 PM by klugesmith »

Offline klugesmith

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Re: Current transformer for narrow spaces
« Reply #8 on: October 12, 2020, 03:28:27 AM »
Couldn't keep away.  Made a 150-turn coil out of 26 AWG magnet wire, to bring 200 ampere-turn stimulus within easier reach of common benchtop instruments and signal sources.

This was the second time my apple peeler served to wind coils and count turns.

To save time, I didn't try to put the wire on in neat layers.  When 150 turns were on, I tied up the bundle with six pieces of waxed lacing tape, which were in place when winding started.  Then began to disassemble the bobbin.

As it turned out, the lacing tape was only temporary.   It held long enough for the coil to get a toroidal wrap with waxed dental floss, which gave the random-wound bundle a nice round cross section about 14.5 times thicker than the wire.

Coil has R of about 2.6 ohms, and could be driven with an audio amplifier for frequencies higher than 60 Hz.
Initial experiment used the variac and 12V transformer. Ran up to 1.56 A in wire, 234 A in bundle (dissipating 6.3 watts).  CT output began to depart from linearity at about 150 A.


Offline rikkitikkitavi

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Re: Current transformer for narrow spaces
« Reply #9 on: October 13, 2020, 12:55:59 PM »
You get almost 50% more , not a bad bargain :)

If you do an R2 calculation on a trend, how far off is it if you limit to 100Amps? Or what accuracy? Or is it limited by your measurment setup?


What is the technical explanation for a current transformer going towards saturation showing less accuracy? is it that you start to have less "inductive behaviour" ? Ie the load starts to get more and more resistive ?
I havent really thought about it. Must do..
 
A man can not have too many variacs

Offline klugesmith

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Re: Current transformer for narrow spaces
« Reply #10 on: October 13, 2020, 05:48:43 PM »
Yes. I expected it linear to at least 120 A, at 60 Hz, if blue transformer is made for 50 or 60 Hz.  Plus some margin for secondary resistance increase, when heated by continuous 1/4 watt dissipation, and when CT application has high ambient temperature (not specified).

Simple computations suggested that the salvaged EI core with one of its red windings could do better, saturation-wise.  Thanks to the power of steel, even though dimension ratios are not as good.  That was easily confirmed in the lab.

Chart below includes a curve showing the roll-off at high current, measured up to 275 A.  At that point more than 8 watts were heating the primary coil.


Thinking about the saturation issue, it may help to model CT secondary as a single heavy turn that needs to conduct almost as much current as the primary. Its cross-sectional area determines the heating rate.  Its resistance (from average turn length divided by area) determines the volts/turn, thus the core flux.  Then from Bmax of the core material, we can figure the required core area.

This EI core came with two windings, and I kept the bigger one.   First strike against it: extra turn length, to go around the middle leg of E.  Another penalty: it doesn't fill the whole width of the core window. Nor the whole length, but that's a different matter.

We could probably reach 250 A without saturation, by winding a new secondary to fit narrow leg of the E, and use full width of core window.  Doing that at home would be easier with wire much heavier than original (I'm thinking of 18 AWG), or even copper ribbon with 1 turn per layer.

The discussion so far applies to the load which CT places on primary circuit, due to reflected secondary winding resistance.  (Average turn length divided by coil area, times resistivity of copper.)  Not yet considered here: the phase-shifted voltage drop from magnetizing the core. It's a term that goes up with increases in core length or decreases in core permeability.

At I_pri =200 A, for ~50 mA in secondary, the induced voltage is about 30 V RMS (in winding designed for 120 V when all legs of E core are working).  That would be about 7.5 mV in the primary circuit, in phase with the current. 
When secondary V-I curve was measured separately, with one leg out of the picture, 30 V went with 3 mA of magnetizing current.  Corresponding to primary magnetizing current of about 12 A in CT service.  I think 90 degrees out of phase, representable as a parasitic inductance, and taking a bigger bite at higher frequencies (where saturation is less of a problem).  Please correct me if that's wrong.

Secondary DC resistance now measures 605 ohms. It used to be over 650, so maybe the exposed fine wire has developed a short.  Must repeat secondary V-I sweeps that were made before the bobbin was broken up and smaller red winding removed.
« Last Edit: October 13, 2020, 07:42:18 PM by klugesmith »

Offline klugesmith

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Re: Current transformer for narrow spaces
« Reply #11 on: October 21, 2020, 02:29:54 AM »
I want to enhance the little EI-core transformer as mentioned above, to handle 250 A without saturation. 
Theory says we can also reduce voltage drop in the primary circuit by a factor of two.
Looking for hints about coil winding.

We need more conductance in the secondary winding (and its single-turn equivalent circuit).
Today there's roughly 625 ohms in 4000 turns.  R/N^2 is 39 micro-ohms, so 200 ampere turns needs 7.8 mV per turn.
The turns are too long, because they go around center leg of E core instead of a side leg.
Winding area is too small because it's not even close to filling the window.
And fill factor is apparently poor, I guess because of "wild" or "jumble" placement of very fine wire.

We could improve things by a factor of five with liquid nitrogen, but there are CT applications where that's impractical.

Or replace the secondary winding with one on outside leg of E core, and try to maximize winding volume and fill factor.
16 or 14 micro-ohms seems to be within reach, requiring primary circuit voltage drop of 3.2 or 2.8 mV.

Here sketched with 18 AWG wire, wound orthocyclically (how hard is that, without using a lathe?)
and with copper strip occupying 0.006" (0.15 mm) per layer. Maybe using painted-on insulation?


Stock video of orthocyclic winding by machine:
/>
A secondary problem comes from the much smaller turn counts (63 and 44 in the drawing), which enable winding by hand.
CT secondary current will be 3 or 4 amperes instead of 50 mA, in 65 or 27 mΩ of copper, for internal voltage drop of 207 or 121 mV.
Now the voltage drop in external burden resistor, and its connection to the secondary coil, are significant.
And we have to make sub-100-mV AC measurement very close to the 200 A current under test.


« Last Edit: October 21, 2020, 03:00:15 AM by klugesmith »

Offline davekni

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Re: Current transformer for narrow spaces
« Reply #12 on: October 21, 2020, 04:42:19 AM »
I think it would be easier to build an active current transformer.  Either cut a slot and insert a hall-effect sensor, or use two secondary windings.  The hall sensor or one of the secondary windings is used to sense magnetic flux.  The other winding is actively driven to force flux towards zero.  Current is monitored in the driven secondary winding.
David Knierim

Offline plasma

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Re: Current transformer for narrow spaces
« Reply #13 on: October 21, 2020, 04:46:55 AM »
If you add a third winding to the primary, and use a current source to send 1A through it, you can I've measure the voltage on the secondary when current is applied to the first primary, or you can wind the second primary anti coupling and increase the current until a induction measurement on the secondary just reads it self.

Offline klugesmith

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Re: Current transformer for narrow spaces
« Reply #14 on: Today at 01:23:15 AM »
Any closed-loop solution (including plain CT) needs about 200 ampere-turns in an instrument winding on the core.
That comes with power dissipation on the order of a watt (less power if winding is bigger).  An active system could furnish that power without it having to come from the primary circuit.

One open-loop solution is Rogowski coil. 

Another open-loop solution uses a closed core with sufficient reluctance that primary current won't saturate it.  Then secondary winding (with negligible ampere-turns) senses dF/dt, thus dI/dt, just like a Rogowski coil, and needs a voltage integrator.  Its sensitivity can be much higher than Rogowski coil, but is proportional to the core's permeability (nonlinear, temperature sensitive, and with hysteresis). Distributed air gap core materials might be good.

Dave mentioned gapped core with Hall effect or other sensor in the gap, which is a popular open-loop configuration.  I have a new one rated for +/- 30 A.  Magnetic circuit can be pretty linear and stable because most of the reluctance comes from the air gap.  If I got my numbers right, 200 amps of MMF concentrated at a 2 mm gap will make B about 1/8 tesla (1250 gausses), RMS.  Are there inexpensive, linear B-field sensors with a large enough range for that?  (High range magnetometer probes seem to be very expensive.) How can we turn down the B, except by making the gap longer?  That will compromise the current transducer's smallness, insensitivity to position of the primary conductor, and rejection of current in nearby conductors that don't thread the core.

[edit] There are coreless sensors with ranges that come close, like this CS-200A ratiometric unit.  (Reminiscent of Weston's Little Bee.) If its output could swing rail to rail, that would correspond to +/- 250 A, not enough for 200 A RMS sinusoid.  And I need a clip-on that can fit through 7 mm gap between primary conductor and a conductor carrying same current in opposite direction.


There are closed loop Hall transducers up to at least 1000 A capacity, unavoidably big enough for 1000 ampere-turn instrument winding.
And plenty that are rated for 100A, all naturally about the same size as my blue 100A current transformer pictured above.
« Last Edit: Today at 03:28:22 AM by klugesmith »

Offline davekni

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Re: Current transformer for narrow spaces
« Reply #15 on: Today at 04:21:50 AM »
I was thinking of the hall sensor as feedback for closed-loop control.  Then it doesn't need to be highly linear or handle large fields.  Agree that the driven coil may dissipate a watt or so.  Another winding is probably easier than a hall sensor, since you don't need response down to DC.
Ebay has a couple permalloy tape-wound cores that would fit a 4 or 5mm gap and have reasonable winding area.  Search "nickel permalloy core".  Those would be good for precision closed-loop sensing given their high permeability.  Not cheap, though, $32-44 with shipping.

"Another open-loop solution uses a closed core with sufficient reluctance that primary current won't saturate it.  Then secondary winding (with negligible ampere-turns) senses dF/dt, thus dI/dt, just like a Rogowski coil, and needs a voltage integrator.  Its sensitivity can be much higher than Rogowski coil, but is proportional to the core's permeability (nonlinear, temperature sensitive, and with hysteresis). Distributed air gap core materials might be good."

For open loop, how about part-way between your above idea and a Rogowski coil.  Two identical rigid coils that are thin enough to fit between soldering gun leads.  Insert one between the leads and the other anti-parallel and adjacent, but outside the leads.  Bridge the top and bottom with blocks of ferrite.  That avoids the need to wind flexible coils.  Or, use a single coil between the leads and a ferrite C-core (or part of an E-core) to finish the loop.  The ferrite blocks/cores could have much more area than the coil, so have insignificant reluctance.
David Knierim

Offline klugesmith

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Re: Current transformer for narrow spaces
« Reply #16 on: Today at 06:19:28 AM »
You guys got me thinking about a closed loop solution with the existing EI core,
maybe even keeping its existing "120 V" winding.  Would use different skills and materials than fabrication of a new secondary winding to reduce R/N^2.  Result would have less disturbance of the primary circuit, and less error from nonlinear magnetizing current.

Add a sense winding on thin leg of core.  Its voltage could be electronically integrated to get a signal proportional to flux.  Servo-drive the main winding to keep flux at zero, minding the DC balance and loop stability. 

Today's main winding can provide 200 ampere turns with a tolerable rate of temperature rise,
but needs about 30 volts RMS because of its high resistance.  Time to get out a consumer audio amplifier?
In original passive CT, as demonstrated above, the error signal (difference between secondary and primary ampere-turns) magnetizes the core strongly enough to induce that much voltage in the secondary.  I think the CT roll-off at high primary currents, where core is nearly saturated, is because magnetizing current becomes disproportionately large (and non-sinusoidal). At best, the magnetizing current is 90 degrees out of phase.  Understanding grows one step at a time.
« Last Edit: Today at 05:22:48 PM by klugesmith »

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Re: Current transformer for narrow spaces
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[Laboratories, Equipment and Tools]
Mads Barnkob
October 20, 2020, 09:38:42 PM
post Re: QCW with replaceable ferrite-core primary
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Uspring
October 20, 2020, 05:08:29 PM
post Re: Quasar60 DRSSTC build using universal driver/interupter
[Dual Resonant Solid State Tesla coils (DRSSTC)]
RoadReaper
October 20, 2020, 03:17:48 AM
post Re: current limiting to parallel resonance circuit
[Beginners]
davekni
October 19, 2020, 11:02:11 PM
post Re: Quasar60 DRSSTC build using universal driver/interupter
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
October 19, 2020, 10:53:26 PM
post Re: Tesla coil circuit draws lots of current but the spark size is small.
[Solid State Tesla Coils (SSTC)]
davekni
October 19, 2020, 10:50:35 PM
post Re: Quasar60 DRSSTC build using universal driver/interupter
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Zipdox
October 19, 2020, 09:51:57 PM
post Re: current limiting to parallel resonance circuit
[Beginners]
Zipdox
October 19, 2020, 09:48:07 PM
post Re: Tesla coil circuit draws lots of current but the spark size is small.
[Solid State Tesla Coils (SSTC)]
SalinsLV
October 19, 2020, 07:27:59 PM
post Re: Quasar60 DRSSTC build using universal driver/interupter
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
October 19, 2020, 06:48:03 PM
post Re: UD2.9 skip pulse assembled
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Hydron
October 19, 2020, 03:54:00 PM
post Re: UD2.9 skip pulse assembled
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Maju
October 19, 2020, 10:25:25 AM
post Re: Quasar60 DRSSTC build using universal driver/interupter
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Zipdox
October 19, 2020, 08:56:13 AM
post Re: UD2.9 skip pulse assembled
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Netzpfuscher
October 19, 2020, 07:54:05 AM
post Re: QCW with replaceable ferrite-core primary
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
October 19, 2020, 05:32:05 AM
post Re: DIY DC-10MHz optical-fiber-isolated scope probe
[Laboratories, Equipment and Tools]
davekni
October 19, 2020, 05:12:05 AM
post Re: Quasar60 DRSSTC build using universal driver/interupter
[Dual Resonant Solid State Tesla coils (DRSSTC)]
RoadReaper
October 19, 2020, 04:13:30 AM
post Re: UD2.9 skip pulse assembled
[Dual Resonant Solid State Tesla coils (DRSSTC)]
profdc9
October 19, 2020, 03:39:49 AM
post Re: 6" Coil Update now 72" and better lighting
[Spark Gap Tesla Coils (SGTC)]
Bradselph
October 19, 2020, 01:53:01 AM
post Re: UD2.9 skip pulse assembled
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Max
October 19, 2020, 12:36:38 AM
post Re: 10 kW Induction Stove Teardown, Huge SMEG 5-Zone Stove
[Electronic Circuits]
Max
October 18, 2020, 11:57:02 PM
post Re: UD2.9 skip pulse assembled
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Maju
October 18, 2020, 11:14:53 PM
post 10 kW Induction Stove Teardown, Huge SMEG 5-Zone Stove
[Electronic Circuits]
Mads Barnkob
October 18, 2020, 10:42:01 PM
post Re: UD2.9 skip pulse assembled
[Dual Resonant Solid State Tesla coils (DRSSTC)]
profdc9
October 18, 2020, 09:54:48 PM
post Re: QCW with replaceable ferrite-core primary
[Dual Resonant Solid State Tesla coils (DRSSTC)]
johnf
October 18, 2020, 08:25:41 PM
post Re: UD2.9 skip pulse assembled
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Maju
October 18, 2020, 03:28:04 PM
post Re: current limiting to parallel resonance circuit
[Beginners]
Hydron
October 18, 2020, 12:08:36 PM
post Re: current limiting to parallel resonance circuit
[Beginners]
plasma
October 18, 2020, 07:31:58 AM
post Re: QCW with replaceable ferrite-core primary
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mads Barnkob
October 18, 2020, 07:18:08 AM
post Re: 6" Coil Update now 72" and better lighting
[Spark Gap Tesla Coils (SGTC)]
Mads Barnkob
October 18, 2020, 07:00:13 AM
post Re: DIY DC-10MHz optical-fiber-isolated scope probe
[Laboratories, Equipment and Tools]
Mads Barnkob
October 18, 2020, 06:50:25 AM

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