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High voltage probe for O-scope, 2 of 2, ( FABRICATION ).

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Patrick

Mon Oct 31 2011, 12:05AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

New work from 10/30/2011:

lower division values are 6.64nF and 37.59 kOhms.
compensator is 51ohms, in parallel with 254-324pF variable capacitor.

Patrick

Sun Nov 06 2011, 03:19AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

New work as of Nov 5... Almost done!

I used non fluxed copper de-soldering briad for the ground/shield connection.

Patrick

Sun Nov 06 2011, 07:09PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Finished!!!!!!!!!!!!!!!!!!!!!!!!!! ( I Hope. )

EDIT: it looks GOOD, real good, so far at low freq (60 Hz) at 6000 Vac RMS... now i really need that callibrator!

EDIT 2: it can resolve on sine waves of 60uS which is about 17kHz, which was way better then the purely resistive dividers ive built in the past...

EDIT 3: it sees all sorts of stuff with an iggy and a 18 V battery... This THING ACTUALLY WORKS !

EDIT 4: I can verify a point proud mary and i pondered, if you disable the X10 button its the normal 10,000:1 ratio, but enable the 10X button and it becomes a 1000:1 ratio! How cool is that!

Testing will begin in a few hours, i have math homework i gotta do now though.

She still needs her permanent tats which ill print out and laminate soon.

Single trimmer for compensation, weeping yet Tektronix p601* users?

Patrick

Wed Nov 09 2011, 03:02AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I gonna try to get this transformer working for some super HV, maybe 30 plus kV....

As, Proud Mary sugggested ive been able to find A 65 volt sub coil, its not intended to be used as a primary but it has the same AWG wire as the orignal primary, and has sbout 0.5 ohms or less.

I dont see any oscillograms of Flybacks here on the forum so ill gather some.

Twisted green wires are for a thermistor at the hot spot. Yellow and black twisted pair is the primary. single black and large red is for secondary HV out. 9v for scale.

OLd variant in oil tank, new mod in fore ground.

EDIT: i have to be careful im getting 2.2 inch HOT sparks between two sharp points. Ill be using a series output resistor to prevent a short lived flyback. I have to admit the internaL primary does seem much better.

Patrick

Mon Dec 19 2011, 04:02AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

OOPS! i made a blunder, the lower division resistor should be 75k ohms, not the quoted 37.5k ohms, DUH. i forgot that the both the C and R parrallel dividers are supposed to divide by 5,000:1 then then the compensation and anti reflection components in the cord divide by 2:1, therefore 5,000:1 in series with 2:1 yields a 10,000:1 total ratio.

in the above schematic R4 is shown as 37.5k ohms, but should be 75k ohms. My error.

Sulaiman

Mon Dec 19 2011, 01:58PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Patrick,
sorry to comment so late in the project but based on the circuit diagram that you posted
the dc attenuation and ac attenuation (or lf and hf if you like) are different,
and the bottom arrangement of 75k (or 37k5) feeding a terminated 50 Ohm transmission line is 'unusual'.

Patrick

Mon Dec 19 2011, 10:23PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Sulaiman wrote ...

Patrick,
sorry to comment so late in the project but based on the circuit diagram that you posted
the dc attenuation and ac attenuation (or lf and hf if you like) are different,
and the bottom arrangement of 75k (or 37k5) feeding a terminated 50 Ohm transmission line is 'unusual'.

please elaborate, keeping in mind i did use this source,

Turkey9

Tue Dec 20 2011, 05:58AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

For the values that he has, it will be pretty linear up to 10 Mhz according to an LTspice sim I just ran.

But that brings up the question, why do you want the capacitors in there? With a purely resistive divider, there are no frequency concerns. Is it because there will be capacitance there anyway since it is a real life circuit and you want to be able to control it?

Patrick

Tue Dec 20 2011, 06:30AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Turkey9 wrote ...

For the values that he has, it will be pretty linear up to 10 Mhz according to an LTspice sim I just ran.

But that brings up the question, why do you want the capacitors in there? With a purely resistive divider, there are no frequency concerns. Is it because there will be capacitance there anyway since it is a real life circuit and you want to be able to control it?

First, yes i cant have a purely resistive divider due to the stray capacitences i need to control.

Second, what happens after 10Mhz?\

Third, Id like to artificailly limit the bandwidth to some value less than about 100Mhz.

EDIT: Im thinking of adding a 18 V bi directional TVS, across the coax shield and center pin. This would protect the Oscope from inductive kick, since i use many Autotransformers which can be dangerously noisy. At 18V id be able to avoid clipping up to 180 kV (for a 42kV capable probe) I dont think the devices stray capacitence would matter if inserted between the 300pF, and two 6.4 nF caps.

EDIT: i think ive found the resonant freq of my best HEI iggy coil.... I think its 3-5kHz...

(EDIT: from tough to trough is 178uS)
I only tapped a 9V battery to the HEI iggy and captured this waveform...
5.08 Kv peak, 800 volt ring below ground. 254 uS for the main pulse (i think) 1/0.000254 = 3937 Hz, i think thats close to its resonant freq.

EDIT: i wonder if those first six concave downs could be integrated to find the arrea under the main 5kV pulse?

If there are 6 cylinders, at 3000 rpm thats (3000/60) x 6 = 300 sparks per second.
1/300 sec divided by 254uS would yield about 13. So the dead space would be 12 time periods, for each 254uS spark.

Turkey9

Tue Dec 20 2011, 09:09PM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

Wow that's really cool! It will be great to actually get wave forms from all the transformers we to get HV. If that wave form came from tapping the 9V to the primary, what are all those little pulses before the big one? Noise from the mechanical contact? I'd expect them not to be as uniform as they are.

I only ran the sweep in the sim to 10 Mhz, but at that point the attenuation had dropped a couple dB. Up at that frequency the ratio will decrease so keep that in mind when making accurate measurements.

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