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Performance tests of induction coils

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LAN_403

Physikfan

Fri Aug 12 2016, 10:16AM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Hi

I have two commercial induction coils by Leybold, 10 cm spark length, 250 windings at the input side and 26 000 windings at the output side.
P1760065TRIM400x302

Both induction coils are working with the WagnerÂ´s hammer as well with a thyristor power supply.

But both secondary coils did not show an ohmic resistance measured with a low voltage ohm meter, DC 1,5 V Unigor or AC HP RCL-meter (1V, 110Hz).

For further experiments I have used both induction coils as normal AC transformers, applying AC voltage 50 Hz, 1 V to 10 V in steps of 1V at the primary coil.
From 0 to about 4 V at the primary coil no signal was at the secondary coil.
From about 5 V to higher voltages at the primary coil at the secondary coil a voltage was measured corresponding to the windings ratio of 26000 / 250.

What do you think about these measurements?
Are there small interruptions of the wire in the coils which lead to small arcs which will destroy as a consequence the complete secondary coil after a longer use the induction coils?

Please, I would like to ask owners of induction coils to measure the ohmic resistance of their respective secondary coils
and report their results in this thread.
Also I am looking forward to your advice, experiences etc.

Regards

Physikfan

Antonio

Mon Aug 15 2016, 12:44AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

A broken wire in the secondary is a (bad) possibility, but a bad contact in the sliding rod is also possible. Verify where are you measuring the resistance, and make it sure that all the contacts are good.

johnf

Mon Aug 15 2016, 07:09PM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

to measure the resistance will take quite some time with an ordinary multimeter as you are fighting the huge inductance of the secondary (many 10's of Henrys) be careful when you remove the meter leads as a substantial shock can result by the collapsing magnetic field in the coil

DerAlbi

Mon Aug 15 2016, 07:36PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

You dont want measure big inductances with a multimeter. This can become confused by the induced 50/60Hz hum. Depends on the multimeter of course. I would suggest you just put constant voltage over it and measure the current in dc mode to get a good resistance measurement.

klugesmith

Tue Aug 16 2016, 12:23AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

To determine the polarity of my first 60 Hz XRT, I put a neon glow lamp across a secondary winding and connected a 1.5 volt AA cell to the primary. Got a momentary glow on one electrode, as expected. The surprise came when I disconnected the battery. The opposite electrode glowed for a while, as the lamp clamped the output voltage of this ad-hoc flyback transformer.

Physikfan

Thu Aug 18 2016, 05:57AM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Hi klugesmith

This is a very surprising and interesting experiment.
I would like to reproduce your results.
Please tell me what XRT means.

Regards

physikfan

Physikfan

Thu Aug 18 2016, 06:21AM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Hi Antonio, johnf, DerAlbi and klugesmith

I have determined the resistance and the inductance of another fully working commercial induction coil comparable to the Leybold induction coils
by measuring

1. the DC resistance and
2. the AC impedance at 50 Hz

and then calculating L.

P1760162trim400x274

induction coil spark length 120 mm

Here are the values:

Secondary coil:
R = 25 kOhm
Inductance 524 H
windings ratio 1:230

Unfortunately I have no exact numbers of the windings of the primary and secondary coils.

The same procedure was not successful by measuring the two Leybold induction coils as reported in fy first posting.

Regards

Physikfan

GrantX

Fri Aug 19 2016, 10:32AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

Physikfan wrote ...

Hi klugesmith

This is a very surprising and interesting experiment.
I would like to reproduce your results.
Please tell me what XRT means.

Regards

physikfan

In this context, XRT refers to an X-ray transformer, the high voltage transformer that supplies the vacuum tube in an X-ray imaging machine.

These transformers have a different construction to a HV induction coil, but have a similarly high turns ratio. They use a regular laminated iron core with no air-gap and produce anywhere from 50-150kV (requiring oil insulation due to the compact size) with a short circuit output current of approx 5-10mA. They are usually only intended to be powered for a few seconds, and will quickly overheat. However, there are some industrial X-ray machines that feature very powerful transformers capable of 250kV+ and many kVA.

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