The Thomas Motor

[gyulasun]

Good Morning Ben,

The smallest OD core available in the 3R1 material is TN14/9/5-3R1, see here http://www.elnamagnetics.com/?s=tn14&type=spec  but perhaps it is too small already?  Not only small for winding the thin wire onto it but may go into saturation just by the core magnet, not to mention the bigger rotor magnets when in the near vicinity of the core.

Gyula

[k4zep]

Good Morning Ben,

The smallest OD core available in the 3R1 material is TN14/9/5-3R1, see here http://www.elnamagnetics.com/?s=tn14&type=spec  but perhaps it is too small already?  Not only small for winding the thin wire onto it but may go into saturation just by the core magnet, not to mention the bigger rotor magnets when in the near vicinity of the core.

Gyula

Thanks Gyula,

They are pretty darn close to what I want. What I am using now is a 21mm OD X 13mm ID The saturation of the core by the core magnet and the rotor magnet is a physical problem.....So many variables here.  With the core I am using now, I get about 600 gauss leakage (Gauss through the core) when touching the rotor magnet and 0 gause leakage through the core with 1/8"spacing which I am using right now.  That could be brought closer to optomize the demo motor but no need to do it right now.  With my core magnet, I am getting about 140 gauss leakage through which means I am starting to saturate it but room there for optomization too.  But building this motor was a learning experience to me and getting up to speed on switching magnetics!  I think my cores are very hi u material around 10,000.  I don't remember for sure. That's what you get for not keeping good notes from 3 years ago. That 3r1 material is much lower u but has a hell of a square switching curve.  If you can get right up to the knee, would take very little energy to switch.  Hummmmmm.  Anyway, thanks again for all the tips.
Will call the place today and get a quote on some cores.

Ben

[k4zep]

Thanks Gyula,

They are pretty darn close to what I want. What I am using now is a 21mm OD X 13mm ID The saturation of the core by the core magnet and the rotor magnet is a physical problem.....So many variables here.  With the core I am using now, I get about 600 gauss leakage (Gauss through the core) when touching the rotor magnet and 0 gause leakage through the core with 1/8"spacing which I am using right now.  That could be brought closer to optomize the demo motor but no need to do it right now.  With my core magnet, I am getting about 140 gauss leakage through which means I am starting to saturate it but room there for optomization too.  But building this motor was a learning experience to me and getting up to speed on switching magnetics!  I think my cores are very hi u material around 10,000.  I don't remember for sure. That's what you get for not keeping good notes from 3 years ago. That 3r1 material is much lower u but has a hell of a square switching curve.  If you can get right up to the knee, would take very little energy to switch.  Hummmmmm.  Anyway, thanks again for all the tips.
Will call the place today and get a quote on some cores.

Ben

Gyula,

Found the packing slip in the bottom of the bin where I keep the cores.  The cores I am using is a Fair-Rite core, PN1N014PD Code 1N017.  As seen here:
http://www.westfloridacomponents.com/IN017/Ferrite+Core+ID%3A+13mm+OD%3A+21mm+Fair-Rite.html, of course that is the only one there that
has no Fair-Rite catalog number.
I downloaded the Fair-Rite catalog from ELNA magnetics but can't find the cross to it to get the Spec. sheet, I'm pretty sure u of 10,000.  Have a request into
Fair-Rite for help.

Ben

[gyulasun]

Hi Ben,

Perhaps if you have an L meter you could check your core (with the core magnet attached as in the motor setup) as follows: just wind 10 turns of a probe coil onto the top of the original winding, and check its inductance when the original coil is floating. Then excite slowly the original coil from your power supply and see how the inductance of the 10 turn coil reduces as the core goes towards saturation.
To approach the 160mA current draw from 19V DC input (if that is what you meant) then adjust that current value with a series resistor of a 120 Ohm (19V/160mA), though you may have to consider the peak current value and reduce the resistor accordingly. A series resistor is a must though because otherwise the supply's internal resistance would short the original coil so the 10 turn probe coil could not be measured correctly (unless the power suply has a  'current source' mode).  This way you could figure out from the percentage reducements of 10 turn coil's inductance values in the function of the input voltage or current that at what input level the original coil is able to saturate the core, it would be interesting to explore the 11-12V voltage area.

I found a Fair-Rite core with your OD/ID/h sizes made from material #75, u=5000   Part Number: 5975000601  but in the u=10,000 (material #76) there was not any such sized toroid, (perhaps it is not produced as standard size any more?) The 21x13x6.4 is produced with a u=2000 and less too.
If your core has indeed u=5000 only, then its A_L value is 2950nH so 10 turns on it should give 10x10x2950nH=295uH inductance if you have an L meter.

Gyula

[k4zep]

Hi Ben,

Perhaps if you have an L meter you could check your core (with the core magnet attached as in the motor setup) as follows: just wind 10 turns of a probe coil onto the top of the original winding, and check its inductance when the original coil is floating. Then excite slowly the original coil from your power supply and see how the inductance of the 10 turn coil reduces as the core goes towards saturation.
To approach the 160mA current draw from 19V DC input (if that is what you meant) then adjust that current value with a series resistor of a 120 Ohm (19V/160mA), though you may have to consider the peak current value and reduce the resistor accordingly. A series resistor is a must though because otherwise the supply's internal resistance would short the original coil so the 10 turn probe coil could not be measured correctly (unless the power suply has a  'current source' mode).  This way you could figure out from the percentage reducements of 10 turn coil's inductance values in the function of the input voltage or current that at what input level the original coil is able to saturate the core, it would be interesting to explore the 11-12V voltage area.

I found a Fair-Rite core with your OD/ID/h sizes made from material #75, u=5000   Part Number: 5975000601  but in the u=10,000 (material #76) there was not any such sized toroid, (perhaps it is not produced as standard size any more?) The 21x13x6.4 is produced with a u=2000 and less too.
If your core has indeed u=5000 only, then its A_L value is 2950nH so 10 turns on it should give 10x10x2950nH=295uH inductance if you have an L meter.

Gyula

Hi Gyula,-
With 10 turns over plain core, it is 54.63uH, therefore I suspect it is a lot less than u=5000 , possibly u=750 with a small magnet on the core, it drops about 5uh to 49uh, within 1/8" of the large magnet it drops to about 4uH....Big magnet on rotor is definitely saturating the core!  I have to wind another coil as I don't want to lift the magnets off the video motor as it might break the wires as they are glued down.  I'll play with the constant current power supply and see how much the big coil does around 12VDC.  Thanks for the input.  I'll get back to you.

Ben