MEMM

[MeggerMan]

Hi Paul,
By adding a resistor (150R) and capacitor(2nf) across the ground and coil inputs you can remove that nasty back emf:

[PaulLowrance]

Hi Kator and Rob,

This experiment is used to determine the amount of MCE in a core.

The attached image is a simpler version. There is a toroid (gray) and a switch (green) and two wires (red & blue). When the switch is position A the current runs down the red wire and then down once again through the blue wire.  When the switch is position B the current runs down the red wire, but then up the blue wire.  In position A there's a net current going through the toroid. In position B the current in the red and blue wire cancel each other out.

The idea is maintain a constant temperature. The amount of heat given off by the wires is equal to Turns * Current. The direction of current does not change the amount of heat given off by the wires. Therefore, the core will receive the same amount of heat from the wires regardless if the switch is in position A or B.

Regards,
Paul Lowrance

[PaulLowrance]

Hi Paul,
By adding a resistor (150R) and capacitor(2nf) across the ground and coil inputs you can remove that nasty back emf:

Yeah, that's a good idea. I just place a cap across the red wire so when the switch breaks the current the cores energy can dissipate across the cap. I think 150 ohms like you said is fine. Also the caps internal resistance is good enough. The lower the R just means the energy dissipates at a slower rate with a little extra ringing. The ringing helps degauss the core a tad.   Although you really need a separate wire through the toroid & circuit to properly degauss the toroid. Do you have a good circuit that would work for degaussing?

Regards,
Paul Lowrance

[MeggerMan]

Hi Paul,
The core should not need to be de-gaussed.
If the field is permanently alligned in some way then surely you have a bad core material.

I suppose the TL494 could be used as de-gauss tool, connected to a "H" bridge so that the single coil can be used.
This way the polarity can be flipped at several khz.

I have been looking at the various PWM chips that Texas Instruments manufacture.
The TL598 looks like a better choice than the TL494 in that it has a totem-pole output stage. So there is not pull-up or pull-down resistor required which should reduce power consumption but more importantly the switching time on/off and off/on will be faster and hence will save power in the switching of the output stage.

Also they have some more recent devices with what I think is called "TrueDrive" for a high speed, high current drive into the output MOSFET. I think these are also available as a device that sits between the pulse chip and the mosfet.

All these bits may add up to a few percent of input efficiency but if the output is twice the input then it would mean that its not too important at this stage and can be looked at later once the concept is proved to work.

Regards

Rob

Regards

Rob

[PaulLowrance]

Hi Rob,

Any word from Naudin?

...

The Metglas cores have square hysteresis curves. If you saturate the core and remove the applied field most of the field will remain. Don't you think it's important to degauss the core for the MCE experiment?

Regards,
Paul Lowrance