MEMM

[MeggerMan]

Hi Stefan,
I think the ratio of tape to ferrous material will be very large, so in effect you will end up with a core made of 99% pastic.
I'm leaving the building of the cores themselves to the experts at Metglas or Hitachi metals.

Hi Paul,

I have emailed JLN to ask what material he used for the permanent and whether he tried altering the DTC - dead time control on the TL494 to allow a gap in between the two input pulses.
What I suspect is that it may be able to get a different peak frequency using this variable DTC and possibly getting an even better COP.
At the moment the two input pulses are right on top of each other(follow one right after the other) and leaving a small gap may allow the output waveform to form its peak at a lower or higher frequency.

I am looking at testing both with and without DTC to see if I can improve upon the experiment that JLN carried out.

Using 555 timers for this will be complex and I suggest sticking with the TL494 as it is built for this push-pull process.
There are even faster/high current and more up to date versions of the TL494 but I think these might be a bridge too far.

Regards

Rob

[lancaIV]

Hello MEMM-audience,
Molina-Martinez used,following his patent description, Hyperco !

S
  dL

[PaulLowrance]

Stefan,
Do you know of any high perm. magnetic tapes? That would be good for my Method #2.  Method #1 is all about having the Eddy currents absorb MCE energy, which is why the MEG relies on electrically conductive cores. Most ferrites will not work for method #1 unless the ferrite has electrically conductive magnetic powder.


Rob,
Do you have any scope shots? Hopefully Naudin will reply because he should have books of tips. It seems Naudin spent a great deal of time precisely replicating the MEG. He'll probably recommend the conditioned resistors, which might be worth a try.


I'm still messing with taking MCE measurements on the Metglas. For some reason the office has been flooded with thermal noise fluctuations, intense electrostatic random fields. It took one day to narrow down and finally accept that my LM741 burnt up.

Anyone who's interested,

---
How to measure MCE:

Place two thick copper wires down the center of toroid core #1-- the thicker the better. Three feet long is fine. The two wires will always be in series. Through out the entire experiment you will run DC current through both the wires. The amount of DC current depends on the core material. You will need to bring the core to at least 1 T or saturation. Core #2 does not have any wires going through it, but it should be slightly above the two wires and close to core #1. There should be no wires touching core #1 or core #2. On top of each core is a Thermistor. You should place heat sync grease under and around the thermistor and core to help thermal conductivity. The thermistors go to an op-amp circuit. See attached image. A gain of 100 is fine for 100K Thermistors. One lead from each Thermistor goes to ground, while one lead from Thermistor #1 goes to op-amp negative input, and one lead from Thermistor #2 goes to op-amp positive input. This will eliminate any op-amp output changes with room temperature change, but a noticeable op-amp output change if the temperature changes in just one core. Therefore, if just core #1 temperature changes then we'll see the op-amp output change, but if the room temperature changes then we'll see no change on the op-amps output. Each Thermistor should be at least 100 KOhm.

Stage #1. The wires are connected so the DC currents create an applied field on toroid core #1. Also your op-amp filter should filter out higher frequencies. Two 22 uF capacitors work just fine; i.e., one cap from output to ?in, and the cap from +in to ground. Make sure the toroid cores are touching the least amount of solid. Stagnate air is one of the best heat insulations. You will need to completely cover the toroids to prevent any air circulating on the cores. It will take some time for the heat waves to settle down. Eventually you get a steady signal from your op-amp output. Note you'll want to use the op-amp balance pins. You can slow adjust a fine precision pot so the op-amps output approaches zero volts.

Stage #2. You will need to quickly swap the two wires so the currents in core #1 are canceled. This means there's no current in the core. IOW, current runs one direction through wire #1, but current runs the opposite direction in wire #2. You should always have a cap across one of the wires to dampen any spikes when you swap the wires. Use two switches such as a solenoid to swap the two wires. You want the wires to carry current as often as possible. The goal is to maintain the same temperature throughout the entire experiment. After you swap the two wires core #1 will need to be degauss. One method of degaussing core #1 is with a 3rd wire going through core #1. You will need to apply AC current (no DC current) through wire #3 and then slowly dampen the AC current until there's eventually no current. The AC current needs to at least be as high as the total current in wire #1 and #2. It should only take a few seconds at most to degauss the core. Although cores with square hysteresis curves may take longer. So now the core is degaussed and the temperature should drop. You need to write down how fast the temperature drops and to what degree. A graph would be great. It will probably take at least one minute before you'll see a good change in temperature and several minutes to reach peak.

When the temperature changes settle down, you can swap the two wires again so there's a net applied field in core #1. Now the core will heat up. You will once again record the temperature changes. This completes one full cycle. Now you can once again swap the wires and degauss the core for another cycle.

You want to make sure the core is truly saturated during stage #1 and completely degaussed in stage #2. You can verify this by running a tiny amount of constant ac current through core #1 and measure the voltage across the core. This will show the permeability factor. The voltage across the core should be maximum when the core is degaussed and minimum when saturated. Remember, the ac current must remain the same.

See the attached image. The POT (R10) is to balance your thermistors since no two thermistors are alike. You'll probably want to make R10 a large resistor in series with a large pot unless you have a pot with enough resistance. I drew the Thermistor (R5) as 98.7K merely as an example to demonstrate that two thermistors are not alike. R6 & R8 should be matched resistors or two adjusted pots since they need to be the same resistance. I find the old LM741 a good choice believe it or not because the 741 doesn't mind big capacitors. Surely there's always a better choice. The circuit drawing does not show the op-amp balance resistors. Op-amp pin 1 goes to one end of a 200 K pot, pin 5 goes to the other end of the 200 K pot, the center of the pot goes to a 200 K resistor, which goes to V+. If 200 K does not offer enough balance then try 100 K values.


Regards,
Paul Lowrance

[Kator01]

Hello PaulL,

I simply can not follow what you are descrining here :

Place two thick copper wires down the center of toroid core #1

Please can you explain by a simple drawing what you mean when you say :
Place ... down the center - and later : the wires  in series

It is really confusing because 2 wires in series ?? why not use one wire then ??

Regards
Kator

[MeggerMan]

Hi Paul,
Yes I am confused too with the arrangement of the wires.
Don't you mean you wind a couple of hundred turns onto the toroidal core?
Using two wires (two coils) means a simple setup but you could use a 2 pole change-over switch and just use one coil.

Regards

Rob