Dual coil for mpp

[Denots]

Thanks guys, things are starting to fall into place now.
Been trying the coils in different configurations with some interesting results, for instance if I join the two coils in parallel and possibly wired the wrong way round, it seems that it reduces overall inductance to roughly one third of what it is joined in series the right way round.
Likewise if I wire them in series but wire the coils opposite it also reduces inductance, seems to me that it is reversing the magnetic field and reducing inductance, so one coil is making inductance the other is undoing it?
I only have one damping tool at the moment and that’s a 10k pot, it doesn’t seem to have the best range so will order up a 1k pot and add a 200ohm and see if that gives me finer control, in my head that gives me a potentiometer that can range from 200ohm up to 1k2 which should be just right?

[waltr]

ok so with your help I think I?m getting somewhere, inductance is .120 capacitance is .430, if I?ve got this right I times capacitance by pi and then inductance is divided by the previous result which gives me 0.0888 and some change. I?m not 100 percent sure how accurate the readings are so will go back and measure again once I?ve got the formula.

0.0888 is correct for the L/(Pi * C) with the values you posted. Now take the Square Root of 0.0888 which is 0.298.
This is just checking the math.

Be careful to use and correct units for the L & C values. These need to be in Henries and Farads to obtain the result in Ohms.
Examples: 300uH = 0.0003H = 300x10e-6, 50pF = 0.00000000005F = 50x10e-12

[Denots]

0.0888 is correct for the L/(Pi * C) with the values you posted. Now take the Square Root of 0.0888 which is 0.298.
This is just checking the math.

Be careful to use and correct units for the L & C values. These need to be in Henries and Farads to obtain the result in Ohms.
Examples: 300uH = 0.0003H = 300x10e-6, 50pF = 0.00000000005F = 50x10e-12

brilliant thanks for clearing that up, been reading through the electronics for dummies book and it’s helping to clear some things up, the settings on my meters are starting to make more sense now as well, like you’ve just mentioned how Henries and farads are bigger units that are broken down to smaller units on smaller or larger scales, same with amps and milliamps and the likes.
this stuff has justified me for years but it is starting to make sense now

[Carl-NC]

Been wondering how to measure coil capacitance with a LCR meter. Found a site explaining how. To measure inductance, test frequency needs to be less than coil resonance. To measure capacitance, test frequency needs to be higher than coil resonance. It didn't say how much higher or lower to get a accurate reading. Does anyone know?

Probably 10x at least. I used to have an HP LCR bench meter that went to 1MHz, which isn't enough. Most handhelds only go to 10kHz.

[Carl-NC]

ok so with your help I think I?m getting somewhere, inductance is .120 capacitance is .430, if I?ve got this right I times capacitance by pi and then inductance is divided by the previous result which gives me 0.0888 and some change. I?m not 100 percent sure how accurate the readings are so will go back and measure again once I?ve got the formula.

You can't measure coil capacitance with a capacitance meter. You need either a sig gen or place it in a pulse circuit and look at the ringing. Either way requires an oscope.

thank you for participating, so am I right in thinking the signal hits the big coil first then passes through the smaller coil before returning to ground?

The current goes through both coils simultaneously.

[Carl-NC]

having a bit of trouble with the math, It?s times like this I wish I had stayed in school
[ATTACH]47532[/ATTACH]

I'm not sure how Dan (Geyer) came up with that equation, but the proper value for RD is



Dan's equation is close though.

The way I would damp a dual-field coil is to measure the SRF of the total coil and calculate the main RD. There will probably be some residual underdamping effect caused by mutual coupling, so then just try different values for the internal RD until things look good.

[dbanner]

I'm not sure how Dan (Geyer) came up with that equation, but the proper value for RD is



Dan's equation is close though.

The way I would damp a dual-field coil is to measure the SRF of the total coil and calculate the main RD. There will probably be some residual underdamping effect caused by mutual coupling, so then just try different values for the internal RD until things look good.

Yes, I felt the inner coil is adjusted last until things look optimum. That is exactly what the description in the patent infers, if one is so inclined to read that patent jargon rubbish.

[godigit1]

Ok I understand that the proper procedure is to damp the inner coil last.
But can I ask a couple questions?

If a coil is critically damped by itself does the damping value for that coil change if another coil is attached ?

I damped my coil that way when I did it and it looked good on the scope when everything was said and done.
It seemed to work so Im trying to understand what Im missing. Just thinking maybe there is more than one way to skin a cat.



Im probably wrong but was thinking coil damping value is set for each individual coil by Inductance resistance capacitance SRF.

So Is it that when the coils are hitched together in series those values change thus the damping would change?

Thanks,

[Carl-NC]

Yes, mutual coupling affects damping.

[dbanner]

Ok I understand that the proper procedure is to damp the inner coil last.
But can I ask a couple questions?

If a coil is critically damped by itself does the damping value for that coil change if another coil is attached ?

I damped my coil that way when I did it and it looked good on the scope when everything was said and done.
It seemed to work so Im trying to understand what Im missing. Just thinking maybe there is more than one way to skin a cat.



Im probably wrong but was thinking coil damping value is set for each individual coil by Inductance resistance capacitance SRF.

So Is it that when the coils are hitched together in series those values change thus the damping would change?

Thanks,

Although I cannot say for sure, but the way I see it, the value of the damping resistor for a mono coil can vary by plus or minus tens of ohms, or even more, before ringing shows up, This would apply also to any mutually coupled coils as well.
The thing is to treat with the two coils as one inductance and capacitance, and damp the overall inductance first, this will bring you closer to less ringing caused by the inner coil, which is finally damped last to eliminate all ringing.
What I find very curious is that after so many years, nobody can give proper data on the White's dual field coil, like inductances of both coils, and value of the damping resistors used, which I would assume to be standard values for all of the dual field coils of that size.

[godigit1]

Thank you Carl And dbanner.

One other thing about the dual fields and maybe most do not experiance this.
But I have two 12 inch Duall fields that came with a used tdi pro.
Both coils sing.
You can hear a audible hum coming from the coils.
The Tdi I bought from a guy going by fried chicken on the whites forum. First whites sent him a new coil.
then it still hummed so the unit was sent to whites and back with no problems found.
Has anyone experianced this as well or with different types of coils.

Ps. I keep going back and forth on sacrificing one for the cause. Hard to ruin a perfectly good coil though.

[dbanner]

Thank you Carl And dbanner.

One other thing about the dual fields and maybe most do not experiance this.
But I have two 12 inch Duall fields that came with a used tdi pro.
Both coils sing.
You can hear a audible hum coming from the coils.
The Tdi I bought from a guy going by fried chicken on the whites forum. First whites sent him a new coil.
then it still hummed so the unit was sent to whites and back with no problems found.
Has anyone experianced this as well or with different types of coils.

Ps. I keep going back and forth on sacrificing one for the cause. Hard to ruin a perfectly good coil though.

DO NOT UNDER ANY CIRCUMSTANCES SACRIFICE ANY GOOD COIL. OH NO, NO!
IF you have old time fillings in the teeth as I do, then you are hearing strange humming sometimes, even high pitch sounds.
Hundreds of hertz PRF is perfectly audible. If you got the right teeth fillings.
Also, I would never buy anything from a guy calling himself fried chicken.

[Carl-NC]

Both coils sing.
You can hear a audible hum coming from the coils.

Not unusual, and of no concern. The coil windings are vibrating. Transformers do this all the time.

[dbanner]

Yes indeed. I imagine that dual field coils moreso.
I was thinking about the Rd formula from the patent Dan(Geyer) vs the formula that Carl-NC posted above, which we are all familiar with.
Although Dan's equation is close(0.56 as opposed to 0.5) I can't help but think that there might be a reason why this formula was used in the case of these coupled coils( it may be more accurate in this particular case, perhaps?). There might be something more to it.

[godigit1]

Thanks Carl,

DO NOT UNDER ANY CIRCUMSTANCES SACRIFICE ANY GOOD COIL. OH NO, NO!
IF you have old time fillings in the teeth as I do, then you are hearing strange humming sometimes, even high pitch sounds.
Hundreds of hertz PRF is perfectly audible. If you got the right teeth fillings.
Also, I would never buy anything from a guy calling himself fried chicken.

yea I thought it was funny he said he just made up something for the forum to ask questions and was eating fried chicken.
He did this video before I bought it
https://www.youtube.com/watch?v=RrR1XBDutCQ

Ill have to check if my Mpp makes the noise as well I dont think so but im not on practice of sticking my head to the coil.