Dual coil for mpp

[Denots]

I hear my monocoil humming on the mpp all the time, seemed like a normal thing considering the frequencies passing through them, a bit like how power lines make noise in the right conditions.

After some one playing around with the dual coil setup one thing I’ve found is that this coated copper wire can be a bit finicky when trying to join things up, sometimes the coating might not scratch off properly and give a bad join, had a few problems arise while soldering with this stuff too. Because of that I decided to wind a new dual coil but this time all from one continuous piece of wire.


I made it a tad bigger so it fits in the outer housing a little better and voila


319mh, just need to straighten out some of the kinks and bundle it up a bit nicer now, for the damping resistor I plan on scraping back some of the coating and soldering it on there, on reflection I should have slid a bit of shrink tube on as I was winding the middle coil but never mind.

Just in case anyone is wondering what happens happens if you fit either of the coils the wrong way round


you get a big drop in inductance, got thinking of a new experiment, got me wondering what would happen if the outer coil were say 600mh and inner coil maybe 300mh and you flip a coil round the wrong way bringing the inductance down, for arguments sake it comes down to 300mh, I wonder how that coil will perform against the coil I just made?

[godigit1]

I think you would end up with more capacitance due to more twists more wire . But experiments are where we learn.

I was looking at this coil and thinking this would be a good form for a dual field that is bundle style like yours.
Its plastic cardboard but its actually made of polypropalene which has good dialectric qualities.
its just rigid enough to hold the loops in a spool like fashion once the ridges have been removed around the edge. I just nipped them out,.
once wound or even before the spool I.D could be cut to size for a shell.
The other benefit of a spool is you can add some spacing between layers dropping capacitance by allot. I used silicon flex tape as a spacer.
Wire mass and resistance stayed the same while both capacitance and inductance dropped.
Just rifing on things a little



Interested to see your final results. Did you ever pull the trigger on a scope?

Just found a local resource in my area maybe they have something like this close to you .
A makers space the one I found has Metal shop complete with cnc plasma cutters forge theres a wood shop plastics foam shop 3d printing and a electronics lab with everything. And this one is open 24/7 for 50 a year. You have a little factory Oh yea and its super stocked with donated components Right to teflon coated wire. Its co-op so its all yours to use.
I was kid in a candy store.

[Denots]

I think you would end up with more capacitance due to more twists more wire . But experiments are where we learn.

I was looking at this coil and thinking this would be a good form for a dual field that is bundle style like yours.
Its plastic cardboard but its actually made of polypropalene which has good dialectric qualities.
its just rigid enough to hold the loops in a spool like fashion once the ridges have been removed around the edge. I just nipped them out,.
once wound or even before the spool I.D could be cut to size for a shell.
The other benefit of a spool is you can add some spacing between layers dropping capacitance by allot. I used silicon flex tape as a spacer.
Wire mass and resistance stayed the same while both capacitance and inductance dropped.
Just rifing on things a little

[ATTACH]47583[/ATTACH]

Interested to see your final results. Did you ever pull the trigger on a scope?

Just found a local resource in my area maybe they have something like this close to you .
A makers space the one I found has Metal shop complete with cnc plasma cutters forge theres a wood shop plastics foam shop 3d printing and a electronics lab with everything. And this one is open 24/7 for 50 a year. You have a little factory Oh yea and its super stocked with donated components Right to teflon coated wire. Its co-op so its all yours to use.
I was kid in a candy store.

The link seems to be broken.
Thats interesting about the makers space, I’d imagine you get some really clever people in them places that could help a lot with this sort of thing.

Yeah ah I got a scope in the end, slowly getting my head around how it all works, watched a few videos and picked up a few tricks and learnt some neat features but still feel a bit out of my depth with some of the later steps in the build guide.
Even when it comes to damping I’m not 100% sure what the scope is meant to say, got a pretty good idea what’s meant by ringing and all but until I start messing around with it again and see the results for myself, for instance I used my damping tool and tuned it to what I thought looked like a nice curve but when I checked the resistance it was well out from the damping resistor value that came with the kit. I need to learn what looks right and what’s wrong that’s all, with all the help and advice on this thread alone I should have enough info to get this set up nice.
Got a couple of 1k pots in the post for a couple of new damping tools, just learning how to test srf from the fast coil guide then gonna make a test circuit for that next.

[Denots]

That’s the test circuit hooked up


I’ll have to wait till back in the office to fire it up but hopefully all will be well.
Who would have thought you could make a 1pf cap out of a piece of wire

[Denots]

I don’t think I can do this properly, the max my signal generator will go is just over 1mhz from that I get 350khz, not exactly sure what that means but it looks like gonna have to wing it with the damping tools

[green]

Tried damping a dual field coil in spice. Best if each coil has a damping resistor with another resistor across the whole coil for critical damping. Simulation included if anyone wants to play with the values.

If making a real dual field coil, I would try winding each coil separate and measure inductance and SRF. Calculate and connect a damping resistor for each coil. Rd=pi*inductance*SRF Then add coils with resistors to shell and complete coil. Find Rd for critical damping using a damping tool and connect Rd if needed.

[Denots]

Tried damping a dual field coil in spice. Best if each coil has a damping resistor with another resistor across the whole coil for critical damping. Simulation included if anyone wants to play with the values.

If making a real dual field coil, I would try winding each coil separate and measure inductance and SRF. Calculate and connect a damping resistor for each coil. Rd=pi*inductance*SRF Then add coils with resistors to shell and complete coil. Find Rd for critical damping using a damping tool and connect Rd if needed.

Just looked up ltspice, gonna have to set that up next time my computers running, should help massively in recent and future projects.

So do you mean the dual coil simulation requires 3 instead of 2 damping resistors?

[dbanner]

Tried damping a dual field coil in spice. Best if each coil has a damping resistor with another resistor across the whole coil for critical damping. Simulation included if anyone wants to play with the values.

If making a real dual field coil, I would try winding each coil separate and measure inductance and SRF. Calculate and connect a damping resistor for each coil. Rd=pi*inductance*SRF Then add coils with resistors to shell and complete coil. Find Rd for critical damping using a damping tool and connect Rd if needed.

Yeh, but you haven't considered how this will affect the overall response to targets. In your setup , with three resistors, the coil may be super stable as well as super desensitized! Having a virtual tap feeds back one coil to another, not good? I'm just speculating here, someone will have to test it out for real.

[Denots]

Yeh, but you haven't considered how this will affect the overall response to targets. In your setup , with three resistors, the coil may be super stable as well as super desensitized! Having a virtual tap feeds back one coil to another, not good? I'm just speculating here, someone will have to test it out for real.

True, if it’s anything like the effects of running two damping resistors accidentally on a monocoil then I’d expect it to slow down so bad it takes at least five seconds to notice a screwdriver held inches away

[green]

True, if it?s anything like the effects of running two damping resistors accidentally on a monocoil then I?d expect it to slow down so bad it takes at least five seconds to notice a screwdriver held inches away

An attempt at adding a target to the simulation. Just learning spice, not sure if simulation is correct. Maybe someone could correct or show how to better damp the circuit with two damping resistors.

[godigit1]

Looking at the circut I would say spice is not seeing the coils as coupled or something.
Both the second and third resistors are in the exact same line of the citcut. so why is spice wanting two damping resistors?
Im not savvey with spice just poke around with the scope so far on your guys circuts.
But it seems something is wrong .

[godigit1]

I rechecked the dual field on my Mpp and it does not hum on the Mpp.
Also noticed the area below the clevas is or appears to be hollow. Tapping on the coil it obvious there is air in there.

Being that this coil is on a mpp with stock on time at the moment. I think it could be hit allot harder but have to upgrade the fet. then maybe the coil will hum on the Mpp.
Im also thinking the hum is exagerated or even cuased by the air intraped in the coil.

[waltr]

Looking at the circut I would say spice is not seeing the coils as coupled or something.
Both the second and third resistors are in the exact same line of the citcut. so why is spice wanting two damping resistors?
Im not savvey with spice just poke around with the scope so far on your guys circuts.
But it seems something is wrong .

I think you are on to something here.
The two coils would be strongly coupled when one is completely inside the other.
But he does have them coupled with this directive "K1 L1 L2 .4".


I tried with the three damping Rs at MegaOhm values and the coil does ring at 966kHz.
I then find that there is no ringing with R2 = 1200 Ohm and Rd at 1500Ohm with R1 = 1100MegOhm (not there). This seems to me to be close to Critical damping.

So no need to have three damping Rs, Just one across L2 and one across both.

[dbanner]

I rechecked the dual field on my Mpp and it does not hum on the Mpp.
Also noticed the area below the clevas is or appears to be hollow. Tapping on the coil it obvious there is air in there.

Being that this coil is on a mpp with stock on time at the moment. I think it could be hit allot harder but have to upgrade the fet. then maybe the coil will hum on the Mpp.
Im also thinking the hum is exagerated or even cuased by the air intraped in the coil.

What' the PRF of the TDI as compared to the MPP, I think that's why the coil sings with one and not the other. The acoustics of the coil shell combined with the PRF of the TDI pulse is likely cause.

[dbanner]

An attempt at adding a target to the simulation. Just learning spice, not sure if simulation is correct. Maybe someone could correct or show how to better damp the circuit with two damping resistors.

Have you tried a simulation using the schematic from the whites patent?
They use an Rd for inner coil and then also another Rd for overall damping of both coils. Your simulation should support the conclusions of the whites patent, otherwise something is wrong with the simulation.
My instincts tell me that three resistors, the way you have shown, is not going to be any better, because it does not isolate the damping of the inner coil with respect to the pulse drive, but it now introduces a path via a third resistor feeding back to the outer coil. This might be ideal for a "centre-tapped bipolar dual field coil", but maybe no good for mono coil, which is what the dual field coil is. It is essentially a mono coil split into two parts.