One issue with such ferrite cores is that they tend to be expensive and hard to find in the 'right' shape. It's no wonder the ones AMP uses are custom made for them. One solution is to buy a toroidal shaped one and cut the gap but the stuff can be very brittle. At the end of the day, experimenting with this stuff can add up for a build count of one.
Induction brass annealer redux
- Thread starter Gina1
- Start date
itchyTF
Gold $$ Contributor
If using a “conventional” coil design I wonder if either of these orientations would work. On the left the thought was to have tight coupling with the shoulder body junction and a greater space for the neck so that all heats more evenly. On the right there would be tight coupling from neck to body/shoulder area.
(I meant flip the drawing.)
(I meant flip the drawing.)
I think you will find that as you shrink the diameter of the coil you lose a lot of coil inductance. Here is a link to an online calculator for air core inductors which is what the conventional work coil is.
Roughly speaking a tightly wrapped coil of 8 turns around 0.75" outer diameter tubing yields a coil diameter of 1", 1.25" long and 8 turns. So circa 1uH.
The goal is to have a 'tighter' field at the shoulder area (and conduction will likely take care of the neck). More turns across a narrower length requires thinner wiring and presents cooling issues. One could try making a coil out of Litz Wire but I think the much better strategy is to deploy an air gapped ferrite approach. (Obviously we need the air gap to have a place to slide the case into.)
Roughly speaking a tightly wrapped coil of 8 turns around 0.75" outer diameter tubing yields a coil diameter of 1", 1.25" long and 8 turns. So circa 1uH.
The goal is to have a 'tighter' field at the shoulder area (and conduction will likely take care of the neck). More turns across a narrower length requires thinner wiring and presents cooling issues. One could try making a coil out of Litz Wire but I think the much better strategy is to deploy an air gapped ferrite approach. (Obviously we need the air gap to have a place to slide the case into.)
Panama Evans
PAYING IT FORWARD EXPECTING NOTHING IN RETURN
Here’s a couple ideas. 1) if you have a 3D printer I’d be happy to pay you to print it and send me a set. If not and you have the file, I can go on thing verse and see if I can find someone to print it. So your thought isn’t waisted. Btw here’s my email for a better response. iwdpo@gmail.com thank you for your help your my rock star today
@SGK since you know where te North Island is I can say Bay of Plenty.
The litz wire wrap is 800 strands and the core is 20 mm diameter with 2 1/2 winds each side of the gap..
I was going to do how you drew the diagram, but was advised to have the turns as close to the air gap as possible.
I am just a trial and error guy, I've toasted my share of parts, especially on the gapped build.
Re the helical style coil from Litz wire, it would need a lot of air cooling ( fans ) I have seen the number of turns I use get pretty hot ( like when a relay fries closed )
PS I am coming over to Napier next week, should catch up for a beer.
The litz wire wrap is 800 strands and the core is 20 mm diameter with 2 1/2 winds each side of the gap..
I was going to do how you drew the diagram, but was advised to have the turns as close to the air gap as possible.
I am just a trial and error guy, I've toasted my share of parts, especially on the gapped build.
Re the helical style coil from Litz wire, it would need a lot of air cooling ( fans ) I have seen the number of turns I use get pretty hot ( like when a relay fries closed )
PS I am coming over to Napier next week, should catch up for a beer.
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Gina,
I need to ask a basic question, and I apologize if this has been answered before.
One layout constraint I expect is to keep the induction coil and induction card away from anything metallic - because I know that any nearby metal will impact the magnetic field (and more so if those metals happen to be ferrous).
Can you please advise a minimum clearance distance from the induction coil to other metals?
Thank you.
Frank from Indianapolis (another retired power engineer)
I need to ask a basic question, and I apologize if this has been answered before.
One layout constraint I expect is to keep the induction coil and induction card away from anything metallic - because I know that any nearby metal will impact the magnetic field (and more so if those metals happen to be ferrous).
Can you please advise a minimum clearance distance from the induction coil to other metals?
Thank you.
Frank from Indianapolis (another retired power engineer)
@SGK
Further thoughts from your comment.
The shoulder has more mass. So needs more heat either by more current or more time.
The existing power supply is (more than) adequate
Higher current in one area has a lot of discussion. So this is hard or complicated.
More time is easier. This just requires some calibration runs for time.
Other issues maybe field collapse.
A short interruption to engage / reengage the field can be adjust out.
At least from a concept it looks doable.
Further thoughts from your comment.
The shoulder has more mass. So needs more heat either by more current or more time.
The existing power supply is (more than) adequate
Higher current in one area has a lot of discussion. So this is hard or complicated.
More time is easier. This just requires some calibration runs for time.
Other issues maybe field collapse.
A short interruption to engage / reengage the field can be adjust out.
At least from a concept it looks doable.
I'm now living in Miami so a beer would be difficult. I wish I was in NZ right now with the roar about to kick off.
Who advised re having the turns as close to the air gap? I've not seen anything to suggest that's necessary. I also wonder what frequency that things oscillates at...
Does your ferrite core get hot?
I would wrap the Litz wire with Kapton tape to stop it from absorbing heat from the hot case.
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Here you can see the AMP's work coil being assembled. Watch from about 3'40 onwards.
And here is a pic. Note the Kapton tape shielding the Litz wire where it gets close to where the hot case will be and what appears to be a temp monitor strapped to the ferrite (covered in Kapton tape). What appears to be a resistor bank is possibly for measuring current accurately. That ferrite would not be cheap.
And here is a pic. Note the Kapton tape shielding the Litz wire where it gets close to where the hot case will be and what appears to be a temp monitor strapped to the ferrite (covered in Kapton tape). What appears to be a resistor bank is possibly for measuring current accurately. That ferrite would not be cheap.
Ferrite Grades & Custom Ferrite Cores Design & Engineering
marquemagnetics.com
At this link LR88 posted his results from monitoring current versus temp and time. I hope he doesn't mind me reposting his results here (again).
X axis -> 1/10 sec
red -> drawn current
blue -> coil temperature
orange -> voltage
A clear maximum at melting point.
@jthor had previously noted that Aztec brings the case to the point of melting (destruction) "which is 915C or 1679F for C26000." At curie the current draw collapses because the resistance of the load (the case) changes abruptly. Aztec likely calculates the time to curie and provides an anneal time that backs things off from there. How much, we have no idea. Note that it took 800W of power to hit melting. That's more than most builds here can deliver.
LR88's example was for a 300 Win Mag case. If we just say it hit Curie at 13 secs (eyeballing the chart), given the linear nature of the change in current we can determine the required anneal time for a temp of brass. If room temp is 75F and Curie is 1679F, then hitting, say, 750F will take 5.47 seconds on his annealer.
From AMP's website:
X axis -> 1/10 sec
red -> drawn current
blue -> coil temperature
orange -> voltage
A clear maximum at melting point.
@jthor had previously noted that Aztec brings the case to the point of melting (destruction) "which is 915C or 1679F for C26000." At curie the current draw collapses because the resistance of the load (the case) changes abruptly. Aztec likely calculates the time to curie and provides an anneal time that backs things off from there. How much, we have no idea. Note that it took 800W of power to hit melting. That's more than most builds here can deliver.
LR88's example was for a 300 Win Mag case. If we just say it hit Curie at 13 secs (eyeballing the chart), given the linear nature of the change in current we can determine the required anneal time for a temp of brass. If room temp is 75F and Curie is 1679F, then hitting, say, 750F will take 5.47 seconds on his annealer.
From AMP's website:
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@SGK pitty about the beer, never mind. I had the standard coil measured at around 90 HZ and 3V A/C at the posts. Havent gotten around to measuring the ferrite unit. The core gets warm but it has a lot of mass.
To bond the Litz wire for a serviceable connection to the ZVS I melted solder into a .22 case, plunged in the prepped ends. Then crimped the shell case and made a connection plate for the 4MM stand offs out of sheet copper
The AMP unit shows 5 full turns and two part turns, thats two up from my unit. I cant recall he said to have them close to the gap....... I had wanted to do a continuous wrap of 5 or so turns on the ferrite body, like when winding an aerial.
My thinking was induction is induction shouldnt matter where on a continuous work piece, but was strongly urged to place it across the gap. Which is a PITA as you have to create a height that the case can pass under.
I have burned the silk(?) layer on the Litz coil with the mouth of case. This will cause the wire to arc at that point when the brass gets too close, a layer of insulation tape alleviated this. I might look into some kapton tape instead!
I would like to see the face of the work coil on the AMP unit.
I have seen folk build them with a bevel to give an even distance from the shell case, as the shoulder shapes away from the neck, but I think this is a wrong move because the case is thicker in the shoulder so by having the coil face closer at this point ( by not shaping it ) is of benefit in as much as the energy transfer happens here first across the narrower gap.
Cases ALWAYS appear to heat from the top ( mouth ) down regardless of induction method, maybe thats a reason that AMP put their cases in mouth down?
I see too that the cores are dunked in the same solution used for motor windings as well.... that ferrite core they use is massive! I wonder if thats so they achieve 50 BMG annealing.
To bond the Litz wire for a serviceable connection to the ZVS I melted solder into a .22 case, plunged in the prepped ends. Then crimped the shell case and made a connection plate for the 4MM stand offs out of sheet copper
The AMP unit shows 5 full turns and two part turns, thats two up from my unit. I cant recall he said to have them close to the gap....... I had wanted to do a continuous wrap of 5 or so turns on the ferrite body, like when winding an aerial.
My thinking was induction is induction shouldnt matter where on a continuous work piece, but was strongly urged to place it across the gap. Which is a PITA as you have to create a height that the case can pass under.
I have burned the silk(?) layer on the Litz coil with the mouth of case. This will cause the wire to arc at that point when the brass gets too close, a layer of insulation tape alleviated this. I might look into some kapton tape instead!
I would like to see the face of the work coil on the AMP unit.
I have seen folk build them with a bevel to give an even distance from the shell case, as the shoulder shapes away from the neck, but I think this is a wrong move because the case is thicker in the shoulder so by having the coil face closer at this point ( by not shaping it ) is of benefit in as much as the energy transfer happens here first across the narrower gap.
Cases ALWAYS appear to heat from the top ( mouth ) down regardless of induction method, maybe thats a reason that AMP put their cases in mouth down?
I see too that the cores are dunked in the same solution used for motor windings as well.... that ferrite core they use is massive! I wonder if thats so they achieve 50 BMG annealing.
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The AMP's ferrite is a simple u shape. You can see this in the shape of the injected molding part used to hold it. (See just a moment after it falls into the basket in the vid above.) If the air gap isn't consistent across the face of the core you get into the peculiarities of 'stepped air gapped cores'. Note they have another part which appears to be hollowed out which fits in the air gap. I have presumed this is just a non-magnetic/conductive part to act as a heat shield so the ferrite doesn't absorb heat from the case. See, for example, 3'40 or 4'04 in the vid.
With respect to the experiments Patrice is doing, it may be worthwhile, if someone nearby has an AMP, that they anneal some cases from Patrice using the AMP. Compare the results from an AMP versus a home built annealer to see if there is any real variance between them.
Frank....
This is just a guess, but I would say 2" from the outside diameter of the induction coil. Few years ago I had one builder run the coil through a metal front front plate, using rubber grommets to guide and insulate through the plate. Problem was the grommets were only 1/4" wide. Front panel got hot and the coil was not receiving full energy. Cut larger holes and replaced them with 2" grommets. All OK after that.
Hope this helps
Gina
ferrite coils are awesome. Currently using one in one of my designs. Folks, cutting these are not too bad, but you have to do it right.
1) only buy a ferrite w/ a paint coating. This reduces chipping
3) tape the cutting edge to help reduce chipping
2) Use a tile saw (w/ water) and with a good blade
done. That's my tip of the week.
this is awesome. thanks for sharing. keep the observations coming!
I built a case from folded sheetmetal ( actually roofing iron flat sheet, before it gets roller formed ) the hole in the front panel was just big enough to pass the coil through, I applied a grommet type rubber edging to it.
It was probably a 40mm elongated hole.
My first Gina design copy use ACM panel ( two thin sheets of ali with a plastic composite in between ) that used 8 mm holes for each copper leg to pass through, insulated with short sections of pvc tubing ( left over from the radiator / pump runs ) both appeared to have no parasitic losses.
Ferrite cores need not be expensive but may take a while to arrive these days. Rather than cut a round toroid i just ground down two of the "legs" on two c shaped cores.
cores via ali express
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I spent 2 days hacking through my first ferrite.ferrite coils are awesome. Currently using one in one of my designs. Folks, cutting these are not too bad, but you have to do it right.
1) only buy a ferrite w/ a paint coating. This reduces chipping
3) tape the cutting edge to help reduce chipping
2) Use a tile saw (w/ water) and with a good blade
done. That's my tip of the week.
Bought a diamond disc for my dremel - and now it's like cutting butter.
If you cut it dry, wear a mask and eyeprotection. Do it outside or use a vacuum-cleaner or other good suction - dust will go literally everywhere, and you (and probably your lungs) will look like you've been working in a coal mine.
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