I'm making a low current, 50ma normal, 80ma max, choke input power supply using an open frame 10H 100ma choke (Hammond 158M), tube rectifier, 40uf after the choke. I want to cut off a 3.5 inch length of rectangular steel tubing I have, mount the choke inside then pot it. Then fabricate end caps from sheet stock, sand and paint, then drill and tap four M4 mounting screw holes.
Should I use beeswax or this electronic epoxy?
below is a photo of the tube stock I have, beeswax and the epoxy all of which I have on hand. I'm leaning toward the beeswax myself, I have a hot plate in my shop, just melt it and pour. I'm afraid the epoxy would be too hard and exert pressure on the choke.
https://www.industrialtube.com/assets/images/content/IMG_9643.JPG
https://www.amazon.com/Stakich-Pure-Yellow-BEESWAX-Block/dp/B00F3CNMV4/ref=sr_1_4_sspa?crid=2TJ3PLND4RTVA&keywords=beeswax&qid=1649610722&sprefix=beeswax,aps,118&sr=8-4-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExOVpDMEhUU1I5WTRMJmVuY3J5cHRlZElkPUEwOTM3NDk5MTRLV1U4QUpDMU4zUyZlbmNyeXB0ZWRBZElkPUEwMDA0NDgxTThZQzI1MVFMSVRRJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1#
https://www.amazon.com/gp/product/B00VXV9YZ2/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
Should I use beeswax or this electronic epoxy?
below is a photo of the tube stock I have, beeswax and the epoxy all of which I have on hand. I'm leaning toward the beeswax myself, I have a hot plate in my shop, just melt it and pour. I'm afraid the epoxy would be too hard and exert pressure on the choke.
https://www.industrialtube.com/assets/images/content/IMG_9643.JPG
https://www.amazon.com/Stakich-Pure-Yellow-BEESWAX-Block/dp/B00F3CNMV4/ref=sr_1_4_sspa?crid=2TJ3PLND4RTVA&keywords=beeswax&qid=1649610722&sprefix=beeswax,aps,118&sr=8-4-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExOVpDMEhUU1I5WTRMJmVuY3J5cHRlZElkPUEwOTM3NDk5MTRLV1U4QUpDMU4zUyZlbmNyeXB0ZWRBZElkPUEwMDA0NDgxTThZQzI1MVFMSVRRJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1#
https://www.amazon.com/gp/product/B00VXV9YZ2/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
Beeswax does have a nice smell and is reversible, you can easily melt the wax and remove the choke from the enclosoure. This may even be unwanted: the wax will spill over the chassis if you ever accidentally overheat the choke. I would consider it for a vintage restoration or recreation.
Triad had a little burb in one of their spec sheets that certain potting materials exert pressure and can affect the specs of the unit. It was probably just a cover your butt statement, I didn't understand it either. I think I'm still leaning to beeswax, hell if my choke is getting hot enough to melt wax I have much bigger problems going on. Beeswax melts at 62-66 degrees C, the nearest tube will be 50mm away from the enclosed choke. But maybe thats an argument for using the epoxy? Running the amp for a long tome on a hot day? Tubes would soften the wax right? BTW this is all for my build of the Salas 6V6 preamp using choke input and a tube rectifier.
Are you using a steel tube because you have some, and want to enclose the choke for looks?
Or, are you using a steel tube, and hoping that it will eliminate magnetic spray from the choke?
Or, are you using a steel tube, and hoping that it will eliminate magnetic spray from the choke?
A wire will only attempt to move if it is in a magnetic field and is also subject to a change in current. That'll happen whether it's movement is constrained mechanically or not. It'd not move at all under constant current assuming the magnetic field it is in is unchanging. I presume that is the "pressure" being referred to.
I would have thought wax would only have been when used in sealed containers, e.g. those old oil filled Parmeco chokes and transformers, otherwise it'd potentially all smell a bit.
Not all epoxies and polyurethanes are hard. Check out what the glass transition temperature is from the data sheet. In case of a fire, natural substances are much much safer fumes wise. Toxic fumes are seriously bad news.
kind regards
Marek
I would have thought wax would only have been when used in sealed containers, e.g. those old oil filled Parmeco chokes and transformers, otherwise it'd potentially all smell a bit.
Not all epoxies and polyurethanes are hard. Check out what the glass transition temperature is from the data sheet. In case of a fire, natural substances are much much safer fumes wise. Toxic fumes are seriously bad news.
kind regards
Marek
Well both actually, it is hot rolled tube, not hardened. It will make a nice enclosure for potting, takes paint and screw taps well, etc. So basically I need a potting container this is as good as any .125 inch thick 2.5 x 3.5 tube I just cut a piece off in the 15 inch metal chop saw. If it can re-route some of the Flux, thats great, mechanical noise too.
I would use self-leveling polyurethane. All you need is a caulking gun. If you need a vibration table you could always set it on top the washer while you wash a comforter.
I think the potential issue with epoxy stress happens during the curing. Years ago, GE and likely others, made potting compounds specifically to minimize windings stress during curing, and of course to have the best dielectric properties and such. Mouser used to have it; might still.
All good fortune,
Chris
All good fortune,
Chris
Interesting... It's not "liquidy" like the electronic potting compound, makes me wonder if it will find it's way deeper into nooks and crannies. I've used this to seal concrete chimney caps, it does drip out and run if not contained. But it is flexible, the electronic epoxy will make it rock hard, polyurethane will be like a soft bowling ball might be an advantage. It is like going halfway between beeswax and rock hard epoxy. And it won't melt like wax which is better. And it won't get hot curing like the epoxy does, that gets plenty hot curing. This my be the ticket.
I'm thinking that too, it does get hot then cools after it hardens, which to me seems a recipe for stress. Let's heat something to 200F, lock it in a vice grip, then have it cool.
Putting a choke inside a steel tube is going to have some effect on the actual performance. Ideally all the magnetic flux is contained in the core of the choke. But as you will find the choke is not ideal.
Leakage flux just might result in heating. Enough heat and wax just might become liquid. Liquid wax raises the possibility of fire. So the obvious conclusion is to make sure your fire insurance is up to date and of the correct amount.
I would test things to see the effect of the cover steel. Then to pot it I would use a nonflammable compound. Silicone rubber might do the trick. It is available in a thin pourable version intended for sealing leaks. There are also commercial products to thin it out.
Leakage flux just might result in heating. Enough heat and wax just might become liquid. Liquid wax raises the possibility of fire. So the obvious conclusion is to make sure your fire insurance is up to date and of the correct amount.
I would test things to see the effect of the cover steel. Then to pot it I would use a nonflammable compound. Silicone rubber might do the trick. It is available in a thin pourable version intended for sealing leaks. There are also commercial products to thin it out.
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OK Chris - you're suggesting the epoxy will exotherm as it cures and expand in the process. That is true, but it ought only to manifest as a problem if it is curing in a confined space. Even then, a flexible mold or one with vents will allow the material to escape, so by definition there is no stress, as the expanding resin simply vents to the outside . You can minimise any effect by choosing a resin with a long pot life, i.e. slow curing. Very thin castings benefit from pre-heating the mold/item to 55-70'c. This stops the resin from "sucking the heat out of" its surroundings as it attempts to cure.
kind regards
Marek
kind regards
Marek
I don't really have a dog in the fight. None of us know enough about it to comment beyond conjecture and good wishes. In the good ole' days, transformers and chokes operating below a KiloJolt or so were potted in tar (whatever that means; it doesn't sound too well chemically defined). High voltage stuff like power pole pigs are reputed to have oil baths. I even have some Raytheon chokes of about-Kilovolt size with cast iron frames with drain plugs (?). simon7000 might know more about this stuff than most of us, and may comment.
But is any of this conjecture relevant? My only recommendation is to find a reputable manufacturer's commercial product. They do exist, so why invent a wheel?
All good fortune,
Chris
But is any of this conjecture relevant? My only recommendation is to find a reputable manufacturer's commercial product. They do exist, so why invent a wheel?
All good fortune,
Chris
Whatever you use, consider vacuum to ensure the resin/wax/whatever gets everywhere. Contrary to popular belief, the component should be vacuumed dry then the potting fluid introduced as the vacuum is released.
Is the choke coil being diy rewound?
After winding you could run it at say 120% of max dc current, with the choke temporarily sealed in the tube, to test what max coil surface temp gets to. You could also set it up in a choke-input test power supply and operate at max voltage/current and confirm noise level without any potting.
Then revisit your options perhaps.
After winding you could run it at say 120% of max dc current, with the choke temporarily sealed in the tube, to test what max coil surface temp gets to. You could also set it up in a choke-input test power supply and operate at max voltage/current and confirm noise level without any potting.
Then revisit your options perhaps.
So far mentioned...
beeswax - risk of melting under use
epoxy - possible heat curing issues, hard as a rock leaving the choke with no "give" at all
self leveling polyurethane - no heat or stress curing, flexible, higher viscosity might need vibration setting or pour in stages
silicone rubber in liquid form - this might be the ticket more give than the polyurethane more liquid also for doing a single pour, but not sure a thick pour fully cures, it may skin over instead.
tar - flexible, requires heating big negative
Here is the liquid silicone rubber we see on TV commercials constantly, flex seal. Good enough for outdoors. But not sure it fully cures as an ingot, it might just "skin over" and remain wet throughout middle.
https://flexsealproducts.com/produc...031c25ce9879c3917fd7bb&variant=32929853603949
https://flexsealproducts.com/products/flex-seal-liquid?msclkid=70021b97b9031c25ce9879c3917fd7bb
beeswax - risk of melting under use
epoxy - possible heat curing issues, hard as a rock leaving the choke with no "give" at all
self leveling polyurethane - no heat or stress curing, flexible, higher viscosity might need vibration setting or pour in stages
silicone rubber in liquid form - this might be the ticket more give than the polyurethane more liquid also for doing a single pour, but not sure a thick pour fully cures, it may skin over instead.
tar - flexible, requires heating big negative
Here is the liquid silicone rubber we see on TV commercials constantly, flex seal. Good enough for outdoors. But not sure it fully cures as an ingot, it might just "skin over" and remain wet throughout middle.
https://flexsealproducts.com/produc...031c25ce9879c3917fd7bb&variant=32929853603949
https://flexsealproducts.com/products/flex-seal-liquid?msclkid=70021b97b9031c25ce9879c3917fd7bb
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Keep in mind noise comes mostly from the core, not as much as the windings. To minimize this, you need to glue the air gap as a start, this is where the bullseye of noise is located.
Second rule when using a choke input - make sure AC flux density doesn't exceed DC flux density. DC flux helps clamping down the core around the airgap.
Second rule when using a choke input - make sure AC flux density doesn't exceed DC flux density. DC flux helps clamping down the core around the airgap.