Instructables
Picture of Homemade Coil Dope
If you wind your own coils whether they are for an electric motor, electromagnet, radio coil or tesla coil or whatever, when you've wound it and have it the way you want it if you paint it with coil dope it will hold it's shape and won't hum in use.

If you're winding an rf coil for a radio receiver or transmitter then it's really important to dope your coil.  An rf coil that has been tuned will change it's characteristics if the windings move.  When this happens your radio is not aligned properly anymore.

You can still buy coil dope but it's expensive and it's really easy and inexpensive to make your own.

All you need are a can of Toluene from the paint store or hardware store, a clean glass jar that has an airtight lid and some white packing peanuts.  Make that a bunch of packing peanuts.  You will be amazed and how many will dissolve in that little bitty glass jar of solvent. 

The peanuts have to be white and they have to be made of polystyrene.  The ones made in the shape of an "S" work best.  The ones that are a figure "8" don't work.  There are some of the white ones that are made of starch that won't work.  If they dissolve in water don't use them.  I've also used the white portions of soft drink cups but they didn't make what I would call "high quality stuff".  The green or pink kind don't dissolve easily and leave a residue that is probably the material added as coloring.
stoobers4 months ago

Hello,

I tried this, but I used styrofoam and acetone.

The foam shrunk right down and suck to the bottom, but it didn't "dissolve" or turn milky. Can acetone be used for this, or will only tolulene work? did i use the wrong kind of foam?

sparhawk75 months ago

how much better is this than using paraffin wax? i can get wax from the wtore and melt it and dip my transformer/coil in it, and that's what most audiophile amp websites say to do(granted they deal with lower voltages) i know paraffin has a dielectric strength of around 200-300 kV per inch, which is why wax paper is fairly common when making diy capacitors... can you point me at some numbers for the toluene based stuff? also, if this comes across as like... aggressive or something, it's not intended as such, i just want to find the best thing for my purposes(diy jacobs ladder from scratch).

iceng2 years ago
A nice  solution to an ever present need :-)
Re-design (author)  iceng2 years ago
Thanks.