It does plainly state that a 10' coil has a resistance of 360 ohms, so 36 ohms per '. You wouldn't believe how many builders use 15amp breakers and 16 gage wire, mixed in with 20 amp breakers and 14 gage to save a few cents. I would never question the correctness of what you say. In this I'm completely out of my league by any measure. But if you ever need to build a platinum ballerina ring from scratch and set it with diamonds, I'm your man.. It'll take a day, maybe a day and a half.. Thats if I don't have to make the wire and sheet. Fredo
I tried to get the resistance reading for you earlier. Even hitting the surface with a file and sandpaper it wouldn't give a reading or continuity. The wire itself was extremely brittle and broke off each time I tried to bend it. On a side note the propane furnace worked like a dream. I just need to buy some borax. Best regards, Chris
It's very hard to get an accurate reading with an Ohm meter because the contact resistance is significant. Wire embrittlement happens on all the resistive wires to different degrees. NiCr is usally more ductile after heating than FeCrAl which is very brittle, which might suggest your coils were the latter but since they have been overheated to failure, it's hard to say. If you are winding your own coil or buying a new coil, the only things that really matter are that it have the correct total resistance, only needs to be stretched 3-5x of solid length, and fit's your groove. You'd also prefer the largest diameter wire that accomplishes all that. I attached a resitance wire chart. It's Kanthal which is just a tradename. K80 is just their flavor of NiCr 80/20, and KA1 is their FeCrAl. Most generic resistance wires will be pretty close to the resistance indicated so this is useful for estimating but you should always use the actual resitance/ft stated with the wire lot/purchase. Best, Kelly
To make sure I'm understanding this right. The 15 Guage wire is the one I need. Is there a specific brand or selection you would recommend over the rest? Best regards, Chris
I managed to find the following site that sells a 50ft spool of the A1 wire: https://duralite.com/shop/ I'll have to see what I can find for creating the coil. Do know of a way to accomplish this without breaking the bank? Best regards, Chris
I have purchased bulk wire from these guys a handful of times. You wont get shipping alerts or tracking numbers but assuming you are in US, the wire has always shown up as ordered about a week later. It will be a continuous length on a spool. I believe you need to order by 1lb increments. https://euclids.com/collections/element-wire Back in post 20 I remarked 1 lb should be enough for at least two coils depending upon the wire you choose so circa $25 each without shipping. 1 lb of 15ga KA1 is about 108ft and $50. The resistance f that wire is .201 ohms/ft. For 9.6 Ohms you would need ~48ft. That wire is .057" in diameter so if you wrapped it around a .125" rod it would produce about 733 coils at .25" OD. The solid wound length (no space between coils) of that coil before stretching is about 42". For 3.5" OD coil x 13 wraps would need to have a stretched length of 143" to fit your groove. That stretch is about 3.4:1 so it is in the acceptable range of 3x-5x. That's a long tightly wound coil which can be a bit tricky to make so you'll need to make a winding jig. Here's some discussion on mine. http://forums.thehomefoundry.org/index.php?threads/furnace-fail-reconstruction.209/page-3#post-3670 It's more elaborate than needed. A piece of hardwood with a hole for the winding rod and another to point the wire at the rod will do. You'll need something to clamp the wire on the winding rod and a helper because you arm wont be long enough to hold the drill and guide/hand tension the wire. Best, Kelly
