DIY Soapstone Power Resistors - Page 1
Forum section: electronics / projects

author: pelud
author_rank: Regular Contributor
timestamp: June 27, 2015, 05:34:06 am
content: I wanted some 3.5 Ohm Power Resistors for some simple load testing, so I used some nichrome wire that I got some time ago and spot welded some battery tabs onto a piece of a soapstone welder's marking pen. I used a simple file to make some flats for holding the battery tab and some grooves for guiding the resistance wire.Here is how they turned out:The first image shows the front side while the second shows the resistors flipped over.I tried to "capture" the wire using a fold-over tab on the one on the left, but I found that it seemed to work just as well to just spot weld the wire directly onto the tab as seen on the right.

author: Ian.M
author_rank: Super Contributor
timestamp: June 27, 2015, 05:46:39 am
content: Now all you need to do is dip them in a pipeclay/frit glaze mixture, practice your penmanship and write the value on them with a metal oxide pigment, fire them in a ceramics kiln and hop a time machine back 100 years to set up shop!You may want to consider using a Mica sheet core notched along the edges so the wire can be wound noninductively as a zigzag rather than as a coil.

author: TerraHertz
author_rank: Super Contributor
timestamp: June 27, 2015, 09:36:19 am
content: I'd like to see how you did the spotwelding.Seeing this post made me wonder what happens to soapstone when heated.Answer: it's quite resilient. After leaving a piece in an oxy-propane jeweler's torch flame for about ten minutes, there's a small glassy patch, but no other change.

author: pelud
author_rank: Regular Contributor
timestamp: June 27, 2015, 04:43:27 pm
content: Quote from: TerraHertz onTodayat 12:36:19 AMI used aSunkko 709Aspot welder. I can post some more detail pictures later today or tomorrow if you are interested.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: June 27, 2015, 05:06:36 pm
content: Quote from: Ian.M on June 27, 2015, 05:46:39 amLaugh all you want, but he had fun, used stock in hand and didn't have to wait for a minimum of a day or two for a mail order. I bet if he had some mica sheet in his stores department (aka scrap pile) he would have used that.I do stuff like this all of the time, and it is often faster for me to generate the necessary part than to run down to the local store (if it is even something they might stock). Certainly wouldn't want to base a business on it in most cases, but for hobby people and for makers/restorers of one of a kind equipment it makes all the sense in the world. I guess if it is going outside of the control of the maker you need to go a few steps on for safety and other certifications.

author: Ian.M
author_rank: Super Contributor
timestamp: June 27, 2015, 05:22:28 pm
content: I wasn't laughing, just commenting that they aren't that far from a commercial product of 100 years ago. I have a few commercial hand labelled wirewound resistors hanging around still that I inherited or salvaged from old equipment. Mostly they use a tubular ceramic core rather than soapstone though.Obviously its not usually cost-effective to make stuff like this, but if its a one-off and it saves you from having to special order something and wait for delivery, it can be worth doing.

author: SeanB
author_rank: Super Contributor
timestamp: June 27, 2015, 05:25:35 pm
content: Not surprising, as soapstone is chemically almost the same as Asbestos, which is well known for it's resistance to high temperature.