DIY  titanium resistor - Page 1
Forum section: electronics / projects

author: daniel444
author_rank: Regular Contributor
timestamp: January 16, 2022, 03:36:46 pm
content: 10 ohm titanium resistor i madeyou can clamp on to different spots to vary the resistance0.9mm titanium wire

author: Swake
author_rank: Frequent Contributor
timestamp: January 16, 2022, 03:48:25 pm
content: What will you use it for?

author: daniel444
author_rank: Regular Contributor
timestamp: January 16, 2022, 04:02:56 pm
content: just for dimming a 24v dc motor

author: Terry Bites
author_rank: Super Contributor
timestamp: January 16, 2022, 05:25:48 pm
content: Is it a very bright motor?

author: jpanhalt
author_rank: Super Contributor
timestamp: January 16, 2022, 05:34:56 pm
content: Quote from: daniel444 on January 16, 2022, 04:02:56 pmThere are better ways to do that. You will lose torque that way. PWM will slow it and maintain good torque.

author: Gyro
author_rank: Super Contributor
timestamp: January 16, 2022, 05:39:10 pm
content: Quote from: Terry Bites on January 16, 2022, 05:25:48 pmIt's worth noting that Titanium is a very reactive metal (protected only by its oxide film, like Aluminium and Magnesium). Ones it catches fire (accidental short?), it burns very hot and is very difficult to extinguish, ie. A very bright resistor. Titanium fires during machining can be very destructive.

author: TheMG
author_rank: Frequent Contributor
timestamp: January 16, 2022, 06:05:41 pm
content: Why titanium? Nichrome wire is normally used for this purpose.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 16, 2022, 06:18:34 pm
content: Quote from: Gyro on January 16, 2022, 05:39:10 pmHmm, I'm not actually sure if wire of this size will catch? I know you can heat bulk to yellow hot or more, and it just gets crusty as all hell. The oxide is quite tenacious, acting something between those of iron and aluminum -- aluminum for the tenacity and inertness, iron for its propensity to form heavy layers of scale which flake off when worked (titanium can indeed be forged just like steel). The critical thing would be, if a hotspot forms and melts through the wire, while already being extremely hot overall, would that light off like a sparkler? Feels like the whole thing would not go up, just the few turns that are hottest, and once the circuit is broken the rest will cool down quickly.And that's assuming it gets hot enough; mind that once it gets above red heat or so, that thickness of scale (surface oxide) may well act to reduce the cross section, which is to say the resistance value increases irreversibly with exposure to high temperatures. I don't know offhand how aggressive this actually is, if it'll matter at all.Probably, 24V can be applied to that continuously, and it doesn't even get red hot? And the surrounding materials are likely to catch fire first (is that a cherry frame? it's a very nice looking piece of wood), or melt (is that tube soda-lime glass, borosilicate, or fused quartz?).But also, yeah, nichrome is better for this as the tempco is smaller, and the resistance to oxidation is better (so that resistance is stable even up to yellow hot). Or get a pre-made resistor, typically the same stuff, wound on a ceramic tube and protected by high temp enamel or glaze. Or better still, a PWM control as mentioned.Tim

author: Gyro
author_rank: Super Contributor
timestamp: January 16, 2022, 06:32:15 pm
content: QuoteNo, nor me, but it seemed worth the warning.Titanium is one of those strange metals, it is strongly reactive but at the same time, a refractory metal. As you say, the bulk metal can be heated to really high temperatures (in fact, needs to be, for forging). The danger in machining is the constant mechanical removal of the oxide film - it is the turnings that catch fire rather than the bulk. I have no idea how that would relate to similarly dimensioned wire though.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 16, 2022, 09:31:45 pm
content: Once it gets too hot, especially if doing this fast, so that no thick oxide layer has formed, there is a chance the wire could catch fire. With the wire already quite hot it may also continue to burn.Titinium chips have some extra risk from catching fire as the conductivity of titanium is relatively low (so not that much heat transfered to the bulk) and with the high stregth the chips get quite hot.The more typical material would be Nichrom or just normal stainless steel.As an additional tricky part titanium tends to have some hydrogen in side and a change in the hydrogen content can effect the resistance. So expect quite some possible drift in the resistance.

author: Benta
author_rank: Super Contributor
timestamp: January 16, 2022, 10:02:41 pm
content: I don't understand why you guys are dissing this so hard.Titanium wire is excellent for a resistor with a very low temperature coefficient, and as long as you keep it below a couple of hundred degrees C, there's no danger of it catching fire.I think this is great, congrats on your double helix!

author: coppercone2
author_rank: Super Contributor
timestamp: January 16, 2022, 10:04:52 pm
content: A while back I tried to make a titanium immersion heater out of a piece of titanium bar, powered by first a tombstone arc welder and then a resistance transformer.I had significant contact resistance problems. The braze used for titanium is quote only, unfortunately.. which prevents easy connection of a copper lug to a titanium bar. (I do believe the military likes this braze, so it might not be easy to get, its probobly critical in submarine construction, particularly soviet subs, braze is used instead of welding since the strength on a big lap joint is stronger then a weld).What could set this on fire is bad contacts. I thought about trying to use the aluminum contact grease (sold in the hardware store), since they are kinda similar metal... but I gave up on this.Since you are still fooling around with this, you might want to tryhttps://www.homedepot.com/p/NOALOX-4-oz-Anti-Oxidant-Compound-30-026/202276208BTW when I was fooling around with this, I had a thermal camera setup to monitor the temperature during the experiments and shut it down when things were getting hot. If I could braze some thick copper bus bar to it, to act as a heat sink and a connection point, I would be much more comfortable with the component.

author: Gyro
author_rank: Super Contributor
timestamp: January 16, 2022, 10:42:00 pm
content: Quote from: Benta on January 16, 2022, 10:02:41 pmNot dissing, just discussing the properties of the metal, Titanium wire for power resistors isn't something you come across every day and it's as well to think about them.Thermal conductivity of Titanium is low - not in itself an issue because heat dissipation is through convection and radiation in this free-air configuration. Its low density though probably translates into low thermal mass, which might be more of an issue in transient situations. I haven't looked up Titaniums' temperature coefficient.Yes the double helix is nicely done.

author: ejeffrey
author_rank: Super Contributor
timestamp: January 16, 2022, 11:45:52 pm
content: Pure titanium has basically the same temperature coefficient as most other pure metals, a few * 10^-3, just like copper. If course you rarely use pure titanium, usually TiAlV. It will have a lower TCR due to disorder but a cursory search didn't turn up much hard data on it. I wouldn't expect it to be as good as constantan or nichrome alloys specifically used for their low temperature coefficient.

author: daniel444
author_rank: Regular Contributor
timestamp: January 17, 2022, 06:19:00 am
content: hi , thanks for the replysi made the thing because i bought heaps of the titanium wire new old stock for a very good pricei have tried to set the wire on fire and its almost impossible, not enough surface areathe wire turns rainbow colored at about 300C so it will need to stay under that temperaturei have a Chinese 100w variable resistor that have been sitting collecting dust in the shed , and it has corroded the surface finish on the nichrome, maybe they used a bad quality nichrome ?i know the titanium wire wont lose its surface finish from dust and moisture

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 17, 2022, 06:33:23 am
content: Nichrome can get a greenish rust to it, under adverse conditions (Idunno, salt spray?). I have a few resistors that are like that. It's harmless, as long as it's not, like, super deep pitted.Neat fact, the green rust is green, for the same reason iron rust is brown; I mean in the sense that, they're both oxidation of the metal, forming a crusty deposit. Chromium happens to corrode a whole lot slower than iron, though! (It's also the active ingredient in stainless steel.)For sure, you'll have a hard time tarnishing that titanium! Outside of nasty corrosive conditions (mineral acids?) anyway, I would suppose.Interesting thing about titanium, it can be anodized; and after such treatment, it should be reasonably insulating against water. (I'm not sure offhand if it behaves as an electrolytic diode, though?) Which means immersing it in water should increase the power rating by orders of magnitude, if the need should arise, and it should be good for quite a long time this way. (You can submerge almost anything in water if you just need it for a little while -- but most things will corrode very quickly indeed when DC is applied.)Tim

author: coppercone2
author_rank: Super Contributor
timestamp: January 17, 2022, 09:12:43 am
content: I kind of want to spark a titanium rod in the arc welder on high current to see if it will ignite actually.

author: Gyro
author_rank: Super Contributor
timestamp: January 17, 2022, 10:10:53 am
content: Quote from: daniel444 on January 17, 2022, 06:19:00 amAn enviable position to be in, lots of possibilities for experimentation.QuoteThat's useful to know.The colour change at 300'C is probably due to to oxide thickness changing. Anodized Titanium jewellery is quite popular. You can get a very wide range of colours by changing the anodizing bath voltage, affecting the oxide layer thickness. I think it's an optical interference effect. I know that it's fairly critical - you only get one chance, it needs to be anodized at one voltage, you can't just ramp up the voltage until you get the colour you want. Possible grounds for experimentation.

author: coppercone2
author_rank: Super Contributor
timestamp: January 17, 2022, 10:19:31 am
content: just be careful anodizing titanium because the voltages required are much higher, so you have HV+conductive fluid (I think titanium anodization goes to 150VDC)I recommend working in plastic trays and GFIC. Short power supply pole to earth ground with a shorting plate and connect it to ground fault circuit I think.

author: Gyro
author_rank: Super Contributor
timestamp: January 17, 2022, 10:20:58 am
content: Quote from: T3sl4co1l on January 17, 2022, 06:33:23 amAn interesting idea. One thing that comes to mind is that due to the low thermal conductivity, the terminations probably need to immersed too, to avoid hotspots. As the oxide layer thickness can be varied significantly, you can probably get a fully (AC) insulating layer - Irrc, with Anodized Aluminium, the final step is to put it in a boiling water bath to close the pores (up to that point, it will accept pigment). I don't know if it's the same with Titanium.

author: mzzj
author_rank: Super Contributor
timestamp: January 17, 2022, 11:50:39 am
content: Quote from: T3sl4co1l on January 16, 2022, 06:18:34 pmSingle wire like that won't be able to maintain combustion even if ignited. You'd need "rats nest" of fine wire or literally truckload of thicker titanium parts ignited with massive thermite charge. (or overheated jet engine)Titanium wood stoves (camping) were discussed on another forum and I happened to have thin 0.1mm titanium foil: Wont ignite with propane torch even at yellow-hot temperatures.Melts and Ignites with arc welder but won't be able to sustain fire once arc is off.Ignition temperature is excess of 1600 Cel and you need nice pile of material to maintain the fire.

author: coppercone2
author_rank: Super Contributor
timestamp: January 17, 2022, 11:59:39 am
content: https://patents.google.com/patent/US5899724A/en