cheap conductor materials other than metal - Page 1
Forum section: electronics / beginners

author: Unknown
author_rank: Unknown
timestamp: April 23, 2014, 02:31:03 am
content: POST REMOVED BY MOD AT USERS REQUEST

author: XOIIO
author_rank: Super Contributor
timestamp: April 23, 2014, 02:32:48 am
content: Graphite, and I think quartz to some extent though not much.Nether of those would suit a moisture probe though.

author: poor_red_neck
author_rank: Newbie
timestamp: April 23, 2014, 03:42:12 am
content: Inexpensive is relative... lol.How about carbon fiber? You can find carbon fiber rods at hobby stores (Remote Control hobby, MAYBE Michael's or AC Moore). I fly R/C helicopters (the large, collective pitch type, not the "toys" at the mall) and our frames are made of carbon fiber, and QUITE conductive... especially when you don't sand down the edges and the 48V 45C 5000mah LiPo shorts across the frame... let's just say it handled a fairly substantial amount of current before puffing a few cells and burning the frame/wiring.

author: Unknown
author_rank: Unknown
timestamp: April 23, 2014, 04:05:16 am
content: Quote from: pereczes on April 23, 2014, 02:31:03 amGraphite, as XOIIO said, or titanium. Certain grades of stainless steel, at a pinch. All are commonly used in both cheap and industrial/lab-grade soil moisture sensors, especially for simple conductive-type moisture sensing. (Remember, any DC on the probes will accelerate electrolytic corrosion).Graphite tends to poison fairly quickly (it adsorbes ionic contaminants). I don't know of carbon fibre rod being used but I'd be suspicious of the same thing happening, given that the polymers binding it are at least nominally porous. Titanium welding rod is probably the most resistant easy-to-get material.Epoxy/ceramic/glass/sapphire coated capacitive probes are typically used for long-term in-situ environmental monitoring, but aren't particularly cheap.

author: Psi
author_rank: Super Contributor
timestamp: April 23, 2014, 04:07:50 am
content: Quote from: pereczes on April 23, 2014, 02:31:03 amHave you tried a good grade stainless steel?

author: miguelvp
author_rank: Super Contributor
timestamp: April 23, 2014, 04:24:29 am
content: You might want to see Dave's last mailbaghttp://wemakethings.net/2013/06/07/chirp-plant-watering-alarm/Dave's part of the video where he opens the device:It's open hardware but you can always buy one here for $15:https://www.tindie.com/products/miceuz/chirp-plant-watering-alarm/Not what you want to do maybe, but it should give you some insight on what to use to sense the moisture.BTW I think this one activates when dry but it should be easy to do the opposite.Edit: and they provide the source for the firmware as well

author: Psi
author_rank: Super Contributor
timestamp: April 23, 2014, 02:00:02 pm
content: electroplate the stainless/titanium with something you can solder to

author: Phaedrus
author_rank: Frequent Contributor
timestamp: April 23, 2014, 02:11:40 pm
content: As much as it's used as a technowank gimmick, electroplated gold should actually be pretty good at resisting corrosion. The electroplating process involves plating your base metal with copper (unless it already is copper), then nickel, then gold. The nickel and gold layers are both extremely corrosion resistant, so as long as the coating is good quality and isn't subjected to too much mechanical wear you shouldn't see any corrosion. Plus you can solder to it, though your joint *will* be subject to corrosion.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: April 23, 2014, 04:17:22 pm
content: Don't try to electroplate gold at home. It requires noxious chemicals like boric acid and aqua regia. The only metals I'd recommend for home electroplating are copper and tin since these can be done with acetic acid and low-strength muriatic acid respectively.You can probably find a company nearby who will do electroplating, but pricing is a bit of a crapshoot.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: April 23, 2014, 04:42:15 pm
content: Quote from: pereczes on April 23, 2014, 04:31:57 pmDangerous, toxic, fuming, corrosive, potentially explosive.Correction, you don't need boric acid for the nickel plating, you need sulfuric acid. You also need aqua regia (mixture of hydrochloric and nitric acids) to electroplate gold.Not saying that you can't do it at home; but it will shorten your life expectancy and probably give your life/medical insurance agent an aneurysm. There is both short term danger (acid spill, poisoning, fume inhalation, explosion, electric shock) and long term (lung damage, cancer).Find someone to do the plating for you. If it's not too expensive, plating could be a good solution. Stainless steel is ok, but keep in mind it's not really stainless; given enough moisture and the presence of mild corrosives (such as those found in soil) stainless steel will still rust. Just, more slowly than carbon steel or copper.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: April 23, 2014, 04:52:01 pm
content: Zinc is a sacrificial metal, it corrodes easily. It's mainly just used as a coating over more durable materials on the basis that it will take five or ten or twenty years before the half inch of zinc rusts through and the metal underneath is attacked.

author: Zero999
author_rank: Super Contributor
timestamp: April 23, 2014, 06:19:36 pm
content: Quote from: pereczes on April 23, 2014, 02:31:03 amPoor design is the main thing which causes corrosion in moisture detectors. If you use AC to measure the conductivity, make sure there's no DC path of current between the electrodes and use the same type of metal for both electrodes, there will be a much lower risk of corrosion.

author: tx8
author_rank: Contributor
timestamp: April 23, 2014, 07:05:02 pm
content: Quote from: pereczes on April 23, 2014, 04:33:02 pmThe green patina is an oxidized layer on the outside so Bronce will look pretty and will not corrode further, i think.

author: yashrk
author_rank: Frequent Contributor
timestamp: April 23, 2014, 07:22:23 pm
content: Try painting rod with galvanized paint on the metal

author: tx8
author_rank: Contributor
timestamp: April 23, 2014, 07:29:26 pm
content: Quote from: pereczes on April 23, 2014, 07:11:36 pmYeah for your purpose its a bit iffy. The thing is for many purposes the blumat is very usefull and it doesnt need any electronics at all but it just in this moment came to my mind it would be super awesome to have a sensor you can put on top of the blumat that will measure the pressure and can then trigger a pump. I never thought of that altough i though of it alot in the past when i was doing some garden automation stuff. I think it would be a top product. Since there is alwasy is the issue with the corrosion and electronics and in this case there would be no contact of the water to the electronics itself....Aesome maybe we should kickstart it.... O0One issue in general though with a "pump and sensor" system is if there are serveral sensors on a large scale you need to disribute the water to the right place... so in the end its maybe useless since the blumat normally regulates that. Hence one would need a system to disribute the water to right place as well.PPS.: And if it is not a large scale the blumat would do the job just fine withoud any batteries or electronics and so on. I tried that drop blumat and its really good!

author: Yago
author_rank: Frequent Contributor
timestamp: April 23, 2014, 07:43:50 pm
content: Quote from: pereczes on April 23, 2014, 04:31:57 pmI had a goggle of "Aqua Regia" and the wiki would be more than enough to ensure it is never near my home!

author: SeanB
author_rank: Super Contributor
timestamp: April 23, 2014, 07:49:46 pm
content: The most common water level detectors use AC to drive the probes, via a DC blocking capacitor even though the probes are simply connected to a transformer secondary via a resistor. The probes are typically 308 or 316 stainless steel for use in water other than salt water, because the stainless corrodes badly with chloride ions present. for salt water graphite is preferred, though they often also use marine bronze alloy, as it will not corrode much in sea water.http://en.wikipedia.org/wiki/Aluminium_bronze

author: tx8
author_rank: Contributor
timestamp: April 23, 2014, 08:13:18 pm
content: The tank "fitting" connectors are often made from brass. dont know if that can be usefull but its pretty cheap.http://www.conexmetals.com/gif-1/brass_components_brass_turned_parts_brass_fittings_machined_components.jpg

author: Unknown
author_rank: Unknown
timestamp: April 23, 2014, 08:57:25 pm
content: Quote from: pereczes on April 23, 2014, 07:20:12 pmMakes me wish I'd mentioned something about avoiding DC and electrolysis earlier. Oh, wait ...But on the subject of connecting wires to probes: what's wrong with screwing or clamping? Use a screw terminal strip for small diameter probes - wire in one side, probe in the other - or an earth/hose clamp for larger probes. Dip it in plasti-dip to seal it up & minimise corrosion, and Bob's your auntie's live-in lover...

author: SeanB
author_rank: Super Contributor
timestamp: April 23, 2014, 09:05:11 pm
content: Dip in plasti seal with moisture makes an electrochemical cell from the different oxygen concentrations if there is a slight separation , and welcome to crevice corrosion which will eat the area under the dip till the probe falls off.

author: FJV
author_rank: Regular Contributor
timestamp: April 23, 2014, 09:17:59 pm
content: For cheap graphite maybe use a pencil lead.You even have pencils entirely made of pencil lead without wood.Diameter about 5mm if I'm not mistakenBuy the grade with the highest graphite content I guess

author: Unknown
author_rank: Unknown
timestamp: April 23, 2014, 09:45:33 pm
content: Quote from: SeanB on April 23, 2014, 09:05:11 pmYes, but you will almost always get that to some degree anyway regardless of connection / sealing method.FWIW, we've got probes built like this - titanium welding rod in nickel-plated brass terminal screw connectors, & sealed in hot plastic-dip - that have been in the field (long-term environmental monitoring of soil adjacent to a coastal estuary - so, very wet & saline) for nearly 4 years now without issue*. It's a matter of how far you need to go for the result you want...(* edit: well, withoutmuchissue. I believe a couple have had to be replaced because some bogan drove over them...)

author: Zero999
author_rank: Super Contributor
timestamp: April 23, 2014, 10:29:52 pm
content: Quote from: pereczes on April 23, 2014, 07:20:12 pmNot really. A simple way to do this is to build an oscillator and connect the output to a peak detector via a resistor with a capacitor going to the probe, so when it becomes wet, the AC signal is short circuited. A similar circuit to that discussed in the thread below should work. You may need to play with the component values and couple the power supply to the water via another capacitor.https://www.eevblog.com/forum/beginners/easiest-touch-sensorswitch/msg429927/#msg429927

author: FrankenPC
author_rank: Unknown
timestamp: April 24, 2014, 02:29:18 am
content: I don't know if anyone mentioned this. Get 303 stainless steel bolts. Test them with a magnet. Good 300 stainless is non-magnetic. This stuff is incredibly difficult to corrode and reasonably priced.

author: SeanB
author_rank: Super Contributor
timestamp: April 24, 2014, 04:33:22 am
content: Stainless steels are only non corroding because they build up, like aluminium, a protective oxide coating on the surface. Thus you really do need an AC excitation, as this will keep the coating intact.With any coating if there is any sharp edge that has a hollow or chip that will create an electrochemical cell. This is the start of surface corrosion and then it advances under the coating. With a zinc coat the zinc corrodes preferably to the exposed steel as it is the anode, but with a massive surface area compared to the steel cathode. When the zinc is all eroded off the steel rust very fast.

author: Whales
author_rank: Super Contributor
timestamp: April 24, 2014, 10:23:33 am
content: Quote from: Yago on April 23, 2014, 07:43:50 pmWikipedia: why I can now casually bring up the wordsaqua regiaandaqua vitaein conversation. Also how I plan to earn my millions: throw aqua regia at people wearing exotic jewellery and collect what remains of them in a puddle on the floor for further purification.Quote from: FJV on April 23, 2014, 09:17:59 pmI've used pencil graphite for low-value (<100ohm, depending on the make) variable resistors before. The difficulty is soldering to them: unless you want to wrap a wire around it tightly or use an alligator clip, the only practical joining method is conductive glue.Stainless steel does seem to be the most available solution, however be warned how much the alloys vary. Somethings labelled as 'stainless' are poor in quality and will rust through like iron, just slower, whilst others will shine forever. Ditto for surface corrosion layers: different sources of stainless steel will behave in different ways -- make sure you try another source if you at first get failure.

author: fcb
author_rank: Super Contributor
timestamp: April 24, 2014, 10:59:30 am
content: I'm not sure why you are looking at alternatives to stainless steel. You'll end up with it in the end.316 grade is used in marine, medical implants, industrial chemical handling etc.. (there are different grades of 316 BTW). 316 costs 5-10% more than more basic grades, but it's all pretty cheap.As for how to seal it in the casing, I would use o-rings to seal it - lots of different grades again (VITON, rubber, butyl, nitrile, etc...) cheap and reliable.To make the electrical connection, you could thread the ends and use a ring terminal, crimps are another good way, even use a piece of choc-strip. Even battery springs will work well and are cheap (god love Keystone Electronics).

author: tx8
author_rank: Contributor
timestamp: April 24, 2014, 02:56:02 pm
content: Quote from: pereczes on April 23, 2014, 10:21:10 pmThere is a little turnable cap on top. Once you know how to make the initaial set up u dont need to change anything till harvest. It serves the plant always the right amount of water. btw i am talking about the deep tank variation where you have the water tank 1m< above the crops.Quote from: pereczes on April 24, 2014, 11:44:04 amThey are made from brass not stainless steel. If that info on that site you postet is correct. Its a copper zinc alloy.

author: SeanB
author_rank: Super Contributor
timestamp: April 24, 2014, 08:18:34 pm
content: The chain ends are thin brass sheet with a very thin gold coat. It may be gold coloured but is likely to be very porous as it will be very thin. It will corrode green in a matter of weeks in salt water.

author: Whales
author_rank: Super Contributor
timestamp: April 25, 2014, 12:00:19 am
content: Quote from: pereczes on April 24, 2014, 09:55:01 pmProbably too small compared to the size of dirt granules. Contact will be intermittent.

author: Witention
author_rank: Contributor
timestamp: April 28, 2014, 08:15:35 am
content: It's not every metal that's a good conductor! There are metalloids and also non metals that are bad conductors.

author: mahjongg
author_rank: Newbie
timestamp: April 28, 2014, 11:06:07 pm
content: want two carbon rods with metal caps? simple, just take two old batteries (non rechargeable) and remove the outer zinc shell and the lignite electrolyte, and whats left over is a carbon rod with a metal top!

author: IanB
author_rank: Super Contributor
timestamp: April 29, 2014, 12:30:51 am
content: Quote from: pereczes on April 28, 2014, 11:50:46 pmThe probes will need to be inserted into the soil to a depth of 5-10 cm. The carbon rods from an AA cell are only about 4 cm long. They are barely large enough.