Carbon Fibre Heating Element - powering - Page 1
Forum section: electronics / beginners

author: nickname
author_rank: Newbie
timestamp: November 29, 2016, 09:53:32 pm
content: Hi, I bought some carbon fibre heating element for warming a seed raising tray. The product is usually used for under floor heating. I want to chop it down and use temperature control via arduino to switch it on and off.This is what I bought:https://www.aliexpress.com/item/PR-infrared-heating-floor-heating-cable-system-carbon-fiber-wire-electric-floor-hotline-Length-10M/32241638232.html?spm=2114.13010608.0.0.rurFuSI don't want to use 220v to power it, but having trouble finding alternatives. My guess is I could use a current limited 12v DC supply.Does anyone know if it matters AC or DC? Is current limiting the way to go? Do I need to bother with limiting current since it already has 33ohm/m internal resistance?More specification from the link are:Product Name: Carbon Fiber WireInsulating materials: silicone rubber (Rou Ruan) / 180 oC limitHeating conductor: 12K.High voltage test: 3000VLeakage current: 0.05mA/mThe product can withstand the power of power: 25W/MRated voltage: 300VComplete the outer diameter: 3MMOptional colors: RedDiameter tolerance: 0.2MMInfrared wavelength: 8UM-18UMConductor resistance: 33 ? / MLength: (custom, recommendation of not less than 10 meters))Product power calculation:Voltage * voltage / resistance = powerFor example: 12K carbon fiber length of 10 meters220V × 220V / (10 m x 33 Ohm) =150 wattsFor example: 12K carbon fiber length of 15 meters220V × 220V / (15 m x 33 Ohm) =100 wattsPower data can be seen using a heating line is long and the smaller the hotlineProduct features:With excellent heat resistance, at 150 C can be used for a long time and almost no change in performance, sustainable useof 180 C for 100000 hours.Excellent insulation, insulation resistance is greater than 500M, the resistance is stable over temperature and a wideThanks.

author: Another Dave
author_rank: Contributor
timestamp: November 29, 2016, 11:03:46 pm
content: I have just popped in to ask a similar question. I dont want to hijack your question but itmaybe related.Im my case i will be building a small electric furnace to melt metals. Bought some nichromewire whic is approx 33 or 34 ohms.Normally connected to mains 240V and i have a PID controller and thermocouple to helpit get to the correct temperature. I didnt think about using the Arduino even though ihave a few in the draw.Oh well i have the controller and SSR.I just popped in to ask "when heating is it voltage or watts or amps thats more important"?eg. 240v @ 5A = 1200WWould 12v @ 100A heat the element to the same degree and stress levels?And as the question above AC or DC? Is one better than the other?Thanks and sorry if i have hijacked the OP above.. Hopefully the question will also help them?

author: nickname
author_rank: Newbie
timestamp: November 29, 2016, 11:19:16 pm
content: I don't know what your purpose is, but this may be something that could work for you:There's no temperature control on this, but trial and error with turning on for 1/2 second then off for 1/2 second may get you there. Second hand microwaves can be sourced for under $10.

author: Audioguru
author_rank: Super Contributor
timestamp: November 30, 2016, 12:26:16 am
content: Nickname:The spec's say that the carbon fiber wire has a resistance of 33 ohms per metre. They recommend no less length than 10 metres.An example shows that 10 metres uses (220V x 220V)/10 x 33 0hms= about 150W.If the wire is in a long line up in the air then it will get warm. If the wire is concentrated in a small space then it will get very hot.You need to know how much heat in how much area you need.Another Dave:150W in 10m is 15W per m. because 220V/10= (22V x 22V)/1 x 33= about 15W.12V/22V= 0.545 so the length of carbon fiber wire powered from 12V is 1m/0.545 and its resistance is 33 ohms x 0.545= 18 ohms. Its power is (12V x 12V)/18 ohms= 8W.To reach 1200W you need 1200W/8W= 150 strings of carbon fiber wire that is 0.545m long.The maximum allowed temperature for the silicone insulation on this wire is 150 degrees C which might not be hot enough for your furnace.

author: Audioguru
author_rank: Super Contributor
timestamp: November 30, 2016, 12:27:58 am
content: I forgot to say that AC power at a certain RMS voltage is the same as DC power at that voltage.

author: Brumby
author_rank: Unknown
timestamp: November 30, 2016, 12:30:11 am
content: With the Carbon fibre element around the 33 ohms per metre mark, you can apply simple calculations - like ohms law - to work out voltage, current and power figures. That's the easy bit. Working out the temperature rise of the system you want to heat will take a little experimentation - unless your thermodynamics skills are above average.Youcanpower this from somethingother thanthe mains. Some sample calculations are as follows:Say -1m of element = 33 ohmsPower supply =33 voltsV = I.RI = V/R= 33v/33ohm= 1 AP = V.I= 33v.1A= 33W.24 voltsV = I.RI = V/R= 24v/33ohm= 0.73 AP = V.I= 24v.0.73A= 17.45W.12 voltsV = I.RI = V/R= 12v/33ohm= 0.36 AP = V.I= 12v.0.36A= 4.36WNote - the power supply can be DC or RMS AC.Parallel or series connection of lengths of element for different results are done exactly as you would for resistors.

author: nickname
author_rank: Newbie
timestamp: November 30, 2016, 01:29:05 am
content: Quote from: Audioguru on November 30, 2016, 12:27:58 amOk, I think I have it sorted. But would like some clarification re:RMS of 220v AC. Or is 220v AC the RMS of what comes from the wall? How does this equate to DC?

author: amyk
author_rank: Super Contributor
timestamp: November 30, 2016, 03:46:08 am
content: Yes, "220VAC" is 220V RMS. Peak will be ~311V but with more common 240V supply it reaches near 340V.

author: Brumby
author_rank: Unknown
timestamp: November 30, 2016, 05:04:50 am
content: Quote from: nickname on November 30, 2016, 01:29:05 amBy definition - 12V RMS AC will create the same power dissipation in a resistive load as 12VDC.

author: Another Dave
author_rank: Contributor
timestamp: November 30, 2016, 10:15:48 pm
content: Quote from: Audioguru on November 30, 2016, 12:26:16 amThis is why i was a bit hesitant joining this thread. Im using Nichrome wire, which coincidently is around 33 ohms also, Now its stretched itscloser to 34.5 ohms.Nickname, thanks. I have seen that video, but require a more controlled melt for aluminium and hopefully silver and gold.I spotted your post and thought, there is my question (almost) Except the Nichrome wire and 700+ degrees C in my case,not sure how much power you need?Tinkering with the wire and a B3603 CC/CV buck regulator i had it at 10V and it drew 327mA. I guess Ohms law is moreaccurate than the ebay seller i bought the wire from.Supposedly 1000W, But it appears to be closer to 1700W and 7Amps. Which is actually a nice figure. Well within my limitsfor the power outlet in the shed. I wanted less than 10Amps.So 12V DC and 12V AC would be the same.Which is worse for nichrome wire high volts or high amps or does it just counteract each other? Its going to be1700 watts (ish) either way right?Thanks and apologies to nickname for jumping in here with my question. Hopefully one of my answers willbe useful to you.

author: thm_w
author_rank: Super Contributor
timestamp: December 05, 2016, 11:08:58 pm
content: From my experience the high current is "worse" as it puts a greater strain on the crimp, but shouldn't matter for the nichrome wire itself.If you are dealing with 12V@100A, its going to be much more difficult to find suitable connectors. There will also be greater I2R losses in your feed wires and crimps.It makes sense to stick with the commonly available voltages/currents and go from there (ie 240V with <20A).HV AC is safer than HV DC.Low voltage AC/DC is much safer but does not make sense due to large power supply required.

author: Another Dave
author_rank: Contributor
timestamp: December 05, 2016, 11:50:15 pm
content: Thanks. Everyone seems to run these at 240V at various amperages, just curious on the affects of runningat lower voltages and higher amps.If anyone buys nichrome wire which needs stretching be very very careful !!Approx 400mm coiled, stretched slowly in stages and got to the 1500mm lengthand it broke free from my retaining clip. My lovely neat and perfectly spaced coils areno longer.. I also have a nice bruise on my hand and stomach.Ordered some more just in case it got stressed. Damn.Thanks