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Best cheap material for diy low power heating element

Discussion in 'General Electronics Discussion' started by Voltaic, May 28, 2015.

  1. Voltaic

    Voltaic

    82
    1
    May 6, 2015
    I want to make a low voltage low power heat element, what would be a good material to use?

    I was thinking of something like aluminium foil but a bit thicker and able to be soldered.
    I want to make a track on a flat surface to make about 6 ohms for my first project.
     
  2. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    431
    98
    Aug 27, 2013
    Hey Voltaic!

    NiChrome Wire is a common answer... http://en.wikipedia.org/wiki/Nichrome It is available under several trade-names as well as generically....ebay is likely a good source for small DIY quantities. Another choice popular in the 3D printer world is simple copper clad board (PCB material) etched/cut in long-thin traces....It is easy enough to calculate the resistance/unit length if you know the copper thickness and width. A third option for relatively low temperatures are TECs (Thermal Electric Coolers). If you simply need low-grade heat, and there is a larger system involved you might even consider using a "heat sink" as your "thermal plate"....For instance, if you need a "heat plate" in the 35C to 50C range and you have a system that has power semiconductors already dissipating enough power to heat the plate, you might consider designing a heat sink for the semiconductors that doubles as your heat plate....you might use a cooling fan to keep the plate at the desired temperature.... In any thermal dynamics project you have to keep numerous variables balanced to get predictable results; the material choices are typically dictated by the temperature range and power requirements....In a simple case you might want to heat a small plate to 50C....tons of ways to achieve this...On the other end of the spectrum you might want to heat 100kg of steel to 1493C....obviously a much more difficult project...You mention "flat surface"......It is important to keep thermal expansion in mind when dimensional stability is a goal....you cannot prevent thermal expansion, engineering a solution to minimize adverse affects is the challenge.

    A bit more detail about the purpose of the heat element, the definition of "low power" and some notion of the temperature range required would make it much easier to narrow the response field....

    Good Luck!

    Fish
     
    hevans1944 likes this.
  3. Voltaic

    Voltaic

    82
    1
    May 6, 2015
    Thanks.

    I had a few projects in mind (foot warmer, heating a bowl of water to about 30 degrees c, maybe seat back warmer). All with low power 12v plug packs.

    Also I want to try making a concrete heat rock with a diy element inside.

    The nichrome wire sounds like a good option, I guess I can just glue it onto a board with some plastic on top or inbetween two layers of fabric or plastic.

    I had heard about the resistive wire but I didn't know what is was called, I had some trouble finding it, so thanks now I know what it's called.
     
    Last edited: May 28, 2015
  4. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    431
    98
    Aug 27, 2013
    Voltaic,

    Nichrome wire is neat stuff....but you really DONT want to:

    If you will take a look at the temperature rise of NiChrome wire wrt Amperage you should notice the rather high temperature with even fairly low current....temperatures that are certainly beyond the melting point of most plastics and potentially above the flash point of some fabrics....Ceramic is a popular choice for production heaters, but a bit tricky for DIY....Because NiChrome wire quickly forms a relatively non-conductive surface oxide layer it is possible you might be able to sandwich the nichrome wire between aluminum plates.....Another option is to use "isolated stand-offs" that rely on convection air currents to minimize heat build-up...

    A couple of other notes....."A Low Powered Heater" is sort of an oxymoron....Something like a "seat warmer" has a fairly large surface area....as a general rule temperature rise decreases rapidly as surface area (and thermal mass) increases for any given amount of power dissipation....In the case of NiChrome wire, it would be very easy to heat the wire itself to well over 500C while not really generating enough heat to keep your bottom warm...but the 500C wire temperature could certainly manifest serious safety hazards. Resistive heating is fairly simple, but you should exercise caution....thermal dynamics is a tricky bit of math and is generally the more important part of resistive heater design...."Ceramic Heaters" and heating elements offer a lot of advantages over NiChrome wire for low temperature applications (less than ~100C)...they are by design self regulating...that is when supplied with a voltage within there design range they reach a specific temperature...because the impedance increases with temperature they are immune to "thermal runaway" and can typically tolerate relatively large supply variations with little impact on performance.

    And the final note is about TECs (Thermal Electric Coolers)....While not nearly as efficient as compressors, they have the potential to be much more efficient that simple resistive heating.....that is they can produce or remove more energy than is input into them. This is NOT a violation of the 3rd Law because the "over-unity" result is "local"....everything "balances" on a global scale....A refrigerator for example pumps the heat out of the interior space and dumps it into the room while an air conditioner pumps heat from the room and dumps it outside....Typical modern compressors in the US are rated on "SEER" which is a measure of the heat pumped (in BTUs) divided by the energy consumed (kWh).....Obviously a meaningless number, but it is psuedo-useful for consumer comparison purposes....The point being that SEER is essentially a relative measure of the local "over-unity" the consumer should expect....In a highly efficient TEC one might hope for a "SEER" of 1.1 to 2.0 if attempting to remove heat, but can expect nearly twice that if adding heat.....So, to heat your bowl of water to 30C a TEC would likely take 1/2 to 1/4 the energy input resistive heating would require.

    Good Luck!

    Fish
     
  5. Voltaic

    Voltaic

    82
    1
    May 6, 2015
    Thanks for your answers, very helpful. :)

    It's definitely looking like nichrome wire is not suited at all to my projects. I definitely don't want 500 degree wire.

    I'll look at peltier modules, or ceramic resistors glued with thermal glue to a surface, what surface would be best?

    I'll probably be moving to another electronics forum now though since someone suggested I should banned for asking too many questions about electronics safety (I'm not sure what's wrong with that exactly, but I'll move elsewhere anyway because people think my posts are not suited to this forum somehow and viewed as a nuisance). Maybe another forum more suited to beginners would be better for me anyway. Also I'm looking to get a more up to date general electronics book that includes information on some of the recent developments that are not in the book I have, then maybe I won't need to ask questions.
     
    Last edited: May 30, 2015
  6. hevans1944

    hevans1944 Hop - AC8NS

    3,942
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    Jun 21, 2012
    I don't think your posts are inappropriate here... just a tad bit on the naive side perhaps, but that is to be expected from a rank beginner still learning the basic concepts of the art. We don't exactly cater to beginners and newbies, but we do cut them a lot of slack if it looks like they benefit from the advice offered here. It's those who don't appear to learn anything that are soon ignored or even kicked off the forum.

    Your question about heater wire is valid. The problem is you know absolutely nothing about thermodynamics. Any conductor will get hotter than ambient temperature if you run an electrical current through it. It's all about power and where that power is dissipated, and to understand that you need at least the rudiments of thermodynamics. Running a heater from a battery power pack is not the best of ideas because the energy density of any common battery is way to low to use it has an electrical heat source. Sure, you can buy battery-heated socks and mittens for winter heating of your extremities, but the battery is quickly depleted and must be replaced or recharged. A car seat heater that runs off the car battery is already built into some automobiles. But the car battery gets recharged after the engine is started.

    The nice thing about nichrome is it has a high specific resistance or resistivity, so it gets hot quicker than, say, the same size copper conductor. That doesn't mean you have to run it "red hot" to be effective. I have also had good success using Hastelloy and stainless steel tapes as low-resistance heating elements, both of which can be easily soldered with the right flux. The temperature you get all depends on how much power you put in and how you manage the heat produced. Electricity is converted to heat with 100% efficiency in a resistance heater. You get a little more bang for the buck if you can "steal" some energy from the environment with a Peltier stack, but IMO that is a waste of effort if all you want to do his heat something.

    Anyway, so do some more research and due diligence on your heater project, then come back here if you need some answers to specific questions. We expect you to learn though, not just parrot stuff you got off the Internet. BTW, there are wire-wound power resistors with mounting tabs on an aluminum case that are sometimes available on Ebay for a good price. They make good heaters, although that is not their original purpose. They are rated by the amount of power they can safely dissipate and that power ranges from a few watts for the tiny ones to several hundred watts for the largeish ones. Resistance varies from a fraction of an ohm to several thousand ohms with most common varieties I have seen (as surplus) being a few hundred ohms.
     
    Bluejets likes this.
  7. Voltaic

    Voltaic

    82
    1
    May 6, 2015
    Ok thanks.

    Oh plug pack means a low voltage output power wall connected power supply not battery pack ie. 12v 500mA, but they are about the same voltage as battery packs.
    I thought of using wire with enough in series or parallel to get enough heat dissipation so it wouldn't have to get that hot.

    OK thanks for the suggestion about the power resistors maybe that's an easier alternative.

    I'll look for a different forum more suited to beginners. I'm sure there are some.

    This site has a diy forum link on the main page so I kind of thought when I first signed up that it was suitable for simple electronics questions but it certainly seems more for advanced electronics discussion rather than simple diy projects and basic questions that I am asking.
     
    Last edited: May 30, 2015
  8. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    431
    98
    Aug 27, 2013
    Voltaic,

    I don't know the history of your posts, or who suggested you should be banned, but I certainly did not see anything ban-worthy in this thread....worst-case, as hevans1944 stated, perhaps a bit naive, but as long as you are making an honest effort to learn I would urge you to continue....That being said, due diligence is an important part of the learning process regardless of venue....for instance, when I posted the Wikipedia link to NiChrome wire, you might have followed it and perhaps even scrolled down to the table that shows the relationship between wire diameter, Amperage and Temperature and noted something along the lines of: #30 NiChrome wire reaches 204C @ 0.875A.......538C @ 1.74A......meanwhile #20 wire reaches 204C @ 3.58A and 538C @ 7.25A .....You might have then scrolled down a bit further and noticed the resistance per linear unit of NiChome wire decreases rapidly with respect to an increase in cross-sectional area (read: diameter)....putting the two things together you might have thought to yourself, "Selecting the right diameter wire is critical to keeping the wire temperature below the melting point of plastics and the flash point of fabrics it might come in contact with"....instead you posted:

    Because it appeared to me you had utterly failed to grasp any of the salient properties of NiChrome wire I immediately began to worry about the potential safety of your experiments....It is completely possible to start a fire using NiChrome wire using even a very limited power source....if the plastic, fabric or glue used were volatile in the temperature range you might even have started a fire that proved difficult to extinguish....so I felt the need to steer you in a direction better suited to safe experimentation by someone who does not bother with due-diligence. In short, there were a myriad of ways you could have responded that might have led to actual help in designing a NiChrome wire based heater for a specific purpose, but they all would have required some effort on your part....because your response suggested you would very likely end up doing something potentially dangerous I was forced to suggest you steer away from starting down the path at all. That is unfortunate, but not, in my opinion, ban worthy in and of itself.

    If you do decide to seek a forum where safety is not a primary concern, then I can honestly say, "I hope you don't find it." Regardless of where you go or what you do, I would urge you to spend your time making an effort to learn, a large percentage of forum responses to neophytes from "experts" are cryptic....a clue more than an answer...a test of sorts of the poster's willingness to seek out answers if given the right place to look....no one wants to spend their time and effort doing other people's work for them, but thankfully there are people who will help point out the right direction to learn so that you can do the work yourself. I cannot think of a single example in this forum of someone being castigated for making an effort to learn by asking for help, this is, after all, the stated purpose of the forum....but their are plenty of examples of people who expect the the forum to solve their problems and design their projects without any effort on their part....these people typically do not remain active or welcome very long. I have never been part of a forum where laziness and/or apathy were highly regarded; on the contrary, all of the forums I have participated in were created by people passionate about the forum subject and almost universally had a deep-seated desire to help others learn about the forum subject.....In none of these forums have I ever encountered experienced, knowledgeable people with a desire to help people who are unwilling to make an effort on their own......

    Just for emphasis:

    Good Luck!

    Fish
     
  9. Voltaic

    Voltaic

    82
    1
    May 6, 2015
    Ok thanks. Perhaps I did not read the whole page before I posted a quick reply to that post but I would have have read more later before buying anything and of course tested anything I got with a multimetre then testing it by briefly connecting an a AA battery with a temperature probe I have first and I would have quickly realised it was not suitable because the resistance would have been too low I would have wasted a few dollars at worst.

    I also assumed despite the temperature listed I could just connect enough in series to get the low temperature that I needed (testing with a AA battery after measuring the resistance with a multimetre). I have a series of alkaline aa test holders from 1x aa, 2x aaa, 2x aa, 3x aa and 4x aa which I use to test things (which have their own resistance being alkaline and they are nearer to empty than full).
    I would have then quickly realised it would not have been practical and looked for other options.

    Some of the theory and equations I find a bit daunting.
    But I was never going to just make something up and run it straight away with high power without testing and measuring the electric properties of the material first!!!!! Like I think you are suggesting?

    Anyway I have a fire extinguisher and fire blanket in case it caught something on fire from the multimetre current or brief aa battery connection.

    Also I'm getting more up to date books. I bought an ebook reader for this purpose but had to take it back when I found out it would not work without wifi which I don't have so it's been a bit of delay I'm looking for a different one that doesn't require wifi to work.

    OK OK so I realise now it would have been totally useless anyway because it wouldn't have had enough surface area or mass to have had any useful effect at the low temperatures I wanted to use it at anyway. But I haven't got any anyway because I just wrote it down as something to think about as one possible option.
     
    Last edited: May 30, 2015
  10. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    431
    98
    Aug 27, 2013
    Hey Voltaic!

    I did not 'suggest' I thought you might head off willy-nilly to do something that might be unsafe; I stated I was concerned you might. Please remember there is no way in a forum to know anything about the person who is posting beyond what they type in their post....among other things, this includes age. I was concerned that you might be both young and foolhardy....From your most recent post perhaps you are not as much of either as I feared....Anyway, some salient facts about NiChrome wire.....

    1) NiChrome wire is used to create the "Vapor" in e-cigarettes, typically powered by tiny "coin style" batteries....

    2) A typical AA battery can easily deliver > 1A of current, so depending on the size/length of wire, you could burn yourself or start a fire even with a "AA" battery.....hence my point about getting a firm grasp on the properties prior to beginning experiments.

    3) NiChrome wire forms a very high resistance oxide layer at elevated temperatures that remains intact when the wire cools. The physical properties of the wire are also (DIY) irreversibly altered at a fairly nominal temperature....specifically the wire becomes much harder and less flexible....in metallurgy the state you purchase the wire in is called "annealed", once it reaches a specific temperature it becomes "hardened"....the "hardening" typically occurs simultaneously with the formation of the exterior Oxide Layer. It is VERY IMPORTANT to form the wire and make any electrical connections PRIOR to first use. This implies that you need to "design" and Build your heating element prior to experimenting with the wire....I am stating here (not suggesting) that in order to build a viable heating element with NiChrome wire you actually have to design it first...in order to successfully design your heating element you will need to get a firm grasp on "Some of the theory and equations I find a bit daunting."

    So, if you want help with this project, define a single heating element you would like to design/make. I (and hopefully others) will help point you toward finding out how to use "the theory and equations" that you currently find daunting to ensure the design is viable. You should not expect more effort on the forum's part than you yourself demonstrate, but if you put time and effort into learning then I can promise there will be a general forum willingness to guide you in the right direction. This is what this and other learning-oriented forums are about....helping people learn....they are not about doing things for other people....So, if you are OK with the ground rules, then lets explore designing a 'special purpose' heating element....

    Fish
     
  11. Voltaic

    Voltaic

    82
    1
    May 6, 2015
    It's ok it all sounds too risky and involved now, I just wanted a simply project without dangers or complex equations to solve, one I could test as I went along and work it out as I go more as a learning experience starting with very low power multimetre and aa testing.

    I did read a beginner electronics book (except for the projects at the end) and it didn't have warnings of serious dangers with aa battery powered testing so I feel a bit stupid now. I'm working on a passive solar design with a black container instead and for the other warmer design I'm just going to buy a ready made usb powered warming module. Anyway the nichrome wire would have never suited my purpose anyway it's the wrong type of material being so thin and massless and also not suitable for my basic level of understanding. It looks like it's more suited to bar heaters etc. which I have no interest in making. I just want a gentle warmer pad not a 500 degree danger wire.
     
    Last edited: May 31, 2015
  12. Voltaic

    Voltaic

    82
    1
    May 6, 2015
    So this is the sort of thing I wanted to make (but spread out over a slightly larger area) but I'll just buy one, it's not worth the trouble trying to try to make.
    [​IMG]


    Definitely not this
    [​IMG]
     
    Last edited: May 31, 2015
  13. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    431
    98
    Aug 27, 2013
    Hey Voltaic!

    If you are looking for a good place to get started with electronics that is both safe and cheap, I would suggest LEDs....At the most basic level you can use a simple resistor to learn about limiting current....at the other end of the spectrum are current regulated forward converters, matrix displays and wireless communications....LEDs are used in one way or another in a vast number of consumer and Industrial and DIY products/projects to provide visual feedback, lighting, signs, isolation and communication....and generally they have the added benefit of being low-power and visible. As an added benefit working with LEDs should allow you to quickly "master" two of the basic formulas crucial to electronics.....E = iR and P=iE....Lots of beginners want to start off with projects that integrate numerous interdependent circuits and get lost in the details...it is much better to learn DIY electronics in discrete units...mastering each unit so that eventually you can combine what you have learned to build more complicated projects....With LEDs being a part of so many projects, they are a natural place to start...Don't be fooled into thinking that connecting a battery to a resistor and an LED is all there is to mastering LEDs....that is just the most basic example of how LEDs might be used....

    It is also important to remember that electronics is a sub-category of physics....at the end of the day every electronic circuit must obey all the laws of physics....a firm grasp on physics is a big help with good circuit design....The language of physics is Calculus; while most DIY electronics tend to avoid direct reference to Calculus, it is in every circuit from the lowly voltage divider to the biggest super-computer....there is no reason to be afraid of it. Obviously with some hands-on experience a huge number of projects can be designed and built w/o directly using it.....But Imagine what you would think of a mechanic who decided sockets and wrenches were too complicated and instead only used pliers and screwdrivers....he might be a brilliant mechanic; able to isolate any problem, but his refusal to use the common tools of the trade would severely limit his ability to get the work done in a timely fashion and would likely cause a fair amount of collateral damage. Physics and Calculus are the tools of the electronic design trade, ignoring them will limit your ability to design and build more complex electronic circuits. This doesn't mean you have to learn Physics and Calculus before you begin learning the basics of electronics; rather it is a suggestion that you keep an open mind about Physics and Calculus...they are not some draconian form of torture designed by sadist to inflict headaches and nausea, but rather powerful tools that can be wielded to simplify the tasks at hand.

    Sorry...that turned into a bit of a lecture, not really where I was headed....Give some consideration to starting/continuing your journey into electronics with LEDs....If you think you have already mastered the basics of LEDs and want to increase the complexity but aren't sure where to go next, I am certain we can help you move forward in suitably incremental steps.....steps that will hopefully teach you about basic electronics and prove fun/useful building blocks.

    Good Luck!

    Fish
     
    hevans1944 likes this.
  14. udhaya

    udhaya

    17
    0
    Feb 26, 2016
    Hi Fish4Fun

    Am also tried this using Nichrome wire with 9vbattery() refer the youtube video but it doesn't heated and also tried in 12v Dc adaptor 15 Ohm nichrome wire(approximately 80cm length) nichrome wire where winded in wood like "s" shape in this case temperature increased, but am placing a aluminium plate on nichrome wire connected with 12 v, circuit will be short circuited LED of adopter will be continuously blinked at this point measured the voltage using multimeter it shows some what 3.5v how to solve this issue please help me on this.


    thanks in advance.
     
  15. Bluejets

    Bluejets

    3,043
    595
    Oct 5, 2014
    Perhaps you also should read Hevans1944 post above #6 and follow his links.
    He has good info there for beginners.

    To add to the sources of heating at low voltages one can also look at automotive bulbs.
     
  16. hevans1944

    hevans1944 Hop - AC8NS

    3,942
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    Jun 21, 2012
    Thanks for the vote of confidence, @Bluejets. I am not going to add any more here because I prefer to respond to posts that actually use punctuation (commas, periods, etc.) and an appropriate mix of upper-case and lower case letters. Life is short: eat dessert first.

    This should be a new thread since the OP has long since abandoned the original thread. Your advice is good: @udhaya should scroll up and read my post #6 and follow the links, perhaps post again as a new topic. The video posted by @udhaya was an "epic fail" at teaching anything useful. Auto brake lights get warm enough for most heating purposes if you pump enough current through them. Also might want to try low-voltage halogen desk lamp bulbs: they get really hot when operated at rated voltage and current.
     
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