How to make warming pads from thin speaker wire - Page 1
Forum section: electronics / beginners

author: electromateria
author_rank: Regular Contributor
timestamp: October 30, 2021, 04:30:52 am
content: I have some really thin speaker wire, it looks very slightly thicker than the wire you use on small breadboard projects. I have maybe 20 meters of it.My plan is to cut a long length of wire, wrap it into a loose coil, put electricity through it to generate heat.My power source is 18v battery. I want to have 4 heating pads running off it, so, 4.5 or 5v for each one. How can I calculate the length I need for each wire? Should I just do trial and error? Should I run a length of wire off 5v and see when I get reasonable heat from the coil?Once I know the proper length of wire I just make 4 of them and chain them all together with a switch and a battery? Any other components needed to make sure I don't spontaneously combust?

author: james_s
author_rank: Super Contributor
timestamp: October 30, 2021, 04:33:39 am
content: Ohms law.Either look up the resistance per meter of the gauge of wire you have or measure the resistance of a known length and calculate the power. 20 meters is probably not nearly enough for 18V unless it's really thin wire.

author: electromateria
author_rank: Regular Contributor
timestamp: October 30, 2021, 05:19:21 am
content: Quote from: james_s on October 30, 2021, 04:33:39 amThink I should buy some carbon heating pads instead?https://www.ebay.ca/itm/143840682124https://www.ebay.ca/itm/373772847309It's very hard to read the wire but I think one spool is 18awg and the other is 22awg. I could maybe buy some thinner wire if needed.

author: m3vuv
author_rank: Super Contributor
timestamp: October 30, 2021, 06:23:54 am
content: why not just buy some nichrome wire?

author: sleemanj
author_rank: Super Contributor
timestamp: October 30, 2021, 06:39:50 am
content: Better to use Nichrome or Kanthal resistance wire, you'd have to push a lot of current through that copper speaker wire to get it to work.If the pads are to be applied directly to the skin, I would guess between 3 and 5 Watts max for maybe 10cm x 10cm pad, you'll definately want them controllable, for Nichrome/Kanthal with approx 5v supply, probably about half a meter.Of course you do have the problem of it not being insulated, so there is potential for shorting (literally making shorter) the wire by folding or scrunching the pad etc, I don't know if you can get insulated resistance wire, I suppose you can.

author: m3vuv
author_rank: Super Contributor
timestamp: October 30, 2021, 06:44:42 am
content: if the op is asking such a question on this silly idea i hope he has good fire insurance!,seems like an accident waiting to happen!.

author: electromateria
author_rank: Regular Contributor
timestamp: October 30, 2021, 07:35:21 am
content: Quote from: m3vuv on October 30, 2021, 06:44:42 amI'm gonna cause all kinds of trouble with my unstable and shoddily made heating device. just wait and see.If you guys don't hear from me again assume the worst happened.What gauge of that wire do you guys recommend I buy? I'd prefer not having to wrap 100 loops if possible. Attached pic of the speaker wire.

author: m3vuv
author_rank: Super Contributor
timestamp: October 30, 2021, 08:23:28 am
content: just look on epay for nichrome wire,its not rocket surgury is it! ? lol

author: Siwastaja
author_rank: Super Contributor
timestamp: October 30, 2021, 09:08:21 am
content: Think about what you are suggesting. Warming pad with PVC insulated thin copper wire is a practical possibility, doing it with uninsulated bare nichrome wire is not.Of course the power you can safely get out of PVC insulated wire is going to be low, but the idea of warming pad is that it'swarm, not hot, isn't it?The PVC insulated wire ismeantto warm up during normal use at rated currents. There is nothing inherently wrong leveraging that normal behavior.This is easily calculated by the American Wire Gauge ohms/meter table (on Wikipedia for example), then Ohm's law, but failing to know the exact gauge of the wires, there's no other way than trial and error.The 18V supply voltage is likely way too much, causing it to run too hot. Start at very low voltages, say 1V, and ramp it up until you have decent tempreature and good margin against unsafe temperatures. Carefully find if you have any hotspots. Note that for long-term use, you don't want the PVC cable surface to exceed 50-60 degC. But if it'swarmingpad someone touches, you want to avoid anything in excess of say 35-40degC. For such low temperatures, PVC cable is just fine and a simple, easily available solution.I have built such heaters from ribbon cable. Soldering the ends into series connections and protecting those solder joints is PITA, though.

author: Jwillis
author_rank: Super Contributor
timestamp: October 30, 2021, 11:57:44 am
content: There is wire available for the OP,s application . It's used in incubators and electric blankets . It's an insulated NiCr wire, usually 33/100m . Insulation is a woven fiber glass and silicon rubber or just silicon rubber .

author: Siwastaja
author_rank: Super Contributor
timestamp: October 30, 2021, 03:22:50 pm
content: If available, that is the best option. At least the insulation won't melt and catch fire. Obviously it still poses danger of fire if ran at too high power.Self-regulating PTC cables are safest but I don't know if this designed for safety extra low voltage is easily available.

author: Jwillis
author_rank: Super Contributor
timestamp: October 30, 2021, 05:08:33 pm
content: Quote from: Siwastaja on October 30, 2021, 03:22:50 pmI had a bunch of it and only did some small tests . Never did a fuse test . I gave it all to a friend that wants to use it to keep his solar batteries warmer in winter here . Weaving it in fibreglass cloth . I'll ask for a piece back and try some tests to see what happens.

author: xrunner
author_rank: Super Contributor
timestamp: October 30, 2021, 05:17:51 pm
content: Quote from: electromateria on October 30, 2021, 04:30:52 amGo to Wal Mart or another store and buy a new heating pad - I think they're pretty cheap. You know the wire in that is the right kind. You can take it apart and use the wire in the new one for your pad. You can also use the controls too.

author: james_s
author_rank: Super Contributor
timestamp: October 30, 2021, 06:12:08 pm
content: If you don't know the gauge of the wire you can measure it with a wire stripper. Just use smaller sizes until you find the smallest one that doesn't cut any strands and that's probably your gauge. From there it is simple calculations to tell you everything you need to know. If you don't know how to use Ohms law figure that out now because you're going to struggle doing almost anything with electronics until you know it.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 31, 2021, 12:14:20 am
content: That wire looks fairly thick (0.3-0.4mm diameter) to be used as a heating element.You can always do it following the wire resistance and isolation limits.You'll need a low voltage, high current power source (usually less efficient than higher voltage lower current), and also keep the isolation from melting down.Some PVC types start to soften at 100°C, while for most enamelled wires the limit is around 150°C, which limits the application to a low power warming source.For anything else, use parts designed for that purpose: ceramic resistors, nicrom/carbon wire, PTCs...

author: electromateria
author_rank: Regular Contributor
timestamp: November 01, 2021, 12:41:40 am
content: Thanks for all the information guys!All the wiring options and calculations have been taken into consideration.Some wires would need to be insulated, others too rare and expensive, or bulky (floor heating wires etc).I went off into the woods and spent days in solitude wracking my brain, thinking "what would nikola tesla do?". I studied electronics textbooks and meditated on ohms law - planning the best way to move forward. After being hit with a "EUREKA moment" I spent 5 hours scheming and crafting this masterfully created blueprint. It maybe a bit technical, if you guys have any questions let me know!Attached:

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 01, 2021, 03:05:57 am
content: At some point you are likely to have to do some experiments, no matter how much calculation you do. But the math is fine to orient you into the right place to do your experiments.First, though usually not formally considered Ohm's law, the power form is a good place to start thinking.Power=Volts^2/Resistance or in your case Power=324/Resistance.How much power do you need to avoid a frost bitten face while running the snow blower? Good question, but you can start by thinking about old incandescent bulbs. The 6-12 W Christmas decoration bulbs are just barely sensibly warm in cold weather while a 100W bulb usually is still too hot to touch in fairly cold weather. So you are probably looking for 20 to 50 watts for your heater as a starting point. 32.4 Watts makes for easy math and suggests 10 ohms for resistance. It will take experiments to get the right answer which will include area of your heating pads, how cold it actually is, how hard the wind is blowing and your personal physiology.Checking a wire table it takes in the neighborhood of 1000 ft (300 meters) of copper wire near 20 gauge to get that resistance. Nichrome starts looking attractive. Particularly if you need less power.Finally, for a bit of good news return to ohms law and find that you will be pulling 1.8 amps The power tool batteries you are using tend to be from 1 to 4 Amp-Hour capacity indicating that you could get up to two hours of blowing snow on a charge. If it takes more than two hours you probably need to look at a pickup mounted plow.Again, all of these numbers will need adjustment based on your specific use case, but they at least tell you which direction to start looking.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 01, 2021, 03:08:37 am
content: Actually the right answer is probably to buy a balaclava.

author: electromateria
author_rank: Regular Contributor
timestamp: November 01, 2021, 04:04:19 am
content: Guys all jokes aside will this work or is it missing components? (fuse, diode, limiting circuit??)My goal is just to create a safe and functional device with a minimal time and effort investment.I don't know anything about making basic circuits so I really need you guys to guide me. With my limited knowledge this device should work fine as long as the heating pads are each rated around 5v.Should I built it this way or will it make the battery explode?

author: electromateria
author_rank: Regular Contributor
timestamp: November 01, 2021, 04:11:53 am
content: I'm considering adding a cheap ebay buck converter to the circuit to control the heat output.

author: james_s
author_rank: Super Contributor
timestamp: November 01, 2021, 07:25:07 am
content: Quote from: electromateria on November 01, 2021, 04:04:19 amThen buy an off the shelf heating pad of the correct voltage to run off the batteries you want to use.We are not your personal consultants, you do not seem the least bit interested in even trying to learn anything and instead are just expecting someone to design something for you and hand you a turnkey solution on a platter, that's not really how it works. If you can't be bothered to learn some basic electrical fundamentals then how can you expect someone to take the time to develop something for you? You could learn Ohms law, Kerchoff's laws, how to read and draw simple schematics and a few other basics in a few hours with nothing more than basic algebra, this is not rocket science.If you have to ask that question you should not be trying to do it.

author: electromateria
author_rank: Regular Contributor
timestamp: November 01, 2021, 07:12:27 pm
content: Quote from: james_s on November 01, 2021, 07:25:07 amYou're not my personal consultant, but you do like answering beginner questions right lolbeginner questions happen to be a specialty of mineIn my mind this should be a VERY simple project. Especially to someone experienced like you. If you asked me a web design question and told me what framework you want to use, then gave me an overview of what you planned to do I could quickly layout what you should change or fix in your plans, even for an absolute beginner. I suppose that's what I expected. granted I was all over the place with my project details (first wanted to use wire), so I think the responses were good and helpful, but now I'm dialed into what I *think* is the easiest way to proceed and just need to know if it will work. I laid out the components I plan to use. In my mind that should be enough to either say:*no dumbass you're gonna blow yourself upbecause: xyz, add this component, change that, etcor*yes that circuit will work fineI get why ohms law is useful if I was going to use wire windings, but I'm not planning on doing that anymore for multiple reasons. those pads are already rated for 5v, so doesn't that mean the work is already done for me? if not, then it would help me to knowwhy specifically.anyway, I'm probably just gonna buy the heating pads and play around, but any relevant advice as always is appreciated.

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: November 01, 2021, 08:01:18 pm
content: This is probably a troll thread, but i'll humour you.5V Pads, 20V battery -> house on fireNo fuse whatsoever -> house on fireWiring of the switch wrong -> battery shorted -> house on fireBattery will deep discharge -> battery dead after one use (if it's not killed first by, you know, your house being on fire).Also, abusing PVC wire as a heating element without using any kind of constant current regulation and temperature sensing whatsoever is the dumbest thing you can do. It *will* heat things up though. Because your house is on fire.So my advise is: buy a fire extinguisher and a book an basic electrical engineering. In that particular order. ;-)BTW you can buy cheap "plant heating pads" that do what you want ready to go, safely.Have a nice day and good luck. You will need it.

author: electromateria
author_rank: Regular Contributor
timestamp: November 01, 2021, 09:07:03 pm
content: Quote from: BreakingOhmsLaw on November 01, 2021, 08:01:18 pmOk, why, specifically? That makes no sense to me. If I have 4x - 5v pads and the battery outputs 18v (just says 20v) what's the issue? Do the pads just draw in unlimited amperage if not regulated? Just explain whats going on.Quote from: BreakingOhmsLaw on November 01, 2021, 08:01:18 pmWhat's a suitable fuse for this project?Quote from: BreakingOhmsLaw on November 01, 2021, 08:01:18 pmAs far as I know the battery already has a built in protection circuit, is it not enough for this application?I have a bunch of those small 20v dewalt batteries I don't care about. If the cells burn up during testing I'll open the casing and put new ones in, then modify the circuit so it doesnt happen again.Quote from: BreakingOhmsLaw on November 01, 2021, 08:01:18 pmMy house isn't gonna catch on fire lol. If anything it will be me catching fire so no worries, then no more annoying questions to answerQuote from: BreakingOhmsLaw on November 01, 2021, 08:01:18 pmWorst advice. I'm not gonna study electrical engineering for months to build a stupid heating pad lol. Just explain the issues please and I'll figure it out. You'll see, if you guys continue to answer my questions and help me I'll get it done safely.Quote from: BreakingOhmsLaw on November 01, 2021, 08:01:18 pmWhy is a plant heating pad safe, yet a clothing heating pad unsafe? The whole idea is to run it off that 20v battery btw, that's an important part of the project. I'll buy plant heating pads if they can run off that battery source.Quote from: BreakingOhmsLaw on November 01, 2021, 08:01:18 pmThank you good sir, luck is always on my side

author: james_s
author_rank: Super Contributor
timestamp: November 01, 2021, 09:10:23 pm
content: Quote from: electromateria on November 01, 2021, 09:07:03 pmYes, you can't be bothered to learn anything, you just want someone to give you all the answers.This thread is a waste of time, I'm out.

author: electromateria
author_rank: Regular Contributor
timestamp: November 01, 2021, 09:25:00 pm
content: Quote from: james_s on November 01, 2021, 09:10:23 pmYes, that's exactly what I want - me asking questions and experts giving me answers is literally me learning. Lets say you quickly lay out all the details to properly build it, how would I not be learning? I'm learning the PROPER WAY TO BUILD THE SPECIFIC DEVICE I NEED. Much of that knowledge can be applied to other projects. Right now I'm not learning because you're gatekeeping by not helping me. You know that answers but tell me "go read ohm law and study circuitry for 6 months then come back if u have questions". That's useless. My goal isn't to learn the basics of electrical engineering, it's to build a simple heating pad and for that I just need simple and precise details.Anyway that's my mentality. I'll learn electrical engineering over a long period of time as I complete projects I'm interested in.

author: Gyro
author_rank: Super Contributor
timestamp: November 01, 2021, 09:34:33 pm
content: Yes, go read Ohms law, it will take you seconds!V=I*RR=V/II=V/RPower (W) = V*I

author: electromateria
author_rank: Regular Contributor
timestamp: November 01, 2021, 11:53:21 pm
content: Quote from: Gyro on November 01, 2021, 09:34:33 pmSo I need to know the resistance of the circuit (mainly the heating pads), the amps put into it from the battery, then calculate what voltage is flowing through (and I guess make sure it doesn't exceed the 5v rating / pad otherwise turn down the amp flow)? That's my initial impression and I already know it's definitely not rightEDIT: seems the voltage will be fine but it's the amps I need to control, if that's too high it will cause too much heat. or maybe I need to split all the current from the battery 4 ways into each pad so the full 20v doesn't all go into the first one.I'll update the thread once the device is made. Probably around 1 month time to get all the parts ingonna hire a university student overseas to fix whatever design flaws there are and spoon feed me the specifics, Ill share it all for free when its done

author: Gregg
author_rank: Super Contributor
timestamp: November 02, 2021, 12:12:08 am
content: You want specifics, here are some possibilities:1. Buy some heating pads at thrift stores or estate sales. Find ones that you can feel the wires inside as these will have resistance wire with either silicone or PTFE insulation and most of the hard work will be done for you.2. Assuming the heating pad(s) are rated for 120V and you want to use a 20V battery, you want to use about ¼ to 1/5 of the length of resistance wire. A little more resistance won’t hurt your application and will not drain your battery as fast. Note: nichrome is difficult to solder; it will be easier to use crimp connectors.3. If you want to control the heating, a PWM DC motor speed control will work well; something like this one:https://www.amazon.com/Bringsmart-Controller-Variable-Inversion-controller/dp/B07BWBQXLFYou will have to figure out a box or other mount for it.4. Use fuses between the battery and PWM controller as well as between the PWM controller and each of your heating pads. Automotive two bladed inline fuse holders are readily available on Amazon and fleabay. Use ohms law and/or a dmm to determine the value needed for the fuses; sorry if ohms law is too much of a learning experience.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 02, 2021, 12:56:36 am
content: You are frustrated by the answers. Those of us on this end are frustrated by your questions. I can't make enough sense of your "circuit" to sensibly comment on it. There is no way to tell what connections you are depicting. But I will try anyway by describing how I would hook it up.Since you have five volt pads you want to connect them in series. That means connect the high end of one to the low end of the next. When you have finished connect the four pads that way you will have two wires unconnected, one high end and one low end. (By the way high end and low end are kind of meaningless for a heating pad, but they are a way to describe the two wires coming out). The low end should be connected to the negative side of the battery. The low end should be connected to one terminal of the switch. The other terminal of the switch should go to a fuse, and the other side of the fuse goes to the positive side of the battery. (Which side connects to negative and positive is not particularly important in this application, but it is a good habit to switch the high side). When connected this way the same current flows in each pad, and each pad gets one fourth of the voltage applied. If they are indeed five volt pads and you have a twenty volt battery this means they are operating at their normal voltage.I am not familiar with the Dewalt batteries you are showing. Some of these portable tool batteries have auxiliary terminals that feed or are controlled by safety circuits. They can shut down the battery output if not connected properly. It is possible that if you use your voltmeter to measure across terminals you will find nothing, or find 20V, but it is not a pair of terminals that is able to supply the normal current from the battery. You may be able to get more information by googling.If you get this all hooked up and current flows you will get some heat. If you are happy with the amount of heat and the battery life you are done. If not, information provided in my prior posts and others comments will give you guidance on what to do.

author: Gyro
author_rank: Super Contributor
timestamp: November 02, 2021, 10:06:01 am
content: Quote from: electromateria on November 01, 2021, 11:53:21 pmYou've actually pretty much got it there. If the resistance of the wire is too low at a given voltage, then the current will be too high. Reducing the voltage will reduce the current, and so, heat output. So will increasing the resistance of the wire.Please don't fall into the trap of using some old speaker wire, just because you have it, if it's not suitable for the job though.

author: Terry Bites
author_rank: Super Contributor
timestamp: November 02, 2021, 04:07:44 pm
content: I've use silcone heaters in the past for a vivariums (vivaria?) I resists snake poop. So it safe if you spill your beer or pee your pants on it.https://www.amazon.ca/Waterproof-Silicone-Flexible-Heating-60MM/dp/B010B2A3KI