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How to replicate electric blanket? (Project)

  1. Oct 21, 2015 #1
    First off, for my EE100 class I chose to replicate the industrial electrical blankets that are out there.
    With that being said, I do own one and can tell that there are some kind of conductive, insulated wires (copper?) that run throughout the blanket which generate the heat. And of course, the blanket plugs into a control which dictates the power level of the heat.

    My main questions are what kind of raw materials will I need?
    My guesses are as follows:
    1.)
    Some type of conductive wire and plastic shield for the wire?
    2.) Some polymer/material that can insulate and protect the blanket from burning.
    3.) I want to incorporate a lithium battery so that no wall plug is needed.
    4.) And the heat controller might be a bit complicated so I won't include this in my project.

    And of course I will need some guidance on how to make the circuit from the battery to the wires and how to even
    control how much heat is generated by the wires (clueless here).

    P.S. I am not an expert EE so please no too-technical terms, haha.

    If more info is needed just ask!

    I appreciate all of the replies.
     
  2. jcsd
  3. Oct 21, 2015 #2
    However you construct it, a typical electric blanket will use around 100 watts on full heat.
    That's quite a lot of power for lithium ion batteries.
    You'll need either a very heavy duty battery or several more modest ones, which will be expensive either way.
    (These would weigh quite a lot too, so portability could become an issue)
     
  4. Oct 21, 2015 #3
    Understood, But I am not looking to make a queen sized or double size blanket, (should have mentioned this) I want to make like a 3.5 square foot blanket or something small. Do you recommend any other type of battery?
     
  5. Oct 21, 2015 #4

    billy_joule

    User Avatar
    Science Advisor

    a Google of 'electric blanket wire' will answer 1) and 2)

    terms like 'DIY heater" 'DIY heat bed' "DIY Nichrome heater' will probably also help.

    for 3)
    How much energy would you like to use on a single charge?
    ( find out the power consumption of similar blankets and multiply by the time you'd like the battery to last for, this will be in Joules, convert to Ampere hours for battery sizing)
    What is the size and cost of a battery of this capacity? Is this reasonable?
     
  6. Oct 21, 2015 #5
    OK if it's small in size, and you are prepared for the warming to be somewhat limited you might get power required down to say 20W.
    That's still quite big for an Li battery but not so much of a monster as 100W.
     
  7. Oct 21, 2015 #6
    I have gone to Google but I would like to have more in-depth answer and a back and forth convo, I believe that will help me understand it more.
    And for the second part, I am not sure how much energy I would or even could use. Ideally on a medium heat setting, maybe 3-5 hours?
    Can you help me with figuring out the Joules for this? And I don't know about battery capacity either, I am fairly new to this field.
     
  8. Oct 21, 2015 #7
    What about a 7v lithium rechargable battery?
     
  9. Oct 21, 2015 #8
    It's not just about the voltage rating.
    The battery should be rated to deliver a maximum continuous output of - ('x' amount of watts - let's say 20W),
    and also rated to deliver that amount for 'y' amount of time before expiring.
     
  10. Oct 21, 2015 #9

    anorlunda

    Staff: Mentor

    To start, how much area? What temperatures do you need relative to the surroundings? Will there be other blankets or insulation above the blanket, or below the object? How massive is the object being heated? Are there requirements for how fast it heats up? What are the weight and size constraints? Does your project have to include recharging the battery?

    The first step to calculate energy needs, are not electric, they are thermodynamic heat calculations. If this is difficult to do, it might be easiest to make a blanket using wall plug power with excess capacity first, then turn it down until it meets the need, then measure how much energy that is using. The next step would be to find a suitable battery to replace the wall plug. The last step is to figure out how to recharge the battery.

    A second thought: have you checked out medical heating pads? You might find one of the right size and power with a variable controller for much less money than building your own.
     
  11. Oct 21, 2015 #10
    Thank you for the detailed reply!
    Well I don't want to just buy a heating pad that'll be against the point of me learning how to make it.
    I'll be honest you asked a few question that I don't have the answer to.

    - I am thinking of a 3.5 foot by 3.5 foot blanket, the heating element(wire) sewed into the blanket with fabric and in a way that can't burn the blanket.
    -Yes, I would prefer the rechargeable battery for my project.
    -It doesn't have to heat up instantaneously but the quicker the better.
     
  12. Oct 21, 2015 #11

    anorlunda

    Staff: Mentor

    Don't worry, if you stay with it you'll get there.

    The essence of engineering is to determine the requirements before beginning the design. Think it through carefully and in detail. What will this pad have to do to call it a success? Start with those questions about temperatures and size.
     
  13. Oct 21, 2015 #12
    Thanks I needed that.
    Well I am a noobie when it comes to EE but I am very passionate about completing this project so I am willing to learn.
    If you have any resources about basic Wattage/Voltage/mah/ and whatever other concepts I will need to learn please share.

    As far as the raw materials go, do you have any idea on what kind of wire, or what material to insulate/cover the wire with to prevent burning of the cloth?
    And maybe any other materials I am not thinking of?
     
  14. Oct 21, 2015 #13
    It will be difficult to produce a safe heating element for your needs from raw materials.
    There are manufacturers who specialise in making this kind of thing.
    Here is an a example from a random google hit.
    http://www.totoku.com/products/heater/cat1/heater-wire-for-electric-blanket-for-1-wire-type.php

    (I you really wanted to work with completely unprocessed raw materials, you would have to make you own wire from copper ore or something similar!, - then insulate it with special plastics produced by your own chemical industry!)
     
    Last edited: Oct 21, 2015
  15. Oct 21, 2015 #14
    Ah thanks for that link!
    I was hoping I could just purchase the insulated wiring haha, awesome.
    Have any specific battery recommendations for this project?
     
  16. Oct 22, 2015 #15

    anorlunda

    Staff: Mentor

    I'm glad you are perisstant, but you are not getting the point of requirements. When you say "I will need" what does that mean. Do you need to heat a boulder 100 degrees, or heat a pizza 10 degrees? Questions like that dominate the requirements. You can't design until you focus on target requirements. You can't ask which way to point your gun until you name the target.

    But you might also be interested tinkering, instead of doing a project. Tinkerers just try things out to see what happens without any specific requirements in mind. A tinkerer might be happy with a battery operated heater that warms something 10 degrees for 10 seconds, he doesn't lay down requirements such as lasting 3 hours.

    Which are you trying to learn, the art of the engineer, or the tinkerer?
     
  17. Oct 22, 2015 #16
    Well I do enjoy tinkering but I do realize that I would be dealing with electricity/voltage so just blindly trying to tinker with that stuff is probably not smart.
    You are right though, Requirements should come before Design. Maybe back to the drawing board to define these. If you don't mind, could I inbox you when I do define some reqs and pick your brain a bit?
     
  18. Oct 22, 2015 #17

    anorlunda

    Staff: Mentor

    Sure, feel free to start a private conversation when you're ready.
     
  19. Oct 23, 2015 #18

    meBigGuy

    User Avatar
    Gold Member

    No reason to go private.
    Write down you requirements in as much detail as you can think of.
    The goal is to get all your thoughts organized so you can begin decomposing different aspects of the problem.

    anorlunda has asked good questions. But you have not precisely answered them.
    Your requirements need to address, for example:

    What you want to heat, its mass, to what temperature above the ambient, and how fast.
    How long do you need to maintain the temperature for
    How will you recharge, and how quickly must it recharge
    size, thickness, weight (including power source)

    As you try to answer the above, you will uncover more questions, and run into tradeoffs (conflicting or interacting requirements)
    (for example length of time vs battery weight)

    Maybe you will decide that the weight is a big issue and you need to back off on the length of time.

    Initially you won't know how to decide what is possible, but that's the reason to start with requirements. The possibilities will become evident as we proceed.

    Once you really have the requirements, we can help you decompose those into engineering decisions.
     
  20. Oct 27, 2015 #19
    Well I came here to seek engineering (technical) advice because I am not educated in this field but I only received technical questions back at me which I cannot answer for obvious reasons.
     
  21. Oct 27, 2015 #20
    There exist positive temperature coefficient ceramics which make great self regulating heaters. By careful ceramic choice the risk of overheating can be greatly reduced.

    These work by increasing resistance sharply at a given knee temperature.
     
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