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Electric Throw Rug Basic Circuit

Discussion in 'Troubleshooting and Repair' started by TheClaw, May 30, 2021.

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  1. TheClaw

    TheClaw

    3
    0
    May 30, 2021
    Hello. During winter I get very cold when sitting at my computer. I like to sit with an electric throw rug. Trouble is I have blown-up 3 or 4 of them over the last few years.

    The most recent failed with an apparently dead controller. I got a new controller sent out under warranty, but that failed with a popping sound the instant I switched it on.

    The rugs all seem to be similar. They have a 4-pin plug, lets call the terminals A,B,C,D
    The resistance A-D is around 240ohms, and B-C is around 900ohms.

    I have a brand new one which works, and I have the old rug which blew 2 controllers. The resistances are similar.

    Can someone please explain the basics of the circuit to me? I'd like to understand what is going wrong, and perhaps how I can do a simple fix to continue using the "faulty" blanket. Perhaps in series with a light bulb??
     
  2. Martaine2005

    Martaine2005

    3,595
    979
    May 12, 2015
    I'd guess that because they both have 4 terminals, they are internally wired differently.
    Can you give us a link or links to the units you have now? It may be obvious why they are not interchangeable.
    I am sure photos of the controller boards will be required as well.

    Martin
     
  3. Martaine2005

    Martaine2005

    3,595
    979
    May 12, 2015
    More than likely a short in the old blanket.

    Martin
     
  4. TheClaw

    TheClaw

    3
    0
    May 30, 2021
    If there was a short in the old rug, it has since gone away. Because the old rug and the new rug show similar resistance readings.
    Does anyone understand the 4-pin circuit inside the rug?
     
  5. Martaine2005

    Martaine2005

    3,595
    979
    May 12, 2015
    They might do if you tell us what brand you have or link to your replacement controller as previously requested.

    Martin
     
  6. Martaine2005

    Martaine2005

    3,595
    979
    May 12, 2015
    Two terminals are most likely A-D the heating element/coil/wire. The other two terminals B-C are most likely the temperature sensor.
    Checking A-D and B-C for resistance is fine. But did you check A-B, A-C, D-B and D-C?.
    Controllers don't normally go 'pop' without a reason.
    The fact that it did 'pop' instantly, suggests the blanket is faulty.

    Martin
     
  7. TheClaw

    TheClaw

    3
    0
    May 30, 2021
    Oxford Square Heated Throw Blanket, model IA4144
    https://www.aldi.com.au/en/special-...saturday-detail-wk18/ps/p/heated-throw-rug-2/

    This is the new rug and it works fine.

    I still have the old rug and it is extremely similar. I want to understand why the old rug failed, and if it can be got working in some crude fashion.
    I want to understand the basic circuit.

    A-B, A-C, D-B and D-C are all infinite on both rugs.

    Do you think the controller applies 240v across A-D to heat the rug via a 240 ohm resistance wire, and monitors B-C which would be a chain of thermistors. If the reading is out of bounds, it switches off.

    Any help would be appreciated.
     
  8. Pejayuk

    Pejayuk

    6
    0
    Dec 6, 2020
    I'm now on my third one of those heated throws. Mine came from Lidl, so very similar to the Aldi one I'd guess. The first two failed within a few months, so I had them replaced under warranty. I'm sure they failed due to the blanket over heating because I used to have it switched to the maximum setting.

    The manual says that if the LED on the controller doesn't light, it cannot be reset. I assumed there must be a non-resettable thermal fuse somewhere.

    This last one is still going strong after several years because I never use it on more than the medium heat setting. I think if a higher setting is used, the blanket must be completely flat so as not to overheat the wires inside.

    Sorry I can't help with the circuit, but if mine does fail again, I will be trying to fix it myself this time.
     
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