Connect with us

Heated Mattress Pad Problem

Discussion in 'Troubleshooting and Repair' started by volvik, Nov 2, 2011.

Scroll to continue with content
  1. volvik

    volvik

    2
    0
    Nov 2, 2011
    I've had a Sunbeam heated mattress pad with dual digital controllers for several years. I've recently noticed that it no longer gets as hot as it used to. In my pea brain I assume that if the element gets warm then the output problem is with the controller.

    If that is correct is there anything I can do as an amateur to fix this? I noticed that one of the controller dials is stiffer to rotate so I wonder if over the years if dust etc can get into the controllers and interfere with the contacts (getting it to the higher heat levels) and maybe some isopropyl alcohol or canned air might resolve.

    :confused:

    Thanks in advance....
     
  2. daddles

    daddles

    443
    3
    Jun 10, 2011
    I haven't taken a controller apart in many years, but they're usually inexpensive and reliable bimetallic contacts. It certainly wouldn't hurt to unplug your controller from the power and open it up to see if that's the case and whether something is interfering with the mechanical action. If it's as you say a digital controller with electronics, then it's going to be harder to troubleshoot unless you can find a schematic for the circuit.

    Another possibility is that something has gone wrong with the heating element in the blanket -- as far as I know, nothing can be done about this except replacing it.
     
  3. shrtrnd

    shrtrnd

    3,701
    462
    Jan 15, 2010
    Odds are there are breaks in the heating elements in the pad itself.
    You can disassemble the controller to have a look, but you're probably going to
    have to replace the pad itself.
     
  4. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Hi volvik.
    Don't use isopropyil alcohol to clean potentiometers as it destroys the carbon track, use a blower and or a small brush, if its totally sealed then replace it for another new unit, but only if that's the problem, it could be the pad or something else, but a stiffer control knob is not right.

    But i doubt your know until you open it up, take care if its mains potential, unplug first.
    Dave. :)
    PS, Save the isopropyil alcohol for switches or other cleaning tasks, it really does strip carbon tracks, i know ive done it, oop's.
     
  5. volvik

    volvik

    2
    0
    Nov 2, 2011
    Thanks for the replies guys. I did take it apart and blow and brush the pcb and inner housing. The control knobs certainly turn more freely but whether it gets hotter than it has been will remain a mystery until tonight.

    As mentioned, the pad does heat up just not as hot as it used to get....and that's on both sides (dual controllers).
     
  6. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    It might be the elements or it could be component degrading like potentiometers, you might need to test them with a meter, power off, hope they warm up, have a good night.
    Dave. :)
     
  7. shiekh

    shiekh

    77
    1
    Oct 11, 2010
    Bimetallic contacts in the controller? One wants to regulate the blanket temperature.
     
  8. duke37

    duke37

    5,301
    740
    Jan 9, 2011
    In the UK the fire service occasionaly arranges for electric blankets to be tested since they are often a cause of fires. Anything over a couple of years old is suspect.
    I would not use one if it is turned on and I am now too old to always remember what I have done!

    You can check whether the thermostat is a switching contact by measuring the current consumed. If the cause of low heating is a broken wire, then you might have an exciting night.
     
  9. shiekh

    shiekh

    77
    1
    Oct 11, 2010
    I thought there was no thermostat, but rather it relied upon the positive temperature coefficient of the material used for the resistive wire; this way hot spots will automatically reduce their heat production, so reducing the fire risk.


    I believe the control works by the old triac trick, varying the amount of wave that is connected; this has the added safety advantage that one can just run on the low voltage part of the mains, so the wires remain at a relatively low voltage. As a result my new controllers would shut down when run on a square wave UPS as there was no low voltage parts of the wave (the controllers they replaced were quite happy with running on a square wave). I ended up with sine-wave UPS units for the heated blankets; this was when I lived on the Navajo reservation where power glitches are very common, and even then I needed high quality sine-wave units that would switch over without a glitch.

    Of course this is the modern design, and I believe that early designs had thermostats IN the blanket itself.

    I'm in the US, but imagine the low voltage trick is even more important in the UK (where I am originally from).


    So the PTC wire may help avoid fires, and the triac trick help avoid electrocution, with shut-down happening if there is an over-voltage condition.
     
    Last edited: Nov 11, 2011
  10. Charles Maness

    Charles Maness

    1
    0
    Nov 14, 2019
    Our control starts blinking after so many hours and you can't turn it off, we have to unplug it and plug it back up. What can we do? The number on thje control is-PAC-448-1E23623F
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-