Repairing a toaster..

Discussion in 'General Electronics Chat' started by BoJ, Jun 30, 2012.

  1. BoJ

    Thread Starter New Member

    May 6, 2008
    2
    0
    Hi everyone!

    I was just trying to repair my toaster - sandwich maker, which is of this type: http://bit.ly/Ng7MM4 (although not the same model as the one in the picture).

    So about a week ago, the resistors just stopped heating up. Although the little indicator light turns on, the heating elements do not heat up.
    So I have opened it up and have checked for any short circuit or problem with the cables but everything seems to be fine.
    There is one thing that is odd and I cannot understand why this is happening:
    I calculated what the resistance value of the heating elements should be, according to the specifications of the device, and it came up that it should be about 26Ohms (It is a 2kW toaster and operating @ 220-240V. The supply as I measured it read 230V).
    So the thing is that I measured the resistance of each heating element without having them connected to the mains. Each one read an extremely large resistance (in the MOhm region, beyond the scope of my multimeter, so it didn't give a precise reading, just the range..). Now as soon as I connected them to the mains, the resistance of each dropped to zero according to my multimeter reading.
    The toaster is still not working and I cannot understand what the resistance readings mean..
    Can anyone please enlighten me?

    thank you very much in advance..
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,761
    924
    The Ohms reading for a length of heating element doesn't mean very much to a calculation of its working resistance. The difference in resistance value between room temp and 'glowing red hot' will be considerable.


    The fact that you read a low resistance with mains attached may simply be a power relay which cuts the elements out of circuit unless the appliance is attached to the correct type of power supply.

    The element may be 'burned out'. I know this sounds counter-intuitive for something that glows red hot to burn out. Or the connection may be faulty. Or it might be in a safety fault mode for some other reason and just appears to be a bad element.

    This is one of those items that require extensive examination of a large number of inter-dependent factors to determine a cause of failure. Remote troubleshooting will be difficult.
     
  3. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    This topic talks about circuits that are connected directly to mains, which isn't allowed here in AAC.
    However, it would seem rather hypocritical and awkward for a site calling itself All About Circuits to leave it at that, so I 'll say a few words.

    BUT before I say anything, I state that the following words refer to theoretical assumptions and may have nothing to do with your problem.
    It seems that you don't have the necessary level of proficiency to repair your appliance, so the best and safest option for you right now is to buy a new one or get it to a repairman (whichever is cheapest).

    That said, it is true that resistance varies with temperature, but I wouldn't expect too much of a variance, greater that two orders of magnitude. After all, the heating element is a piece of metal. A ΜΩ resistance is an indication of an interrupted connection.

    The next point is important: Never connect your multimeter that is set to resistance to a powered circuit. You have a high chance to blow your instrument, shock yourself and you are sure to get a wrong reading.
    The multimeter measures resistance by checking how much effort it takes for it to push a current load through a resistor. If the element is powered, it takes no effort, since the load is transferred to the voltage source of the circuit.

    Be careful and stay safe.
     
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