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variable supply problem

Discussion in 'General Electronics Discussion' started by colin north, Aug 17, 2011.

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  1. colin north

    colin north

    3
    0
    Aug 17, 2011
    I have been using a 110 Volt 1080 watt heating blanket on a UK 220V supply (with transformer), through a 110V variable speed router controller to the blanket to control the temperature as recommended and supplied from a reputable supplier in the US.
    Twice this set-up has worked first time and then failed next time, each time resulting in a full output to the blanket continuously (maximum temperature).
    Any suggestings as to why?
    Would it be possible to use a normal 220 Volt dimmer switch (lighting) between the supply and transformer to control temperature?
    If not, what other (relatively inexpensive) alternatives may be available?
    Thanks in advance!
     
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    I take it that you used a 240-110V transformer, but what was the power spec' on the router controller? 1080W on 110V is just about 10A.
    When a semiconductor (triac) is overloaded it usually fails short-circuit, which in this case implies that the load gets the full voltage.
    It would (should) be possible to run the blanket direcly off 240V via a triac dimmer, but the setting gets more finicky, and the current peaks get quite large.
    The dimmer must thus be generously rated (at least 10A / 2.4kW, but 22A / 5.2kW would make it completely safe).
     
  3. colin north

    colin north

    3
    0
    Aug 17, 2011
    Yes, 240/110 1500 watt transformer for supply - router speed controller is rated at 1500 watts, 15 A,
    So what you are saying is that the unit has likely been overloaded?
     
  4. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    According to the spec's the setup should've been ok but the symptoms says otherwise. Idk. How long was it working?
    High voltage spikes may also cause a triac to short out, but the transformer should in theory give some protection against that.
     
  5. colin north

    colin north

    3
    0
    Aug 17, 2011
    Both new and replacement router controllers only worked for about 20 minutes use first time, 15 minutes the second unit.
    I should have mentioned earlier, the supply is on an extention 40 metres long to my workshop. I have also checked - the transformer output is 100 V, blanket resistance 15 Ohms, so wattage is actually lower than that stated specs.
     
  6. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Hmm.. I can't come up with a reasonable explanation for that, but you could try to Google that specific dimmer make/model for failure to see if it's common.
     
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