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repairing hair dryer

Discussion in 'Electronic Repair' started by Al, Feb 9, 2005.

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  1. Al

    Al Guest

    My boots were a little wet inside, so I put the nozzle of the blow dryer into
    one. It ran okay. But when I manually shut it off after a minute or two, it
    never would come back on again. Does that tell what is probably wrong with it?
    If so, how to fix? Thanks.

    I've taken it apart but there is no visible problem.
  2. Assuming the power cord, GFI and switch are OK, you probably blew a
    thermal fuse that protects the heater elements from overtemperature.
    Normally when this happens the blower will still run but the dryer won't
    heat up.
  3. Kevin R

    Kevin R Guest

    not with my ones once it has blown a thermal fuse its dead
  4. Sounds like that is the most likely cause, then.
  5. Al

    Al Guest

    wow, thanks to both for the quick replies. Here is a photo:

    I had noticed what looked to be a bi-metal circuit breaker and another axial
    component that I took to be something like a diode. But the 'diode' must
    really be the thernal fuse, right?

    So, I just used alligator clips to bypass the fuse and the dryer now works. Is
    the other component (the block-like one in the right of the photo) a circuit

    What are the odds of me buying a thermal fuse locally? Or is it likely to be a
    case where a $1 part needs to be ordered online, with $10 shipping. The fuse
    looke to be green, with a white tip.
  6. If you are really in love with the hair dryer, I'd stop by a local
    Salvation Army / Goodwill store and pick up the cheapest $2 hair dryer
    they have, and cannibalize the part. You'll probably want to crimp
    connect the new fuse (don't solder it in, for obvious reasons, unless
    you have REALLY good heat sinks).
  7. Bob Shuman

    Bob Shuman Guest

    I have purchased these thermal fuses retail from Radio Shack for a couple
    bucks each. They usually have two critical ratings that you will need to
    use to find a substitute part. The first is a standard current limit which
    will be in Amperes and he second is a temperature limit, usually expressed
    in degrees centigrade. You rarely can match both exactly, so just get as
    close as possible without going over the previous values to retain the
    designed safety margins. If you can't get anywhere close, ask them to see
    the special order catalog or find a suitable replacement part on the web.

  8. Great information...I had no idea that RS carried these.

    The choices seem to be 128, 141, or 228 degrees (C). If I were the OP
    I'd take the lower rating which is 262 F. Should be "safe enough".
  9. Guest

    i seem to recall this question came up only a few weeks back.
    Be sure to use the correct rated fuse and don't even think about
    leaving it bridged!
  10. Al

    Al Guest

    thanks. But I haven't been able to find a guide to the color ratings (on the
    web or in tbis group's archives), so as to know what temp I need. (It's
    apparently purple/lilac with white tip.)

    While on the subject, here are some recommendations for the faq, from an
    amateurs point of view (having never heard of "thermal fuse" until today):

    I had already read the faq's section on hair dryers before posting. It
    mentions "thermal protector" but not thermal fuse. The thing that eventually
    surprised me about this dryer is that there is not only a bi-metallic
    protector, but *also* a thermal fuse in series.

    Also, in the reverse, the section on thermal fuses does mention hair dryers.
    But a following section ("More on thermal fuses") gave me the impression they
    are all of some spring type. The one in my dryer is the kind pointed out here
    by Bob as being at RS, that look something like an axial diode.
  11. I'll add some clarifications.


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  12. Guest

    I have seen this and repaired it by replacing the part from an
    identical broken unit. Looking at a couple dryers in my house they have
    both the resetting thermal bimetalic type that resets after the unit
    goes over temp but then you also see the thermal fuse. Is it there
    because of reliability issues with the bimetal part? If so then it may
    have blown because the bimetal is faulty and (if you're like me and use
    it to shrink heat shrink) it may blow again. BTW I got a real heat gun,
    much better!

  13. Jim Adney

    Jim Adney Guest

    The color is no help, but sometimes there is a number on them which
    might be the temp (but it could be in F or C.) Radio Shack used to
    have 3 different temps of these.

    Yours probably opened because it was sucking warm air that came back
    from inside your boots and it overheated. The internal parts actually
    got hottest AFTER you turned the blower off. The dryer is probably
    fine. I would just replace the thermal fuse.

    Yes, crimp them. Don't try to solder them.

  14. James Sweet

    James Sweet Guest

    Probably was just the lack of airflow due to being stuck down into a boot
    that did it rather than sucking hot air in the back. IIRC Radio Shack sells
    two thermal fuses, try the lower temp one first, if it blows in normal use
    then go with the higher one.
  15. Ken Weitzel

    Ken Weitzel Guest

    Hi Jim...

    Been sitting here thinking about this; how often it comes
    up; the terrible risks involved; and the many things we
    find these thermal fuses in. (coffee makers, electric clothers
    dryers, etc)

    If - and that's a big if - it sucked hot air or even suffered
    an almost complete lack of air input - then why oh why didn't
    the thermostat open? (yes, I know, some of you are calling it
    a bimetal thermal fuse, but what the heck - it's a non-adjustable
    thermostat, right?)

    I opened one of my grandkids to read the temperature rating
    for the fellow previous to this occurence - and it the
    "thermostat" one was sitting open and in plain view.
    It does switch pretty good current - and it is in an airflow
    that's warm, probably humid, and quite likely to corrode.
    That I suspect would make it pretty easy to arc; and weld
    itself closed.

    I'm proposing then, that for the current poster, and the
    ones that are surely to follow, that it might be worth
    suggesting giving it a bit of a push with something to be
    sure that the contacts aren't welded shut.

    Just my 2 cents.

  16. Al

    Al Guest

    okay, that's a good point so I did that, Ken. It opened without any
    discernable sticking. But, I notice this: current goes through the thermal
    fuse, then splits in two. Part goes directly to the shorter run of heating
    coils, and part goes to the bimetal component then on to the longer run of
    coils . (The dryer has two switches and therefore four settings for temp.) So,
    the bimetal can interrupt the longer series of coils, but not the shorter
    series. The fuse cuts power to both.

    I'd been thinking that the bimetal might open when the current running through
    it gets too high, like a regular fuse. No? And conversely the thermal fuse
    melts and opens from ambient, rather than internally generated, heat. That
    doesn't explain what happened in the boot, though - unless the bimetal opened
    and reduced heat, but the dryer was still chugging away on low heat until the
    fuse melted. I don't remember, it wasn't recent.

    I also can't figure why the fuse didn't melt until the dryer was turned off -
    unless the coils were still radiating heat long enough after the airflow
    ceased to take it away - as Jim and/or James seemed to be saying.

    Also, I notice there is no soldering whatsoever anywhere that's in the tube
    where the hot air flows through - as if the hot air might melt any solder
    there. That's a surprise.

    I uncrimped the fuse. There is no writing on it that I can see - so I'll go
    with the lowest fuse I can get, as recommended.
  17. Bob Shuman

    Bob Shuman Guest

    Yes, this is the explanation. Once the blower was turned off, the airflow
    ceased and the radiating heat had no where to go so the fuse opened at or
    near its designated temperature.
    Yes, this is also true. On the hair dryers, curling irons, and toaster
    oveens that I have repaired, I have used a combination of crimping and
    silver solder (it has a higher melting temperature). I only use a minimal
    amount of this solder to assure a good conenction and have never had any
    trouble doing this.
    You can probably estimate the current rating by dividing the maximum wattage
    by the voltage. temperature will be the more difficult one to figure out.
    Starting with lowest value is the best strategy if you can't determine the
    actual value.
  18. Guest

    Hmm This is from:

    "* A safety cut-off switch - Your scalp can be burned by temperatures
    more than 140 degrees Fahrenheit (approximately 60 degrees Celsius). To
    ensure that the air coming out of the barrel never nears this
    temperature, hair dryers have some type of heat sensor that trips the
    circuit and shuts off the motor when the temperature rises too much.
    This hair dryer and many others rely on a simple bimetallic strip as a
    cut off switch.

    * A thermal fuse - For further protection against overheating and
    catching fire, there is often a thermal fuse included in the heating
    element circuit. This fuse will blow and break the circuit if the
    temperature and current are excessively high. "

    These thermal fuses are in a lot of things. I've seen them in motors,
    esp fans if they're stalled or bearings get frozen no air flow temp
    rises thermal fuse blows, no go. Some hair dryers also won't run if the
    thermal blows or will run cold.

  19. Guest

    Also on the subject of crimping. I know there are tools that will crimp
    with tremendous force 10,000 lbs for instance to cold weld Cu and Al
    wire together. I'm wondering if anyone has built or adapted a device
    that will do that in the instance of what we're talking about here. I
    know spot welding would also work well.
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