Electric Iron Repaired
I was told that this electric iron quietly stopped functioning, that is, it was not getting hot anymore when connected to the power. I opened the outer cover and see the circuit arrangement. See photo below.
The Bi – metallic strip is made of two metals of different temperature characteristics: one expand with heat more than the other. The principle of operation of a Bi – metallic strip is that as the iron heats up one of the two metals will expand more than the other. This makes the metallic to bend up (in this case) and break the electrical contact, thus breaking the current flow to the heating element.
There was no any visible symptom of failure of any part. I used my digital multimeter set on Ohmic range. I tested the heating element, it tested well. I followed the circuit from the entry point of a power cable to the heating element.
Current ought to pass from pole 1, through thermostat, a component in white coloured sleeves to pole 2. From pole 2 it passes through the element back to pole 3. To my surprise there was no continuity between thermostat and pole 2. I took out that part in white sleeves and measured its continuity separately. It was giving me infinity. This means it was open circuited.
Honestly, I didn’t have any idea of what this component is. The marking on its body is Tt 240°C D242 ZSXJ. It is pointed on one end and has a coloured band near the other end. It looks like a diode, I don’t think it is. When I searched on internet I found that it is a Thermal Cut-Offs (Organic Thermal Element Type). These devices are used to prevent fires caused by abnormal heat generation from circuits and other heat producing electrical products. (http://www.digikey.com/catalog/en/partgroup/sdf-series/24120)
I bought a new component marked Tt 240 °C 250V AC 10A. The new one measures 4 Ohms in both directions. The device finds its application, among others, in Electric home appliances and heating devices.
I replaced the faulty component with a new one. Note that I put the new device into the original sleeves. I tested the continuity of the complete circuit: from pole 1 through heat control devices to pole 2 via the Device, to heat element and back to pole 3, the result was satisfactory. I connected the power cable; I made sure that it was safe to power it up. It worked so well! At different temperature ranges the heat was controlled by the thermostat by the operation of the Bi – metallic strip as expected. Glory to God!
Luciano Francisco Thomas Khware (Malawian) studied Electrical and Electronics at Comboni Technical College and at Polytechnic (University of Malawi). Currently, he is a student at Tangaza University in Nairobi Kenya.
Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments. By the way if you have any good repair article that you want me to publish in this blog please do contact me HERE.
August 12, 2014 at 10:16 pm
Good job Luciano. I fixed my son's electric fan and all that was wrong with it was the thermal cut-off fuse on the motor. I didn't have a camera at that time to send in an article about the repair.
August 14, 2014 at 4:23 am
Thanks so much for the comment! surely it was my first time to see this Thermal cut off fuse.
August 14, 2014 at 8:52 pm
You are welcome my friend. The manufacturer of the fan hid the thermal cut-off fuse well. I had to take the motor apart to find it! Most people would just throw the fan away and buy another one since it is cheap at Wal-Mart. So instead of my son spending $20 for a new fan, I fixed it for $1.
August 12, 2014 at 10:35 pm
Clear photographs and point to point clarification well done my friend keep on sharing the article.
August 14, 2014 at 4:42 am
You are welcome my friend!
August 13, 2014 at 9:06 am
Be careful when replacing thermal cutoffs by soldering. Sometimes the heat from soldering is enough to cause them to open. (Been there, done that!) Use an adequate heat sink, or use crimp-on connections. Themal cutoffs are available in different temperature ratings, and the lower temperature ones are sometimes sold with a pair of crimp-on collars.
August 14, 2014 at 4:47 am
I totally agree with you. soldering heating elements is not a good option. in my case i used clamp on connectors. i clamped on both sides tightly.
thanks for the comment
August 13, 2014 at 11:21 am
Well done Luciano. I came across a couple of those when I repaired my coffee machine. They were opened because the temperature sensor was faulty so the the heater did not turn off when the set temperature was reached. It avoided a meltdown of the machine...
As Ken correctly wrote they were connected with crimp-on collars. I used the same system when replacing them.
August 14, 2014 at 4:54 am
Welcome Gerald. i appreciate your sharing too
June 19, 2018 at 11:19 pm
Nice one,just finish repairing my iron now.thanks
August 13, 2014 at 11:40 am
Good article.Thank you.
August 14, 2014 at 4:55 am
You are most welcome!
August 13, 2014 at 12:42 pm
Hi Luciano.thanks for sharing the Article.sometimes geting thermal cut-off at our local elect-shops is a problem,i guess you got it locally?otherwise keep up the good work.God bless.
August 13, 2014 at 5:42 pm
When I buy things like that I usually buy 10 or more of them so I will have one the next time I need one. When I ordered the SMD bridge rectifier for the camera battery charger I repaired, I bought 10 of them because they are cheap. So I still have 9 of them and the next time I need one I don't have to order or drive somewhere to get one!
When I ordered the thermal cut-off fuse for my son's fan, I ordered a bunch of them in different degrees C. ICAIW, yes my son's fan is still working great all last summer and this summer also!!
August 14, 2014 at 5:03 am
In fact i do the same. this time i got a good number of Thermal cut off fuses and i have new other components in stoke.
August 14, 2014 at 4:59 am
Yeah i got them in one of the shops along Lithuli Avenue, Nairobi and at a reasonable price. It was nice meeting you face to face that day... i feel blessed and got some inspiration from you through our sharing. May God grant you all the blessings you need.
August 14, 2014 at 5:03 pm
Thermal fuses I guess you have figured out are used in almost any heating appliance including air conditioning heat
Strips. Local appliance stores usually stock thermal fuses also.
Thx for the article !
August 13, 2014 at 7:47 pm
August 14, 2014 at 5:04 am
Taring K Arioka
August 14, 2014 at 1:04 am
Thank you so much again for this very nice article.
I found the same component in rice cookers but have no idea what it purpose while being there. The rice cooker remained untouched as I dont what to do with it. Now is the right time to chase and have it fixed. Thank you again.
August 14, 2014 at 1:07 am
Good Job Luciano, I had repair a couple of item with those thermal cut-offs.. I also buy 10 or more components when I buy in order to have them readily available especially if I am working at nights. Thanks for sharing.
August 14, 2014 at 4:18 am
very good once again as usual
thank u sir
August 17, 2014 at 5:38 pm
You are most welcome Shahid
August 17, 2014 at 2:10 pm
Thank you very much for such a good and educative article. Keep the good work.
August 18, 2014 at 10:02 pm
You are most welcome!!
August 19, 2014 at 12:01 am
Good repair Mr. Luciano. Congratulations
August 27, 2014 at 4:25 pm
great thanks sir
August 29, 2014 at 6:07 pm
those thermal fuses can also be found on some rice cooker and deep fryers pan it can`t be soldered but, can be connected through bolted connectors then protect it by asbestos tubes.
November 6, 2016 at 4:42 pm
Thanks a lot
surprisingly, my problem was exactly your problem
June 6, 2017 at 4:16 pm
Very informative thanks a lot dear for sharing this clear information and for uploading hd images, please keep it up.
March 27, 2018 at 2:41 pm
does d thermal cut off fuse limit d current flowing into the heating element of the pressing iron?
May 21, 2018 at 4:48 am
which side connect to thermostat? flat side or other?
December 22, 2018 at 9:03 pm
dad is on my neck to look after every electrical appliance in the house as his junior engineer... Thanks for knowledge add!
May 2, 2019 at 1:51 am
Thanks Luciano. Your article is a God send to me. One morning my I/ box went dead, and after going through all the wires everything was ok, except one small capacitor-like component neatly hidden inside a tube, which couldnt pass a continuity test, and I didn't even know what it was.
Waqar Ali Shah
May 29, 2019 at 2:15 am
Great bro. I was ignoring that thermal wire thing... was thinking iron is broken permanently. Saved extra expenses!!