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Author: Subject: Failing heating mantle

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sad.gif posted on 20-9-2021 at 08:06
Failing heating mantle

Hi there!

I already UTFSE about the problem I'm experiencing but did not find anything relevant....

Few years ago I bought a 1L heating/stirring mantle on ebay from some big Chinese seller (maybe Deschem). When I received the item, I did not find "appropriate" or important to check the device and months went by before I decided to use it - which turned out to be a real big mistake :/

The magnetic stirrer works fine and the speed regulation is nicely adjusted. Regarding the heating it is a whole different story!! Whatever the position of the potentiometer, the temperature just rise to the max :mad:

I am far from being a specialist in electronics but I would be encline to say that the problem comes from the quality of the elements, especially the potentiometer ... What do you think ?? Do you have any advice on diagnosing the fault and possibly fixing it? It would be damn embarrassing to throw in a still "new" heating mantle :/

Thank you in advance folks !

PS : Some pics of the beast are attached to my prose. The #4 is the potentiometer for the heating, and 5 the one for the stirring. On pic 1, organisation is standard - at left heating regulation and at right stirring one

01.jpg - 174kB 02.jpg - 119kB 03.jpg - 216kB 04.jpg - 136kB 05.jpg - 167kB
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International Hazard

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[*] posted on 20-9-2021 at 23:03

It is unlikely that the pots are to be blamed for the nonfunctioning heating regulation. Rather I would suspect the thyristor or diac circuit that is used to "clip" the alternating line voltage to the heating mantle has failed or was defective from the beginning on. Such dimmer modules can be bought online for very cheap prices and be incorporated into the device separately to allow for heat control.
BTW are you sure the heat control does not work? Have you tested it with a flask of liquid by bringing it to a boil? Observing the behaviour of the heat mantle without a thermal load can leave the impression that it heats up full blast no matter the regulator setting...just a thought.

Exact science is a figment of imagination.......
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National Hazard

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[*] posted on 21-9-2021 at 00:48

I also would suggest to buy this and connect it to heating element.

Would be tough to figure out what's wrong without probing the circuit.

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draculic acid69
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[*] posted on 22-9-2021 at 03:44

Ok I've had a very similar experience with a new mantle as well except mine was
one with an attached thermometer your supposed to insert in the side neck of a flask.
The useless piece of junk would just randomly shoot the temp up hundreds of degrees no matter how low the temp was set. Best thing I did was just rip the guts out and replaced the internal circuitry with a mini device that is similar to what Mr bungee showed. I found those ones to be less effective than the ones I use. Firstly I recommend typing the following into Google:

2000w 25A 240v thyristor dimmer eBay

you'll see the following pictures or some variation of it.there the same circuit just different angles

images.jpeg - 26kB

images (1).jpeg - 25kB

This is a very effective and reliable piece of equipment
that I have in my mantle and it's as reliable as if it was a super
expensive high quality brand.these circuits are like a $5 Variac.
They do what a Variac does but at a fraction of the cost.
There excellent circuits, they won't let you down
As for the ones Mr bungee suggested my one of those
needs to be turned to halfway before any electricity gets through to start warming the mantle. it needs to be turned to more than halfway to heat anything even slightly and would need to be turned up to almost 3/4 to all the way to full to boil water.
whereas the ones I suggested are far more sensitive and easier to control I've never turned it past halfway to heat stuff and rarely turn it past 1/3 of the way.
My advice is rip the crap circuit board out of the mantle go to eBay and buy the $6 circuit I won't be disappointed.
And thanks to markx who helped me out last time I had this exact same problem

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[*] posted on 24-9-2021 at 11:48

Many thanks for all your good advices, I will try to applicate it and pray to get a working heating mantle^^

@ Markx > Yes I did test the device with a RBF filled with some mineral oil and a temp probe. When the pot. is turned to the 1st graduation, the led is lighting but no heat is applied. If I turn it a bit again, then temperature raise well above what it should at this level, more than 200°C... For sure, Chinese manufacturers use really cheap electronic elements and not perform any quality test. But I rather prefer pay a bit more for a good device than win some dollars to get shitty equipment !

Again, many thanks to all of ya ;)
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