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>70C ferrite surface is too hot for finger touch?

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Flyback

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When I worked at Panasonic, we reckoned that above 70degC was the point above which it was not possible to keep your finger on a ferrite transformer or inductor surface.
Is this correct?
 
No idea - but if you lick your finger before you touch something, and it sizzles when you touch it, then it's too hot (or at least too hot to touch).

The actual figure for 'too hot' is going to vary greatly depending on the circumstances and the individual who wrote the specification.
 
Flyback...you are still around. My little project relies on the regulator keeping itself happy.

I am not an EE. However......through years of experience of fixing TV's..I get a gut feeling. I know if a set is going to last or not....heatsinks at 80 Degree Celcius burn or sizzle spit on a finger....yes. There is something else wrong....

In fact, this is true for most Electronic stuff. 80 Degrees Celcius is way too high on a heatsink. On anything.

Please remember this though...unless....the IC/component you are using is happy at those Temps. Some are.

tvtech
 
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My fingers are calibrated for 50C. (+/- a large number)

My fingers are calibrated to 60°C. It is generally said that is the point at which hot just turns to painful. One can stand a higher temperature, but the pain increases. I try to teach students a couple of temperature points like that, as they are useful in a laboratory setting. Also, American students are generally not that good at estimating Celsius temperatures.

Here is some scientific support for the 60°C threshold: https://www.electro-tech-online.com/custompdfs/2013/09/Insulative_Coating_Evaluation_NACE.pdf

70°C would definitely be hot to the touch, and I suspect 70 to 80° might be the point at which a normal person could not maintain contact, but I have no data in that regard.

John
 
Thanks, I see the 60C is for metals...............it looks from the article as if material like ferrite could be a lot hotter than 60C and one could still touch it and keep the finger on it?
 
Hello,


The point where a person feels that something is too hot is entirely subjective. This falls under the general category of the human threshold of pain and varies from person to person and even varies with the same person over time. So it is really not possible to create a standard like that because it would vary too much. There are also people with much higher than what seems normal pain thresholds.

You might be able to place a drop of say room temperature water on top of the component and see how long it takes to evaporate. You might even see it bubble if the item is very hot.

The temperature is directly proportional to the number of expletives uttered after the 'measurement' :)
You could breed "touch monkeys" that can tell the difference between 60C and 65C :)
 
Shortly followed by some bad words.

No, that's the point of licking your finger first, the 'sizzle' is the liquid 'boiling' off, giving you chance to remove your finger as soon as you hear it, and before you can feel anything.

When you don't lick your finger (as I stupidly didn't on a PIC one day) by the time you feel it's hot you're already burnt - hence the (still working) PIC I have that has my fingerprint burnt in it's top :p
 
What is the difference? touch monkey, breading students.

Sorry, but I really don't see your (or MrAl's for that matter) point. I would never refer to my students as monkeys -- I must be old school.

There are many times in life that ones senses and brain must be relied upon. I was once discussing an organic reaction with a student in which the stoichiometry was 1:2. She knew the "1" part. The amount for the"2" part was 2X30 g (or something easy like that). I asked her how many grams of "2" she would need. She reached for her calculator. She was one of the best students, but she had been conditioned by our current educational system not to think. We eventually laughed about it.

The sense of temperature is very important -- life would be extremely difficult without it. I can't see any logic in ridiculing teaching the awareness of that sense.

John
 
The sense of temperature is very important -- life would be extremely difficult without it. I can't see any logic in ridiculing teaching the awareness of that sense.
well , yes , you re right, and i'm in a pile of sewage if my sepic inductor melts off the pcb whilst in use at high ambient.
I had to use a low inductance (47uh) in order to keep the switching frequency above the audible range when at low vin & 3W =Pout and vout = 60v. I could not find a bigger 47uh coupled inductor off the shelf, and they wanted it cheap and off the shelf.
I am wondering what is the limiting temperature for ferrite of msd1583 inductors?
 
These are probably a little large for your use (ca. 15 mm), but smaller versions are available for showing temp. There are single use and reversible versions of labels, waxes (crayons), etc. available that will help you pin-point the transformer's temp. Have you considered them? Search on "temperature indicating" + whatever format you want.

https://www.coleparmer.com/buy/prod...temperature-points-140-180f-60-82c-25-pk.html

John
 
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Hi,

I was kidding when i said "breed touch monkeys", and what i meant was genetically altering some monkey species to be able to discern temperatures more accurately and repeatable than a human can.

Sure, we as humans need to be able to tell when something is hot, but we dont need to be able to tell when something is 100 degrees C by touch.

Another technique is used in ceramic firing ovens. They use a piece of material that melts at a known temperature and deforms significantly so when it deforms it's done. For our purposes maybe some hot glue on the top of the device would tell the story. A little 'cone' of hot glue would deform once it got hot. Alternately, some of that low temp poly plastic...that stuff melts around 160 F i think so that would tell when it got pretty hot but not really really hot.

Also, how about a piece of temperature sensitive liquid crystal? Turns to a different color when it reaches a fairly precise temperature.
 
@John
While in a pharmacy, some girl was convinced that 5'12" was taller than 6 feet.
At times I migh give someone $21 for an item that costs 10.50 and I would be given the $1.00 back because I "paid too much".
The fun one is when some cashier mistake happens that they panic and cannot make change the "old-fashioned" way.
Before long, new students won't be able to read an analog clock. I'm sure some can't use a rotary telephone,
 
The picture is in your mind.
 

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