#1780

Рет қаралды 8,625

IMSAI Guy

4 ай бұрын

Episode 1780 chip of the day
Negative Temperature Coefficient Thermistor
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Пікірлер: 55

@Hellhound604 4 ай бұрын

And the NTC is the reason why you should wait some time after unplugging a PSU before you plug it in again. Gives some time for the NTC to cool down, so that it can do its job preventing the high inrush current.

@1kreature 4 ай бұрын

Yep, and it's why shorter interruptions in power can blow the built in fuse rendering your brand new psu useless after just first short supply interruption. I've had this happen on a UPS of all things. Needless to say, a UPS that blows it's input fuse first time there's a supply disturbance went right back to the store!

@snakezdewiggle6084 4 ай бұрын

Why does it have to be a "brand new" psu.?

@1kreature 4 ай бұрын

@@snakezdewiggle6084 I was "painting a picture" of your future experience... Call it a foreshadowing.

@snakezdewiggle6084 4 ай бұрын

@1kreature. Oh, well thank you. Good luck with it. 😉

@captainmother1268 4 ай бұрын

The downside of these devices is when the power drops for just a moment and then comes back - they won't be an in-rush current limiter anymore since they haven't cooled down. Can be a problem if you don't plan for that.

@bobdoritique7347 4 ай бұрын

I wanted to thank you for all the videos you make, they are very appreciated. A big THANK YOU for everything, I imagine it's a lot of work...

@gorak9000 4 ай бұрын

I'm very impressed that there's a new video EVERY day, and never a bad one!

@pault6533 4 ай бұрын

I have a bunch of take-off parts from power supplies and noise filters. You have covered the shiny yellow ones and dull green ones. Now I have shiny red ones and shiny blue ones too. Can’t wait for the next installments to understand what they are too😊

@Edisson. 4 ай бұрын

The color is not decisive, you always need to be oriented according to the marking - yellow can be, for example, Polyfuse - self-resetting fuse, or Varistor. The varistor can be blue, the X1 type capacitor can also be blue. NTC thermistor does not have to be green, for example they are black etc. Nice day 🙂 Tom

@pault6533 4 ай бұрын

@@Edisson.thanks Tom, I looked up some of them and found out these other colors are also MOV’s and other safety caps. I’d like to know the reason for the different colors- if there is any.

@Edisson. 4 ай бұрын

@@pault6533 If the color is not part of the coded color marking, then I would say that the change in the color of the case is just a manufacturer's difference, this also applies to other components. For example: I have X2 capacitors in yellow, red or gray design, and not only the color is different, but also the marking for the maximum voltage, some manufacturers give the value in AC, another in DC - again, you always have to check the marking - but it is still a capacitor with a functional properties of X2

@englishrupe01 4 ай бұрын

Don't forget that there are better thermal temperature guns, if you need them. Mine goes up to 1800F. Great video.....many thanks.

@MyProjectBoxChannel 4 ай бұрын

I have seen them being used in self heating mode, as a "proof of airflow" sensor. Some amount of current is used to trigger it, and if the airflow is significant, it will cool it back down, and the current draw will increase.

@Oldclunker-ge5zp 4 ай бұрын

I use a relay to short out the NTC when the voltage at the car headlight halogen bulbs has reached approximately 75% of final value. It improves the lifetime of the bulbs while not losing any brightness. The NTC cools down within seconds after the relay has engaged. It's ready for the next start and avoids heating up the dashboard and cable harness.

@MrHerhor67 4 ай бұрын

How did you detect the 75%? Coil connected parallel with bulb?

@Oldclunker-ge5zp 4 ай бұрын

Yes, coil in parallel to bulbs. Very simple but effective.

@WestCoastMole 4 ай бұрын

Hi Mark Thanks for introducing the NTC to your audience. There are numerous applications for them including Soft Start Circuits. Hams use them in Vacuum Tube Power Amps that use tubes with Thoriated Tungsten Filaments. That type of tube filament generates svery high inrush current for an instant at power-on. It also generates a very intense magnetic firld which can also damage the filament, thus the requirement for a Soft-Start Circuit. Even in a Steady State On condition after everything has settles down there is still a residual power dissiption that can heat the NTC which necessitates providing airflow to keep the device coolER. In the Inrush Application it is a simple matter to tie the normally open contacts of a relay across the NTC and install half second delay in the coil line of the relay. That makes for s subdtantial increase in the life of the device. The failure mode of the NTC is a short circuit. That is in contrast to the MOV Device which you covered in a separate video yesterday. MOVs can only be "rapped" a finite number of times before they go kapput. Their failure mode is an open circuit. Why can't life be simple ?

@Mr_Meowingtons 4 ай бұрын

Nice I used PTC Thermistors on crystals in CB radios that I had in a car when it was winter it helped heat up the crystal so when on SSB it would stabilize way faster. i took the crystal off the board and made a little insolated can attached the PTC with conductive glue to the crystal.

@flapjack9495 4 ай бұрын

Thanks for covering this! I built three different iterations of a linear power supply once (to power a shortwave receiver and a couple of Raspberry Pis without acting as a localized jammer). The third iteration included an NTC thermistor to limit the inrush current to the big smoothing cap I was using. It also had what can best be described as an absurdly oversized heat sink. I wasn't taking any chances after my first two attempts failed over time. The latest version has been running 24/7 for many months and hasn't given me any trouble at all!

@ericksonengineering7011 4 ай бұрын

Great video, thanks! Those things saved my butt on a medical system. We used a medical-grade toroidal AC isolation transformer to feed various equipment, about 300W total. The transformer blew 5A slow-blow fuses, but only when the system was plugged in near an electrical panel. Even 50' of 12-2 AC building wire was enough added resistance to prevent fuses from blowing. Adding an AC extension cord also prevented fuse blowing. I measured over 100A inrush current on power-up of the transformer. Two 4 ohm NTCs later (one in series with each 120V primary winding), and problem permanently solved. This same problem can be found on many AC transformers, especially large ones.

@sstorholm 4 ай бұрын

There’s also a phenomenon that I can’t remember the name of, but essentially a transformer core “remembers” in what phase of the AC cycle it was disconnected, and if you happen to reconnect it 180 degrees out of phase you’ll see really large inrush currents. Small transformers are the worst, it can be 100 times the rating of the transformer, bigger power transformers designed for 100+ MW are a bit more tame, around 4 times the nameplate power, but still a big issue. On transformers over 25MW they use a synchronized phase breaker, so that each phase core is disconnected and reconnected at the zero crossing of the wave form to avoid this problem.

@thomass7877 4 ай бұрын

It happened that I got a large isolation transformer for small money. 1500W, 6A. I turn it on via a 500W halogen bulb in series. Of course, I have a voltage drop that I compensate with a variac. Which NTC would you recommend, or a combination instead of my method? Thx.

@sstorholm 4 ай бұрын

@@thomass7877 on my isolation transformer I use an NTC and a time delay circuit that bypasses the NTC with a relay after a while, 6-7 components is all it takes.

@thomass7877 4 ай бұрын

@@sstorholm thank you...

@analoghardwaretops3976 4 ай бұрын

@@sstorholm..transformer ferromagnetic core magnetization & de magnetization , depend according to their B- H curve..which is also known as Hysteresis curve...and is a function of the frequency of the alternating current that produces its magnetic field ( flux ).. In each half ac cycle this flux polarity reverses.... Loaded or unloaded transformers (& inductors too) must have " equal Volt.-Sec. ..so also Amp.- Sec. " product in each half cycle..( or during " t-on & t-off in pwm) to cancel out, for net Zero Residual flux after one complete cycle. If this does not happen , there is a gradual flux buildup of one polarity..... Therefore even if the current is within limits...,that gradual flux build up over some time, causes the core to reach its peak saturation point....Thereafter even the smallest amount of current in the next (t-on)/half cycle , it crosses its saturation point.leading to mosfet/bjt blowing or circuit breaker tripping. as the case may be.

@robertmeyer4744 4 ай бұрын

that a great park. love the testing on new antenna . I bet it works great with 100 watt radio. has anyone done digital yet on it. like JS8 call of FT8 ? wondering about ferrite heating . nice coax feed line. I put chokes on my Pota flex 7 reel kit coax. love the bright yellow . 73's

@mikefinn2101 4 ай бұрын

Very nice explanation and learned something new very thankful for this video.

@paultomlinson528 4 ай бұрын

Fantastic explanation and love the HP calculator!! Looks retro TI

@Duckariffic 4 ай бұрын

AWESOME!! TY!!

@dimBulb5 4 ай бұрын

Very helpful! Thanks 😀

@onecircuit-as 4 ай бұрын

Oh snap! I've just made a soft start circuit for fume extracting fans based on the LM317 and a PNP. Thank you for the video! 👍😀

@mikebond6328 4 ай бұрын

Schematic or it didn’t happen.

@onecircuit-as 4 ай бұрын

@@mikebond6328 on my channel. 👍😀

@guy4698 4 ай бұрын

thxs for this info

@aduedc 4 ай бұрын

Problem I anticipate with NTC: Lets say we use it to limit the inrush current of a Drill motor. At first, when you turn on your drill it works fine and limits the current. Now you turn the drill off and turn it on again in a short time. Your NTC is still warm and does not limit the current, now you burn your fuse. I have seen active circuits that limits inrush current and force the device to soft start without having this problem.

@RedDeckRedemption 4 ай бұрын

Huh, and i thought those were capacitors. Does anyone know what the thermister things of that style are made of?

@1kreature 4 ай бұрын

Btw: I've seen plenty of PSU's having the hot inrush limiter next to a capacitor degrading it's life significantly.

@RensePosthumus 4 ай бұрын

What a coincidence, while your video appeared I was looking into a non working power strip.The circuit had two MOV's (20D168K and 20D_V3.0) that sandwich a T115 Setfuse (the trio was enclosed by black tape) no I have a legal excuse for some further tinkering ;-).

@thevoidedwarranty 4 ай бұрын

I've seen black ones too

@snakezdewiggle6084 4 ай бұрын

But why does it do that. How does it work. Why not SCR, or Zener.

@Forensic1Man 4 ай бұрын

Hi! Again, you have presented a really nice video. Could one use these NTCs to switch on a relay in a very hot attic so as to turn on a fan? If the NTC has less resistance with heat, a circuit could be built that allows a relay to close when the temperature is hot and thus switch on the fan motor.

@IMSAIGuy 4 ай бұрын

no, I would use a thermal switch, like the one I showed attached to the heatsink.

@paulgraf4140 4 ай бұрын

👍👍👍

@aaax9410 4 ай бұрын

👍

@TheDigitalAura 4 ай бұрын

How do these and MOVs fail? Is there a way they can be tested using a multimeter, or other common lab equipment? I, like so many people don't have a curve tracer.

@loukashareangas4420 4 ай бұрын

Both usually blow up or break apart when they fail, so they should be easy to spot. NTCs can be measured with a multimeter, as they are resistors basically, and check against the value they have printed on them. MOVs should appear open circuit when tested with a multimeter (not sure if you'll see anything on the larger resistor scales). If they are low resistance, they are faulty, but at that point they will probably have blown up on their own.

@TheDigitalAura 4 ай бұрын

@@loukashareangas4420 Thank you.

@byronwatkins2565 4 ай бұрын

They are often black.

@tfrerich 4 ай бұрын

Now that you've done NTCs you'll have to do PTCs next. To be honest, about the only place I've seen them used is in old color TV (CRT) automatic de-gaussing coils. I suppose you could use them as temperature sensors or self-limiting heaters, but I'm sure you have an old color CRT someplace in that garage. That'd be more fun to watch. - grin

@rfburns5601 4 ай бұрын

PTC's are in most every refrigerator. I got an education on these last year when the PTC motor starter fried and opened up. Ruined a few hundred bucks worth of food. The PTC starts out at 5 ohms giving current into the compressor start winding. After a few seconds, it'll go up to several hundred ohms so the start winding doesn't burn up. The PTC and overload (thermal circuit breaker) was $8 from amazon. In the olden days, they used the klixon starter relays that would drop the start winding when current in main winding dropped as the motor came up to speed. PTCs allowed for cheaper cost, as a quality relay with reliable contacts is more expensive than a chunk of semiconductor material.

@Edisson. 4 ай бұрын

Yes - a three-pin Pozistor for coil control, I still have one original Grundig in the drawer 🙂

@englishrupe01 4 ай бұрын

You will also find PTC's in any good quality multimeter, for protection.