🔴 What Is Inside ? - High Wattage Resistor - Is It Fake ? - No.1054

Is It Fake ? - What Is Inside a High Wattage Resistor ?

I dismantle a blown high power resistor to see what is inside.

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[apollorobb]

I pulled a 100 W 22 Ohm Dale apart and it was the exact same

[AntoninKral]

And with sand you also get the benefit of arc suppression in case it actually blow.

[SeanBZA]

The better ones use a much finer sand fill, basically a magnesia powder that is vibrated into the unit, after the element and one side is inserted. Then they might also vacuum impregnate with a compliant silicone resin, and then place the end cap on the open side.

Remember that those are not actually classed as insulating, you need to either ground the heatsink it is bolted to, or arrange separate insulation if it is exposed ungrounded metal, as the element inside can run hot enough to get to red heat, and make the silica conductive. If you want to see this take a 5W ceramic one, and run it till it is at red heat, with a steel wire wound tight around the ceramic, and check insulation resistance between the inner element and the steel wire when it is at dull red, and it will be measurable.

In mains applications I have seen them sustain current flow and stay red hot, as the thermal cutout and control was on the neutral side, and the equipment did not have RCD protection. That was added on later, even if it did mean I replaced a good few cartridge heaters that were leaky slightly, especially after a week of non use, when the magnesia fill had adsorbed a tiny amount of water.

[coldfingersub]

Do the same thing with a high dollar brand name non-inductive and thermal resistor

[helmuthschultes]

The construction with silica sand is the normal way these power resistors are constructed. However I do hope there was considerably more sand the first time you opened it up.
Epoxy fill is hard as these resistors can safely operate well above 200°C, that few epoxies take well long term. Certainly not pure epoxy but would need powder filled variety itself hard to squeeze into the internal space and curing properly. Usually the end seal is almost a glassy substance, the fine sand fill if properly done, has excellent thermal flow and very good high temperature handling and being dry powder relatively easy filling with a little vibration to settle in well. Manufacturing process cheaper and easier than pressure feeding powder filled epoxy paste, that itself is costly and beginning hardening process, messy and cleaning issues. Yes some power devices have what almost looks like dried cement fill, that is some form of powder filled epoxy. These gold colour power resistors normally are sand fill and glassy looking end cover.

In this case I do wonder about the fine wire used. With 0.2 ohm at 100 W, means only just under 22.4A (using P= I^2×R) so actually bad, looking very prone to fusing, as little contact area with both sand fill and core ceramic cylinder, especially if not thoroughly packed with filling sand, and so any region with air void and you have a fuse as much as a resistor.
For this I would have presumed and infact have seen low ohms power resistors using a flat wrap of nichrome strip, with near complete surface of ceramic core covered. Far less prone to blocking sand fill leaving no voids and maximum surface for thermal flow.

Yes likely cheap manufacture item, taking short cuts with lowest cost materials and processing.

[IanScottJohnston]

Quartz sand (aka silica) very commonly used in offshore certified electronics equipment to fill voids and is very heat resistant so that in your resistor the wire stays an equal temp along it's length. Another property is it's purity, meaning contaminant free thus would never be the slightest conductive. We used to make ultrasonic level sensors and filled them with the stuff back in the day.

[noggin]

Definitely worth ordering a power resistor from Farnell etc to compare.

[hectorpascal]

The problem with this style of high power resistor seems to be that the quoted maximum power rating depends entirely on the size of the heatsink they are attached to. This is never stated in the adverts. It would be interesting to see some test results.

[E_STI]

I used to use these for hyper flash on leds but now I use led flasher relays instead.

[artursmihelsons]

Great, that it didn't touch aluminum case when blowing.. This failure is ok.. Only, I expect more heat dissipation and insulation material inside..
Thanks for sharing issue!

[ovnprojects]

I opened one of those loong time ago and it did not have sand in it. The real ones are much tougher to open. Best bet to open those is maby to heat it up really hot and then pull it apart. Or use brute forse and vise to get it started. If i remember right it was ceramic in the senter and black epoxy between it and the aluminium housing.

[simonbaxter]

That was surprising Scott! I would have thought that they were fully thermally hard potted (although that would cause thermal expansion issues and would put mechanical stress on the resistance wire as it heats up) or filled with thermal paste (an expensive option), but I guess the 'sand' is silica which should have good enough thermal conductivity properties for what these resistors need.

[patim]

The "sand" is needed, without it the resistor has no cooling, only the air inside but air is a bad thermal conductor. It is also there for safety isolation. If the wire brakes and carries a high voltage you do not want it to touch the housing. You see the same thing in those square ceramic resistors and in the big fuses in DMMs. The Chinese do not use the sand because it makes the stuff cheaper.

[ebirper]

Thanks for the video. I have the same resistance as the one in the video on which is written: 12R J 1139. but the wattage does not appear. Question: what means J 1139 THANKS.



[fullwaverecked]

I've got some small ones from the '60s... I still can't get my head around how some could be 8 ohms, ect... Looks like a dead short wire wrapped...

[GannDolph]

I have a bunch of these, been good for various utility. For example one is mated to a 5mm silicone heat sink pad and used as a soldering pre-heater for those aluminum circuit boards found in LED lamp . It has 160 ° C thermal switch on its backside to keep it around that temp.

I'm impressed you killed one. Did you really dump 3000W into it, or was it current limited?

[mrpetit]

Interesting. I would've expected them to be filled with some kind of ceramic cement.
I use these resistors in a large bank (on a large tunnel heatsink) to test powersupplies. But I never load them to 100W/piece, ususlly between 25 and 50w and they get plenty hot.
But they are so cheap, that it's no big deal that you have to use more.

[danishnative]

No way 100 watts without external cooling/heat pump. Maybe 10 watts in free air. Chinese are so good at misleading ratings. So Scott, do a destructive test on one, and let it dissipate a full 100W free air. That would be fun. Simon Spiers did a test on some of those shoddy over-rated jumper leads a while ago. 😆

[TheEmbeddedHobbyist]

There is another issue with these types of high power loads, they are also quite inductive, and so the resistance changes to be impedance as now you have a reactive element. So as the frequency goes up so does their impedance.

[patprop]

That's good ol' China Junk for ya! i swear they put sand in everything just to bulk up the weight. even though they go throw all the trouble to make products look as close to the original as possible, and yet the products always falls short, pun intended.