Archive for April, 2020

Tim Tears It Apart: SunGrow Betta Heater, a Sketchy Preset Aquarium Heater

Spoiler alert time. Did you know there are ferrous metal composites with arbitrary Curie points, extending down to room temperature and even below freezing? You never know where a teardown of a theoretically boring product will lead. Seriously, take more stuff apart, it’s good for you.

I’ll spare you the lengthy story of the goldfish that finally decided it was big enough to turn cannibal, but I needed to evict some sundew plants from a small betta tank I had on the windowsill, and make it habitable for actual fish on short notice in winter. Hurry, right? It turns out the options for tiny low-wattage heaters for small tanks are kind of limited, so click, click, buy. Soon, gracing me with its presence is this cute little heater stick. The size is right, but the hairs on the back of my neck stood up a bit on noticing this fine Chinese gadget’s 120VAC cord is meant to go from the wall socket directly into the water. If you had the kind of parents itching to slap that spoonful of raw-egg cookie dough out of your mouth, or the kind that made your do all chainsaw juggling outside, they’d probably have a thing or two to say about this too. Not only is it a fully submersible heater, but the instructions actually warn against leaving the top (cord entrypoint) of the heater out of the water (or tilting it, but that’s neither here or there).

To my pleasant surprise, this thing worked as advertised, maintaining the tank at more-or less a balmy 78F, and not electrocuting anyone or anything. However, just shy of a whopping 6 months after purchase, I notice the heating indicator light is staying on constantly, but it’s no longer actually producing any heat. So, let’s have a peek inside and see what happened! You can probably guess, but the innards are mildly interesting regardless. Let’s take a look.

According to the actual marking on the unit, this is the “Aqua Thermo Nano Plastic Aquarium Heater”. Through a cursory search on Amazon, the exact same heater is sold under a wide variety of manufacturer names, including a collection of randomish all-caps names like GOOBAT, VIBIRIT, PGFUNNY and dozens more, in some cases with claimed power ratings up to 300 Watts(!).

These small “betta heaters” seem to come in two varieties, those with a preset (and fairly high) temperature around 78F, and those that are just a fixed resistor that continuously injects a certain number of watts of heat into the tank. (There is a third kind advertising a PTC thermal control element, that according to reviews, are actually just a fixed resistor.)

Heater top
Heater bottom

The submersible unit has only one obvious seam, near the top where the “cap” receiving the power cord enters (the seam-like line around the bottom face appears to be a moulding artifact; this is all a single piece). The top cap is mostly decorative; popping it off reveals, along with a bit of trapped water, a second, rubber cap glued in place by an adhesive resembling RTV silicone caulk. This is the seal protecting the 120V cord and innards from water intrusion. Removing this inner cap reveals the simple circuit inside.

The first thing to note, aside from the complete lack of fusing, GFCI or any other safety measures, is that the inside of this compartment is dry (a small amount of water trapped between the white plug and decorative black cap leaked out onto the workbench). Leakage into this area was not the cause of failure. Cutting into the power cord reveals that it is also dry inside, with at least individually-insulated mains wires inside the outer insulation jacket. This chamber contains nearly the entire circuit, except for the heating element, buried beneath a final plug of black epoxy. Sawing the package open reveals the final component.

Sawing into the bottom, the first thing to emerge was a pile of damp(!) sand, along with a bit of fiber fill (cotton ball?) and a not-faint “fishy” smell. While many unique smells are described as fishy, this reminded me of the smell released by an electrolytic capacitor going bang in the night. Don’t ask me how the sand got damp; the plastic package appears to be a sensible one-piece design apart from the plug where the cord comes in and did not appear obviously damaged, and again, the upper components beneath the plug were bone dry.

With the sand and some heatshrink out of the way, here is the full circuit, exposed for your viewing pleasure. As you might expect, there’s not much to it. The component marked “CTR-34” is a thermal switch in series with the heating element; the only other components are a current-limiting resistor and reverse-blocking diode protecting a small red indicator LED glued into the white cap. Interestingly, the heating element is an off-the-shelf radial wirewound resistor, rather than a bespoke Nichrome wire coil or similar. You can find very similar-looking name-brand parts. This is marked with a generous 15W rating – a pleasant surprise for our 10W-rated heater (more on this in a bit) – and 780-ohm resistance. It’s also marked as… no, wait, that’s a giant crack extending most of the way down the package. This was not suffered during the disassembly effort. Gently removing the cracked-off portion reveals discoloration and corrosion, as well as an even stronger waft of “fishy” smell. If the wet sand wasn’t enough to give it away, I think we’ve found our failure mode. That said, quick math on our “10 Watt” heater has the resistor dissipating 18.5W on 120VAC North American power. For the curious, the “120V” figure quoted is an RMS value – an average of sorts that already accounts for the fact that AC voltage, and thus its resistive heating power, varies throughout its 60Hz cycle (the peak voltage from the wall is around 170V).

So, we’ve done it, right? Nothing left to take apart! We even had a look inside the resistor! (pause for reverent sighs)

The “CTR-34” component is a bit of a mystery to me; I’ve never seen a thermal switch of this style before, with its sleekly polished package. The ad copy makes reference to an “Intelligent Temperature Chip”. So let’s saw it open, amirite?

With only a little mangling in the process, we liberate the contents and see some surprising complexity. There is a tiny glass-encapsulated reed switch – not a bimetallic switch, but a magnetic reed switch – encased by a stack of black donuts, further encased in the sealed metal shell. The black donuts turn out to be a pair of small permanent magnets surrounding a piece of ferrite material with a carefully-engineered Curie point. One such material is known by the trade name Thermorite, although many competing vendors offer similar switches using the same approach. By carefully controlling the mix of dopants and particle size of the ferrite material, it can be engineered to have arbitrary Curie temperatures as low as -10C or lower. (Holy shit, that’s a thing?) Below the Curie temperature, the soft-iron ferrite is permeable to the permanent magnets’ field and holds the switch inside closed. Above the Curie temperature, the ferrite loses its permeability, allowing the switch to open and turn off the heat. If I were to guess, the sleek silver shell is a special alloy such as mu-metal that protects it somewhat from external magnetic fields.

As far as I can find, switches made using this approach are simply known as thermal reed switches. I have to admit I am a little baffled by the design choice, as this is otherwise a “cost-optimized” overseas import product, but these switches run several dollars a pop (at least domestically; the cheapest I found on Mouser was $3.20@1000pcs). My best guess is that once you eat the actual cost of the component, it’s idiotproof and can be crammed into the case by trained monkeys without any manual adjustment, calibration or chance of getting out-of-whack due to rough handling.

Other Utricularia for aquascaping besides UG

Utricularia graminifolia (UG) is a popular foreground plant for planted aquariums, with grass-like leaves that eventually form a lush green carpet over the substrate. It is considered anywhere between easy and impossible to grow, and has some special needs that make it not a beginner’s plant. However, there are a whole range of Utricularia that might grow fully submerged and give you a different look, and might even be easier for you to grow.

Below is a dump list of suspected submersion-friendly Utricularia, mostly for my future self to try growing when the world grows out of the current pandemic, my kids start sleeping during the night and I have a lick of free time for stuff like that again. This is by no means a comprehensive list. If you want that, head to Barry Rice’s extremely comprehensive Carnivorous Plant FAQ, find the Utricularia section and start clicking. He breaks them out by subgenus (so get your clicking finger warmed up), but under each is a table listing the growth habit (those listed as affixed aquatic and possibly subaffixed aquatic are good candidates). For photo references below, I tried to find some showing the foliage – for many Utricularia growers, and specific species, it’s all about the flowers.

If you do have any experience growing these fully submersed, please sound off in the comments!

  • U. bifida – (photo) (Source: webforum post)
  • U. caerulea – (photo/description) Note, may be synonymous with U. nivea (Source: webforum post)
  • U. dichotoma – (photo) Better known as Fairy Aprons for their unique flowers. (Sources: Besides this webforum post, and this other one, Carnivorous Plant Nursery until recently sold this plant with a mention of use as an aquarium foreground plant.)
  • U. geofrayii – To a depth of 5cm before flowering ceased (Source: webforum post)
  • U. limosa – (Source: webforum post)
  • U. livida – (photos/info) “easier to grow than UG and forms nice, thick mats in the aquarium”. More bulbous, grayish foliage compared to UG. (Sources: this fishkeeping article. Carnivorous Plant Nursery sold it as an aquarium foreground plant comparable to UG, but has since stopped carrying it.)
  • U. monanthos – (Source: webforum post)
  • U. nivea – To a depth of 5cm before flowering ceased (Source: webforum post)
  • U. praelonga – “easier to grow than UG and forms nice, thick mats in the aquarium” (Source: fishkeeping article). Appears to have significantly larger foliage than others in this list.
  • U. sandersonii – (photo) “The leaves are roughly the size and shape of duckweed, with small bladders interspersed throughout. It is much easier to grow than U. graminifolia and forms a beautiful dense carpet” (Source: fishkeeping article). Outside aquascaping, this plant is widely available commerically and known for having flowers that look like a cute bunny.
  • U. tricolor (Source: webforum post)
  • U. uliginosa – “Some varieties […] thrive at a depth of 30-40cm” (Source: webforum post)
  • U. volubilis – Twining bladderwort. “It has long leaves that are arranged in a rosette, and each rosette produces long stolons that produce additional plantlets.” (Source: The Carnivorous Plant FAQ. You can also see a picture of this growing in an aquarium with sand substrate)

For my own part, UG has been somewhere in the middle, between easy and impossible to grow (or between dead and flourishing). I did get it to grow densely (if incredibly slowly) in basically just dirty water – a bed of terrarium gravel full of runoff from watering other CP pots – and even flower, but for anything resembling fully submerged in an aquarium, it just gradually uproots (ahem, up-submerged-stems?) and floats away rather than establishing. I’m almost certainly Doing it Wrong(tm), but figure it might be easier to adapt the plant load to the growing conditions rather than the other way around.

Utricularia graminifolia flowering in a bed of river gravel

So far, my UG seems to survive in a wide range of lighting and fertilization conditions, tolerating pretty crap lighting on my windowsill and more, ahem, tank-borne nutrient (produced naturally by the fish) than I would expect for a carnivorous plant, although it doesn’t seem to love any of those conditions. Grown semi-emersed in a peat:sand mix and well protected from nibbly fish, it produces the patchy carpet shown below. This is the better part of a year’s growth starting from a couple small sprigs.

Disable automatic reboots on Windows 10 (maybe)

Look, I get it, updates are important, and so is installing them timely. But after waking up this morning to find yet-another overnight job lost to an automatic reboot, it’s the last straw. To afford nice things (you know, like computers), I need to do my job, and that requires actually using my computer and delivering the results, including the output of long-running jobs.

For Windows 10 Professional/Enterprise/whatchamacallit, this can be done through the group policy editor (gpedit.msc), but this is not available on the Home edition (and workarounds involve sketchy download sites). So, trying this to defeat auto-updates instead (from this thread). Note, these files are protected and you need admin privileges to touch them of course:

  • Open %windir%\System32\Tasks\Microsoft\Windows\UpdateOrchestrator
  • Rename ‘Reboot’ to Reboot.old
  • Create a dummy folder named Reboot (I assume this prevents the “missing” file being restored or overwritten).

We’ll see if this does anything, or for how long…!