Scales that refuse to measure if the battery isn't brand new
I hate this scale, it says low battery and shuts off after just 3 months of sitting in the drawer. It infuriates me that there's still a lot of energy in the battery, I can use that in remote controls with no issues
If there's enough battery to say "low battery", then there's enough battery to show the measurements!
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That's because of the way these scales work. They use a material that deforms under stress and when it deforms the resistance changes. By putting current through this material and measuring the voltage drop, it can be mapped to how much stress the material is under and thus how much weight is on the scale.
This is a pretty roundabout way and has a lot of caveats, but it is very cheap. So cheap scales always work this way. That's why they aren't super accurate and have deviations depending on things like temperature. Another big downside is any permanent deformation ruins the calibration, giving incorrect results. That's why you never put more weight on kitchen scales than it says, it will break them.
The issue you are running into is the way it measures. It applies a very specific voltage and current in order to get the result. The lookup table it uses is only valid within a narrow range. When the battery voltage goes outside that range, it can no longer perform the measurement. Even though there's plenty of juice for things like the little processing chip and the LCD display. They don't need a lot of power and can do with low voltages. But it can no longer weigh anything so it just errors out with a low battery warning.
Mighty informative, thank you
Look up piezolectric materials if you wanna know more
The GP is not describing a piezoelectric scale. And you won't be able to find any piezoelectric scale that is anything similar to "cheap".
Well which principle do the cheap ones operate on?
It's actually a plastic ribbon with a metallic foil in a zigzag pattern on top of it. It's extremely cheap and does a pretty good job. It usually sits on top of a metal bar that can deflect a tiny little bit.
You can read all about it here: https://en.wikipedia.org/wiki/Strain_gauge
The main effect is that the resistance depends on the geometry. So as that changes, the resistance changes as well.
Ah okay.
All of which is fixed by a voltage regulator
Except the cheap part. But likely not by much.
You can order 3000 3.3V low drop out (LDO) voltage regulators on LCSC for $25.50. That’s less than a penny each.
Yeah, but it's more than 0 pennies each.
Doesn’t help when you need 3.3V and the batteries are now down to 2.5V they are not putting a boost converter in there.
Right. If your design requires 3.3V minimum then putting in a 3.3V battery and no boost converter is just dumb (or extremely user-hostile).
Batteries have one advantage over over supplies: extremely low noise. Even an good LDO will bump up the noise floor, and a cheap lcsc part will do so too. Plus you's want a reasonably low dropout and quiescent current, which also increases price. Maybe 10ct in volume is reasonable for such a part - and yes, that will absolutely eat the margin
That’s definitely true. But I would definitely pay more for a scale with ultra long battery life.
I made the mistake of buying an off brand digital calliper and now like an idiot I find myself removing the battery when it’s not in use just to avoid damn thing running flat in one month thanks to its atrocious standby current which enables the display to turn on instantly when I move the slide (rendering the on/off entirely moot).
Next time I’ll just bite the bullet and buy a Mitutoyo.
Same story here. You described it perfectly. Mitutoyo comes next.
I find spending a bit more on batteries goes along way. Although the nominal voltage and size may be the same, better batteries have lower internal resistance, ie provide the same current with less voltage sag. This prevent the low bat detection from tripping prematurely.
The problem would be solved if these scales would take a AAA battery which has a lot more capacity than a tiny cell.
Lol I must have one similar. Burned through a battery in storage and when I replaced it, I noticed that the display is still active even when off - such a weird design. I pop the battery half out for storage every time now.
It’s a terrible design. If they removed that dumb always on feature and used a proper physical power button the battery would last basically forever.
Absolutely, My kitchen scale remains accurate and can use the same battery for years.
Eventually, the battery drops lower than the device needs. So no, none of which is fixed by a voltage regulator.
No, not voltage, current.
Which in this case means: you need a constant supply voltage
This is probably not what you wanna hear, but when the battery gets low, the current gets weaker. If the current gets too weak, the scale becomes more and more inaccurate. Like, wildly so. In other words, the alternative is to lie to you. Badly.
Agree. For clarity, the circuits that show the low-voltage status are much less hungry for current than the circuits that measure weight. So no, having enough battery to report low voltage does not imply that there is enough to make an accurate weight measurement.
I'm bummed that when I had a Thinner bathroom scale, I could weigh myself before and after using the bathroom to see how much I expelled. It was consistent and really useful knowing its precision during keto months (lost up to 3lbs a week). Now I have a Taylor scale that will report the same weight over and over if it's relatively awake and you change less than 5lbs. So, no thanks to scales that lie.
That's not really how it works. The components of the scale require a certain amount of current especially if it's digital in nature. As a battery approaches being drained, it produces less current. Less current can often power an analog device to a lesser degree, like lighting up an indicator light or LCD or even the IR LED light on a remote, just very dimly. But the tolerance of the weighing components is probably much less than the tolerance of the LCD panel or LED bulb. So many devices use an LCD or indicator LED bulb to show that the device isn't necessarily broken, it just needs new batteries.
If it's sitting in a drawer and getting drained, then it's probably not turned off properly or it may be the type that turns on automatically when it gets pressed down and inside the drawer it's getting activated. Instead try taking the batteries out of any device that sits around for a long time without use. It will prevent accidental draining and also reduction the likelihood that the batteries will leak after a time. I usually pop the batteries part way out or put them in a small bag that I attach to the device with tape or a twist tie. Just make sure they aren't touching anything metal and that the poles aren't touching each other. Batteries will lose charge over time, but with alkaline batteries, that's usually years, not months. Rechargeables generally take much less time, though.
I have the same scale and bought a few rechargable ithium-Ion AAAs and they work line a charm having a constant voltage until empty.
Only downside is that you don't get any warning when they are about to run.
(Something like that: https://www.mediamarkt.de/de/product/_verico-verico-li-ion-akku-loop-energy-aaa-mit-usb-c-buchse-2er-pack-lithium-ionen-akku-109861637.html )
Edit: nvm, just saw your comment about yours usung a coin cell it seems like there are some deviations between different models of the scale.
Normal AA or AAA battery, or a CR button? If it is a button cell, try wiping it with alcohol before you insert it. Many modern button cells have a coating that tastes horrible to prevent people (children) from taking them into the mouth. I've noticed that on some brands, this coating measurably increases the resistance of the cell, not only reducing the the power it can deliver, but als making it appear "emptier" than they are ofor the measuring circuits. Wiping off the coating with alcohol (90% isopropanol) expanded the cells' life (in a kitchen scale to boot!) significantly.
It's a cr2032 from Duracell with that coating, later I'm going to try that
I wonder if this is why my car’s key fob never works well even with fresh batteries
Could be. Key fobs use button cells.
My cheap scale will not work with my freshly recharged amazon basics AAAs. Apparently those do not hold up well enough under load. And of course any set of batteries that does work, discharges over a few months.
So I just bought a cheap mechanical scale (not from Amazon) and I eyeball it for weights under 50g. Good enough and dead reliable.
This may or may not help, but a nickel is very close to 5 grams. You may be able to slap something silly together with a bunch of nickels taped together :P
CR2032 batteries are hit and miss in my experience. Sometimes my car FOB burns through one a month2 and other times they'll last years.
Get brand name CR2032, the cheap stuff doesn't supply enough voltage and electronics don't like em.
In my experience you can feel how good they are by how heavy they weight in your hand.
I actually just bought some Panasonic CR2032 and opened the packaging yesterday and I did notice they were heavier 😁
Funny that you mention Panasonic, because that's the brand I noticed it first with.
The Panasonic cells that come with a device are usually garbage, also the stuff you get on flee markets and cheap packages on the Internet.
They apparently have cells that hold up and weight noticeably more.
For the standard sizes like AAA, AA and D cells there's only Duracell for me. They're still miles ahead of their competitors imo.
It's my first time getting name brand in a while, but it's possible it's like OEM tires, where the tires that come with your car don't have as much tread as a new tire you bought yourself, even of the same model.
Exactly. They don't want to provide them at all, but customers would get furious, so they cheap out as much as they can.
I know this isn't helping but your scale is saying "ok lol"
For decades scales worked just fine without any electricity. Maybe get one of those.
There's also the option of electronic scales which are rechargeable via USB
I replaced mine with a usb cable. No batteries.
My scale looks similar to this. If I leave it on it goes into sleep mode which still drains power slowly but turn on instantly as soon as there is weight on it. If I hold the power button when I'm done it turns off and makes a beep and then I have no issues turning it back on months later. Still on original batteries after 2 years.
I have a scale that charges with usb-c. It's also accurate to 0.1g
Nice, which brand/model? I have a scale for making pour-over coffee that has 0.1g precision, but I seriously doubt my scale is actually accurate to 0.1g.
Chef Matteo Preciso, though you can only get one if you live in Scandinavia or Finland as it's a store brand.
I have a 0.1 accuracy scale from aliexpress and it works everyday with its soon to be 10 year old coin battery.
I'll buy a rechargeable one if ever it goes to scale heaven.
Didn't think you were going to get a bunch of nerds telling you exactly why it works this way 🙄
"Bruh just use the finger scale to weigh out your weed. 1 finger = 1.7g and 2 fingers = 3.5g"
LOL genuinely thought it was a case of "engineer hates the user", instead it was a case "management said we need to save 5 cents for the voltage regulator"
😄 it happens
I have to charge the battery EVERY TIME! There is a wheel on the top I have to spin else it won't do ANYTHING.
Infuriating
Buy an analog, non digital scale. That piece of junk is just e-waste.
I believe I have this exact same scale, and I also hate it. My main problem is that those capacitative buttons sometimes refuse to work, and it's real nice when I'm trying to measure something in grams and it randomly gets stuck in pounds.