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Forum Index : Microcontroller and PC projects : 12v DC UPS?
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bigmik Guru  Joined: 20/06/2011 Location: AustraliaPosts: 2950 |
Hi Craig, All, Before the 50AHr (hahahaha) battery pack was suggested I was going to suggest a 5VDc battery pack with a good step up regulator to 12v. Now the charge and output at the same time is a problem but the Xiaomi battery packs (at least the earlier fatter models advertised charge and output simultaneously.. That is one option. But what about simply powering the control module from a different mains power point so when the machine is powered down the control still remains powered. That should be the simplest option I think. Failing that power the controller from a standard UPS as these are designed to provide power and charge at the same time. Anyway, those 50A (hahaha) look interesting but I think they look like there are only 6 x 18650s in the pack probably 3 sets of parallel pairs in series (4.2v x 3 = 12.6). These generally only output 2500mAh so it would most likely be 5000maHr @12v a far cry from 50000 Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3378 |
But that's 9.9Ahr at 3.7V, not at 12V--36Whr as opposed to 118Whr. PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
That doesn't stop advertisers. The battery says 9.9Ah, so that's what it's advertised as. It's very unlikely that a AliExpress Chinese company would differentiate the theoretical from reality. :) In actual fact you're lucky if it works to spec, doubly lucky if it doesn't catch fire at some point. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3378 |
I still think that 6-cell 12V 18650 configuration has interesting possibilities. The input charger is 12V. It could, in theory, have an in-line 3P2S bms circuit board (I've seen a 2-cell version, and don't know why it couldn't scale up). With a nominal voltage of 3V7, the parallel output would only be 11V1, so would need a boost to 12V8 (or so), but that's a trivial module--a few dimes (but maybe beefed up some to provide 2A continuous). 2-cell 18650 BMS: here  Edited 2022-11-03 22:45 by lizby PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5091 |
Last time, and then I will shut up. A lead acid battery with a simple diode does the job. Nothing simpler, nothing more reliable. You can pick a size (1.8A....20A) you need and pick a suitible diode. Volhout PicomiteVGA PETSCII ROBOTS |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
 I can attest to the fact that this is total BS  |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
Agreed - the simpler the better. There are problems with the simplest systems (restricted charging rate, dissipation in the output diode, not all equipment is happy to run down to the discharge endpoint of a lead-acid battery) but you can generally work round them. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
Hi Mick. Typically, the power to the machine is dropped from an overhead 3-phase busbar. Running an extension cord to a wall socket is not an option. Furthermore, apart from keeping the control alive during a quick off/on of the main isolator it will also come in to play during the typical north American brownouts which disrupt the entire electrical installation. The reason that I like this solution is that; it will fit inside my control enclosure, under the PCB. It will be a built-in feature.  Craig |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
10A... for an hour... I'll eat what's left of my hair if that 18650 comes anywhere close. |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
What's your 12v drop-out voltage, Craig? The point below which your system is no longer reliable? You can rarely use a 12V battery to maintain a 12V system that drops out at, say, 11V. You also need the current draw of your system and how long you want the system to maintain in order to calculate the mAh capacity that you need. Using a lead-acid battery has the advantage that you can monitor the terminal voltage to get an idea of the current state of the battery under load. That's because the discharge curve is predictable. Li-ion etc. maintain a highish terminal voltage for quite a long time then the voltage drops suddenly, with little warning. Close to minimum you can signal the control system to load safe values into everything and shut down. You may not always get that to work with Li-ion. The 18650 has its place, but not in a critical UPS IMHO. It's fine for keeping your router running but I wouldn't do much more with one. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
With a CNC tube-former, it's not uncommon to have a crash-condition and something like a Servo-Motor-Amplifier will shut-down with an overcurrent fault. It's rare to find a machine with some form of external reset (probably because motion can be dangerous and you don't want a machine moving unexpectedly). So, it's the old; shut the main isolator off, count to ten and switch on again. If power to the control is removed, the axis-encoder positions are lost and so the machine needs to be re-homed....but the workpiece material that caused the initial crash, is still stuck in the machine. Can't use the robot to clear it because the material is out of the programmed off-load position. So now we have to get the overhead crane or fork-truck involved. It's a real pain. If my backup can sustain the control+encoders during the power-cycle, the re-homing won't be necessary. I did a few sums and it seems that even 25W would be enough for this "Microsoft-Reset" cycle. The control PSU input voltage spec is 11 to 13V DC. |
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