Another Power Supply

tmp5507Here’s another one for you – Banggood do a small UPS which looks like it might be useful…     DC 12V 2A Mini UPS Power Supply On-line Type -- https://goo.gl/cyZyPD

So just what exactly is this?

The unit comes complete with a lead which plugs into the output and splits to two similar connectors…. that’s it. You organise the power supply to charge it yourself. You need 12v at 2 amps for this. I had a couple of 12v supplies lying around but unfortunately the connectors were slightly too large. Consult the ad for connector info.

So – basically the unit has a battery pack inside comprising 3 normal Lithium batteries, of the kind you might expect to have 2000ma to 3000ma capacity. You plug it in, charge it up – it supplies 12v at 2 amps out – simples.  The claim is up to 2 amps in, up to 2 amps out and 2000ma capacity – UPS – so this is specifically designed to be un-interruptible. The back comes off easily to reveal the batteries without undoing screws.

Let’s look further as there is not a lot of meat in the advert.  The unit has 4 blue lights which light up successively until the unit is charged. There is also a red light which indicates charging – and a green light indicating fully charged.

Not having a plug-in-the-wall supply with the right connector and eager to know how this thing performs, I put it onto my bench power supply at exactly 12v input.

Over several hours the unit (with no output) charged at 300ma. One would expect that after 8 hours of this – it would be fully charged with the green light showing. In fact, it did get near fully charged after 8 hours as per claims, however, after 20 hours it was no further forward, just about charged, red light still on. I have no reason to believe it will EVER come up fully charged – however the blue lights indicated it was all but there – so I’m happy with that.

The twin outputs are intended to power things like routers etc  - you’d have to be careful and check out the combined current requirements of two units ensure they were not more than 2 amps.

But wait – it really doesn’t quite work out that way. If the input is a maximum 2 amps as claimed – and the charging rate is 300ma, then in fact it is reasonable to suggest that you’re not going to get more than 1.7 amps out – otherwise you ain’t charging the battery!!!!  I really do wish that manufacturers would not treat us as idiots – the maths is simple enough.

And that’s about it – at 1.7 amps output you would get somewhat better than an hour backup – but then remember that’s at 12v, if you were to use a switched supply to drop this to 5v then you’d be looking at nearer 4 amps… so with a typical Rasperry Pi you could be looking at 4 hours without power.

Be aware however, let’s say the power goes off and the battery runs right down as your Pi continues to charge – then the power comes back up!! You are now running from the input while the battery charges but you won’t be able to handle another 4 hour blackout for at least 8 hours as the battery recovers.

This unit has the advantage of being all boxed up and ready to go as against many of the cheap UPS solutions we see which could be used by our little boards.  I understand from the info that they also do a version with 5v out which might be better for those with soldering iron aversion.

Here also is the version with 5v out but note that this is 2 amps at 5v, the one I have with a suitable buck convertor could put out over twice that amount – but it’s more messy…. http://bit.ly/2y7qLMF

No, I’ve not abandoned doing our own – but my PCB friend is away on holiday so this’ll do for now.

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16 thoughts on “Another Power Supply

  1. Good find, Pete. This looks like our most promising 'off the shelf' option so far as it's actually intended to be used as a UPS rather than us trying to stretch the functionality of a rechargeable battery pack (i.e. Tomo) so in theory it should stand a better chance of working.

    I'll be interested to see how you get on with your testing, especially since the price of the unit is pretty attractive.

  2. Hm... Interesting. Not really the expected use-case but I'm currently building some "off-grid event lighting" - i.e. lighting some outdoor stalls at a community event after dark somewhere with no mains power! Reckoning on needing about 10w of 12v LED bulbs per stall - one of these might do the job, maybe.

  3. Would 12V be enough to fully charge it? A lithium battery fully charges at 4.2V so with three in series, you’d need a 12.6V supply to reach full charge. Or am I misreading this?

      1. Or the batteries are wired in parallel & they use a converter to drop the 12 volts to the charging voltage & afterwards use a boost converter to give you the 12 volts back out, this would work but not very efficient, any rating on the batteries?

            1. By the look of the markings inside the box - and having taken the first layer off the batteries - not wanting to rip the thing to bits - I'm going to say almost definitely it is 3 batteries in parallel.

  4. Pete,
    If you have a few Lithium batteries laying around get one of these https://www.banggood.com/3S-20A-Li-ion-Lithium-Battery-18650-Charger-PCB-BMS-Protection-Board-12_6V-Cell-p-1118043.html?rmmds=search
    Then connect it to your favorite DC-DC buck converter maybe this one https://www.banggood.com/DC-DC-Boost-Buck-Adjustable-Step-Up-Step-Down-Automatic-Converter-XL6009-Module-p-1087346.html?rmmds=search.

    I remember seeing a circuit with a resistor or diode ladder that can provide a low voltage signal to feed the Pi and tell it to shut down though a GPIO.
    I jut got one Lithium charger so Ill go to the recicler and get a few old computer batteries.

    1. Hi Scott

      Now, bearing in mind I'm on my 3rd glass of wine for the night... seriously - are they saying for a couple of quid - you can dharge, from a nominal - presumably car battery or whatever, 12v supply, a single or parallel set of Lithiums at 20 amps and not blow the whole lot to kingdom come?

      If so - I want one.

      Oh, I'm looking at the diagram - so up to 3 batteries in series - connected to the board... but 20 amps - isn't that WAY beyond recommended charging for a typical battery - or am I missing something... please DO elaborate...

      The buck-boost convertors - well familiar with those - good.

      1. Can you clarify - are these JUST PROTECTION or actual charging circuits - i.e. if you stick 12.6v on there - and just leave it forever - will they protect the cells? What latitude do you have on that 12.6v???

        As you can see, you have my interest.

        1. Salud compadre with the 4th glass of wine...

          When we talk about Li-Ion batteries we need to educate our self before playing with a device that stores a lot of energy. PCM or PCB (protection circuit module or board) is "heart" of Li-Ion battery pack. It will protect Li-Ion battery pack from overcharging, over-discharging and over-drain, therefore it is must have to avoid Li-Ion battery pack from exploding, firing and damage.

          To answer your question the Charger Protection device there will provide 20 A... or so they say but not from 3 18650 batteries. The output transistors look pretty beefed up.
          Good place to start: http://www.egr.msu.edu/classes/ece480/capstone/fall08/group10/file/Kovalcik_Application_Notes_ECE480_Team10_FS08.doc

          Not everybody uses a PCB/PCM/CMB on their batteries like Tesla, what they do instead of using an advanced BMS (battery manage system) to lower cost is charge them to the max voltage and then bring them down to a certain voltage. Now if you are using unbalanced and used batteries this is recommended. Here is a good guide http://www.batteryspace.com/prod-specs/pcb_wiring.pdf.

          Take a look at this page http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries for more info. This is where I first found out about these charging and balancing circuits http://www.batteryspace.com/pcmforli-coli-mn-nibatterypacks.aspx.

          Unfortunately I don't have any 18650 cells right now to test it, I meant to go to the recyclers a few weeks ago but was hit by Irma and slowly coming back to normality.

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