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Author Topic: Compact 12V UPS for modem/router  (Read 622 times)

IanG

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Compact 12V UPS for modem/router
« on: July 02, 2019, 11:03:43 AM »

Prompted by jack21, I tried to find a compact 12V UPS suitable for powering a modem/router. It would have a 12V DC input, a regulated 12V output, and an internal battery to supply power when the input failed, thereby avoiding the complexity and inefficiency of the 12V DC -> 240V AC -> 12V DC conversions when using a conventional UPS. Powering the modem only would suit those who normally use a laptop or tablet to connect to the Internet.

There are a number of such devices on the market - search for "12V UPS" - but most are grossly substandard, if not illegal. According to reviews, one didn't have a CE marking. Another had as its output the 3 internal 3.7V Li batteries in series, which hardly counts as regulated. And it was common to quote the mAh rating of internal 3.7V batteries while implying that the rating applied to the 12V output, whereas the real 12V rating is probably a quarter of the quoted value, and less at high load currents.

Eventually, at more than twice the price and a fraction of the claimed capacity, I found one with a reasonably complete data sheet that I could believe in.

https://www.elmdene.co.uk/product/31/power-supply-accessories/118/ups/562/miniature-ups

Does anyone here have experience of this unit, or can recommend reliable alternatives, as a higher capacity version would be useful?

Disclaimer: I have no connection whatsoever with Elmdene or any other UPS supplier.
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Ixel

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Re: Compact 12V UPS for modem/router
« Reply #1 on: July 02, 2019, 12:31:21 PM »

I recommend checking out https://www.powerinspired.com/store/ipower-dc-ups-c-123.html - I've used this without problems. Has less mA capacity but worked fine and I've had other products from this supplier before without issues. Another option could also be a USB powerbank with appropriate DC output and compatible connection.
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johnson

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Re: Compact 12V UPS for modem/router
« Reply #2 on: July 02, 2019, 05:37:04 PM »

Eventually, at more than twice the price and a fraction of the claimed capacity, I found one with a reasonably complete data sheet that I could believe in.

https://www.elmdene.co.uk/product/31/power-supply-accessories/118/ups/562/miniature-ups

Does anyone here have experience of this unit, or can recommend reliable alternatives, as a higher capacity version would be useful?

From a glance at the datasheet I wouldn't trust its rating either, it claims 4400mAh but weighs just 140g.

The li-po batteries inside will be either 3 18650 metal cans or (less likely) 3 pouch type cells. Even expensive high capacity panasonic 18650s are rarely above 3000mAh and weigh about 50g each. So thats 150g without case, regulator PCB connectors etc.

As for pouch type, I just measured a 1300mAh 3C high discharge pack I had lying around, little over 100g grams with charging connector.

So either way I cant see this unit having true 4400mAh capacity. Whether thats really a problem is another question, as I'm sure this would keep a 5W router going during a short power cut, or during changing 12V supplies for testing.


If I were looking into doing a UPS properly I'd start looking at SLAs and an accompanying trickle charger. E.g this 7Ah 12V for £17.
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sevenlayermuddle

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Re: Compact 12V UPS for modem/router
« Reply #3 on: July 02, 2019, 06:47:16 PM »

Does the spec actually say it has three cells?   If it does, I failed to spot it.

The device clearly performs internal voltage conversions from the battery voltage to the required output voltage, which might be a source of interference.   The target  market seems to be cctv, I wonder if interference might be less of an issue, or more of an issue with, cctv vs vdsl modems?

Re mAh capacity, forgive me if I am wrong, but... is it not meaningless, unless they state the reference transfer voltage?   

Specifically, if there are indeed three cellls, of (say) 1500 mAh each,  and if the internal conversion were configured to produce an output voltage that matched that of an individual cell (approx 3.7V) surely it would be reasonable to advertise a mAh capacity of 3 times the individual cell’s capacity, ie 4500 mAh at 3V?

If that is correct, you can’t blame them for advertising the best case, which might be, say, an effective 4400 mAh at 5V (the lowest voltage available), assuming each cell is actually  bit better than my example 1500mAh.  But if the conversion is producing a higher voltage, say 12V, I reason that the real capacity would be just under a half of the ‘best case’  ie more like circa 2000 mAh.

I don’t pretend to be an authority or expert, just thinking aloud, won’t be offended if somebody wishes to explain that I am mistaken, :)
 



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burakkucat

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Re: Compact 12V UPS for modem/router
« Reply #4 on: July 02, 2019, 06:56:20 PM »

Something else to consider, maybe, is the battery backup unit that Openreach install with the Huawei HG8240/HG8110 GPON Terminals for FTTP[oD] services.

The one I'm looking at was paired with an HG8240 (the original 4 + 2) device and the label shows --

Model Name:    Ni-MH BBU15-D
Rating Input:  12V 2A
Rating Output: 12V 1.5A

On the inside of the battery compartment cover it states --

This device requires rechargeable (Ni-MH) batteries
with a minimum capacity of 2000mAh to work
correctly during a power failure.




(Q) When is a battery not a battery? (A) When it is a cell.

A battery consists of two or more cells.  :-X
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sevenlayermuddle

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Re: Compact 12V UPS for modem/router
« Reply #5 on: July 02, 2019, 07:28:29 PM »


(Q) When is a battery not a battery? (A) When it is a cell.

A battery consists of two or more cells.  :-X

I have never encountered that definition, have you a reference to it?   

It would seem to imply that when, as a child, I used to purchase PP3 batteries for my radio that was fine as each PP3 contained six cells, but the U2 batteries for my torch were being misrepresented, as each U2 contained just a single 1.5V zinc carbon cell?  I live and learn.
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johnson

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Re: Compact 12V UPS for modem/router
« Reply #6 on: July 02, 2019, 07:39:47 PM »

Does the spec actually say it has three cells?   If it does, I failed to spot it.

It does not, but for a device designed to run off and produce 12V, 3x 3.7-4.2V li-pos minimum feels like a sensible assumption. But you are right I guess it could have fewer cells (or more but in parallel) and be stepping up voltage for 12V output.

Quote
If that is correct, you can’t blame them for advertising the best case, which might be, say, an effective 4400 mAh at 5V (the lowest voltage available), assuming each cell is actually  bit better than my example 1500mAh.  But if the conversion is producing a higher voltage, say 12V, I reason that the real capacity would be just under a half of the ‘best case’  ie more like circa 2000 mAh.

You are quite right, I wasn't thinking about the lower voltage output options.
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IanG

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Re: Compact 12V UPS for modem/router
« Reply #7 on: July 02, 2019, 08:52:08 PM »

@sevenlayermuddle: you are quite right about mAh being meaningless on its own as a measure of energy storage. mWh, or Wh if over 1000, is appropriate.

While the weight of 140g is astonishing, it is not impossible. I have just weighed a mobile phone battery cell (3.85V, 3.27 Ah minimum) at 53 g on two scales (one kitchen, one precision).

If rating the Elmdene unit, I would subtract points for not having a replaceable battery cell. It is not a fashion item, and ought to be designed to last for many years. 
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burakkucat

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Re: Compact 12V UPS for modem/router
« Reply #8 on: July 02, 2019, 09:52:09 PM »

I have never encountered that definition, have you a reference to it?

Nothing that I easily lay a handpaw upon . . .

I offer a further comment that the word "battery" is a short-form contraction of the phrase "battery of cells".

I fully expect that your car is equipped with a battery of six lead-acid cells, connected in series. My laptop computer uses a battery of six Li-Ion cells. My tower computer, beside my desk, uses one 3V Li-Ion button cell to power the CMOS RAM containing the BIOS settings and configuration. The torch, beside my bed, takes three 1.5V cells of size D. (In our younger years we would refer to them as either U2 or HP2.)
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petef

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Re: Compact 12V UPS for modem/router
« Reply #9 on: July 02, 2019, 10:24:30 PM »

The OED's definition of a galvanic battery says "whether of one cell or more".
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sevenlayermuddle

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Re: Compact 12V UPS for modem/router
« Reply #10 on: July 02, 2019, 10:28:28 PM »

Still not convinced Burakkucat. :)   

If said torch used three U2 ‘energy sources’,  and they needed replaced, we’d definitely have referred to fitting new batteries, plural not singular.

Per the 2032 (or similar) power source on a typical motherboard I do agree, most people  would refer to it as a button cell.   But might that be related to the possibility that most people (geeks aside) don’t expect a PC to contain a battery?  In my experience the same device, in a car’s remote control keyfob, would more often than not be called a battery.

I did check two different ‘proper’ dictionaries earlier (‘proper’ as in made mainly of paper, a couple of decades old, and reasonably concise, occupying an inch or two on a shelf).   One, Chambers-branded, supported the suggestion that a battery was two or more cells, but also that a battery could be a single voltaic cell.   The other, Oxford-branded, suggested this meaning (among others) of ‘battery’ was “an electric cell or group of cells supplying current”. :-\


The OED's definition of a galvanic battery says "whether of one cell or more".

Ah, that makes a best out of three. ;D

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roseway

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Re: Compact 12V UPS for modem/router
« Reply #11 on: July 03, 2019, 07:07:21 AM »

There's no doubt that in common usage the word 'battery' is used to mean one or more cells. Dictionary definitions are adaptive as usage changes, they're not prescriptive. But there's equally no doubt in my mind that the scientific definition is that 'battery' means two or more cells. Also, in the wider context, when we refer to a battery of something we mean several items.

So I suppose we have to say that both protagonists are right here, but my vote is definitely on the scientific side.
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  Eric

tubaman

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Re: Compact 12V UPS for modem/router
« Reply #12 on: July 03, 2019, 08:42:40 AM »

...

So I suppose we have to say that both protagonists are right here, but my vote is definitely on the scientific side.

I agree. A battery contains more than one cell. AA (C,D etc) cells being referred to as batteries has come from common usage, not because it is technically correct.
 :)
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IanG

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Re: Compact 12V UPS for modem/router
« Reply #13 on: July 03, 2019, 08:48:41 AM »

If we are being scientific, the unit of energy storage is of course the joule, or watt-second. However, since 1 Wh = 3.6 kJ, its use is liable to confuse the masses, but might please those who would rather honour an Englishman than a Scotsman. :)
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sevenlayermuddle

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Re: Compact 12V UPS for modem/router
« Reply #14 on: July 03, 2019, 09:13:20 AM »


I can see both sides of the story. :)

So far as I have been able to ascertain from internet sources as well as my own dictionaries, the original term 'battery' seems to have been assigned to a collection of big artillery pieces, used for battering your  enemy, hence the word.    If wikipedia is to believed, and who am I to doubt it, Benjamin Franklin then used the word 'Battery' to describe a collection of Leyden Jars, by analogy to a battery of cannon.    I wonder whether the fact that such a setup might have looked threatening and sinister to a contemporary audience, might have  played a part in his decision to use that term?

Thereafter, following Franklin's precedent, which was modern usage itself in his days, 'battery' seems to have fallen into use to describe any collection of similar things.

On balance though for the things that power my portable radios and torches,  I'm sticking with modern usage, which is one or more cells.  I think I'd argue that if we are going to object to modern usage of 'battery' to describe a single cell, should we not also object to Franklin's decision to use the word in the first place, as no matter how many cells are used, they are not actually battering anything in the way that the originally artillery battery did?

If we are being scientific, the unit of energy storage is of course the joule, or watt-second. However, since 1 Wh = 3.6 kJ, its use is liable to confuse the masses, but might please those who would rather honour an Englishman than a Scotsman. :)

I certainly agree, mAh is a rather useless term in the usual context.  I have designed devices that I know will consume certain currents, and I want to know how long they will last on a set of batteries before the lights go out.  In practice, the mAh capacity does not tell me that.  Instead I need to find some rather elusive manufacturer's discharge curves, and identify the point on the graph at which the voltage will drop to the point at which my device's lights go out, with my device's current draw.  But I am not sure either of these terms solves that problem, so no strong preference. :D
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