Here’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.