Why do UPS have such tiny batteries?

It's a BIOS setting (usually).

Sometimes it's called "S3 action" or similar.

Back in 2007 we had an SQL server that took 90 minutes to come up. We had to do quite a bit of planning when it was virtualised to live without it for that time. I think the whole procedure was complicated by it being clustered - so 2 servers but one disk server.

Coupled with local power generation (solar panels) that's a greenie wet dream.

Pius don't really have a bios as such. Or an on off switch

Well local solar panels are simply not good enough.

In winter....

Doesn't solve the solar problem.

My solution to this is to power lots of 'small' kit (networking, phone, Raspberry Pi, etc) from power-over-ethernet (PoE), using cheap PoE to

Then everything is powered by 48V from the PoE switch. Should I need to, I can stack some drill batteries to get that power, or just put the switch on a UPS and it'll then feed power all the nodes that are plugged into it.

Obviously this needs an ethernet run to each node so is no good for mesh nodes without a wired backhaul. But it is an option if running a few strategic ethernet cables is easier than running a full mains circuit, and likely gets better runtime than having a swarm of wallwarts powered from a UPS.

One other nice thing about PoE is you can turn ports on and off from the PoE switch (web UI or SSH command line), and see their power consumption. So if you do have to sequence the power-up of the ports, you could do that from a browser or write a script to do that.

(although having wired backhaul for your mesh nodes may eliminate the reason for the sequencing in the first place!)

Theo

Everything before the Pi 5 will just turn on when power is applied - there's no power management or anything. The Pi 5 has a more conventional 'soft' on/off button (ie you can 'shutdown' and later press the button to power on again), but I'm not sure you can set it to not boot when power is applied - I think it'll always boot the first time.

Theo

I have been running a RasPi for a few years powered by PoE. I used a cheap Chinese PoE to 5V adapter but discovered one gotcha on the way. Some of these adapters are isolated between input and output which is fine, but others have a DC connection between the negative input and the negative output. If the PoE switch uses positive ground - which is not unusual - then interesting things happen when the i/o of the Pi is connected to some other earthed device. John

You can play silly buggers with shutdown for a safe stop and using a few other methods to 'add' a power switch.

I suppose you could do something with a relay latch circuit or whatever so that power restore keeps it in the 'off' position and you have to actively press a button to turn it on. You could do that with pretty much anything mains powered - not specific to Pis.

Theo

Sure, but *86 doesn't need it .

Not exactly a UPS but if you want to keep things running during a power cut then consider some of the portable power stations like Jackery, Anker and Bluetti just to name a few. I do not think you can leave permanently plugged in like a UPS but could get several hours of power during a power cut the only problem is if the components that make up your network are spread about then you may have a number of extension leads snaking about.

Richard

Nice, although I expect many SOHO users might find the ~£8,700 price a tad on the steep side :-)

One of the limitations on economical UPS design, and using extra batteries, is that customers expect them to be able to charge up the batteries again quickly. A custom solution can trade speed of charge up against economy on the size and cost of the electronics.

That's interesting, I hadn't come across that. Most of the cheap adapters are non-isolated, but I was working on the basis that that's not a problem if everything connected has a common ground rail. If you're doing GPIO stuff then it might be more of an issue - there are isolated PoE adapters for that use case (including the official PoE hat). Microcontroller boards with integral PoE (like ESP32s) can come with either non-isolated or (more expensive) isolated power.

I hadn't considered the PoE might be positive-earth! What kind of gear does that?

Theo

One of the problems with lead acid batteries, is lifetime and replacement policy. If you had four of them hooked up, you might have a need to match their behavior for best performance. That means after three years, you could be replacing all four. You would want to run the numbers and see how this rental scheme looks. You are running the SLA version of battery, because it does not emit hydrogen (most of the time).

My first UPS battery lasted ten years, the replacement(s) have lasted only three years. The last battery, three cells were failed short, and the battery was a "six volt" when pulled :-) I could tell something was wrong, because my SPS class UPS was "warm" and such UPS are supposed to be ice-cold most of the time. There is nothing wrong with the UPS itself, it floats the 12V battery at 13.5V . When I replace the UPS battery, I leave the cover off for the first day, and check the float when it is fully charged (it's a UPS without an LCD on it).

The Tesla Power Wall, has an interface on it for a short string of solar panels or so, which does not allow you to isolate yourself from the grid, but under some circumstances allows running a very limited number of loads. (It serves to prop the battery up a tiny bit.) It's going to be hard to find a competitor with exactly the same feature set, to help drive the price down. Some large battery solutions have lousy feature sets by comparison (limited modes, manual switching).

Such devices do have the advantage of actually working and not being a science experiment. They may have sufficient inverter capacity, to turn over fractional horsepower electric motors. Without the lights blinking all the time.

If you run a "whole-house battery" from an emergency generator, it allows the generator to be run in episodic mode and you could, say, charge the batteries in four hours and run off the battery for the next twenty hours. This avoids the normal wasted petrol or diesel on running the emergency generator 24 hours a day (even though some intervals are drawing minimal power). The emergency generator should not be run at rated load, because it isn't really rated properly (it overheats at rated load). When charging the batteries, the charger has to be set to take it easy on the generator. Maybe you run your 22kW generator at 11kW.

Some solutions, you can run them in charge mode or you can run them in battery mode, but not both at the same time. The Powerwall allows both as far as I know. And that's what a full-featured solution offers. Even if you can afford only one of those, you can provide support electricity for the heating system with it (just barely, for the motor start issue). Inverters don't really like inductive loads, which is why the rating must be about 10x the motor nameplate (10x being the "stall rating"). A typical Powerwall install in the past, used two of them. When teamed, the model number of each unit might be different.

One potential source of stationary power, would be "rejected automotive BEV packs". If they only offer 70% of their original range, the driver might no longer be using that for mobile operation. But such a pack, would be the start of a nice stationary home power solution. When the thing is parted out, it will likely be devoid of charging infrastructure (that's the DIY part of the experiment).

Some BEV vehicles already come with V2H or V2V capability, but not usually at a level sufficient to run absolutely everything. If you were a two vehicle home, the V2H vehicle could stay home, while the family shares the other car. Maybe you could run one motor off that, intermittently, for a day or two or three.

Lead acid is a stable chemistry, but most suppliers cut corners on fabrication, making it a miserable investment. That's why I can't get too excited over the prospect of using them. If they lasted seven years, that's a lot better than "almost making it to three years".

When I quote a Tesla Powerwall, it's not because I want you to buy one. It's the feature set which is an aspiration for some competitor to match, and we wait for that to happen. One home power source company, does lots of advertising and promotion, but their feature set is "somewhat or completely, lacking". You're supposed to enjoy unplugging the load and connecting the generator to it in the dark.

Lithium has dropped in price from a thousand per kwH to maybe one fifty. Yet, when you price some of these items, the retail price is still around the thousand level per kWh. That's why a used BEV pack could be attractive, assuming it isn't (outright) damaged and the capacity loss is just the normal level of loss.

One commercial company, is already recycling BEV packs for stationary power purposes. I don't think they have shipped too much product quite yet. I'm sure the insurance industry is trying to figure out what premium to charge, when this is slapped up-side the house :-)

Paul

I had actually wondered if this would be a good alternative for a home battery often offered with Solar panels.

Charge up with solar during the day, charge overnight with E7 electricity and then run the whole house off the APC UPS provided (a) you dont mind the (a) periodic beeping in cases of insufficient solar and (b) you dont have high loads like electric showers or electric cookers!

We have gas hot water, gas central heating and gas cookers here so going from a 100A capable national grid supply (22kW) to an UPS based 40A supply (10kW) would be doable.