A friend of mine lives in a remote area. The power grid voltage fluctuates causing problems with his equipment. He has tried line filters with no success.
I suggested using a bank of SLA batteries as a "buffer".
IOW a grid-connected charger would keep the batteries topped up and current could be redrawn via a 110V inverter to power appliances.
In a nutshell, what would be the design criteria and limitations of such a system?
To what extent would it be practical to power an entire house?
The most economical solution to protect against fluctuations and also have protection against longer-term total outages would be to get one of the UPSes that can hold up critical equipment for a couple of minutes until a signal to the backup gas or diesel generator has been sent and it's powered up and ready to take over
The devil is in the details. Which equipment? What kind of problems? overvoltage? undervoltage? spikes? starting issues? ?????? real numbers on each? Can he be satisfied with 110V only? What happens when you turn on a 220V device like stove or clothes dryer or air conditioner?
What are the statistics and timing of the instabilities? What does the utility recommend? What does google have to say about it?
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Line filters are good for taking out very short spikes.
I have a small variac with a motor on it that takes out longer-term variations. It's only 500W, but the concept scales. There's an old concept that uses a ferroresonant transformer to provide some regulation. The name escapes me at the moment.
You might be able to do something similar with an active magnetic amplifier.
IMHO, anything requiring a huge battery capacity is a non-starter when you have the grid available. Depending on the details of the problem, it might be simpler to use a transformer to raise the minimum allowable voltage to an acceptable level and use something to buck it down below the maximum allowable. Magnetic amplifiers seem to apply here...depending on the requirements.
Requirements definition is the first hard part of the problem.
That's roughly what the Tesla Powerwall does. The problem is that it wasn't quite designed to deal with major outages and regulation issues. It's primary purpose is to charge up when the cost of electricity is cheap, and discharge when it's expensive. In other words, save money by reducing peak power requirements. That's not the same as what you're suggesting, which essentially is a off-grid solution, using grid power as a backup.
Ummm... cost, cost, and cost. Stationary batteries suitable for running a house are not cheap. In off grid power service, lead-acid batteries typical last 5 to 10 years and then need to be replaced. What kills them is mostly the number of charge/discharge cycles and the depth of discharge. In other words, the more you use it, the quicker you lose it. This article on various battery chemistries should help: The problem is that while lead-acid batteries are awful, the other alternatives can be equally awful. It's just that they have a different set of disadvantages.
More reading:
Switching to alternative or stored energy may also require your friend to make some lifestyle and consumption changes.
I have no idea because you haven't supplied any numbers. It's easy enough to do a back of the envelope estimate on the practicality of running on alternative energy sources and battery power. However, I need numbers in order to produce anything useful. There are numerous calculators online which should give you some idea of what numbers are required. For example: etc...
A good resource would be Home Power Magazine: If your friend has a way to generator power (solar, wind, hydro), and can reduce electicity consumption to a reasonable level, he can probably operate without any grid power. Or he could use grid power as a backup for his alternative energy system. There are lots of examples of such systems in the various articles.
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What is his load energy requirements ? Is this an intermittent flicker kind of issue or is it a constant voltage swing and constant brownouts ?
A complete house like in the city typically requires somewhere around
30 kW-Hours per day so might be harder to power. Battery based grid-tied inverter might help depending on how fast the voltage variations are. Could pass-through the grid to critical loads and if slow enough swings, generator-support or grid-support modes can smooth out drops in input voltage from the grid. But a WHOLE 200 amp service house would be a bit much unless it was divied up with more inverter/battery systems.
Check outbackpower and Schneider Electric (Xantrex) and SMA etc.
It would make much more sense to protect only the equipment that is prone to line fluctuations rather than the whole house.
For how long and with what criterion and budget? The way we did it for big telescopes was to have a reinforced flywheel going at a fair lick driven by an electric motor driving a dynamo. If the mains fails the clutch decouples the motor and the stored energy in the flywheel is used to stow the scopes and shut down the computers gracefully.
You have to be very careful where you point the flywheel - if it ever broke free it would go for miles. The reason for such an eleborate setup was that power would usually go at the onset of a storm and leaving the scopes unstowed could do untold damage. More than one big radio telescope has been trashed by wind loading problems or bad luck.
The problem you have is that to get a decent energy density storage is very expensive and comparatively high maintenance whether you do it chemically in batteries or mechanically in a flywheel or pumped storage.
About 30 years ago, I attended a trade show where they exhibited flywheel systems. I never understood how it was possible, and they sure didn't want to tell me, but they claimed that they wrote magnetic domains on the "flywheel" in real time so that the output frequency was RPM independent as the energy was extracted as a PM AC generator.
ISTR ours was quite crude in frequency regulation once decoupled. It was designed in the late 1960's. It was good for about 15 minutes and the computer shutdown things in order of their sensitivity/risk of damage.
Wright university have some materials on telescope construction and flywheels online that discusses optimal choice of materials.
You have to specify min max and duration of disturbances. There are many ways, apart from Tesla for long outrages, for just variations in voltage some of these may or may not work....
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At the top end building your own nuclear plant and making plutonium and developing the bomb and then declaring independence may get you support from the US weapon lobby MIC.
At the low end buy a Honda generator and store up on petrol. Price of petrol will go up with republicans in power, so buy long running call options on it too. You cannot go wrong, can always sell the fluid for more.
And you can cook on it too, and run a car on it. reps do not care about air pollution, so you will be fine. Sell electrickety to your neighbors and use the money for ura.. OK
An Online UPS does exactly what you need. The limitation usually would be the amount of power it can supply (dependent on the electronics) and the time it can supply that (dependent on the batteries).
Yep, it's a printed-pole generator. Those used to be standard for big computer rooms; I knew an architect who had to reinforce a concrete room in a new building, to hold one. Not a spectacularly bad idea, but you don't want to miss the bearing maintenance schedule.
Even older systems used an AC motor to drive a DC generator, with field winding modulation at the generator, to regulate computers' DC power.
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