Hi, I’ve been looking at for example Powerwalker AVR (Automatic Voltage Regulators) units. They are not very expensive and provide a more stabilized mains voltage. I’m curious how they make it work. Given the price there cannot be too much magic inside the box.
Regards, Gerrit
Regards, Gerrit
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Usually it has an autotransformer (like variak) with stepped winding. And of cause some microcontroller (with relays) which choose needed step (output winding).
Steps can be about -10%, -5%, 0%, +5%, +10%.
Steps can be about -10%, -5%, 0%, +5%, +10%.
I believe the model you show is an Uninterruptible Power Supply (UPS). They are often designed as an AC-DC-AC converter. You convert a varying or noisy AC at the input into a stable DC-link voltage (AC-DC). That DC-link voltage you may buffer with an accumulator/accu (battery). The stable DC-link voltage you then convert into a stable AC output voltage (DC-AC). You may know the rather cheap DC-AC inverters used for mobile use. The AC-DC convertion may be even simpler to make than the DC-AC part.
Hi FauxFrench, this is not a UPS (it has no battery) and it’s too cheap to allow for AC-DC-AC conversions. I have enough experience with UPS devices from 500 to 5000 VA. This is different, as Vovk Z already pointed out. I would like to see a schematic in detail.
Regards, Gerrit
Regards, Gerrit
This AVR device and cheap UPS with AVR has almost the same AVR unit. The difference is that UPS has transformer (but not autotransformer) and batttery with DC-AC coverter which feeds low-voltage winding. I mean high-voltage winding and core of the transformer and autotransformer is the same in general.
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There are several types. The oldest is a resonant constant voltage transformer. It use a saturated core to allow any voltage above the minimum design value to saturate the core. That way the secondary produces a consistent voltage, although with high distortion. They are noted for having a resonant capacitor with them to minimize power waste. Sola is perhaps the best known brand.
A more current technique is to use a small transformer and place the primary across the AC mains and the secondary in series with the mains. By using a tapped secondary the output voltage can be adjusted. By reversing the primary leads the output voltage can be dropped if needed. Typically the taps are spaced about 3 volts apart. Five taps would give a 30 volt correction range. This is called a boost or buck transformer type.
Now a system that uses a boost transformer into a voltage doubler circuit could then be used to essentially use a power amplifier stage to reproduce a clean sine wave of the correct voltage and frequency. However it turns out many audio loads work better if the frequency of the AC mains is increased by about 50%.
Then there is the UPS approach. Turn the mains power into a lower DC voltage that is backed up by a battery and then use an inverter to provide the AC mains voltage. Cheap ones produce a high distortion output sine wave. Better ones use pulse width modulation to make the output look more likes sine wave. For voltage correction only no battery is needed.
The final method I know of is to use a small amplifier and to place it in series with the AC mains and adjust the driving sine wave source to adjust voltage, frequency and phase to produce a clean stable output voltage.
A more current technique is to use a small transformer and place the primary across the AC mains and the secondary in series with the mains. By using a tapped secondary the output voltage can be adjusted. By reversing the primary leads the output voltage can be dropped if needed. Typically the taps are spaced about 3 volts apart. Five taps would give a 30 volt correction range. This is called a boost or buck transformer type.
Now a system that uses a boost transformer into a voltage doubler circuit could then be used to essentially use a power amplifier stage to reproduce a clean sine wave of the correct voltage and frequency. However it turns out many audio loads work better if the frequency of the AC mains is increased by about 50%.
Then there is the UPS approach. Turn the mains power into a lower DC voltage that is backed up by a battery and then use an inverter to provide the AC mains voltage. Cheap ones produce a high distortion output sine wave. Better ones use pulse width modulation to make the output look more likes sine wave. For voltage correction only no battery is needed.
The final method I know of is to use a small amplifier and to place it in series with the AC mains and adjust the driving sine wave source to adjust voltage, frequency and phase to produce a clean stable output voltage.
I've repaired an old unit one time (broken analog voltmeter).
Inside there was a toroidal variac and an arm connected to a motor which swung over the transformer windings. There was also a little board for controlling the motor.
Inside there was a toroidal variac and an arm connected to a motor which swung over the transformer windings. There was also a little board for controlling the motor.
Hi, I once made this myself using a 3KW variac with an electromotor. I measured the filament voltage on high power transmitter tubes and a small circuit adjusted the variac with the motor. It worked fine, but of course the reaction time was very slow (but fine for keeping the filament voltage within a few percent).
Regards, Gerrit
Regards, Gerrit
There is a remarkably cogent explanation HERE. You did not cite/link it so you may not have read it.
The drawing includes battery models but you say you found one with no battery. So where the graph says "battery" yours does nothing (I hope it cuts-out, doesn't pass proportional over/under-voltage).
It is just a 3-tap autotransfomer. Actually the "Normal" is straight-through and the Boost and Buck may be the same winding wired one way or the other. So it reduces to a 30VAC winding rated for load current. So the 1500VA model is a 30V 6.5A or 200VA transformer, a couple line-current relays, and logic. (One I had was a heap of TTL DIPs; today would be a $2 PIC.)
It does not regulate "tight". It appears it will allow a bad voltage to persist for quite some time, 10s to 3 minutes.
Ah, text indicates this model has -10%, 0%, +20%, +40% corrections (4 taps). In my terms, the output is "almost legal" but far from "constant". I hope I never live/work any place this would do any good. So far I have not, even when flooding or backhoes caused longterm strain on a city power distribution.