Single Phase Compressor 110 V @ 230 V

Get hold of a small "site transformer". Many small and large industrial equipment runs on 115V and uses these transformers to provide safety isolation while dropping 230V down to 115V. The compressor might run a little slower (maybe a little less pressure) but it should still work OK.

Brian.

Hi,

maybe a (second hand) autotransformer is all you need.

Klaus

Hi,

I already thought about a site-transformer / autotransformer, but my friend does not want to put an other place consuming device in his quite limited "working area", especially as a new 230 V compressor does not cost that much compared to a transformer solution (cheapest used autotransformer including shipping ~50 €).

Thanks for your input!

AC-to-AC voltage doubler. Uses few components. Hasn't been tested at your expected power levels. Your weblink is to a compressor rated 1/3 HP (which calculates as 250 Watts according to convention of 760 W per HP).

The concept is a bridge-style charge pump. Normally it outputs DC. To make the converter provide AC, install a half-bridge. Auto-biasing turns each transistor on-and-off appropriately. Current declines through each transistor as a capacitor discharges, making wasted power less severe.

The 1 ohm resistor is unnecessary. The inductor corrects power factor to some extent, reducing spike-y behavior.

Hi @BradtheRad

thank you for your effort and input, but actually a 110 V load/compressor schould be operated in europe with 230 V. So there is no 110 V supply available at all. Prefarable, the 110 V rated compressor should be operated by the 230 V power-grid.

BR

stenzer said:

110 V load/compressor schould be operated in europe with 230 V.

Click to expand...

Aha, I get it now. Trying a second time...

This simulation is an AC in AC out voltage reducer. Four capacitors, 8 diodes, PNP, NPN.
The network at top creates positive polarity. Bottom network creates negative.

The concept is like a voltage multipler in reverse. C1 C2 charge in series, then discharge in parallel through load.
C3 C4 perform similar cycle. Transistors are auto-biased at appropriate moments.

Hi Brad,

thank you for this interesting circutry! As this solution makes use of smiconductors I was curious about the power dissipation of the circuitry, so I performed an initial Spice simulation with arbitrary chosen components (just kept current and voltage rating in mind). The simulation shown below ended up in a power loss of about 295 W, which corrsponds to a loss of about 60 %.



Is there a way to increase the efficiency of the circuitry? The main loss-contributer here is the NPN transistor with about 115 W. Further, I had to decrease the base resistor values quite heavily, to achieve the desired 110 Vrms output voltage.

BR

Factor into account that the motor will run slower and may draw more current than it's normal rating would suggest.
Personally, I would go down the transformer route. From similar items on that page it would seem to be rated at approximately 150VA and may need more while building up pressure or starting.

Brian

stenzer said:

The simulation shown below ended up in a power loss of about 295 W, which corrsponds to a loss of about 60 %.

Is there a way to increase the efficiency of the circuitry? The main loss-contributer here is the NPN transistor with about 115 W. Further, I had to decrease the base resistor values quite heavily, to achieve the desired 110 Vrms output voltage.

Click to expand...

I reworked my simulation so it indicates power readings.
320 W drawn from mains (average).
220 W to load (average).
41 W wasted in each transistor (average).
68 percent efficient.

Transistors need careful adjusting in this design.
Bias resistor 1k causes 1/2 Amp peak current in the bias terminal!
Mosfet gates are ruined by high voltage.
IGBT may be a better choice for this topology.

I find there's a certain bias range where increasing the ohm value increases output voltage. (In simulation, that is. Real hardware may perform otherwise.)

Hi,

I guess the inductive part of the motor (phase shift) makes efficiency worse. And I expect the power to vary with air flow, how does the circuit react (output voltage, efficiency) when you reduce and increase (start up) the power drawn.

Klaus

Then there's this remarkably simple method to reduce AC voltage. Inductive impedance.
You can do it via:
* choke (single inductor of sufficient Henry value)
* coupled coils (of lesser Henry value).

Inductive reactance doesn't generate heat so it doesn't waste power (as does ohmic resistance).)
However inductive impedance does introduce power factor error. It can be corrected by a capacitor if you choose.



Getting back to ohmic resistance method of reducing 230 VAC...
A space heater with a nichrome element can do the job. Put it in series with the compressor. The idea is for it to present an equal ohm value as your compressor (possibly by choosing the proper High or Low intensity). Thus it drops 50% of AC voltage.

Hi,

all the methods expect a constant load. I´m not sure if this is the case.
I expect a differnt motor current on differnt operation modes (high/low pressure, high/low air flow)

If inductive voltage drop, why not capacitive voltage drop.
Both have their benefits and drawbacks. Both work with a constant ohmic load very satisfactory.

****
From my experience.
I once had the "brilliant" idea to use a capacitive voltage drop to drive a 110V transformer on 230V/50Hz mains.
Just a capacitor in series with the transformer primary.
The idea: V_capacitor = V_mains - V_transformer.
(Hint: While this formala is true for every V(t) it is not true for V(RMS) ).

So what happened:
The transformer at 100V drew about 4mA. The transformer with my "capacitive" voltage drop drew several 100mA.
Why: It´s because of the phase shift. The internal of a transformer could be simulated with a big inductance (reducing the no load current) in series with the resistance representing the copper winding.
So the inductance reduces the current and the copper winding sees only a tiny current (with a tiny voltage across the copper winding)
But in my circuit the capacitance "compensated" the series inductance. Almost forming a resonance. The series inductance could not limit the current anymore, resulting in high no load current.

What I want to say:
While it is more safe to use an "inductive" voltage drop on an inductive or resistive load
and using a capacitive voltage drop on a capacitive or resistive load.
.. one should not ignore the phase shift in the load.
To work properly one has to include the phase shift into calculation.
But neither the motor current, nor the pahse shift is known. And both can not be considered as constant.
So: it might work, but it also might cause problems.


Klaus

I admit my schematics above are more conceptual than practical.
Untested in hardware. They illustrate what might be possible among the list of 'second best' solutions if we can't use the preferred solution due to being unavailable or too expensive or takes up a lot of space, etc.

In order to work these into usable converters, an experimenter ought to have various inductors and capacitors on hand, to test how they affect waveforms. The aim is to optimize performance and maximize efficiency.
As well as to include safeguards.

What the world needs is an inductor (and coupled inductor, and transformer) whose Henry value is easily adjustable. Then a great many concepts would become practical which at present are not widely used because of lacking versatility with a variety of loads and operating modes.

stenzer said:

Hi,

a friend of mine bought a compressor for 110 V & 60 Hz [1] while he was living abroad. Now he would like to operate it at 230 V & 50 Hz. The compressor does not host any electronics, there is only a pressure sensor which breaks the mains-power when a certain pressure is reached. There is no wire diagram on the compressor, so I'm not sure if it can be rewired. Further, there are only 4 wires coming from the motor. Two of this wires are connected by a 250 V AC capacitor, which I assume belongs to the starter winidng. As there are only 4 wires available I assume it can not be rewired, as access two 3 windings (6 wires) would be required to do so. Unfortunatly, the compressor does not indicate who's the manufacturer, so I'm not able to get in contact with the manufacturer.

Is a rewiring/operation at 230 V & 50 Hz possible at all? What's the influence of the freuency?

BR

--- Updated Oct 22, 2022 ---

.... here the link.

[1] https://www.amazon.ca/gp/product/B07MDKB4YD/ref=ppx_yo_dt_b_search_asin_image?ie=UTF8&psc=1

Click to expand...

Maybe just a quibble, but...
The link shows a 230v/50Hz motor nameplate.