Convert half-wave rectified to AC?

What's the question?

John

Per snipped-for-privacy@aol.com, the OP:

"I have a half-wave rectified signal (half of 120 Vac passed through a diode), and I would like to convert it to a ~60 Vrms wave that is clean enough to run a small AC motor.

Is this even possible?"

--Winston

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Very nice! :-)

Thanks, John!

--Winston

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That's not very considerate, John.

Instead of that .gif bullshit, why didn't you just post the circuit
list so that we could run it without having to copy it manually?

Bullwhat?

If you were interested in what's going on here - which you probably aren't - you could enter it yourself in 30 seconds.

I post an interesting circuit, and you have nothing to say about the electronics content, you just snivel about the way I posted it.

You have become a chronic whiner. Nobody likes a whiner.

John

Yes, but it's expensive. You could put a BMF capacitor in series with the pulsating DC; I'm not going to speculate about the cap value - too many variables. Like, what's the impedance and PF of the load?

Good Luck! Rich

interesting, the transformer sees about the same flux it would have without the diode present. (only 10% more) and the settling time is reduced. so a tranformer wound for 10% extra voltage should be fine. probably easiest to just use a 230V transformer

I notice that the capacitor despite being specified to 6 digits can be varied +/- 50% with little effect on the transformer

with a capacitor of that size something should be done to protect the rectifier from power-on transients. (set the phase to -180 degrees (on the AC supply) and turn on "skip initial operating point" (under "edit run command"))

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?? 100% natural

"Winston"

** A power transformer primary is NOT an inductor !!!

Any current flow in the primary winding that is not the result of load current in the secondary must not exceed I mag or gross core saturation will occur.

( I mag ranges from about 0.5% to 10% of rated primary current for commercial transformers.)

Iron cored * inductors * have deliberate air gaps in the core (while transformers have none) which sets up a usable current level that will avoid core saturation. Such gaps also dramatically reduce the inductance figure compared to the un-gapped case.

As I have already posted, the OP merely needs a suitable series cap ( poly film) to drop 60 volts off the AC supply to his motor.

Here's a tip, never suggest anyone feed a mains transformer primary via a diode - less you want to start a fire.

.... Phil

Most don't. Welding transformers can have a large adjustable air gap. Ignition coils (autotransformers, yes?) operate with large amounts of D.C. present through the primary.

Could you post your LTSpice .asc of that for me please?

If the supply were alternating current, that'd work if efficiency and D.C. offset across the motor weren't considerations. The supply is pulsed D.C. though.

If we are free to change the request, I hereby redefine the OP's requirement:

WAS:"I have a half-wave rectified signal (half of 120 Vac passed through a diode), and I would like to convert it to a ~60 Vrms wave that is clean enough to run a small AC motor."

IS:"I have a 60 Vrms sinewave, and I would like to convert it to a ~60 Vrms sinewave that is clean enough to run a small AC motor."

The task is now somewhat simpler, yes? :)

Normally a good idea. If you run the simulation, you'll see that the worst-case D.C. component through the unloaded primary is ca. 9 milliamps. Any EI core transformer over 250 W should have no problem.

--Winston

Have you considered a brushed motor? A big capacitor and a half wave source should drive it easy. It may have to be a 24 volt motor, though.

The brushed motor will run on either AC or DC. mike

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You didn't understand it then, huh?

An even simpler circuit might be good enough for a motor. We may have = lost=20 the OP, but I don't believe he really means to require the half wave = diode.=20 It was probably just an example of an easy way to get 1/2 the voltage = from a=20 common AC source, just as a simple diode lamp dimmer. The following = circuit=20 merely adds a resistor load for the pulsing DC and a capacitor to remove =

(most of) the DC component to the motor (which I simulate with an = inductor).

Paul

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=

Version 4 SHEET 1 880 680 WIRE 160 96 64 96 WIRE 256 96 224 96 WIRE 288 96 256 96 WIRE 400 96 352 96 WIRE 64 144 64 96 WIRE 256 144 256 96 WIRE 400 144 400 96 WIRE 64 272 64 224 WIRE 256 272 256 224 WIRE 256 272 64 272 WIRE 400 272 400 224 WIRE 400 272 256 272 FLAG 64 272 0 SYMBOL voltage 64 128 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value SINE(0 172 60 0 0 0 60) SYMBOL diode 160 112 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D1 SYMATTR Value MUR460 SYMBOL res 240 128 R0 SYMATTR InstName R1 SYMATTR Value 100 SYMBOL cap 352 80 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C1 SYMATTR Value 5000=B5 SYMBOL ind 384 128 R0 SYMATTR InstName L1 SYMATTR Value 100m TEXT 30 296 Left 0 !.tran 1 startup=20

"P E Schoen"

An even simpler circuit might be good enough for a motor. We may have lost the OP, but I don't believe he really means to require the half wave diode. It was probably just an example of an easy way to get 1/2 the voltage from a common AC source, just as a simple diode lamp dimmer.

** The OP could even use a common, triac based, wall plate dimmer set to about 1/3 duty cycle.

This will give 60 volts rms.

.... Phil

I agree but without clarification from the OP, we're stuck with the constraints and requirements in his post.

That probably would work, though we'd be depending on back EMF to clean up the waveforms. :) It appears to be about 20% efficient and there'll probably be vibration and power factor penalties to be paid due to the very non-sinusoidal power into the motor.

The resonant transformer appears to provide somewhat better efficiency and very sinewavey voltage and current.

Thanks, Paul.

--Winston

More blather.

John

From past posts in other forums I believe Mr. "eromlignod" does not have that modus operandi. He may have been left behind on the far side of the Google divide...

-- Roberto Waltman

[ Please reply to the group. Return address is invalid ]

Ah. That's too bad.

Based on his posts here, he appears to be a fine fellow, even if he does spell 'dongilmore' strangely.

:)

--Winston

But "Eromlignod" sounds so much more fun - it brings to mind castles and dragons and warrior princes an' shit. ;-)

Cheers! Rich