Convert half-wave rectified to AC?

E

eromlignod

Guest
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?

Don
 
In article <18bb3070-9af7-43ed-b262-
9e34190ba8f5@e7g2000vbw.googlegroups.com>,
eromlignod@aol.com says...
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?
Click to expand...
An Uninterruptible Power Supply from your
local computer store might work.

Not sure how they'd react to pre-rectified
power, but you could always experiment...
 
On Fri, 29 Jul 2011 08:57:45 -0700, eromlignod wrote:

Gentlemen:

I'm an ME, not a EE so be gentle with me.

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.
Click to expand...
It'd be much easier if you could reach across that diode and just apply
your 120VAC to a 2:1 step-down transformer.

How small a motor? How much current is available on the half-wave
rectified DC?

I'm not sure that there's an off the shelf device that could do this
(unless the suggestion of a UPS pans out). Filtering the DC and then
converting it to AC may work. How you'd do that without building most of
a UPS, or hacking it, I don't know.

Filter the DC, find a DC-DC converter that can go from that raw DC to
12V, plug the output of that converter into the battery port of a UPS,
plug your motor into that. It's way overkill, but it may work.

Use the DC to actuate a relay, that switches a 2:1 stepdown transformer,
plug the thing into the wall...

If it's really half an AC wave and it stays that way no matter how you
load it, then putting in a honking big blocking cap and applying it
directly to the motor may work. It may not, and if it did it may be more
expensive than custom electronics in quantities more than 10 or so, but
it may work.

--
www.wescottdesign.com
 
eromlignod wrote:
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?
Click to expand...
For a small enough motor, I think it is.
(This would not perhaps be practical for
production.) :)

Push the half wave into a parallel 'tuned tank'
composed of a power transformer primary in parallel
with a lot of 'motor run' capacitors. You have a resonant
transformer that synthesizes the negative half
cycles to create a full A.C. sine wave output
on the secondary.

http://en.wikipedia.org/wiki/LC_circuit
http://www.play-hookey.com/ac_theory/ac_transformers.html

Plug 7.036201 microfarads and 1 Henry
into this calculator to see how close you can
get to 60 Hz:
http://www.calculatoredge.com/new/resonance.htm

--Winston
 
Winston wrote:
eromlignod wrote:
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?

For a small enough motor, I think it is.
(This would not perhaps be practical for
production.) :)

Push the half wave into a parallel 'tuned tank'
composed of a power transformer primary in parallel
with a lot of 'motor run' capacitors. You have a resonant
transformer that synthesizes the negative half
cycles to create a full A.C. sine wave output
on the secondary.

http://en.wikipedia.org/wiki/LC_circuit
http://www.play-hookey.com/ac_theory/ac_transformers.html

Plug 7.036201 microfarads and 1 Henry
into this calculator to see how close you can
get to 60 Hz:
http://www.calculatoredge.com/new/resonance.htm

--Winston
Click to expand...
http://www.surpluscenter.com/sort.asp?catname=electric&keyword=EMRC
 
"eromlignod"
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?
Click to expand...

** No

Rectified AC is DC, the ripple frequency is 30Hz.

Run your motor via a suitable cap from the 120V.


..... Phil
 
On Sat, 30 Jul 2011 08:49:30 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"eromlignod"
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?


** No

Rectified AC is DC, the ripple frequency is 30Hz.
Click to expand...
Uh, would you please tell us how a diode divides the frequency by two?

John
 
eromlignod expressed precisely :
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?

Don
Click to expand...
Wots your REAL Problem?
This sounds like a silly thing to want to do so you will only get silly
answers.
If your starting SIGNAL is only a SIGNAL i.e. no real power, then you
are not going to get anywhere without some form of amplification to get
the power and in that you could generate whatever type of output you
need.

Hypothetical questions are very difficult to answer.
Please tell us your REAL problem. :-?

--
John G.
 
eromlignod wrote:
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?

Don
I suppose you could construct a bridge that would pass the ON time
Click to expand...
of the 120v to the motor lead while the other lead is connected to the
common. Mean while as this is taking place, it is also
charging a large cap.. WHen the incoming sine wave drops near 0 volts
you then would have a triggered circuit to switch that bridge so that
now the charged cap is in a reverse manner and thus generating a (-)
signal. The start of the sine wave regenerating from the incoming
will simply shut this switch off and go back to repeat the cycle.

Actually, as I think about it, you wouldn't even need a full bridge, a
half bridge would do it, you only need to short the (+) of the cap to
the common lead of the motor and open the common of the cap from the
common of the system coming in. You can do this because the DIODE you
are using will block the (-) coming in and there for, shorting this
will not cause any unwanted blue smoke!

If you look at charge pump voltage generating circuits, you can
see where opposite polarities of power can be obtained. Many times

Why not just use a step down transformer?

Jamie
 
"John Larkin"
"Phil Allison"
"eromlignod"


I'm an ME, not a EE so be gentle with me.

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?


** No

Rectified AC is DC, the ripple frequency is 30Hz.

Uh, would you please tell us how a diode divides the frequency by two?
Click to expand...

** My bad.

Was thinking about half and full wave rectification.

You cannot connect an AC motor via diode or diode plus cap in series, it
will fail to spin and or burn.



..... Phil
 
"John Git"
eromlignod

I'm an ME, not a EE so be gentle with me.

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?


Wots your REAL Problem?
Click to expand...
** The OP has stated it.


If your starting SIGNAL is only a SIGNAL i.e. no real power,
Click to expand...

** Read the OP's first line.

He has no idea of the special meaning of the term "signal" in electronics.


Hypothetical questions are very difficult to answer.
Please tell us your REAL problem. :-?
Click to expand...

** The unwritten rules of usenet require that posters never reveal their
actual purpose.

Cos that would spoil the magic.



..... Phil
 
On 2011-07-29, eromlignod <eromlignod@aol.com> wrote:
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?
Click to expand...
the functional opposite of a rectifier is an inverter, so yes it's
possible. it's not simple however.



Don
Click to expand...

--
⚂⚃ 100% natural
 
On 2011-07-29, eromlignod <eromlignod@aol.com> wrote:
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?
Click to expand...
Usualy you need an inverter to get AC from DC. someone else suggested
a UPS, Common Uninterruptable power supplies use an inverters to convert DC from
a secondary battery to AC in th event of a power falure.


If your DC supply is also poweing a DC load you may be able to extract
a small amount of AC by puttign a choke in series with the rectifier

||
+---||----------
| ||
| AC load
|
----->|-+--wwwww--+-----
===== |
|
in ===== DC load
|
|
-----------------+-----


The waveform that the AC load sees will have lots of harmonics and
the voltage will vary depending on the size of the DC load and the AC
load

it may be a easier idea change to a motor that can handle DC
(eg BLDC, PM, or universal)

--
⚂⚃ 100% natural
 
Winston wrote:
Winston wrote:
eromlignod wrote:
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?
Click to expand...
Notice how the current in the primary becomes
'almost symmetrical' within about half a second
of startup:

Version 4
SHEET 1 880 680
WIRE -64 16 -128 16
WIRE 224 16 0 16
WIRE 448 16 224 16
WIRE -128 80 -128 16
WIRE 656 80 560 80
WIRE 448 96 448 16
WIRE 560 96 560 80
WIRE 224 112 224 16
WIRE 656 112 656 80
WIRE 560 224 560 176
WIRE 656 224 656 192
WIRE 656 224 560 224
WIRE 448 240 448 176
WIRE 560 240 560 224
WIRE -128 256 -128 160
WIRE 224 256 224 176
FLAG 224 256 0
FLAG -128 256 0
FLAG 448 240 0
FLAG 560 240 0
SYMBOL cap 208 112 R0
SYMATTR InstName C2
SYMATTR Value 7.036201ľF
SYMBOL ind2 432 80 R0
SYMATTR InstName L1
SYMATTR Value 1
SYMATTR SpiceLine Rser=.01
SYMATTR Type ind
 
Winston wrote:
Winston wrote:
Winston wrote:
eromlignod wrote:
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?

Notice how the current in the primary becomes
'almost symmetrical' within about half a second
of startup:
Rather:
Click to expand...

Version 4
SHEET 1 880 680
WIRE -64 16 -128 16
WIRE 224 16 0 16
WIRE 448 16 224 16
WIRE -128 80 -128 16
WIRE 656 80 560 80
WIRE 448 96 448 16
WIRE 560 96 560 80
WIRE 224 112 224 16
WIRE 656 112 656 80
WIRE 560 224 560 176
WIRE 656 224 656 192
WIRE 656 224 560 224
WIRE 448 240 448 176
WIRE 560 240 560 224
WIRE -128 256 -128 160
WIRE 224 256 224 176
FLAG 224 256 0
FLAG -128 256 0
FLAG 448 240 0
FLAG 560 240 0
SYMBOL cap 208 112 R0
SYMATTR InstName C2
SYMATTR Value 7.036201ľF
SYMBOL ind2 432 80 R0
SYMATTR InstName L1
SYMATTR Value 1
SYMATTR SpiceLine Rser=.01
SYMATTR Type ind
SYMBOL voltage -128 64 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value SINE(0 170 60 0 0 0 100000)
SYMBOL diode -64 32 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D1
SYMATTR Value MUR460
SYMBOL ind2 576 192 R180
WINDOW 0 36 80 Left 0
WINDOW 3 36 40 Left 0
SYMATTR InstName L2
SYMATTR Value .2525
SYMATTR SpiceLine Rser=.01
SYMATTR Type ind
SYMBOL res 640 96 R0
SYMATTR InstName R1
SYMATTR Value 600
TEXT -160 472 Left 0 !.tran 0 10 0
TEXT 464 56 Left 0 !K L1 L2 0.99
 
Jasen Betts wrote:
On 2011-07-29, eromlignod<eromlignod@aol.com> wrote:
Gentlemen:

I'm an ME, not a EE so be gentle with me.

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?

the functional opposite of a rectifier is an inverter, so yes it's
possible. it's not simple however.
Click to expand...
One transformer, one capacitor.

That's pretty simple. :)

--Winston
 
Jamie wrote:

(...)

Why not just use a step down transformer?
Click to expand...
Efficiency.
Add a tuning cap to the primary of that transformer
and input power falls by about 50%.

--Winston
 
On Sat, 30 Jul 2011 11:09:33 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"John Larkin"
"Phil Allison"
"eromlignod"


I'm an ME, not a EE so be gentle with me.

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?


** No

Rectified AC is DC, the ripple frequency is 30Hz.

Uh, would you please tell us how a diode divides the frequency by two?


** My bad.

Was thinking about half and full wave rectification.

You cannot connect an AC motor via diode or diode plus cap in series, it
will fail to spin and or burn.



.... Phil
Click to expand...
I can think of a magic black box that would work. The front-end would
have just the right size fuze across the input, and the first thing it
would do is blow out his half-wave rectifier, shorted.

John
 
On Sat, 30 Jul 2011 11:14:17 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"John Git"
eromlignod

I'm an ME, not a EE so be gentle with me.

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?


Wots your REAL Problem?

** The OP has stated it.


If your starting SIGNAL is only a SIGNAL i.e. no real power,


** Read the OP's first line.

He has no idea of the special meaning of the term "signal" in electronics.


Hypothetical questions are very difficult to answer.
Please tell us your REAL problem. :-?


** The unwritten rules of usenet require that posters never reveal their
actual purpose.

Cos that would spoil the magic.
Click to expand...
The second rule is that they post the question and never return,
leaving the regulars to debate the issues for some weeks.


John
 
On Sat, 30 Jul 2011 11:09:33 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"John Larkin"
"Phil Allison"
"eromlignod"


I'm an ME, not a EE so be gentle with me.

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?


** No

Rectified AC is DC, the ripple frequency is 30Hz.

Uh, would you please tell us how a diode divides the frequency by two?


** My bad.

Was thinking about half and full wave rectification.

You cannot connect an AC motor via diode or diode plus cap in series, it
will fail to spin and or burn.



.... Phil
Click to expand...
Actually, you can use a diode to generate subharmonics:

ftp://66.117.156.8/SubHarmonic.gif

John
 
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