supplying accurate output voltage < input voltage

L

Laurav

Guest
Can one get a control where you can specify the output AC voltage very
accurately, even though the input voltage isn't accurate?
It would be for input to my air turbine. The air turbine always needs
input voltage much lower than the line voltage. So the control
wouldn't need step-up circuitry.
With the rheostat that comes with my air turbine, it's very sensitive
to changes in the line voltage.
So I was thinking about bypassing the rheostat instead of buying a
power conditioner and trying to supply very accurate voltage to the
rheostat.
Laura
 
Does the voltage have to be regulated -- that is, automatically adjust as
the line voltage changes?

If not -- just stick a cheap DVM on the turbine!
 
On Jun 15, 8:37 am, "William Sommerwerck" &lt;grizzledgee...@comcast.net&gt;
wrote:
Does the voltage have to be regulated -- that is, automatically adjust as
the line voltage changes?
Click to expand...
I'm not sure. The turbine is very sensitive to changes in line
voltage. A change of 1 volt in line voltage causes a noticeable
change in airflow. However, there's a rheostat between the turbine
and the power source, could be the rheostat is very sensitive to
changes in line voltage. I could check that with my voltmeter I
guess.

If not -- just stick a cheap DVM on the turbine!
Digital voltmeter?
Click to expand...
 
On 6/15/2012 7:34 AM, Laurav wrote:
On Jun 15, 9:31 am, Robert Macy&lt;robert.a.m...@gmail.com&gt; wrote:

you didn't say how much power the turbine takes. and if it cycles once
in a while, or a lot.
I checked the output voltage of the rheostat on the AC setting of the
voltmeter, and it's about 104 volts.
I turn it up sometimes briefly. It uses about 1-2 amps.
Laura
I have a regulator box that has inside a motorized variac.
Click to expand...
Moves the variac to compensate for input voltage changes.
But its reaction time isn't very fast.
 
On Jun 15, 5:29 am, Laurav &lt;p...@cyberspace.org&gt; wrote:
Can one get a control where you can specify the output AC voltage very
accurately, even though the input voltage isn't accurate?
It would be for input to my air turbine.  The air turbine always needs
input voltage much lower than the line voltage.  So the control
wouldn't need step-up circuitry.
With the rheostat that comes with my air turbine, it's very sensitive
to changes in the line voltage.
So I was thinking about bypassing the rheostat instead of buying a
power conditioner and trying to supply very accurate voltage to the
rheostat.
Laura
Click to expand...
you didn't say how much power the turbine takes. and if it cycles once
in a while, or a lot.

Two ways come to mind:
1. you can use a passive 'regulator' [by Solar?] It's a resonating
transformer, so you have to specificy 50 or 60Hz. Very large for the
amount of power that goes through them, but they regulate to 1%, which
is around 1 Volt, then you could put a Variac after the regulator and
adjust the voltage pretty exactly. Not much wasted power here.

2. Another, but complicated way, is to use a Saturable Core Reactor in
series with your load. No current through control winding on core,
very small voltage to load. Maximum DC current through control winding
on core, and the reactor 'disappears', gone, so you get a lot of
voltage to the load, but not all. Combine with simple AC to DC bridge
circuit, resistors, and feed that current back into the control
winding [right phase] and voila! pretty EXACT voltage, and automatic.
If the technology is too daunting, post your request on craigslist,
http://YOUR_REGION.craigslist.org/egr for like $25 you can pick up a
technician or engineer who'll put it all together for you.
 
On 6/15/2012 5:29 AM, Laurav wrote:
Can one get a control where you can specify the output AC voltage very
accurately, even though the input voltage isn't accurate?
It would be for input to my air turbine. The air turbine always needs
input voltage much lower than the line voltage. So the control
wouldn't need step-up circuitry.
With the rheostat that comes with my air turbine, it's very sensitive
to changes in the line voltage.
So I was thinking about bypassing the rheostat instead of buying a
power conditioner and trying to supply very accurate voltage to the
rheostat.
Laura

You could use a Uninterruptible Power Supply (UPS). You'd need the kind
Click to expand...
that is always regulating the output voltage (an online UPS), rather
than just turning on when power is lost or sagging badly (a standby UPS).

See this article for further explanation:
http://www.pcmag.com/encyclopedia_term/0,1237,t=UPS&amp;i=53509,00.asp
 
On Fri, 15 Jun 2012 08:30:50 -0700 (PDT), spamtrap1888
&lt;spamtrap1888@gmail.com&gt; wrote:

The cheapest Sola constant voltage transformer still costs several
hundred dollars.
Click to expand...
Times have changed. While Sola products are rather expensive, there
are plenty of cheap constant voltage transformers on the market. For
example:
&lt;http://www.ebay.com/itm/260591849083&gt;
&lt;http://www.ebay.com/itm/360320802787&gt;
Like all good resonant power transformers, they buzz and run warm.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
spamtrap1888 wrote:

The cheapest Sola constant voltage transformer still costs several
hundred dollars.
Click to expand...
http://www.ebay.com/itm/Sola-Constant-Voltage-Transformer-23-22-125-Harmonic-Neutralized-Type-CVS-/270829055529?pt=LH_DefaultDomain_0&amp;hash=item3f0eab6e29

Yes, for *very* small values of 'several hundred'. :)

--Winston
 
On Jun 15, 9:31 am, Robert Macy &lt;robert.a.m...@gmail.com&gt; wrote:

you didn't say how much power the turbine takes. and if it cycles once
in a while, or a lot.
I checked the output voltage of the rheostat on the AC setting of the
Click to expand...
voltmeter, and it's about 104 volts.
I turn it up sometimes briefly. It uses about 1-2 amps.
Laura
 
On Jun 15, 6:31 am, Robert Macy &lt;robert.a.m...@gmail.com&gt; wrote:
On Jun 15, 5:29 am, Laurav &lt;p...@cyberspace.org&gt; wrote:

Can one get a control where you can specify the output AC voltage very
accurately, even though the input voltage isn't accurate?
It would be for input to my air turbine.  The air turbine always needs
input voltage much lower than the line voltage.  So the control
wouldn't need step-up circuitry.
With the rheostat that comes with my air turbine, it's very sensitive
to changes in the line voltage.
So I was thinking about bypassing the rheostat instead of buying a
power conditioner and trying to supply very accurate voltage to the
rheostat.
Laura

you didn't say how much power the turbine takes. and if it cycles once
in a while, or a lot.

Two ways come to mind:
1. you can use a passive 'regulator' [by Solar?] It's a resonating
transformer, so you have to specificy 50 or 60Hz. Very large for the
amount of power that goes through them, but they regulate to 1%, which
is around 1 Volt, then you could put a Variac after the regulator and
adjust the voltage pretty exactly. Not much wasted power here.
Click to expand...
The cheapest Sola constant voltage transformer still costs several
hundred dollars.
 
On Jun 15, 9:19 am, Winston &lt;Wins...@Bigbrother.net&gt; wrote:
spamtrap1888 wrote:
The cheapest Sola constant voltage transformer still costs several
hundred dollars.

http://www.ebay.com/itm/Sola-Constant-Voltage-Transformer-23-22-125-H...

Yes, for *very* small values of 'several hundred'.  :)
Click to expand...
In that case: even the cheapest Mercedes still costs $300, because
that's how much someone wants for one in the Penny Saver.
 
spamtrap1888 wrote:
On Jun 15, 9:19 am, Winston&lt;Wins...@Bigbrother.net&gt; wrote:
spamtrap1888 wrote:
The cheapest Sola constant voltage transformer still costs several
hundred dollars.

http://www.ebay.com/itm/Sola-Constant-Voltage-Transformer-23-22-125-H...

Yes, for *very* small values of 'several hundred'. :)


In that case: even the cheapest Mercedes still costs $300, because
that's how much someone wants for one in the Penny Saver.
Click to expand...
Yup.

There aren't too many $300 Mercedes that the seller will
accept back if the buyer is not satisfied however. :)

BTDT, forgot to pick up the teeshirt.

--Winston
 
Laurav wrote:

Can one get a control where you can specify the output AC voltage very
accurately, even though the input voltage isn't accurate?
It would be for input to my air turbine. The air turbine always needs
input voltage much lower than the line voltage. So the control
wouldn't need step-up circuitry.
With the rheostat that comes with my air turbine, it's very sensitive
to changes in the line voltage.
So I was thinking about bypassing the rheostat instead of buying a
power conditioner and trying to supply very accurate voltage to the
rheostat.
Laura
Click to expand...
Ah, now comes the clue.... You don't have problems with your
voltage..

It's a simple matter of mass air flow and your motor design..

You need a closed loop PID controller to keep that steady..


Jamie
 
Laurav wrote:

On Jun 15, 7:43 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net&gt; wrote:

Ah, now comes the clue.... You don't have problems with your
voltage..

It's a simple matter of mass air flow and your motor design..

You need a closed loop PID controller to keep that steady..


No, it's definitely very voltage-sensitive.
The guy who makes and sells the turbine told me that the motor speed
is linear with the voltage, in the range of 100-120 V.
The motor speed varies greatly over that range, from close to zero to
max.
Laura
Click to expand...
Yes, I hear you and still, it is a mass air flow and motor design
problem..

You most likely got a split phase shaded pole/capacitor motor that
is improperly being controlled.

Just your basic window fan motor that shifts greatly in speed under
just slightly altered conditions, including mass flow.

You need to closed loop controller...

Jamie
 
Laurav wrote:

On Jun 15, 8:58 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net&gt; wrote:


Yes, I hear you and still, it is a mass air flow and motor design
problem..


I haven't noticed that the motor speed is sensitive to anything else
besides voltage, and the guy who makes the motor says that's the only
thing that causes changes in speed.
You could send your suggestions to Turbine Products, see what he says.
In any case I need to deal with this particular motor, not some future
version.
Laura

Regulating the voltage is only going to fix part of your problem, the
Click to expand...
issues are that your motor design is very sensitive to RPM changes with
load changes.

If you were to sit down and attempt to calculate the difference in
voltage needed per RPM, you'll find that it's all over the place..

Motor speed in your case is like an inverse log, once you get it out
of the hole, it'll speed up greater than expected. It's all about slip
in an AC motor under load changes. AC motors do not have much torque at
the lower RPM, unless of course, you're doing vector mode, and I know
for a fact you're not doing that.

Your problem will not go away that easy how ever, a thyristor
controller may work a little better over having a rheostat, but then
again, you may have a slight drop on the high end of those.

what you have there is a low end design.. What you should have is a
brushless DC motor which requires a speed controller.. THey do make
integrated Brushless DC motors. We use them at work in vacuum loaders
and they are good at maintaining speed. They are integrated motors of
high RPM with a 0..10 volt input speed control reference. They are a
closed loop and thus can monitor its own RPM.


Jamie
 
On Jun 15, 11:49 am, Bennett &lt;bjpr...@cal.berkeley.edu&gt; wrote:

You could use a Uninterruptible Power Supply (UPS).  You'd need the kind
that is always regulating the output voltage (an online UPS), rather
than just turning on when power is lost or sagging badly (a standby UPS).
Click to expand...
Would a UPS that outputs voltage exact to within 1% or so be very
expensive?
Also, can one get a UPS with adjustable output voltage?
Laura
 
On Jun 15, 8:58 pm, Jamie
&lt;jamie_ka1lpa_not_valid_after_ka1l...@charter.net&gt; wrote:

  Yes, I hear you and still, it is a mass air flow and motor design
problem..
Click to expand...
I haven't noticed that the motor speed is sensitive to anything else
besides voltage, and the guy who makes the motor says that's the only
thing that causes changes in speed.
You could send your suggestions to Turbine Products, see what he says.
In any case I need to deal with this particular motor, not some future
version.
Laura
 
On Jun 15, 11:49 am, Bennett &lt;bjpr...@cal.berkeley.edu&gt; wrote:

You could use a Uninterruptible Power Supply (UPS). You'd need the kind
that is always regulating the output voltage (an online UPS), rather
than just turning on when power is lost or sagging badly (a standby UPS).
Click to expand...
Would a UPS that outputs voltage exact to within 1% or so be very
expensive?
Also, can one get a UPS with adjustable output voltage?
Laura
 
On Jun 15, 7:43 pm, Jamie
&lt;jamie_ka1lpa_not_valid_after_ka1l...@charter.net&gt; wrote:
  Ah, now comes the clue.... You don't have problems with your
voltage..

   It's a simple matter of mass air flow and your motor design..

  You need a closed loop PID controller to keep that steady..
Click to expand...
No, it's definitely very voltage-sensitive.
The guy who makes and sells the turbine told me that the motor speed
is linear with the voltage, in the range of 100-120 V.
The motor speed varies greatly over that range, from close to zero to
max.
Laura
 
On 6/15/2012 5:29 PM, Laurav wrote:
On Jun 15, 11:49 am, Bennett &lt;bjpr...@cal.berkeley.edu&gt; wrote:

You could use a Uninterruptible Power Supply (UPS). You'd need the kind
that is always regulating the output voltage (an online UPS), rather
than just turning on when power is lost or sagging badly (a standby UPS).

Would a UPS that outputs voltage exact to within 1% or so be very
expensive?
Also, can one get a UPS with adjustable output voltage?
Laura

They are pretty expensive - $350 and up. Output voltage usually not
Click to expand...
adjustable; the built in rheostat that you've got would adjust the voltage.

BTW, what is an Air Turbine; what does it do?
 
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