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
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.
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:
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.
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,
for like you can pick up a technician or engineer who'll put it all together for you.
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).
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
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 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.
Have you considered that Turbine Products, whatever that may be, have sold you a piece of unusable garbage? Why are they not modifying their equipment to make it usable? Or at least providing you the applications support that you are seeking here? They're responsible for the halfassed design of this POS.