Voltage Flucuating /Stablizer

[damunk]

I have built an air flow bench using vacuum cleaner motors and there is a voltage fluctuation from the wall of around +-4 volts.

This is causing the readings on the manometer to be erratic and is defeating the object of the project.

Is it possible to stabilize the voltage to accurace of 99.5%?

Thank you.

 

[MisterE]

Look into using an Uninterruptable Power Supply (UPS) :-
Uninterruptible power supply - Wikipedia - https://en.wikipedia.org/wiki/Uninterruptible_power_supply

Line Interactive or Online "may" do the trick

 

[Lucien Nunes]

I don't think you will get an AC-output stabiliser stable to 0.5% off-the-shelf or at a sensble price. No commercial equipment requires this stability - note the distinction between stability (voltage not changing) and accuracy (knowing what the voltage is). I would also be surprised if vacuum cleaner motors are that stable, for example the IR drop will vary with winding resistance which varies with temperature.

I would suggest using a closed-loop control system, where the controlled variable is monitored and used to correct the motor voltage. If you want constant speed, then you could use an optical tacho looking at a black sector painted on the fan impeller visible through the suction eye. If you want constant pressure (removing the fan curve from the delivery characteristic) then get the feedback from a pressure sensor. This kind of system will give you your 0.5% but setting up a PID controller is a bit complicated to describe on a forum!

BTW what engines do you tune?

 

[damunk]

Would a voltage stabilizer be able to keep the voltage at 230V at all the time?

Don't know why a UPS would work better than a voltage stabiliser?

 

[Lucien Nunes]

Can you find any ordinary voltage stabiliser that will work to 0.5%?

One way I might tackle it it is to run the motors on DC (normal vacuum motors are universal and actually run slightly cooler and quieter on DC). An old machine spindle drive would do nicely, if a single-phase unit could be found or a 3-phase one hacked to run on single. The tach input would have to be referenced to the output.

Alternatively, a functional but Heath robinson solution would be to transform the incoming AC down, rectify and then add an isolated, stabilised DC supply in series, of say double the voltage fluctuation it needs to correct. Then, by taking its feedback not from its own output but by a suitable fraction of the motor voltage, it would adjust its output to stabilise that. With careful adjustment of the loop gain and compensation to keep it stable, I don't think there would be any trouble achieving the 0.5%.

A nice form of AC voltage stabiliser that can achieve good accuracy although with a slow response is the old servocontrolled Variac. By working it through a buck/boost step-down transformer you can trade accuracy with controllable range, by changing taps on the bucking transformer. Again no difficulty in reaching 0.5% but first you have to find / make your motorised Variac.

 

[damunk]

I don't think you will get an AC-output stabiliser stable to 0.5% off-the-shelf or at a sensble price. No commercial equipment requires this stability - note the distinction between stability (voltage not changing) and accuracy (knowing what the voltage is). I would also be surprised if vacuum cleaner motors are that stable, for example the IR drop will vary with winding resistance which varies with temperature.

I would suggest using a closed-loop control system, where the controlled variable is monitored and used to correct the motor voltage. If you want constant speed, then you could use an optical tacho looking at a black sector painted on the fan impeller visible through the suction eye. If you want constant pressure (removing the fan curve from the delivery characteristic) then get the feedback from a pressure sensor. This kind of system will give you your 0.5% but setting up a PID controller is a bit complicated to describe on a forum!

BTW what engines do you tune?

1)Someone else mentioned close loop system. I don't quite understand that. Is this a system where there is some feedback device (mechanical or electrical) that can keep the characteristics constant?



2) Just small block 1.4 16v Head

 

[UKMeterman]

Hi,
An introduction to closed loop feedback theory and the maths can be found within https://focus.ti.com/lit/an/slod006b/slod006b.pdf

 

[Marvo]

A vacuum cleaner motor might not be the best choice especially if it's a series configured motor with brushes which will be prone to speed changes with varying static pressures across it.

 

[dmxtothemax]

I would be approaching UPS manufactures,
I would imagine such systems are available
But we are talking high end stuff
As such expect a large price sticker !

 

[marconi]

What about regulating the air itself using something like this:

Low Pressure Precision Pressure Regulator M11 by Fairchild Industrial Products - http://fairchildproducts.com/product/low-pressure-precision-pressure-regulator-m11/

 

[damunk]

There are three motors in the bench. Each one using it's own power supply on separate sockets to prevent over load.

If there a way to have a display unit that can read all three voltages and display the average?

If there is then the problem is solved because I can then take all my manometer readings when the voltage hits 235V.

The UPS machine 2kva was very expensive.

 

[damunk]

I believe a closed loop system is required. I have not taken into account motors warming n cooling down which affects air flow. thanks for your help.