0
\$\begingroup\$

I want to provide constant 24 volts AC to an inductive load using a transformer - regardless of "brown-out" (low voltage) conditions at the primary and I am not sure it is possible. During the summer months where I live it is common to have low supply voltage issues, the 208v supply dropping to 200. I though if there was a way to regulate the 48 v output voltage of two 24v transformers, secondary's wired in series; then if the primary voltage drops there would still be plenty of voltage on the secondary. Of course this device would have to be a variable self adjusting resistance, adjusting to its own down-stream voltage... a simple resistor obviously would not work.

Is this even possible without redesigning a U.P.S. wheel? Has anyone ever heard of such a device? This is electro-mechanical equipment using standard 24 volt AC controls and contactors to operate compressor motors. The motors can operate with the reduced voltage, but the contactors and control board in this unit are sensitive to a drop in the 24 v.enter image description here

\$\endgroup\$
5
  • 2
    \$\begingroup\$ Does the 24V control load require pure-sine, and is your supply frequency stable? One thing that came to mind was a ferroresonant transformer as a way of avoiding a whole UPS, but that has its own issues with significant harmonic distortion and electrical/acoustic noise - as a result I'm hesitant to recommend it in an answer until the assumptions are more clarified. \$\endgroup\$
    – nanofarad
    Aug 7, 2022 at 2:50
  • 2
    \$\begingroup\$ Will the contactors and whatnot operate OK with voltage above 24V? Can you just use a transformer that delivers a higher voltage overall without having an overvoltage condition when the line voltage is at 208V? Or use a couple of volts of boost? Usually AC-operated equipment is designed to "expect" considerable variation in line voltage -- if your nominal 24V is coming from a transformer designed for 240V input then you'd be clinging to the low end of the range just with 208V in. \$\endgroup\$
    – TimWescott
    Aug 7, 2022 at 4:19
  • \$\begingroup\$ I would believe that the textbook + 10% would apply to be safe. So I can apply about 26.5 volts to the contactors and control boards. I do not know if there is a standard transformer rated to convert 208v to 27. I did search for a 190-195 volt primary with a 24 output with the same idea in mind but of course without much success. \$\endgroup\$
    – John N
    Aug 8, 2022 at 17:46
  • \$\begingroup\$ There is nothing special about the supplied 208. Frequency stable - probably not from an engineering standpoint. Utility supplier feeds a transformer and then the unit is powered from the panel. That's all we have on this site. Plain vanilla. \$\endgroup\$
    – John N
    Aug 8, 2022 at 17:55
  • \$\begingroup\$ As you are aware there are also "scheduled" brownouts when the grid is overloaded due to a heat wave for instance. The infrastructures capacity in this NY metro area is always in question. This is why I am hesitant to get the utility company involved - been down that long road before and my current thinking (no pun intended) are that the chances of this being caused by a defective transformer or something is minimal. \$\endgroup\$
    – John N
    Aug 8, 2022 at 17:55

1 Answer 1

Reset to default
3
\$\begingroup\$

Rather than try to regulate the output of the transformers you could regulate the input to them.

There are plenty of commercial power line conditioners available that will keep the line voltage constant, which in turn will keep the output voltage of the transformers constant. You just need to find one that fits your power requirements.

\$\endgroup\$
0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.