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I want to run the 120vac blower less agressively. Like 9ov instead. I find that I can series install an inductor and that works well. Q1 Would it be best to use a buck xfmr instead? Q2 How does the inductor method affect cost of operation? Q3 I note that the motor runs cooler either way. What is happening regarding phase shift, like EIcos theta? Thats about it. I do plan to measure phase w analog scope but fear line isolation. I wonder if my amp clamp and fluke can give meaningful data. I think the pf is about .86, or 30 degrees. Just curious about how things work. Thanks


Maybe I am wrong but this inductive blower works good at 100 vac. Do common inductor motors tend to make it to sync rpm and like lock up to line freq. within certain limits? That is what I observe. All in all I get a cool quiet blower at about 40 percent less heating. Is this believable in your opinion?

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  • \$\begingroup\$ Does the inductor get hot? How big is it? \$\endgroup\$ – Tony Stewart EE75 Feb 24 at 6:11
  • \$\begingroup\$ Small blower; Like 3Amp 120VAC.. I use a small 40va xfmr 28 volt secondary for my reactor. Gets slight warmth. \$\endgroup\$ – kscope Feb 24 at 23:44
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Q1 Would it be best to use a buck xfmr instead?

If the blower is running the way you like with a series inductor, there is no need to change that. It is a wash whether the transformer would be more or less efficient. One disadvantage of the inductor method is that it affects power factor, as you are aware. Did didn't specify the power of your blower, but my guess is that it is relatively small, and power factor for such a device is only an issue if you want to make it one.

Q2 How does the inductor method affect cost of operation?

I don't know how the power utility bills in your location. Where I live, they charge based upon real or true power, not apparent power. This means that people can actually run their meters in reverse by supplying power to the grid. Your true power will be approximately the same whether you use an inductor or transformer.

Q3 I note that the motor runs cooler either way. What is happening regarding phase shift, like EIcos theta?

The inductor is forming a voltage divider with your blower, and current is, in all likelihood, out of phase with your line voltage. Most motors tend to be inductive loads on their own, so how much your inductor has influenced the pf is hard to say.

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  • \$\begingroup\$ I hear pure reactor is non power consuming, hence the inductor rather than a 15 Ohm power resistor. The blower is small 3 Amp 120vac ac motor. I use a common 40va transformer 28 v secondary, as luck would have it , it works to run the blower cooler, quieter, at 100v across the motor load. The inductor stays almost cool. \$\endgroup\$ – kscope Feb 24 at 23:54
  • \$\begingroup\$ I also note that the motor makes it to the normal speed so I figure that the blower was over-designed and simply did not need all the "drive". Better for me that I am not wasting resistor heat. I do wonder if inductive motors are kinda like synchronous motors, and as long as imotor spins up to expected speed, then all my needs are fulfilled. A happy outcome from small onhand "inductor. Seemingly a non power consuming limiter through the magic of phase shiftery. \$\endgroup\$ – kscope Feb 25 at 0:04
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The main thing to keep in mind is that inserting the inductor reduces the motor voltage and the torque capability of the motor as shown in my answer to: Speed control for PSC induction motor. The diagram provided there shows that the torque required to drive a fan reduces drastically with speed. The required torque is proportional to speed squared. As a result, the motor speed is reduced and the required power and current are reduced. As a result, the motor runs cooler. The power factor will probably decrease, but that is due to the real portion of the current decreasing with little or no reduction in reactive current.

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  • \$\begingroup\$ The little blower motor seems to get full rpm. Are such inductor motors sort of like synch motors, an as long as slippage is minimal, all just might be the same as normal,.Luckey, the motor is ok with 100v rather than 120vac. \$\endgroup\$ – kscope Feb 25 at 0:13

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