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RPC Capacitor Switching

Paul_NJ

Plastic
Joined
Jan 11, 2010
Location
New Jersey
I'm in the process of designing/building a RPC using a 5 HP idler motor. I've studied the few good "definitive" articles on the subject, and recognize you have to combine them all to really come up with a usable scheme. I found the book, and youtube video, by "unique3phase" particularly interesting where a network of run capacitors are arranged with switches so that the 3 legs can be "tuned", based upon load, by capacitor choice. A dual Volt/ammeter is provided into for each phase leg. I'm putting the meters in, but the switchable capacitors have me a little spooked.

Has anyone built one with this capability?

The author uses simple household 15A toggle switches. The author claims good experience with household switches, and the cheaper (looser tolerances) the better.

Here's a photo from youtube.

capacitor box 2.jpg

Cutting 1/2" dia holes for panel toggle switches would sure be easier, and there are plastic ones available that might be less "shock proof".

This seems like a really convenient design, but I'd sure like to hear other's experience with doing something like this, and also concerning switching in and out live capacitors in an operating system. Any experience using the panel switches?

I'd really appreciate some good practical experiences and advice.

Paul
 
I'm in the process of designing/building a RPC using a 5 HP idler motor. I've studied the few good "definitive" articles on the subject, and recognize you have to combine them all to really come up with a usable scheme. I found the book, and youtube video, by "unique3phase" particularly interesting where a network of run capacitors are arranged with switches so that the 3 legs can be "tuned", based upon load, by capacitor choice. A dual Volt/ammeter is provided into for each phase leg. I'm putting the meters in, but the switchable capacitors have me a little spooked.

Has anyone built one with this capability?

The author uses simple household 15A toggle switches. The author claims good experience with household switches, and the cheaper (looser tolerances) the better.

Here's a photo from youtube.

View attachment 194777

Cutting 1/2" dia holes for panel toggle switches would sure be easier, and there are plastic ones available that might be less "shock proof".

This seems like a really convenient design, but I'd sure like to hear other's experience with doing something like this, and also concerning switching in and out live capacitors in an operating system. Any experience using the panel switches?

I'd really appreciate some good practical experiences and advice.

Paul

The question might be "WHY"

Simple systems with only a few basic considerations have proven useful for many for many years.

'just OCD?.. I suppose that is reason enough. But match the AMPS, disregard the volts.
 
Has anyone built one with this capability?

View attachment 194777

Any experience using the panel switches?

I'd really appreciate some good practical experiences and advice.

Paul

I think this guy might have a lot of experience using panel switches. You can find him underground somewhere in the midwest.

vlcsnap-2015-09-25-18h25m21s515.jpg

vlcsnap-2015-09-25-17h36m40s707.jpg

Seriously, I think it is a waste of materials. I built a 5hp RPC and it has 3 run capacitors, 50uf & 40uf in parallel between T1 & T2 and a 50uf between T1 and T3. It just takes a few jumper cables, a note pad, & a volt/amp meter. You also have to realize that the balance act depends on the target load, the load changes and so will the balance. Therefore it is a waste to manually tune with small capacitor values. When you get into a electronic switching RPC that dynamically balances the network, then I'm for it.
 
I set up a Variac with a capacitor across it and an oscilloscope which really allowed me to see what it was doing and could adjust exactly for any load. I have posted that multiple times and there is no response. I doubt that many understand it.

Bill
 
I set up a Variac with a capacitor across it and an oscilloscope which really allowed me to see what it was doing and could adjust exactly for any load. I have posted that multiple times and there is no response. I doubt that many understand it.

Bill



Similar commonly done back when capacitors were more expensive than transformers :eek:. THEM days is surely past....... Except they usually used a step-UP to reduce the capacitor size and make it cheaper.

A tapped autoformer would do the job and take up little room.

For extra credit..... explain how the effective capacitance varies with transformer ratio !
 
I've never had a reason to build a RPC, so I'm far from being an expert on the subject. Perhaps a power factor relay would be better than a bunch of light switches, and maybe automate the process a bit?

http://www.beluk.de/en/index.php?pg=pfc_relays.php

I like the capacitor/variac combo idea. Motor operated variacs are available, and could be set up to automatically raise/lower.

I'm going to stick with my VFDs.
 
Similar commonly done back when capacitors were more expensive than transformers :eek:. THEM days is surely past....... Except they usually used a step-UP to reduce the capacitor size and make it cheaper.

A tapped autoformer would do the job and take up little room.

For extra credit..... explain how the effective capacitance varies with transformer ratio !

New Variacs would be expensive but they are around electronic junk stores and flea markets.

If the Variac is connected between a line leg and the manufactured one and the capacitor is connected between the line leg and transformer wiper, when it is turned all the way up, the capacitor delivers its full current. When the wiper is turned down, the voltage to the capacitor is lower and it doesn't capacit as much, so it reflects a lower value. The function can be made to work the other way by connecting the capacitor across the full winding and the manufactured leg to the wiper, but as it is turned down the voltage across the winding and capacitor increases so higher voltage ratings are needed and there needs to be a stop to keep out of dangerous territory.

An automatic version could be made with a Variac run by a DC geared motor and a high level demodulator of the type that nulls when the input voltages are 90 degrees apart. Read from the neutral point of the line, the voltages are 90 degrees apart on a proper three phase service. The DC motor could be made to drive to a null with no amplifier. The constant change would wear the Variac.

Note to Jerry- If you want anything from The Electronics Exchange (one of the junk stores to those outside the area) do it soon. Bruce has the building for sale and is getting out of the business.

Bill
 
I set up a Variac with a capacitor across it and an oscilloscope which really allowed me to see what it was doing and could adjust exactly for any load. I have posted that multiple times and there is no response. I doubt that many understand it.

Bill

Well heck I built one with no capacitors at all, and nobody seems to understand that one either, even though it's been in use for about
28 years.
 
Well heck I built one with no capacitors at all, and nobody seems to understand that one either, even though it's been in use for about
28 years.

You could drive your three phase motor with a single phase one (or a gas engine) and get three phase power. You could lock one leg to the line and overspeed the driver motor, the same thing a lot of the windmills do. You could also lock a flywheel or other varying source of rotation to the line by a power selsyn, but I doubt many understand that as well.

I don't know any non religious subject with more voodoo and less logic than this one.

Bill
 
Yeah, I was past there a while back and noticed that. he's still got a fair bit of stuff, but it's mostly stuff you don't need usually, That's the kind of place you want around to find odd things when you need them, but it's hard to know what to stock up on beforehand.

I guess you mean RPCs for Voodoo and no logic..... yeah, have to agree. You really need to know what the parts do, and you need to know about the "parts" that are really inside the motor, or there is no hope of understanding what is going on.

An induction motor can be a stand-alone generator. I tried it out once, and it works. You need to flash the windings to get a starting excitation, and you need to load it with capacitance to provide AC excitation when not under load, but it works.

Problem is, it is unstable if self-excited (fine if line-excited like a wind turbine). it will completely die if shorted, which is a good characteristic sometimes, but it also dies if overloaded, and has some trouble with load changes. But for lights in some remote area of the Andes mountains, it might be the best thing going, and is cheap enough to be used there.

Well heck I built one with no capacitors at all, and nobody seems to understand that one either, even though it's been in use for about
28 years.


What's not to understand?

If the idler is big enough, it will pretty much "just work". The only issue is that the generated voltage is nearly always lower than the line volts, just because it has to be, But the bigger the motor, the closer to line volts it tends to be..

The impedance is low enough that there is little to compensate out with balance caps, and the phase sequence angles are mechanically set.

Folks get all kinds of upset thinking about "balance caps" (that are really power factor correcting caps). But if the idler is a fair bit larger than the load, I tell them to try NO caps FIRST. Only if there is an obvious problem is it worth adding balancing caps.

Agree, that conflicts with what "everyone says" and they look at me funny for saying it. But that does not affect its truth.
 
You could drive your three phase motor with a single phase one (or a gas engine) and get three phase power. You could lock one leg to the line and overspeed the driver motor, the same thing a lot of the windmills do. You could also lock a flywheel or other varying source of rotation to the line by a power selsyn, but I doubt many understand that as well.

I don't know any non religious subject with more voodoo and less logic than this one.

Bill

Take a graduate course in Nuclear Engineering or in Fields and Waves in Communication Electronics.
 
Well heck I built one with no capacitors at all, and nobody seems to understand that one either, even though it's been in use for about
28 years.

Everyone has their own comfort zone and level of understanding. Even what they DO NOT want to understand.
 
Take a graduate course in Nuclear Engineering or in Fields and Waves in Communication Electronics.

Nuclear engineering is all right as long as you don't try to tell God what to do.

The quickest way to separate the physicists in a group from the masses- relate this story.

Werner Heisenberg was driving on an autobahn when a cop pulled him over and said "Do you realize how fast you were going back there?" Heisenberg replied "No, but I know where I was."

Bill
 
Nuclear engineering is all right as long as you don't try to tell God what to do.

The quickest way to separate the physicists in a group from the masses- relate this story.

Werner Heisenberg was driving on an autobahn when a cop pulled him over and said "Do you realize how fast you were going back there?" Heisenberg replied "No, but I know where I was."

Bill

Bill, I like the joke told the other way.

When the cop pulled over Heisenberg, he said "do you know you were going 125 km/hr?"
In reply, Heisenberg responded "Great!, Now we are lost!".
 
I guess you mean RPCs for Voodoo and no logic..... yeah, have to agree. You really need to know what the parts do, and you need to know about the "parts" that are really inside the motor, or there is no hope of understanding what is going on.

To be fair, though, I think the majority of people who come here with questions about RPCs are not primarily electrical types and only want their machines to run. They often say as much, that they are machinists, not electricians. If this were a mold making forum for instance, we might find the shoe very much on the other foot.

Bill
 
I'd heard it told in a bit more obscure fashion where the police officer knew some physics. Heisenberg is stopped for speeding and the officer walks up to the window.

Officer: Sir, do you know how fast you were going?
Driver: No, but I know where I am.
Officer: It is an honor to meet you, Herr Doctor!
 
To be fair, though, I think the majority of people who come here with questions about RPCs are not primarily electrical types and only want their machines to run. They often say as much, that they are machinists, not electricians. If this were a mold making forum for instance, we might find the shoe very much on the other foot.

Bill


yes, for sure.

But there are fewer moldmaking websites with folks spouting the "only" way to make a good mold..... For RPCs there are lots of them, and info all over the map from sound theory to wild suggestions.
 
don't know why I listened to recommendations to come to this site for help. mistake. what a bunch of self absorbed bullshit. adios
 
What's not to understand?

Most folks figure, this has to be complicated. There has to be some sort of voodoo magic involved. It's the
same midset that says, you need a digital tach on the VFD, or need to have a rotary converter fully instrumented
with ammeters, voltmeters, and so on.

Cf. the OP on this thread.
 








 
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