Home built Static Phase Converter chattering potential relay

2Slow · May 3, 2018

Hello,

Although it has been a while, I have built I have built several RPCs and all worked well.

A friend bought a new lathe and asked if I could build a static phase converter for him. Although I never built a static converter, I said sure figuring it was just a RPC without an idler. . I took my standard RPC design and eliminated most of the components. In the end it was just a Steveco 90-65 potential relay & 300uF of run cap used as starting caps. I wired everything up the way I would for an RPC. When I gave it power, the steveco 90-65 potential relay chattered immediately so I didn't even try to close the lathe contactor. I didn't have the bleed resistors on the caps, but thought that would just prevent chatter on shut down, not chatter whenever it had power... My design is below, What did I do wrong?

Thanks,
-Joe

thermite · May 3, 2018

2Slow said:
A friend bought a new lathe and asked if I could build a static phase converter for him. Although I never built a static converter, I said sure
...

B

Already answered. See above.

And/or here:

http://www.practicalmachinist.com/v...hp-late-motor-348995-post3156063/#post3156063

Those who do not learn from "physics" are doomed to diarrhea.

And "static phase converter" is an oxymoron. It does not "convert".

Had a 10 HP 3-P motor? Now it is a 3 HP 1-P motor. And runs hot. Maybe that is all he needs?

2Slow · May 3, 2018

Thanks for the input. I understand the limitations of a static unit, but it is what my friend wants. He has a "phase a matic" static on his mill and is satisfied with the performance and ease of use. He temporarily hooked it to his lathe and he was satisfied with how it worked. (it is a 3HP lathe, and the phase a matic had a 274 - 324uF starting cap in it that started it easily.)

I offered to build him an RPC with an extra idler motor I have, but he doesn't want the 2 button operation or the noise of the idler. He wants a static and I want to build him something nicer than the phase a matic he is satisfied with.

Any advice on the chattering potential relay?

Thanks,
-Joe

thermite · May 3, 2018

2Slow said:
Thanks for the input. I understand the limitations of a static unit, but it is what my friend wants. He has a "phase a matic" static on his mill and is satisfied with the performance and ease of use. He temporarily hooked it to his lathe and he was satisfied with how it worked. (it is a 3HP lathe, and the phase a matic had a 274 - 324uF starting cap in it that started it easily.)

I offered to build him an RPC with an extra idler motor I have, but he doesn't want the 2 button operation or the noise of the idler. He wants a static and I want to build him something nicer than the phase a matic he is satisfied with.

Any advice on the chattering potential relay?

Thanks,
-Joe

Dunno. There's a Phase-A-Matic 10 HP laying around here somewhere, but I don't have any cause to dislike you enough to help waste your time by opening it to look at how they built it.

Learned all I needed to know about static-NON-converters by the mid 1960's.

They haven't changed. Nor the laws of Physics. "Nicer" only needs a better grade of paint or polish.

If you want nicer OPERATING? Just hide an idler and grease the belts on his lathe so he THINKS he has been cut-down to 1 HP.

An RPC doesn't need any particular count of buttons. Electrical components exist. You can rig it to work with no obvious buttons at all. Motion-sensor when he approaches the lathe, f'rinstance.

Somewhere.. I have a digital voice recording that says" "What would you like me to do?"

Downside is.. it sounds like Raquel Welch in her early 20's.

He might get more turned-on than the lathe?

rons · May 4, 2018

2Slow said:
He wants a static and I want to build him something nicer than the phase a matic he is satisfied with.

That shouldn't be hard.

2Slow said:
Any advice on the chattering potential relay?

It's clicking away at 60Hz. Go back and look at the Steveco data sheet and then see why that is happening. I already gave you a hint.

Is that 300uF capacitor really a "Run" capacitor?

2Slow · May 5, 2018

Ron,

Thanks for the tip. I would say it is clicking a bit slower than 60Hz. It is as if the caps are charging, then discharging through the potential relay coil. I considered changing pin 5 (one end of coil) from L1 to L2 because I think I am charging and discharging the caps through the normally closed path between pin 1 and 2 then the coil from 2 and 5. This results in a circuit that connects L2 to one side of the cap, then a path through the NC switch than through the coil to L1.

Swapping the reference on Pin 5 from L2 to L1 is counter to how Peter5322 says to wire the Potential Relay. He says the caps should be fed with one of the 220v legs, and pin 5 should be monitoring the other. If I swap pin 5 from L2 to L1 I am pretty sure the clicking will stop because all of the pins 1, 2, and 5 will be at the same potential without load. What I I don't know is if the Steveco 90-65 potential relay will pull out based on Peter 5322's description of its operation below: Will there ever be a potential between Pin 2 and Pin 5 to open the relay if they are both connected to L1?

http://www.practicalmachinist.com/v...lp-needed-my-brain-isnt-working-today-273013/

I thought adding the bleed resistors might help - but I don't think it would solve the problem based on a test I did with my RPC. On my RPC (schematic below, and it has worked flawlessly for years) I pulled the fuses that go to the idler motor, than pushed the start button to pull in the contactor to sort of simulate what I built at my friend's house for a static that will have power but not immediately see load. Without the idler motor load, my RPC potential relay clicked in and out (a little lower frequency than my friend's static but I have bleed resistors in place and a light which are paths to discharge the caps.

And the "300uf run cap" in the diagram for my friend's static is actually six 50uF run caps. I did that to allow frequent starting and stopping of the lathe without having to worry about start cap duty cycle.

-Joe

rons · May 5, 2018

I meant that the "Run" cap should be the "Start" cap.

If you read this 20 year old article (1st paragraph) the chattering relay is mentioned:

Phase Converters

1. You should get the relay out of there. And just use a momentary switch.
2. Then relabel the "Run" cap to a "Start" cap.
3. Then add a couple of "Run" caps, between L1 & T3 and between L2 and T3. T3 being the blue wire.

I have never used a potential relay because I don't care for them. A octal connect timer with a 0-5 sec delay or a manual push button is better. The Steveco rave on this forum reminds of the articles in electronics magazines. A circuit is designed around one integrated circuit or specialized part. So everybody buys that one part. When you look at the author of the article, he works for the company making the part.

2Slow · May 5, 2018

Ron,

Thanks for the link, I don't have a neutral available, but can look at getting a dual primary transformer. I have built several RPCs, and helped a few people build some more. I did all the RPCs without a neutral or transformer to generate the reference but they had magnetic starters on the input side. This is my first static and it is giving me fits.

Using a push and hold or a timer will not provide the functionality my friend wants. He would like to be able to walk up to the lathe and just use the controls normally without pressing any other buttons. Even if he was willing to do so, a push and hold would require two hands, one to do the push and hold, and the other to operate the lathe control. Unlike an RPC everything in the static "converter" is always powered and we are switching the load side in and out with the lathe controls. For that reason, I don't think the timer would work either as it wouldn't know when the load was switched in or out. Unlike an RPC, there is no switch magnetic or mechanical ahead of the converter, it is all downstream and the load is switched.

The phase a matic box works exactly as he wants, and I feel we should be able to build something that works the same, but uses better components (like 220V rated oil filled caps instead of the 125V rated start cap phase a matic used.)

-Joe

SAF · May 5, 2018

Have a look here.

phaseconverter

SAF Ω

rons · May 6, 2018

SAF said:
Have a look here.

phaseconverter

SAF Ω

I looked, and did not like this. The article is 20 years old.

Diode: I don't know why I needed this, but it was a necessary part nonetheless. My relay was rated to operate on AC voltage. A diode blocks part of the voltage which results in a "sloppy" DC voltage. Without this diode, the system was self-defeating. As soon as the start button was pushed, the starting capacitors resulted in a high enough voltage to activate the relay. The relay would then disengage the capacitors, but they were the cause of the higher voltage. As soon as the capacitors were disengaged, the voltage was too low to activate the relay, and the relay would re-engage the capacitors. The bottom line was that the relay would flicker on and off, but the motor would not start. I fully expected this to happen when I used a DC rated relay, but the AC rated relay shouldn't have done this. I can only surmise that it is because I cut the voltage in half by using the diode.

SAF · May 6, 2018

I looked, and did not like this. The article is 20 years old.

Yes I get that, but It was meant to be an example of a static converter for a lathe, which is what he was looking for, and not covered here much.

I assumed that he could glean something from it, and interpose his potential relay since he already has that.
I also know that you don't like those either. So it surprises me that you don't like a sensing relay built out of standard parts. Maybe you could suggest an alternative design for a voltage sensing relay, fabricated from standard components?

Most likely he could get away with a standard 240V relay coil, from a small ice cube relay. If I remember correctly that's what Phase Craft uses, and he seems to not get any complaints here.

SAF Ω

rons · May 6, 2018

SAF said:
Yes I get that, but It was meant to be an example of a static converter for a lathe, which is what he was looking for, and not covered here much.

I assumed that he could glean something from it, and interpose his potential relay since he already has that.
I also know that you don't like those either. So it surprises me that you don't like a sensing relay built out of standard parts. Maybe you could suggest an alternative design for a voltage sensing relay, fabricated from standard components?

Most likely he could get away with a standard 240V relay coil, from a small ice cube relay. If I remember correctly that's what Phase Craft uses, and he seems to not get any complaints here.

SAF Ω

I first looked at the article in 2001.

A RC circuit timer in a small octal relay with time delay control knob has been around for years. I would couple that to a larger single pole double throw relay. I would use two oil filled capacitors for the start. When the relay operates after the start one of the two oil filled caps would switch (via large relay) to the other power line. Appropriately sized the two caps would add together for starting, then would split something like 60/40 in run mode. I would also use a energy absorbing device across the large relay points.

jim rozen · May 6, 2018

2Slow said:
Hello,

Although it has been a while, I have built I have built several RPCs and all worked well.

A friend bought a new lathe and asked if I could build a static phase converter for him. Although I never built a static converter, I said sure figuring it was just a RPC without an idler. . I took my standard RPC design and eliminated most of the components. In the end it was just a Steveco 90-65 potential relay & 300uF of run cap used as starting caps. I wired everything up the way I would for an RPC. When I gave it power, the steveco 90-65 potential relay chattered immediately so I didn't even try to close the lathe contactor. I didn't have the bleed resistors on the caps, but thought that would just prevent chatter on shut down, not chatter whenever it had power... My design is below, What did I do wrong?

You don't have the load motor attached.

The relay is looking for a particular voltage at the sensing terminal. It doesn't like that terminal being open.

You made what's known as a relaxation oscillator.

Consider putting the load motor on-line before you power the system via the relay.

rons · May 6, 2018

jim rozen said:
You don't have the load motor attached.

The relay is looking for a particular voltage at the sensing terminal. It doesn't like that terminal being open.

You made what's known as a relaxation oscillator.

Consider putting the load motor on-line before you power the system via the relay.

It's not what his friend wants. Read #8

SAF · May 6, 2018

Dosen't want a one shot timer either.

SAF Ω

rons · May 6, 2018

Will have to settle for what works given the criteria.

I have a couple of these AC/DC current transducers. He could build his static converter with one of these or something like it.

http://www.shoreline-electronics.de/250CT.pdf

jim rozen · May 6, 2018

rons said:
It's not what his friend wants. Read #8

Don't care.

This is what he's doing wrong. Read number one.

rons · May 7, 2018

jim rozen said:
Don't care.

This is what he's doing wrong. Read number one.

We know what is wrong. What is your suggestion other than "Consider putting the load motor on-line before you power the system via the relay."
Number 8 is not for that.

Strostkovy · May 7, 2018

thermite said:
Already answered. See above.

And/or here:

http://www.practicalmachinist.com/v...hp-late-motor-348995-post3156063/#post3156063

Those who do not learn from "physics" are doomed to diarrhea.

And "static phase converter" is an oxymoron. It does not "convert".

Had a 10 HP 3-P motor? Now it is a 3 HP 1-P motor. And runs hot. Maybe that is all he needs?

Maybe I'm arguing semantics here, but you don't need something physically turning to convert phases, it's just that capacitors alone aren't good at it.

Capacitors will make a 90 degree leading phase, but you need very large capacitors to reduce the reactance enough to get your phase voltage up. What you need to add is an inductor, which produces a 90 degree lagging phase from the other side of the line. The result, if you set your values properly, is a series resonant circuit that resonates with mains power, and can actually magnify the voltage to dangerously high levels (wind your inductor to be near saturation so that any extra voltage ruins the q factor of the resonator, and thus regulates the phase).

This will give you a 2 phase output with 90 degree separation between phases. Run that through a Scott T transformer (can be partially done with an autotransformer to reduce cost) and you will have true, clean three phase for just the cost of the run capacitors, inductor, autotransformer, and stepdown transformer.

Still more expensive than an RPC, but way more elegant and could probably be made into a very clean, affordable product.

SAF · May 7, 2018

You mean like this?

SAF Ω

Home built Static Phase Converter chattering potential relay

Hot Rolled

Attachments

Diamond

Hot Rolled

Diamond

Diamond

Hot Rolled

Diamond

Hot Rolled

Stainless

Diamond

Stainless

Diamond

Diamond

Diamond

Stainless

Diamond

Diamond

Diamond

Titanium

Stainless

Similar threads