rotary converter problems

[kelLOGg]

Four years ago I put together a rotary converter to power my 5 HP Powermatic. It consisted of a 7.5 HP 3 phase idler motor operated on 220 VAC single phase and a bank of capacitors. This week it started tripping the breaker (30 amp) just as it approached running rpm. To diagonse the problem I did the following:

1. With the converter running and the planer off I measured the voltage at the planer. I got L1=125, L2=125, L3=220 VAC. When I put the system together all were about 125 as they should be. Where is 220 coming from now? shorted cap?

2. I measured the capacitance of all the caps (except the idler starting caps) and all were very close to specs.

3. I measured the resistance of the idler windings: L1 - L2, L1 - L3 and L2 - L3 and all were about 1 ohm. So no winding was dramatically different from the others.

I don't know what else there is to measure. Any ideas? It has run well for 4+ years so I doubt there was a wiring error. I got the circuit diagram off the net but cannot now find it and the web site I got it from is now non-existant. :(
Help,
Bob

[SPIKER]

you can measure resistance across the CAPs one at a time by setting a analog meter to OHMS and watch the needle is should swing to very high and then as the CAP charges decrease in value at a steady charging rate.

the windings are all good by the sounds of it but you should be measuring line to line and you should have 240v L1 to L3, 240v L2 to L3 and L1 to L2  line may be lower 228 or so.   the lower voltage is the line that is POWERING the 7.5hp.   

Mark

[kelLOGg]

you can measure resistance across the CAPs one at a time by setting a analog meter to OHMS and watch the needle is should swing to very high and then as the CAP charges decrease in value at a steady charging rate.
What would these resistance measurements tell me ? I already know the capacitance values are OK.


the windings are all good by the sounds of it but you should be measuring line to line and you should have 240v L1 to L3, 240v L2 to L3 and L1 to L2  line may be lower 228 or so.   the lower voltage is the line that is POWERING the 7.5hp.   

What is measuring line to line?
So is the 220VAC measurement the correct one? and the two 125s are the bad ones?

Mark

[SPIKER]

Kelog:

the measurement of the caps will tell you if they are charging.  resistive measurement on a analog meter sends out enough power to charge them and as they charge up the resistance measurement goes down (cap charging and it's voltage is going UP) hence the meter thinks the resistance is changing as cap charges.   they should charge pretty evenly as long as the meter battery is good:) and yes the cap will charge up and zap ya if you cross the leads with a finger or ?? 

line to line is 240v on normal home voltage there are 2 lines and a Neutral.   it sounds like you checked line to neutral which would be 120v or so (wall outlet voltage.)     

other things to look for are weak connections at all of the points starting at the breaker panel.   back thru the wires to the caps & motor leads as well as leaving those motors to the other machine you are running.


last item may be the breaker its self they do go bad if you are flipping it on/off that can lessen the life of them.   For that you will need to measure actual current on the lines leaving the breaker tripping off.


mark

[Al_Smith]

You need a couple hundred microfarad cap or preferabley a thousand MF electrolytic for the start cap .For the run cap on 240 it's approx 7.5 Mf per HP oil cap at least 330 VAC rating .

If the generated leg is below line voltage the run cap is too small .Above line voltage it's too large  .On 240 volt you'll want the dummy leg below 300 volts .

If you suspect the run cap being shorted simpley unhook  it and see if it will start .If so you've found your  problem .Don't use it like that though else not connected to a load you'll smoke the motor winding by the induced voltage  .If the start  cap is bad it will usually blow the breakers as soon as you push the start  switch .

If you've used a timer in the circuit as some do perhaps for whatever reason the timer got off and is keeping the run cap in the start circuit too long .It only takes about a second to get enough rotation to start it .

[kelLOGg]

Thanks for the input. The voltage measurements I reported in the 1st post were from the line(s) to ground. Yesterday I measured line-to-line as Spiker suggested and I got 0. Yes, 0. L1-L2, L1-L3 and L2-L3 all 0. The capacitance function on the meter I used read correct values for all caps, BUT I read on an electrical web site that a cap could still fail under operation conditions even though it tests OK via a meter. So, now I am back to thinking I have a bad cap(s) but I don't know which one. So, to summarize my findings I have 0 volts between the 3 lines and 125, 125 and 220 volts from each line to ground. I have no neutral.

I do turn it on/off via the breaker (not recommended)  but the idler motor starts so the breaker makes and breaks contact so it must be OK.
Bob

[Al_Smith]

You're loosing me on this .

You should have 240 between the two hot leads .The dummy leg won't have any unless the thing is generating .

It's an induction generater .Most rotarys just use a pair of caps in parrellel .The start cap has a contact in series with it .Could be a contact from a momentary relay or just a secondary contact from the start push button .

In essence what it does is throw enough capacatance between one hot leg and the dummy to create a phase lag which allows it to self start .The dummy on start up is essentually a start winding .

That's a self start set up but I've seen people use a single phase motor to create rotation .I've even seen them started with a rope wrapped around the shaft .Give it a tug and throw on the power once it's spinning .Off it goes .

A 240 volt three phase motor will draw 2.5 amps per HP full load .Generally speaking a motor used as an induction phase converter will draw about 1/2 load .

[Larry]

Yesterday I measured line-to-line as Spiker suggested and I got 0. Yes, 0. L1-L2, L1-L3 and L2-L3 all 0.

Those readings don't sound right.

This week it started tripping the breaker (30 amp) just as it approached running rpm.
Bob

From this description it sounds like a bad cap in the start circuit. 

[Al_Smith]

I suppose I've built 20-25 of these things from 5 HP to I think 30 was the largest .

My shop is somewhat different which has a 5 HP . I generate at 480 Volts which comes from two 10 KVA single phase transformers hooked up boost then go through another step down three phase transformer to get 240 delta three phase .

And it goes on also single 277 volt ,208/365 wye Europian Looks like an electricians night mare .So all said I can make just about any voltage one could possible think of .I used to joke and say if I had enough transformers I could make a bolt of lightning .

If I can regain my composure with this photo sharing puzzle I'll post some pics later on of the last rotary I built which is a 10 HP . It seems at times I think I must have a touch of ADD or something .I have a gallery just can't seem get a pic to it . ???

[Al_Smith]

 :D  I must have been holding my mouth right or something because miracle of miracles I got it downloaded .Now getting it in a post might be the crowning glory .

Anyhoo this thing is the control box with a number 2 magnetic starter and a relay to pull the starter circuit in which is that big blue Mallory capaciter .The run caps are stacked 4 high with two added as spares not connected .

This thing is in Dowagiac Mich powering a punch press for a buddy of mine who is also an ex sub sailor and I believe he's nuttier than I am which is saying something . :D



 

[Ironwood]

Al, Nice wiring job.
Ironwood

[Al_Smith]

Thanks but I usually do a neater job than that .As it was it was like stuffing 10 pounds of potatoes in a 5 pound bag.

[scsmith42]

You're loosing me on this .

You should have 240 between the two hot leads .The dummy leg won't have any unless the thing is generating .

+1. 

[kelLOGg]

OK, OK - dumb mistake. My meter was on DC when I made those 0 voltage measurements. :-[ :-[ . Go ahead and give me the dope slap - I already have too. So here are the real voltages: L1-L2, 240 VAC; L1-L3, 245 VAC and L1 - L3, 247 VAC and that is with the planer motor only running (belts to the planer removed). So it would appear that the rotary converter is working and operating the 5HP planer motor alone. When I put the belts on the machine starts revving up slowly and trips the 30 A breaker. Sounds like an overload? I've greased all the fittings and gears (1966 model Powermatic) with no results.

It may be helpful to describe what I was doing when this problem first occurred. I was planing a green oak board (6" wide) to correct a fat end before I stickered it for drying. I noticed the dust collector was not sucking up the chips so I blew them out with compressed air. The collector is single phase and is on a completely different circuit from the planer. The breaker soon tripped. I started it again, planed a little longer and tripped again. That was the last time it ran. I opened up the planer for cleaning but never saw anything that would cause jamming or on overload nor do I know why the chips defied the dust collector. I fail to see how this could be the cause.

At this point I plan to change all the caps in the rotary converter under the assumption that they (or one of them) fails under operating conditions even though they test (via meter) OK and will operate th planer motor under idle conditions. What would you do?

One more thing - I use the breaker as a switch. Not a good idea, I know. An electrician neighbor suggesting replacing it since they are not designed as a switch.
Bob

[scsmith42]

Bob, do you have an ammeter? Where I'm headed is that before you start throwing parts at it, I would suggest that you measure output voltages / amperages from the converter while your planer is spinning up, as well as while it is under load.

Your problem could be the motor on your planer, not the RPC.

[Den Socling]

I'd swap out the breaker. Or, as Scott says, check the current draw, at least.

[kelLOGg]

The motor runs when it is isolated from the load (planer). I measured the winding resistance of the planer motor and got ~2 ohms on all 3. Take the power off the motor and it must spin for several minutes. Could it still be the planer motor?

I have only a few seconds to make measurements after powering up before the breaker trips. I'll work on making the measurements while revving up; it never gets under load. I think I will change the breaker first.
Bob

[kelLOGg]

I temporarily installed our water heater breaker in the RPC and it still did not work.
Bob

[kelLOGg]

I got a neighbor to help make volt measurements and got:

L1 - L2          L1 - L3         L2 - L3
210                110               150               measurements taken while planer revving up (prior to trip)
240                245               247               planer motor only running (from a previous post)

What does this tell you?

(I don't trust my clamp-on amp measurements so I did not make any)

Bob

[Al_Smith]

Well the planer motor itself will draw 12.5 amps or so full load .On start up it could draw 3 times that amount .

The 7.5HP convertor should be around 9-10 after it's running  I'd guess .If you have the whole kit and kabootle on a 30 amp breaker it might not take the start up in rush current of the planer motor  .

I don't get why the voltage is going so low on start up .Almost sounds like a wiring connection came loose someplace .I dunno maybe you have too long of a run or the wire is way undersized because that's a huge line lose .

Say if you have a magnetic starter  on that planer motor it might not be a bad idea to check the over load heaters .Although very rare I've seen the wire wound heaters partly burn into which gives almost a "single phasing  " condition .Check the contacts on the starter to while your at it because something is definately  amiss .

Just for test purposes you can bypass the heater overloads .If that fixes it though I wouldn't run it very long that way because the overloads are your motor running protection .

[kelLOGg]

It's the same run of wire that has operated the planer for 4+ years so that can't be a problem now. I have not thought about the heaters; they look OK but the contacts may need burnishing. I guess they can be removed? The planer is in an unheated shop on a concrete floor so the system is at the mercy of the weather except for precipitation.

Is it possible that the caps are failing under load? If the capacitance is now too low they wouldn't charge/discharge enough to supply startup voltage?
Bob

[kelLOGg]

Wait a minute. I have been measuring the voltage at the input to the contactor. If the contactor contacts have high resistance I would not see the voltage drop register on the meter. The drop must occur between the contactor input and the RPC. I think wiring is not the cause nor is the 30 A breaker because I have used both for 4+ years. I have re-screwed on all (I think) of the wire nuts. That leaves only the caps. Am I totally bonkers to assume the capacitance changes under load? If I had caps on hand I would switch them out but it takes 10 days to get them from the Surplus Center and I had rather not wait that long without more reason to believe they are the culprit.

Tomorrow I will make voltage measurements on the output of the contactor; if I get the same drop as on the input I will know the contactor is good.
Bob

[Al_Smith]

Even  if you had no run caps at all that rotary should start that motor .

When I mentioned rope starting a pony motor I was not joking because I did it to test a lathe out for a guy who had no three phase .Just gave it a tug and threw the breaker ,off it went .Started  the lathe no problem no caps ,no magnetic starter nothing but a 5 HP motor running on the floor .Kinda crude but it worked .

[Al_Smith]

If you unhook the run caps you most likely will get perhaps 205 or so volts out the dummy leg .Now you can run that planer with that much unballance but most likely the pony will run hot if you disconnect the load and let it idle unloaded . That would be one method though to test  if you suspect the run caps are funky .Obviously the start cap must be okay because it starts .

[SPIKER]

You can start/run the pony motor without caps like mentioned, there will be a greater voltage miss match as mentioned as well as a lower output power available.   If there is a cap that is falling under load that can cause issues.   You can get a HF meter pretty cheap that has a AMP METER so you can test all 3 legs for power use/loss and current draw.   simply measuring voltage only gives you part of the information and not the best part.

motor starters do fail and the contacts can melt fall apart or fuse and cause issues.   pull the cover off the motors and inspect the motor wires.   Typically a start that runs slowly or slower up to speed is doing so because there is a voltage drop/short in one leg or a wire/winding that has partly failed that wont show up under a voltage measurement but shows up when amp draw is done.

the Planer is not hooked up directly by the sounds of it so the 10HP pony should only be starting its self correct?   If it is tripping only when you fire up the planner then start w the planer or the 3legs leaving it.   It sounded like it was tripping all by its self though.   Check for free planner movement nothing binding or dragging?

pop the motor boxes and inspect the wiring & wire nuts, remove them and replace the nuts and make all new wire twist connections on BOTH motors and any junction boxes in between.   If there are Plugs or Boxes check those as well.   Motor Windings can be tested best with a 4 wire insulation breakdown tester but a simple resistance check can also find some issues but not many.

Only if you are somewhat good about working with electricity the nest steps would be to get a look at the incoming cables to the load center if you find nothing wrong at the motors.   The voltage seems a little low at the L1-L2 =210VAC (power into the 10hp PONY motor.)   That being the case I would inspect the incoming wire to the garage? and where it leaves the House? or Meter Base going to the garage.   Aluminum wire corrodes and can cause a voltage dip under higher load like this.   It might be that you need to break open the load center main power cables at both ends & inspect or re-place the termination points.   a inspection of the cable coming into the barn/garage (above ground? or Below Ground?)   

We had a Shop Electrician was having a 40HP sub Pump pulled because at the company I worked for because it was tripping out.   Motor was only 18 months old or so.   I started checking amps, & voltages found under start up one of the legs voltage would go wonky dipping and jumping bad which tripped the VFD.   The issue was 50 yards 4 walls & hallway away at a main buss / main disconnect under the 200 amp fused Buss Bar system...   Took me and one good electrician about 20 min troubleshooting and an hour to replace the box, had to move it to next bus bar slot.   Was all run in ridged 4" metal conduit 4/0copper THHN.   Luckily the last 6 feet was run in Liquid Tight and there was a free space one slot closer as the buss par was shot at the old location...

Mark M

[kelLOGg]

I re-connected all wire nuts and re-greased the main (Al wire) to the shop and re-torqued.  It made no difference.
I made voltage measurements on the output of the contactor and added it to the table below. As best as I could read my analog meter there was no difference in input and output voltages, so I think contacts and heaters are OK.

L1 - L2          L1 - L3         L2 - L3
210                115               150               output of contactor while revving up
210                110               150               input to contactor while revving up
240                245               247               planer motor only running (from a previous post)

Bob

[Gary_C]

After reading this, I still believe you have a high resistance connection, most likely in the Al wire. I have seen some connections cause problems that required cutting off the end of the wire and reconnecting it using plenty of lubricant and using a torque wrench on the connector. And it could be in the buss bar in the panel. Look for discoloration around anything and even use a temperature gun to find any hot connection.

If that all fails to find the problem, you still could have a bad breaker. Switching them to start motors is not a good practice. Plus you do need a contactor in that circuit so if there is a momentary power interruption, you will have to manually restart. Its never good to automatically start a converter with the load connected.

[Den Socling]

It sure will be interesting when this problem is nailed down!

[Al_Smith]

Well face facts it's nearly impossible to trouble shoot anything over the internet although we all try to do our best at it .

To be quit honest those voltage reading are so screwy I have no idea what the problem is and all I can  do is guess .Now granted myself and a dozen others could probabley figure it out in ten minutes if we were there but we aren't .

Grabbing at straws it could be one of the windings became undone because it  rattled loose from a connection .Most industrial motors are connected within the motor junction box with ring terminals and screws .I've seen a connection come apart right at the "stakon" .Then you are running with one leg disconnected from a parrellel winding of a three phase moter connected for low volatge  IE: 240 volts

It does some wierd stuff then .Oh it'll be something simple once it's found but at present is like looking for the proverbial needle in a hay stack .

FWIW I've been at this biz since I was 19 years old and I'm 64 now .I've seen a lot but I certainly haven't seen it all . :D

[kelLOGg]

I have ordered replacement capacitors and while I am waiting for them I am going to try to disassemble this 1200 lb machine to see what I can see. I can turn the sheave by hand and there is a lot attached to it: cutterhead, gearing and belts and mechanical feed controllers. It is a dirty, greasy job. >:(
Bob

[Al_Smith]

If that motor is belt driven ,unbelt it and listen to the motor .If it moans and groans like a threshing machine it could have a bad bearing .If so by the armature walking around it will cause some real problems .Being a planer with all the machine goodies connected it would wake the dead anyway and you'd never hear a thing if it were under power much less running a board through it .

Aluminum wire was mentioned which in my opinion should be outlawed .Never the less if so it's entirely possible the connections are funky especially if it's connected with Scotch locs .Best thing to do in that case is cut the wire back and reconnect the joints using compound with crimped connectors rated for aluminum .

Aluminum is a good enough conductor but the oxide of aluminum is an insulator .It resembles glass under a microscope .Fact aluminumm oxide is used for sand paper if that tells  you anything .

[kelLOGg]

Motor runs very quietly. I don't have Scotch Locks but I do have split bolt connecters for aluminum in my crawl space. I re-lubed them and re-torqued.

Long Link

[Al_Smith]

Say is that aluminum  buried in the ground per chance ???

If so  all it takes is a pin hole in the insulation to cause big problems down the road .Aluminum is what's called a sacrificing metal .Meaning it's very susceptable to galvanic reaction causing the metal to be leached out of the conductor .

You might for example take a voltage reading under a no load condition and it may be right up where it's supposed to be .If however one of the conductors has experianced some deteriation because of electrolisis ,once a higher amperage load is placed upon it those voltage figures will do some strange things .

Now that I have seen not only on direct burial cable but also those within steel ridged conduit .

[Al_Smith]

I have no idea what you have being 7-800 miles away .If you have a roll of number 10 romex and the planer etc aren't a mile away from the source you could always stretch out a temporary line to either confirm or rule out if the aluminum feeder  has gone funky on you .You could probabley wing it with a number 12 just for a short test .

[kelLOGg]

Yes, it's #4 Al about 200 - 300 feet underground.

[Al_Smith]

If I were a betting man I'd say that's the problem then .Well shucks .

I'd suggest testing  the line side with a load ,and without .If the voltage changes dramatically that's your problem .

Now if you used aerial triplex with a bare ground/messenger instead of direct burial most likely the bare gave up the ghost .If so early on like 35 years ago I mistakenly did the same thing .If you have regular direct burial triplex insulated try changing the ground over with one of the hot wires IE : the one that's  showing low voltage .

[kelLOGg]

That's a good measurement to make, Al. Here's what I found.

I meaured across the main (line-to-line and line to ground) in the shop breaker box as the planer was turned on starting to ramp up.

The line-to-line changed from 240 to 225
line to ground changed from  125 to 115  (same data for both lines)

I did the same measurement but only on the line-to-line at the house which supplies the shop and found

The line-to-line changed from 240 to 230 during ramping up.

What do you think? Any red flags?

Bob

[Al_Smith]

Sounds within reason .So much for that idea .

[kelLOGg]

 ;D ;D ;D ;D ;D
It works now!
I installed new caps today and turned it on and it ramped up to speed fast and stayed there. Capacitors can fail under load and test OK under test conditions. Here is the link that put me onto that:

http://www.angelfire.com/electronic/funwithtubes/Testing_caps.html

I will put it all back together and re-connect the dust collector and test it under planing conditions. I hope I still have good news.  Right now I'm content to just wallow in the present good news.
Bob

[Den Socling]

 8) to you!

[kelLOGg]

After my success I installed a 2-pole switch the next day so I wouldn't have to use the breaker as a routine switch. Fired it up and  >:( >:( >:( >:( >:( same old DanG problem crept right back - ramped up slowly and tripped the breaker. I removed the idler and planer motors and took them to a shop for testing. They were fine - no problems with them the technician said.  ??? ??? ???

I found a source for rotary converter controllers Link
These units consist of everything except the idler and enclosure. They look more sophisticated than what I put together and I am thinking of buying one. What would you do? I haven't talked to the company yet but will before I buy.

Bob

[DouginUtah]

I have their 5 HP rotary converter sitting here by me. I haven't gotten around to hooking it up yet--have to have a garage sale first. It appears to be well made.

Their one-page Setup Guide was a bit disappointing, with outdated picture and information, but you won't have any problem hooking it up.

My concern is that I have a 3 HP, 208 V., 3-phase work motor and they implied that the converter puts out around 230 V.
(My idler is 240 V., 5 HP.)

[Al_Smith]

A 208 motor running on 240 volts won't hurt it .It will just put out a tad more power .

[DouginUtah]

Thanks, Al. I was hoping that you would say that.  ;D

[r44astro]

Wow did not read every post but what a pain. unless you need  close to max output at planer, buy a good static converter and run the planer, you can always use a static with a idler if more power needed, typically I only use idler on lathes because of forward reverse. use to design and build these things when I was a kid for local farmers.
Bill

[kelLOGg]

I have made progress in solving this dilemma but before cut to the chase I want to summarize.
1. The original RC I made worked for 4.5 y then started tripping the breaker.
2. Replaced all caps in it - still didn't work. The manufactured phases voltages were 110 and 150 VAC.
3. Still convinced it was an electrical problem, I purchased RC kit from WNY. (It has a nice auto detect of the third phase - something my unit lacked) Guess what. Still didn't work.

After the initial failure in 1 above I was attempting to just start the planer, not put any load on it like actually planing. So it fails to reach full rpm under no load. In all these attempts to start I began to notice two audible frequencies - one a normal hum and the other a faint high pitched squeal. Bad bearing? I asked. I removed them and they felt OK turning by hand but I purchased new ones anyway. The new bearings felt pretty much like the old ones when turning by hand. I installed them not expecting much difference. But there WAS a difference! The planer ramped up to full rpm and stayed there. The knives have been removed for sharpening so the planer is still under no load but at least it ramps to full rpm - something it hasn't done in months. Tomorrow I expect to get the knives back and I will then know to if this is the ending to the story.

My clutching-at-straws analysis is that at high rpm the bearings exhibited high load (friction) and the RCs (my version and the commercial one) could not produce enough voltage under this condition in the manufactured phases to get the speed up and the motor current draw exceded the breaker limit. What do you think?
Bob

[Al_Smith]

Wow did not read every post but what a pain. unless you need  close to max output at planer, buy a good static converter and run the planer, you can always use a static with a idler if more power needed, typically I only use idler on lathes because of forward reverse. use to design and build these things when I was a kid for local farmers.
Bill

A static converter is in essence just the same as a start circuit for a real rotary .Yes it will run a motor but only at around 58 percent power level . A lot of people use them though .

[r44astro]

Wow did not read every post but what a pain. unless you need  close to max output at planer, buy a good static converter and run the planer, you can always use a static with a idler if more power needed, typically I only use idler on lathes because of forward reverse. use to design and build these things when I was a kid for local farmers.
Bill

A static converter is in essence just the same as a start circuit for a real rotary .Yes it will run a motor but only at around 58 percent power level . A lot of people use them though .

Yes I meant that, you said better, Years ago I built a rotary converter that sensed PF and switched caps in and out, after that experience (it worked great but not worth the trouble, just buy a solid state converter) I never concern myself with amps being equal at all phases in a normal converter only if motor starts, sounds, and runs cool because of PF.

[kelLOGg]

I put the knives in today AND PLANED OAK!!!! 8)

I am still stunned that all the time the problem was bearings!!
Bob

[r44astro]

I put the knives in today AND PLANED OAK!!!! 8)

I am still stunned that all the time the problem was bearings!!
Bob

I have so often not been able to see the trees because of the forest. I repaired CNC machinery for years and have been screwed by my single mindedness all too often.

[Al_Smith]

If you are running multiple motors from a rotary converter and are really all that concerned with power factor here's a simple solutuion .Simpley add the appropriate sized running caps to the individual motors .

Unless a person were running voltage senstive CNC machinery it's really of little consiquence .Most people on this forum or the ones I've made rotarys for are just tickled to death to be able to run a Bridgeport mill,big table saw  or something of the like .

Just like most things ,you can get elaborate about it .I myself have enough brains to design a voltage sensative network to stage capactors in and out as needed except for the fact I subscribe to the KISS principle --Keep -It -Simple -Stupid . ;)--junk yard dawg --still . :D

[kelLOGg]

If you are running multiple motors from a rotary converter and are really all that concerned with power factor here's a simple solutuion .Simpley add the appropriate sized running caps to the individual motors .

That is a clever idea for multiple motors.  If I start running more I will keep that in mind.

Bob