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rotary converter problems

Started by kelLOGg, February 11, 2012, 09:01:41 PM

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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
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

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
I'm looking for help all the shrinks have given up on me :o

kelLOGg

Quote from: SPIKER on February 11, 2012, 09:18:35 PM
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
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

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
I'm looking for help all the shrinks have given up on me :o

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
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

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

Quote from: kelLOGg on February 13, 2012, 05:53:06 AM
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.

Quote from: kelLOGg on February 11, 2012, 09:01:41 PM
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. 
Larry, making useful and beautiful things out of the most environmental friendly material on the planet.

We need to insure our customers understand the importance of our craft.

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

There is no scarcity of opportunity to make a living at what you love to do, there is only scarcity of resolve to make it happen.- Wayne Dyer

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

Quote from: Al_Smith on February 13, 2012, 07:20:23 AM
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. 
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

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
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

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.
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

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
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

kelLOGg

I temporarily installed our water heater breaker in the RPC and it still did not work.
Bob
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

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


Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

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
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

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
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

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

I'm looking for help all the shrinks have given up on me :o

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