20hp 3 phase motor on 15hp phase converter controller?

[jmlcolorado]

I picked up a 3 phase 7.5hp lathe and planned on building a RPC.
I bought this 15 hp controller before I sourced the motor.
I found a 20hp motor for $100.
http://m.ebay.com/itm/15-Hp-phase-c...3A2d4105ee1590a6a8e7d1dde5ffd06de4%7Ciid%3A17

In retrospect, I suppose I should have sourced a motor first, then bought the controller after.

Will I be able to run the 20 horse motor?
If not, can I change out parts in the converter to run the 20?

I suppose I could cut my losses and sell the 15 hp converter and buy the proper converter, but entertaining options first.

 

[Radix2]

you are replacing a 7.5hp motor with a 20hp motor on a lathe...?

ahhh... you want to use the 20hp motor as your phase converter...I think the issue would be if or when you actually have a large load. IMO if you stay at the 7.5hp level it would be ok. With the obvious risk.

 

[Speedy Petey]

you are replacing a 7.5hp motor with a 20hp motor on a lathe...?

Was thinking the same thing. Two very different animals.

Not nearly worth the effort to shoehorn the 20HP in there.

 

[jmlcolorado]

No. leaving the 7.5hp in the lathe. Building a Robert phase converter to gain the 3rd phase to run the 7.5 in the lathe.
Using the 20hp as the idler motor to the 3rd phase.

 

[larry_g]

I would suggest that you contact the maker of your controller. We have no specs on your controller so cannot make an informed opinion. Those that do are guessing.

lg
no neat sig line

 

[jmlcolorado]

I would suggest that you contact the maker of your controller. We have no specs on your controller so cannot make an informed opinion. Those that do are guessing.

lg
no neat sig line

Thanks for the honest feedback Larry.
I'll do just that.

 

[Radix2]

the issue is that the starting and run caps are a little miss-sized for the 20hp motor. But since you are running load less than 50% of the idler, you should still have pretty good 3ph. It is all a guesstimate anyway - you would need different sizes for any different load anyway. Even with the correct motor, they would still be a compromise at 7.5 or 3 or 10hp anyway. See what the manufacturer says, it may be within the gray zone anyway.

 

[jmlcolorado]

I figured I'd temperally wire up the converter to the motor tonight to see if it would even start it.
It started the motor up the the mag switch clicks on and off rapidly till the motor is up to speed. It only takes about 3 second to get up to speed.
Once up to speed it runs smooth.
I tested the voltage across the legs and got some strange readings.
1-236 volts
2-326 volts
3-315 volts.

Is this because the capacitors aren't setup to handle the 20hp motor?

P.s. I did reach out to the manufacturer to see what I need to bump this up to support 20hp.

Bear with me here guys, I'm still learning the in's and outs of this type of technology.

 

[larry_g]

I'm assuming that you don't have the system loaded? Put it under load before you worry to much about what your seeing. Also understand that your not measuring perfect sine waves and your meter will not interpret them correctly. Have you gone through the Hanrahan document on building converters? I followed his instructions and mine worked great.

http://www.metalwebnews.com/howto/ph-conv/ph-conv.html You have to open the figures separately when reading this document.

lg
no neat sig line

 

[jmlcolorado]

I'm assuming that you don't have the system loaded? Put it under load before you worry to much about what your seeing. Also understand that your not measuring perfect sine waves and your meter will not interpret them correctly. Have you gone through the Hanrahan document on building converters? I followed his instructions and mine worked great.

http://www.metalwebnews.com/howto/ph-conv/ph-conv.html You have to open the figures separately when reading this document.

lg
no neat sig line

You are correct. No load present currently.
I did expect some variation across each leg, but I was surprised to see 100 volt difference though.

That looks like a great document! Off to reading I go
Thanks again Larry

 

[matt_i]

Here's some other reading if interested.

http://www.metalwebnews.com/howto/phase-converter/3-phase.pdf

My opinion is that with a "capacitor" phase converter you can spend a bunch of time trying to equalize the voltages perfectly. However as soon as you change the loading the generated-leg voltage will then move on you. So in my mind its wasteful to try to chase the balance around with run caps. Just get the motor started. Once started...it doesn't care if it only runs on a single phase. There will be lower hp for sure, but does it matter? Making a 1hp cut on a lathe is a serious affair.

Also there's very little current flow on the generated leg. Its not enough to even hold in a set 3-4 of relay coils reliably if that gives you an idea. The general caveat is to always locate the control wiring and make sure you wire those two legs to the (single phase) utility power and use the generated leg for motor power.

Imo, using a 20hp idler is a little overkill, and you face the conundrum of whether to wire for 7.5hp, 15hp or 20hp worth of 240vac current.

Personally I'd try to trade your 20hp idler (isn't that like a 300 lb motor?) for a 7.5hp idler. The 15hp-start is likely going to just be the wiring and Start-Capacitor bank size inside the enclosure and the oversize there does not matter.

Adding: you are likely going to have to jumper the NC contact of any classic overload heaters as they are going to detect phase loss every time. My opinion is that since you run the machine 100% of the time, its no big deal. Just shut it off if you somehow stalled the motor or its humming with a locked rotor.

 

[Radix2]

You are correct. No load present currently.
I did expect some variation across each leg, but I was surprised to see 100 volt difference though.

That looks like a great document! Off to reading I go
Thanks again Larry

Yes, it is because you have no load. See what you have with the lathe motor on it. It will also change as the motor is loaded or different motors, the whole deal is not very precise, so unless you have objectionable noise or vibration it is good enough.

Now. A 7.5 hp lathe? Can we see pictures please?, that has to be some kinda monster! Making railroad car axles ?

 

[jmlcolorado]

Yeah, it has some girth to it
But hey, it's the "junior" model.
You should see the Goliath











I'm having a heck of a time finding a manual for it though. I've reached to a company in Germany but haven't gotten a response.
Have also reached out to two guys I found on practical machinist that have one asking if they would burn me a copy for a fee, with no lice there either.

 

[matt_i]

Looks like a nice machine. I have never seen one of those before but it looks well-built. Did you get to test run it before putting it on the trailer?

Is it inch/metric? I was studying the threading chart for a minute and didn't really reach a conclusion...

Do you have a gantry or forklift to unload it from the trailer?

 

[jmlcolorado]

Looks like a nice machine. I have never seen one of those before but it looks well-built. Did you get to test run it before putting it on the trailer?

Is it inch/metric? I was studying the threading chart for a minute and didn't really reach a conclusion...

Do you have a gantry or forklift to unload it from the trailer?

It appears very well built and solid. I didn't get to test run it, but I could turn it through all the gears be hand and it was smooth with no binding or grinding.
I was into the camaro I traded for it $1800, so technically, I'm into the lathe $1800. The camaro was sitting in the back 40 waiting for a replacement smog pump and hadn't been driven for a year, so I felt the deal was worth it.

The threading chart has both metric and standard. It's going to take me awhile to figure all those out for sure.

No forklift, but I have 2, 2 ton engine hoists and a buddy with a large skid steer. He says he's picked up 4200 with his machine, so I think we should be able to manage.
Worse comes to worse, I'll winch it to the end of the trailer, lift each side with engine hoists, and roll the trailer out from under it.
Should be interesting.

 

[Radix2]

Cool lathe, I am surprised it is 7.5hp - since a lathe cuts with a single point tool, the loads can really only be so big, so I was imagining a really huge one to be that high of hp. It certainly looks stout, and if it runs well will be really nice.

Are you certain it is 7.5hp?

 

[cvairwerks]

Interesting..did this one come out of Mead, Co.?

 

[jmlcolorado]

Cool lathe, I am surprised it is 7.5hp - since a lathe cuts with a single point tool, the loads can really only be so big, so I was imagining a really huge one to be that high of hp. It certainly looks stout, and if it runs well will be really nice.

Are you certain it is 7.5hp?

Definitely 7.5 hp. Motor says 5.5 kw.

Interesting..did this one come out of Mead, Co.?

No, there is a guy up there that has one too. I've been trying to get in touch with him to see if he has a manual

 

[jmlcolorado]

I got a wild hair up my **** and decided not to wait for my buddy's machine to offload. Figured I could handle it myself.
Used the winch on the trailer to turn the lathe 90*. I wanted the heavy end off first.
Got it to the end of the trailer then lifted the end with an engine hoist. Dragged it an inch at a time more with a pulley hooked to a hook I have in the garage floor to pull off more. Once off far enough, I dropped the heavy end, and rolled the engine hoist beside the lathe and picked up the "light" end and drove out from under it.
Once in the garage, I had to rotate it 180* to get it into place. Went Egyptian style and used bars and levers to inch it around.
About 3 hours total.

 

[jmlcolorado]

Figured I'd hook up the RPC and see if this machine turns under its own power.
A few weird things.
Video with what it's doing.

What do you think the issue is?

 

[930dreamer]

What does the controller say it's max hp rating is?

 

[jmlcolorado]

What does the controller say it's max hp rating is?

It's only rated for 15HP, which is likely the issue.

 

[930dreamer]

Do you have a smaller 3 phase motor to try?

 

[larry_g]

Figured I'd hook up the RPC and see if this machine turns under its own power.
A few weird things.
Video with what it's doing.

What do you think the issue is?

My big mill did the same with the chattering relay. Problem is that you are trying to run your controls off of the generated leg. Move the feed wires to the lathe all one position to the right and the one pushed off to the far left. If that doesn't help try the move right one more time. You want the controls connected to the two non-generated legs of the system.

With out a schematic I would not venture a guess at the control box on the RPC. Some have a potential relay in them that could be a problem or you just have to much inrush to the idler motor, and the supply cannot handle it. You may end up having a smaller motor to spin up the idler motor before starting the rpc.


Try this. Start the RPC, bring it up to speed and then hit the off button to it. Let the motor spool down to 1/2 speed or so then hit the start button. If the relay does not chatter then I'd suspect inrush.

lg
no neat sig line

 

[Strouty]

With the chatter on the RPC, I think that is the start capacitor size. Once the motor gets turning it switches to the run capacitor and that doesn't care as much.

If you run the RPC for a few minutes before starting the lathe, does it make the same amount of noise?

Also when I built mine, I had no where near the voltage difference that you have, I think I had something like 25 volts difference between all the legs.

 

[EOC_Jason]

What was the voltage while the lathe was running?

 

[larry_g]

I figured I'd temperally wire up the converter to the motor tonight to see if it would even start it.
It started the motor up the the mag switch clicks on and off rapidly till the motor is up to speed. It only takes about 3 second to get up to speed.
Once up to speed it runs smooth.
I tested the voltage across the legs and got some strange readings.
1-236 volts
2-326 volts
3-315 volts.

Is this because the capacitors aren't setup to handle the 20hp motor?

P.s. I did reach out to the manufacturer to see what I need to bump this up to support 20hp.

Bear with me here guys, I'm still learning the in's and outs of this type of technology.

On second thought about these voltages, What is the voltage rating on the motor? Does it have a 230/480v wiring option and is it wired correctly for the lower voltage?

lg
no neat sig line

 

[jmlcolorado]

What does the controller say it's max hp rating is?

The controller is rated for 15HP. Motor is 20hp. I've reached out to the seller to see what I can do to up size this one to support 20hp.

Do you have a smaller 3 phase motor to try?

Unfortunately, no. This is my madin venture into 3 phase, so I'm limited on what I have.

My big mill did the same with the chattering relay. Problem is that you are trying to run your controls off of the generated leg. Move the feed wires to the lathe all one position to the right and the one pushed off to the far left. If that doesn't help try the move right one more time. You want the controls connected to the two non-generated legs of the system.

With out a schematic I would not venture a guess at the control box on the RPC. Some have a potential relay in them that could be a problem or you just have to much inrush to the idler motor, and the supply cannot handle it. You may end up having a smaller motor to spin up the idler motor before starting the rpc.


Try this. Start the RPC, bring it up to speed and then hit the off button to it. Let the motor spool down to 1/2 speed or so then hit the start button. If the relay does not chatter then I'd suspect inrush.

lg
no neat sig line

I did this and there was one combination that the lathe motor just growled. The next combo, the lathe chattered for about 5 seconds before starting up, and the 3rd combo, it fired up almost instantly. Sounds like you were right about that.

With the chatter on the RPC, I think that is the start capacitor size. Once the motor gets turning it switches to the run capacitor and that doesn't care as much.

If you run the RPC for a few minutes before starting the lathe, does it make the same amount of noise?

Also when I built mine, I had no where near the voltage difference that you have, I think I had something like 25 volts difference between all the legs.

I'm probably fighting a RPC controller too small. I surprised nobody has kicked me in the teeth for even attempting this

It certainly fires up quicker once powered down for a few seconds to half speed.

What was the voltage while the lathe was running?

I ran 4 gauge thhn wire to a new 70 amp breaker tonight to see if this helped some of the issues. Hoping the welder feeder I had was undersized.
This seems to have helped slightly.

Voltage readings WITH lathe running now are:
1-233
2-252
3-254



So, I think I'm on the right track. I feel like if I can modify the control box to support the 20hp idler motor, I think I'm home free.

 

[jmlcolorado]

For anyone curious, here are the guts of the controller.

 

[Radix2]

The differences between controllers for 15 or 20 hp should not be a big effect to you as you are running. The difference is in the capacitor size, which is in any case a crude approximation. But at this point you are running basically without a load, not even at a tenth of the rated hp. At this operating point, the caps won't make much difference - they are in the circuit to improve the efficiency as you load the thing up. Some people run RPCs without any caps at all, it should work free wheelin..

Larry has the right idea above, the generated leg should be avoided for running controls.

Since you have only a 7.5hp motor, you should never run anywhere close to 20hp at the idler.

Hope the supplier has some good support for you.

 

[jmlcolorado]

The differences between controllers for 15 or 20 hp should not be a big effect to you as you are running. The difference is in the capacitor size, which is in any case a crude approximation. But at this point you are running basically without a load, not even at a tenth of the rated hp. At this operating point, the caps won't make much difference - they are in the circuit to improve the efficiency as you load the thing up. Some people run RPCs without any caps at all, it should work free wheelin..

Larry has the right idea above, the generated leg should be avoided for running controls.

Since you have only a 7.5hp motor, you should never run anywhere close to 20hp at the idler.

Hope the supplier has some good support for you.

If that's the case, I think I might tool up and start flinging chips and see what happens.

 

[Radix2]

I used to run a 1 1/2hp Bridgeport off of a 2hp idler...the RPC consisted of a fused switch, a 3ph motor and a piece of rope... no caps, no box... you need the other stuff if you want convience or if things get too noise and hot under load.

If you think you have it connected right, and it is running decent without load, load it up.

 

[larry_g]

Voltage readings WITH lathe running now are:
1-233
2-252
3-254



So, I think I'm on the right track. I feel like if I can modify the control box to support the 20hp idler motor, I think I'm home free.

Lets refine your voltage readings some.

Label your three legs as L1 , L2, L3 . Now identify which leg is the generated leg if you can. From now on identify your readings as;
L1 to L2=
L2 to L3=
L1 to L3=

Then you have better idea of what is happening and we will also.

lg
no neat sig line