Quieting / Muffling a Rotary Phase Converter

Hey guys, it's been a while...

It looks like I may be moving into a new space and setting up my machine (Schaublin 102N) again after another (damned) year in storage.

Unfortunately the new location does not have 3 Phase power. Fortunately I do still have my RPC (Arco Roto-Phase MG). This unit was quite noisy in its stock self-starting configuration.

I am very grateful for the quality of information on this forum. Back in 2009 I inexpensively modified it to a capacitor/relay start and balanced the phases, using the valuable information from this forum. That quieted the idler substantially but it is still not quiet.

In my new location, there will be a retail showroom (for cine cameras and lenses) in the same building. So I want to be able to limit the noise of my machines. The Schaublin is belt driven and relatively quiet when running on true 3 Ph power. I also don't take heavy cuts since I don't do production work. So it's just the RPC noise I'm concerned with.

The Schaublin is a 380V machine with an internal step-up transformer. This greatly complicates the easy path of using a VFD with single phase input. Replacing the motor is also not a viable option due to the motor's unique configuration.

I know a digital phase converter like Phase Perfect would be the ideal solution, but that is out of reach for a good while due to cost.

Does anyone have any suggestions about quieting / muffling a RPC?

I had thought of building a box around it with sound absorbing material. My main concern is heat buildup. The box could be ventilated, but that may allow some of the sound energy to escape.

Any suggestions / links would be appreciated.

I would build a box to go around it with the acoustical insulation on it, and have a gap where air can get in and out, just has to go around corners to get there. Also mount the motor on acoustical mounts.

Do you have a schematic of the machine. VFD may not be a bid deal. Should just have to order a 380V vfd, and maybe a transformer (depending on kva) to go 240 1ph to 380 1ph.

Looks like its a 1.5kW / 2hp motor. According to Square D there 480 class drive works for 380 also.
Setup VFD downstream of transformer and you are good to go. There may be enough transformer there to handle it, as the vfd will significantly lower your inrush current.

I built a aluminum and dynamat box around my converter in the shop. It works great and dropped the sound by half.

jakefreese said:

I would build a box to go around it with the acoustical insulation on it, and have a gap where air can get in and out, just has to go around corners to get there. Also mount the motor on acoustical mounts.

Do you have a schematic of the machine. VFD may not be a bid deal. Should just have to order a 380V vfd, and maybe a transformer (depending on kva) to go 240 1ph to 380 1ph.

Looks like its a 1.5kW / 2hp motor. According to Square D there 480 class drive works for 380 also.
Setup VFD downstream of transformer and you are good to go. There may be enough transformer there to handle it, as the vfd will significantly lower your inrush current.

I built a aluminum and dynamat box around my converter in the shop. It works great and dropped the sound by half.

Click to expand...

Put it outside.

What kind of noise is it?

I have an Arco of similar size, which produces a low whine that is barely audible around the corner. When I got it, it shook like a cold dog and sounded like a garbage truck. I balanced the rotor, and tightened the sheet metal, all done.

I put it on rubber feet, but on a concrete floor that probably was not important.

JST said:

What kind of noise is it?

I balanced the rotor, and tightened the sheet metal, all done.

I put it on rubber feet, but on a concrete floor that probably was not important.

Click to expand...

What balance method secrets do you use? Static, dynamic?

What is the RPM of the motor? I understand that you want to quiet the unit that you have but slower motors are generally quieter. My home-built RPC uses a 1,750 rpm motor and it's not unpleasant to listen to.

My first RPC had a 3,450 rpm motor and I had to sell it to quiet it down.

Newman109 said:

What is the RPM of the motor? I understand that you want to quiet the unit that you have but slower motors are generally quieter. My home-built RPC uses a 1,750 rpm motor and it's not unpleasant to listen to.

My first RPC had a 3,450 rpm motor and I had to sell it to quiet it down.

Click to expand...

Yeah speed makes a huge difference. My 10hp is a 1750, not terrible. The 30hp 3500 sucks. That's the one that got the aluminum box. If that motor had space heaters I would have put it outside.

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rons said:

What balance method secrets do you use? Static, dynamic?

Click to expand...

I just did it static, seemed to work, so I left it alone. The issue was a partly broken off "fan blade" on the rotor, as I recall, so a couple washers riveted on the helpfully provided studs did the job.

JST said:

I just did it static, seemed to work, so I left it alone. The issue was a partly broken off "fan blade" on the rotor, as I recall, so a couple washers riveted on the helpfully provided studs did the job.

Click to expand...

You did it the right way. The first time I saw a rotor balanced with putty I thought it was a bad way to do it. It looked like someone stuck their chewing gum their. The funny thing is that there were mounting studs for weights.

I had to make my own schematic. The manual from Schaublin does not include one and there are too many variations in electrical equipment on these machines.

What you are proposing is basically what I'm planning to do except that I will use a 460V GE inverter I already have and the Schaublin's internal (and Swiss made) step-up transformer. So I need to feed it 230V 3Ph. The GE inverter, as most 460V inverters, won't run on single phase input.

That's where the RPC comes in. I just want to limit the noise level. I'm thinking the same as what's being suggested: A box (going to use MDF), lined with engine box insulation.

jakefreese said:

Do you have a schematic of the machine. VFD may not be a big deal. Should just have to order a 380V vfd, and maybe a transformer (depending on kva) to go 240 1ph to 380 1ph...

...I built a aluminum and dynamat box around my converter in the shop. It works great and dropped the sound by half.

Click to expand...

Any of the inverters will run on single phase 480, just need to run a bigger one and disable the phase loss protection. Just need to make sure that particular drive would run on 380 to be happy.

Am aluminum enclosure with dyna mat worked fine with my RPC. Look at diesel generator enclosures. That's where i came up with my idea.

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OK... let's say that I find that I can disable phase loss protection on that drive. Will a 3 phase step-up transformer work with just two of the coils energized?

I do know that I can feed the VFD a higher voltage and then just specify 380V as the output voltage.

jakefreese said:

Any of the inverters will run on single phase 480, just need to run a bigger one and disable the phase loss protection. Just need to make sure that particular drive would run on 380 to be happy.

Am aluminum enclosure with dyna mat worked fine with my RPC. Look at diesel generator enclosures. That's where i came up with my idea.

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Click to expand...

cinematechnic said:

OK... let's say that I find that I can disable phase loss protection on that drive. Will a 3 phase step-up transformer work with just two of the coils energized?

I do know that I can feed the VFD a higher voltage and then just specify 380V as the output voltage.

Click to expand...

Yes the transformer will work running on two phases. Just need to see what size it is to make sure that it can handle the current you need only using 66% of the transformer. That original transformer should have been sized to handle full line starts with that motor. With a drive you will have significantly reduced starting current so that transformer should be able to handle it running single phase. It's best if you have access to all the taps within the transformer so you can disconnect the phase your not using.

The vfd has limited ability to change voltage. It's intended to change frequency. In your case with a 380v motor you want ~380v going to it.

Is the transformer 480 to 380 buck transformer? Or is it knocking the voltage down to 200v? Can you get a picture of the transformer name plate and motor plate?

The Square D transformer I posted you can disable the phase loss protection. I have two of them in the shop running like that.

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I believe it's meant to work as a step-up transformer. My Schaublin was set up to be exported to USA. I think it might be a 3 phase autotransformer.

Here's a photo and info on the transformer:



TRANSFOR S.A.
CH-6981 Molinazzo Di Montenegro (Swiss Made)

SNT nm 2k 3ph
Sn: 2.5 KVA f: 50/60 Hz
Raffered: AW Classe: 3b
Gruppo: Ion

P 220/500 V
S 380/457 V
3.8/3.1 A

jakefreese said:

...Is the transformer 480 to 380 buck transformer? Or is it knocking the voltage down to 200v? Can you get a picture of the transformer name plate and motor plate?

Click to expand...

That transformer can be used with the two phases, the challenge is your going to have a step up transformer to go from your 120/240v service to 240/480, then 240/480 back to the 380v. I would get a 240 to 380v transformer and feed the VFD and motor. Is there another control transformer in the machine also?

I realize it's confusing from those specs, but the transformer IS a step-up transformer and I have successfully used it to boost 208V 3Ph Wye and 230V 3Ph delta to 380V. The only difference was when I was getting 3Ø Delta (from my rotary phase converter) I did not have a separate neutral going to the transformer.

So the question is: What happens if I just feed it 230V 1Ph as the input?

Thanks!

jakefreese said:

That transformer can be used with the two phases, the challenge is your going to have a step up transformer to go from your 120/240v service to 240/480, then 240/480 back to the 380v. I would get a 240 to 380v transformer and feed the VFD and motor. Is there another control transformer in the machine also?

Click to expand...

Ok it looks like it's tapped for 480 input. If you have had 230v going to it it's good to go. Running two phases to it, it's right at 1.5kw which is also what your motor is so your right at the capacity of the transformer. It should be good to go. You just have to use the two phases on the output to feed your drive. I would monitor voltage and temp of the transformer to make sure it's not getting to hot. But how often are you at full load on the motor, and it sounds like your in a climate controlled environment. Not a 100 + degree shop.

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