Rotary or static converter?

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JP McG
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Rotary or static converter?

Post by JP McG »

Total beginner to three phase/single phase conversation and have a basic question.

I've a SAG12 graziano - runs at 380 or 220V three phase. I want to run the motor at 380V for full power, and don't want to go down the VFD route as I need to get the machine going sooner rather than later, and I'm not up for trying to figure running the DC clutches outside the VFD and rewiring the pump etc. (and i think i'm right in thinking I'll lose some power when rewiring for 220V from 380v)

Will I get away with a static converter (was thinking of getting a 5.5hp to run the 3hp machine)- or do I have to shell out for a rotary converter? I've been chatting with the folks at Hucol and he's been fairly into selling me a rotary converter (>1500€) -- the static converters are ~500€. Got the lathe for 1k€ so it'll be a sad day to have to shell out €1500 for the converter.

Anyone have any thoughts? will I get away with the static and still get full functionality out of the lathe?
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GlennW
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Re: Rotary or static converter?

Post by GlennW »

You will loose a considerable amount of power for sure if you use a static converter.

Rotary or Phase Perfect is the way to go.

380v to 220v shouldn't reduce power, but will increase amperage draw. The difference involved should be on the data plate.
Glenn

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Bill Shields
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Re: Rotary or static converter?

Post by Bill Shields »

Go rotary..

Converting to run on 2 VFDs would probably not be that difficult. Especially if the only thing you use them for is to provide 60 cycle 3 phase power.

Take everything after the main motor starter and put it on one...everything else goes on the other..

Clutch power supply should be fused separately and easy to segregate.

So says the guy from several 1000 KMs away...

Or sell me the lathe for what you paid for it... :D
Too many things going on to bother listing them.
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BadDog
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Re: Rotary or static converter?

Post by BadDog »

Simple rotary converters are very easy to build with lots of references on the web. I've built 3 now, the first shortly after i got my first mill. Practically free if you can source (cheap to free) suitable 3ph idler motors and go with rope start, or use a 1ph scrap/trash sourced "pony motor" start, or just a little more for an electronic with manual push button or potential relay for a touch of class. The latter was used for my first built with help from some local club guys (including Marty, board admin, much thanks!). The next two were increasingly higher capacity and complexity, incorporating multiple stages, and run-caps for balance with built in balance gauges. And I'm not particularly (or at all) electrically proficient.
Russ
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JackF
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Re: Rotary or static converter?

Post by JackF »

I'm with BadDog. I've built two myself, both with push button start. Before I added the push button start I tried spinning the idler motor with my hands as fast as I could then threw the power to the two legs of the idler and it started right up, producing 3 ph power. :D
Give it a try.
JP McG
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Re: Rotary or static converter?

Post by JP McG »

Alright ye have convinced me... I'll have a go at making a rotary phase converter -- having built loads yourselves are there any things that can blow up the lathe or myself that might not be obvious? I remember trying to wire a three phase motor to delta and add a start capacitor, not realizing (b/c the videos i was watching didn't mention it) that you need to use a switch on the capacitor to take it out of the circuit once the motor starts -- booommm.

What size idler motor should I get for the phase converter then so? Same size as motor?
John Evans
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Re: Rotary or static converter?

Post by John Evans »

rule of thumb for starting lathes without a clutch use 1.5 times highest lathe motor HP . ie 5HP use a 7.5 idler.
www.chaski.com
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liveaboard
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Re: Rotary or static converter?

Post by liveaboard »

I like the electronic inverter.
Just saying.
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BadDog
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Re: Rotary or static converter?

Post by BadDog »

Yeah, you need more idler over-size for harder starting loads, like lathes, big chuck, big work pieces. A lot more than a typical mill. Sourcing old big heavy massive motors for the idler is also a good move that substantially reduces the over-spec otherwise required. A massive 100 lb 5 HP motor from the 40s in good condition may make as good an idler as a modern 10HP Hi-E motor. That's just anecdotal, and I lack engineering chops to support it, so that's more provided as a general reference rather than suggesting you use such a motor as stated. But the right take away is old-n-heavy better than new-n-fancy.

And don't try to use the generated "wild leg" for anything other than powering the load motor. For example, don't use it tied to the coil of a magnetic starter/relay, it'll chatter and drop out on you. I recently confused the heck out of myself doing just that. It's been a few years since I fooled with these things, but I should have remembered that, or at least figured it out sooner than I did...

Other than that, there's really nothing I know of that could cause problems other than general electrical stuff (undersize wires, bad connections, bad design, etc). If you get a well respected plan to build from, and take basic precautions to do quality work, it's pretty cut-n-dried for a basic RPC. If you get stuck, the PM (Practical Machinist Forum) site has a fantastic group of guys that inhabit their RPC forum. Just don't try to ask or talk about "hobby grade machines" and you can get some great help there. They helped me work out the details of my 3-stage 3/10/15 HP balanced and corrected RPC, and I dare say I would have failed at that without their input.
Russ
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SteveM
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Re: Rotary or static converter?

Post by SteveM »

I don't have the link, but there is a company out there that will sell you a complete box to mount to your motor to turn it into a rotary phase converter.

The smallest one they have is 3 or 5 horsepower, but if you have a smaller motor they can change components (I think the caps) to suit a smaller motor.

I have an ancient boat anchor 1-1/2hp GE motor I will eventually turn into a converter.

Steve
JP McG
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Re: Rotary or static converter?

Post by JP McG »

I was looking at the kits as it seems like a good balance between cost and actually making something that works in a shortish amount of time. Most of the kits seem to come from stateside. They are ~220 input single phase and similar output ~220 three phase. Not being an electrical expert at all any thoughts on if this would have any issues working in uk/ireland? Or anyone know of a european/uk supplier of those boxes where ya just need the motor?

here's an example of the usa jobbies.
https://www.ebay.ie/itm/CP-10-Pro-Line- ... 0894402581
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NP317
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Re: Rotary or static converter?

Post by NP317 »

The 60 Hz vs 50 Hz in the UK could be an issue. Research that out.
I have experienced issues the other way around, getting 5 Spanish-built Clausing-Metosa lathes for use in the USA.
RussN
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