Rotary Converter

[m_c]

Still confused. Mine runs my lathe perfectly and has done for years. But I thought thats what a static phase converter did anyway...allowed you to run a 3 phase motor from single phase?

It does, but it has limitations.
The static converter relies on the load motor to stabilise the false phase (the actual produced phase, is an interaction between the induction load, and the capacitors). If all you want to do is run a single motor, then a static converter can work well.

The benefit of adding an idler motor, is you can power things other than just motors.
I ran my CNC lathe from a rotary converter, but I couldn't do that with a static converter.

Now I run everything from a 240 -> 380V VFD, although I still kept the idler motor to provide a bit buffer for shock loads, and to ensure the VFD had a bit load.

One thing I have noticed since going to the VFD, is the idler motor runs noticeable smoother.
A limitation of using capacitors, is the false phase is rarely perfect, both in voltage, and timing, even if your measured voltages are perfectly matched, the phase timing can still be off. This shows up as vibration as the motor accelerates/decelerates when the false phase is the main power source, in a similar way to how a single phase motors speed varies as it rotates. It's especially more noticeable when using modern light weight motors, which don't have the same rotating mass to help smooth things.

 

[Hopefuldave]

Rough notes made on each of the two 3P motors I have here, windings in balance but both damp after living "outside" albeit under cover for years. The IR was rising as I kept 500V on them so hopeful they might "dry out" a bit more.

View attachment 315488

I dried my lathe's motor by hooking a 12v battery charger up to the windings for a couple of days, got it nice and warm and dried it out well...

Dave H. (the other one)

 

[Onoff]

I dried my lathe's motor by hooking a 12v battery charger up to the windings for a couple of days, got it nice and warm and dried it out well...

Dave H. (the other one)

Used to bring them home from site and put in the oven on a low heat for a bit. Take back and fit the next day.

Used to get less grief for that than when I used to put my tins of cutting compound on the hob and gently heat them so all the swarf sank to the bottom. SWMBO used to kick off about the smell.

 

[Hopefuldave]

Used to bring them home from site and put in the oven on a low heat for a bit. Take back and fit the next day.

Used to get less grief for that than when I used to put my tins of cutting compound on the hob and gently heat them so all the swarf sank to the bottom. SWMBO used to kick off about the smell.

The BTH motor in the Holbrook would need a bloody big oven...

Dave H. (the other one)

 

[Turbo]

So why does mine work without an idling motor?

It does work with your lathe because the capacitors in it have been selected to suit that KW rating of motor but as you found out it doesn't work as well for different sized motors. Adding the idler motor helps smooth things out allowing the same static converter to work better with different sized motors without having to swap capacitor sizes.

 

[Turbo]

They're a Sod when they drop onto something hard aren't they! I too have a fibreglass (or similar) cased one that's a bit worse for wear like that.

I had 2 that were damaged at a building site & skipped, A friend rescued them & I was able to build one usable unit from the 2 and its being used regularly at our Mens shed. The remaining one is beyond saving, there is nothing left to attach the 110v sockets to! But the transformer is still intact so I'll be following your thread so I can make my own static/rotary converter! Thanks for the info.

 

[Onoff]

How do you work out what capacitors are needed.
I have a static converter running my master 2500 lathe but when I tried it on my linisher the motor started smoking.
I don't really want to gamble with my drill so I keep chickening out.

Buy Workshop Practice books 16, 24 and 47 and get ready for some maths and experimentation...hang on that's ME atm!

 

[Onoff]

I had 2 that were damaged at a building site & skipped, A friend rescued them & I was able to build one usable unit from the 2 and its being used regularly at our Mens shed. The remaining one is beyond saving, there is nothing left to attach the 110v sockets to! But the transformer is still intact so I'll be following your thread so I can make my own static/rotary converter! Thanks for the info.

As @Anguz said earlier make sure you disconnect the earth on the side where its centre tapped to earth. My mate who designed the rotary board I have here was very particular about the same thing, he wrote:

"One point, disconnect the earth and wire an earth from the motor direct to earth. The transformer is originally wired 55-0-55 on the secondary with the 0 tapped to earth. By the time you have the windings in series it would be 295V to earth!!

john.."

By "earth" John means connect to a good earth on the incoming side.

Can anyone suggest to me why a bigger 5kVA transformer is better for this project that a 2.2 or 3kVA one?

Physically this is going to be a beast for certain!

 

[Onoff]

I'm hopefully off to the garage in a little while to delve into a 110V transformer. Pictures to follow.

 

[Onoff]

...don't wait up, I'm still trying to make bench space!

 

[Onoff]

Debating how to house these 2 large 'ish 3kW motors and the rotary converter board.

- Custom frame out of 25mm box (I have lots).

- House it all in a old filing cabinet. Haven't actually got a h.duty 2 drawer one but...

- Angle iron base frame...got some 50x50 here.

Got some ali sheet for a cover.

In all cases castors on the bottom.

One complication is one motor is foot and other flange mounted.

 

[Onoff]

A bit of an aside, (but I am getting closer to starting):

As an avid collector of tat I picked this rpm/frequency meter up years ago out of some other kit going in the bin. Up to 1950rpm and 65Hz.

Thinking of adding it as a bit of bling. Just two 1/4" spade connectors on the back, one marked +.

How does it wire in?

 

[Anguz]

I may have some voltmeters and an ammeter to match that

 

[Agroshield]

How does it wire in?

The FG reference is FG Wilson, the generator manufacturer. So look for 'generator Hz meter wiring'. Google translate this one:

That meter was used in their 1002T analogue control panel (I think it is no longer a current model): https://pdf.directindustry.com/pdf/fg-wilson/control-panel-range/19697-395039.html

See http://www.crompton-instruments.com/downloads/2019/EPP-2042-03-19-analogue-cat.pdf (page 6 or page 9).

See also: https://uk.rs-online.com/web/p/energy-meters/9010576/ (RS always have the technical documents easily available).

 

[m_c]

How does it wire in?

Attach to suitable 200-250VAC supply.
As it's a frequency meter, the polarity doesn't matter, as it's always changing anyway.

I'm guessing the + is probably a generic marking for the housing, rather than being specific to that meter.

 

[Pete.]

As @Anguz said earlier make sure you disconnect the earth on the side where its centre tapped to earth. My mate who designed the rotary board I have here was very particular about the same thing, he wrote:

"One point, disconnect the earth and wire an earth from the motor direct to earth. The transformer is originally wired 55-0-55 on the secondary with the 0 tapped to earth. By the time you have the windings in series it would be 295V to earth!!

john.."

By "earth" John means connect to a good earth on the incoming side.

Can anyone suggest to me why a bigger 5kVA transformer is better for this project that a 2.2 or 3kVA one?

Physically this is going to be a beast for certain!

I use a CTE site transformer wired as an autotransformer to get 300vac for my DC drive on the Monarch lathe. I do it by only using half of the CTE winding in series with the primary, using the centre tap as my 300V output.

5kva is better than 3kva because it will be more likely to handle the load continuously. The 3kva one is probably not 3kva continuous in fact the 5kva one is probably only 3kva continuous.

BTW I don't know if he still has it but @awemawson had a big transformer on offer some time ago which would be entirely suitable for the job.

 

[GRW]

How do you work out what capacitors are needed.
I have a static converter running my master 2500 lathe but when I tried it on my linisher the motor started smoking.
I don't really want to gamble with my drill so I keep chickening out.

Statics have a minimum motor size they'll run. Quite likely that any motor under maybe 1-2hp might not "like" the static ph conv one bit.
BUT... if you started the lathe first so it acted as a pilot motor and takes the load on the static Conv above it's min threshold - then chances are the drill or linisher might then work fine.... but a drill motor is almost certainly too small on its own.

 

[ukracer]

Statics have a minimum motor size they'll run. Quite likely that any motor under maybe 1-2hp might not "like" the static ph conv one bit.
BUT... if you started the lathe first so it acted as a pilot motor and takes the load on the static Conv above it's min threshold - then chances are the drill or linisher might then work fine.... but a drill motor is almost certainly too small on its own.

Interesting....I had hoped to grab one of the cheap 240 to 440 inverters @Kram found in Amazon. Sadly I missed them and ended up with a 440 to 440 one instead. I could do with sorting something sooner rather than later.

 

[GRW]

Interesting....I had hoped to grab one of the cheap 240 to 440 inverters @Kram found in Amazon. Sadly I missed them and ended up with a 440 to 440 one instead. I could do with sorting something sooner rather than later.

Info from dealing with Transwave on and off for years. Firm I worked for bought kit from T-wave, and Peter from T-wave used to refer any queries for 3ph generators (I.e. when a Ph Conv wasn't suitable) to us.
I might even still have some of Transwaves useful tech sheets on the work 'Puter drive somewhere

 

[Onoff]

Here's a mad question...

Could you build a simple rotary phase converter and feed a 440 to 440 inverter like the one @ukracer just bought?


I can't think why you would but could you?