Rotary phase converter (pics)

[Brad Buchanan]

Hey folks.

This is an update on my project to build a rotary
phase converter.

I bought a 36" bandsaw at an auction and it needs
550volt 3 phase power. I bought a 5hp 575 volt
motor and a transformer to boost my 240volt line
power to 570 volts.

I assembled my main panel with start and run
capacitors (red and blue tags), 600 volt
contactors and the hookups.

My first attempt to start the idler failed as I
had the start caps wired to T1 and T2 instead of
T1 and T3.

After that was fixed I threw the main switch which
powers the transformer, the 110 volt switch that
closed the contactor powering T1 and T2 at 570
volts and the monentary switch that brought the
start caps online.

The 5hp idler motor started in less than a second
and ran smoothly.

Unfortunately the run caps were not in the circuit
when I tested.

Voltages on the 3-phase output were:

T1 to T2 554
T1 to T3 460
T2 to T3 466

Amperage Draws were:

Line to transformer (240v) 6.6
High side (570v) 2.3

I patched in the bandsaw and it started without
drama and ran smoothly. I cut some hardwood with
it and it worked perfectly however I noted some
slight noise from the motor when ripping some 2
by.

With the saw idling the line in was drawing 23
amps and the high side 9.6 amps.

Qoustion: Can I balance the voltages better with
the start caps?

Also I was under the impression that the caps did
not store energy (at least much) when operating on
AC power. This misconception was dispelled when I
touched my finger to a terminal accidentally. I
touched the terminals with leads from a 100watt
spotlight I had handy to drain the caps down and
it smoked the bulb instantly and I had a fat, blue
spark when I touched the lead to the terminal.

Sorry for the long post but I am pleased and
excited that I can see progress in this project.

As always comments pro and con are welcomed.

Brad

 

[Russ from MN]

Looks good! Does the cat still have a full length tail?

 

[Steve@Advance]

So with this setup, you can use the start caps to start the idler motor through an intermittent switch and a contactor? Always wondered if that was possible, never heard of it being done but seems it would work.

I'd sure like to see a schematic once you get the bugs worked out.

 

[retired farmer]

I hope you don't end up electrocuting you and the cat.

 

[buickandeere]

That is the problem with a rotary converter. Voltage, current and phase angles are not true and consistent like utility and VFD"s.
Most of the time however the motors fed the quasi three phase are not worked to rated load or for extended periods of time.

 

[Geo-TH,In]

Brad,
Congrats, you stuck with it.

Yes, you use run capacitors to balance the wild leg. At this point it comes down to a matter of trial and error.

Keep records of the voltages and currents for L1, L2 and L3. Different size run capacitors will rock the phase angle, changing things a little.

Not to mention, each time you add a different 3 phase motor, things will change a little.

You won't get things perfect, but it will come close.

My dad would cut the shaft off the phaser motor, safety I guess. He would also put the rotor in a lathe and remove some of the rotor. Don't know how much. I was never really that interested. Again, it was a matter of trial and error for him to come up with the best balance. 3 phase converters may be about 75% at best, so a 4 hp motor may give you 3 hp.

You will do it. Isn't electricity fun?
George

 

[Greg 2N (TX)]

The voltage level that gets stored on a particular cap depends on the last state of the source or generated waveform at the time of disconnect.
If the sine wave happens to be going through zero at disconnect time then the stored voltage will be minimal.
Unfortunately more time is spent away from zero either positive or negative throughout the full cycle.
Boy if the sine wave is at its peak (1.414 x rms value) at disconnect we're talking REAL danger there!
For instance 550 x 1.414 = 777.7 V peak! Ouch!
For 240 x 1.414 = 340 V peak approximately.

Greg

 

[MF294-4]

I built a rotary converter for 240 last year. I don't think you can use the start caps for the balance caps if I understand right about what you are asking. The balance caps are a lot smaller value than a start cap and a different makeup. Go to one of the machine shop forums. Hobby-Machinist.com is just one that I use and there is a lot of good help there on building converters.

 

[buickanddeere]

As recipusly stated.Starting caps are not for continuous operation . They will fail.
The oil filled PF correction caps are near indistructable .

 

[Brad Buchanan]

Start caps joined the circuit via a magnetic contactor and a momentary switch. They were disconnected as soon as the idler motor started.

 

[Brad Buchanan]

The run capacitors on the main board (silver) will be added to the circuit to adjust the phase angle and voltage. The start caps are just used for starting the idler motor.

 

[Brad Buchanan]

hey Greg.

Thanks for the info. I got shocked across my hand and whether peak or rms it was quite a snap!!

Brad

 

[Brad Buchanan]

Hey George.

Thanks for the kind words. I have learned a lot just researching this project and from all the help I got on the forum.

I am currently installing the equipment in appropriate enclosures and when I have the system in a safer for I am going to experiment with the run caps and will keep updating as there is interest.

I was really happy that I got the saw going and my wife Barbara is looking forward to trying it out for some projects.

Brad

 

[Brad Buchanan]

Hey Steve.

Check your e-mail.

 

[Brad Buchanan]

Buster the cat has never seen anything he is afraid of and still retains his tail.

But he is still just a RCD (rodent control device).

 

[Geo-TH,In]

Brad,
When we made phasers and with air conditioner motors, the run capacitors are connected all the time. No need to pick them up after you remove the start caps.

Like someone said, if the start's are left in there they go BOOM. Starts are good for a few seconds at a time.

Just experiment with the run caps to balance currents.

Keep up the good work. Good luck.
George