Rotophase

[ptonsparky]

Son in law is looking at buying some equipment from an old welding shop. He’s 7 hours away.
They are driving a 15 hp 3Ph motor with a 1 hp single phase via belts to generate 3 phase for 5 hp. SEWAG tells me there are some capacitors in the mix somewhere but I didn’t see them via FaceTime this afternoon. They have a similar set up driven by a 1/2 hp 1 Ph, for 1 Hp 3ph.

Can someone point me to info on these homemade phase converters?

 

[MTW]

The small motor “pony” is just to get the RPC generator up to speed. After that the RPC runs on single phase and generates the third leg or phase, as similar to a center tapped delta.

Transformers, Phase Converters and VFD

Machine voltage issues, three phase via single phase power, and variable frequency drives discussion >> moderator JST

www.practicalmachinist.com

 

[Jraef]

The small motor “pony” is just to get the RPC generator up to speed. After that the RPC runs on single phase and generates the third leg or phase, as similar to a center tapped delta.

Transformers, Phase Converters and VFD

Machine voltage issues, three phase via single phase power, and variable frequency drives discussion >> moderator JST

www.practicalmachinist.com

Yeah, otherwise you would be getting free energy!

The capacitors are just yo balance the voltages better.

You can peruse plans at this site from Practical Machinist, these guys do that a lot.

Rotary Phase Converter Designs and Plans

Post 'em here !

www.practicalmachinist.com

 

[ptonsparky]

What HP will I be able to run from that 15?

 

[Jraef]

Load wise, the 15HP motor will draw 1.732 x its normal current from the single phase supply. So that motor has a FLC limit, based on the thermal effects of that current. So working that backward, it means you can load it to 58% of its FLC (58% is the inverse of 1.732). I don’t have a chart here, but let’s say the 15HP motor is 21A. That means the maximum load you can pull off of it is around 12A, so a little less than an average 10HP motor at full load.

In other words, with a load of 12A at 3 phase connected to that motor as an RPC, the 15HP motor will draw 21A from the single phase source, and since 21A is the FLC of that motor, any more than that is going to overload it.

If you are willing to run that 15HP motor into its service factor, that takes you up to 14A, a full 10HP old fashion motor.

 

[junkhound]

my shop's rotary phase converter is a 100 HP, 1200 rpm, 460V motor. Bring it to speed with a 3/4 hp 1725 rpm motor which is switched off at 1300 rpm no load, then 240 single phase applied to one 460 phase works great, runs 5 HP 3 phase motors just fine

 

[herding_cats]

Yaskawa guy here. If you want the best setup, speed control etc, you can run single phase input for three phase output on a VFD. Use a line reactor, double the amperage size of the drive and you are good to go. Use the GA 500 series drive.

 

[Jraef]

Yaskawa guy here. If you want the best setup, speed control etc, you can run single phase input for three phase output on a VFD. Use a line reactor, double the amperage size of the drive and you are good to go. Use the GA 500 series drive.

Only if the load is a 3 phase motor.

 

[herding_cats]

Yes exactly. Stay above 20 Hz also.

 

[ptonsparky]

Yaskawa guy here. If you want the best setup, speed control etc, you can run single phase input for three phase output on a VFD. Use a line reactor, double the amperage size of the drive and you are good to go. Use the GA 500 series drive.

I've done that often enough.
The pony setup comes with this OLD equipment and his budget is nil. I had never seen this done before.

One of the cobbled up systems has a brake on the motor. Old crane or manlift motor.

 

[Electromatic]

One small detail of advice for the motor brake: Try not to have that part of the machine circuit on the generated phase. I had a customer with a large wood lathe running from a RPC. We had to swap phases around until the brake was not using the generated phase.

 

[ptonsparky]

On a side note, I am now getting a clearer picture why a phase loss monitor reliant on voltage does not always work in areas with multiple motors, especially with larger lightly loaded motor(s)

 

[Jraef]

On a side note, I am now getting a clearer picture why a phase loss monitor reliant on voltage does not always work in areas with multiple motors, especially with larger lightly loaded motor(s)

Yep. I’ve made this point many times to people worried about phase loss. Some of the voltage monitor mfrs claim to have some secret sauce that will not be fooled by regen from spinning motors, I’m a skeptic in that regard. I prefer detecting phase loss in a motor by monitoring current. Most solid state OL relays do a great job of that now, and some are around the same cost as thermal OLs.

 

[jim dungar]

Yep. I’ve made this point many times to people worried about phase loss. Some of the voltage monitor mfrs claim to have some secret sauce that will not be fooled by regen from spinning motors, I’m a skeptic in that regard. I prefer detecting phase loss in a motor by monitoring current. Most solid state OL relays do a great job of that now, and some are around the same cost as thermal OLs.

I use the phase loss relays with Negative Sequence sensing, especially in rural areas. They are very good at reacting to a blown fuse or phase lose even on the primary side of a utility owned transformer.

 

[winnie]

Last year a dredged up an archived link to this old rotorphase setup. Mostly worth an OMG with lots of exclaimation points:

using old motor to transform 240v to 460v ?? - ECN Discussion Forums

This was a multi-stage setup, where the guy used a pony motor to get 25 hp up to speed for phase conversion, then a separate pony motor to get a 40 hp load motor up to speed before connecting it, and then used the synthesized phase to run other loads. It was a DIY question where the guy wanted to switch everything to 480V in hopes of getting more power out of his 200A 240V single phase service....

-Jon