[How do I?] Another Rotary Phase Converter Question

[John Hasler]

I guess I could bring in a 100 amps to run my ''irrigation pump''. A lot of those out in this area, in fact, that's the main reason there is 3 phase everywhere out here. A saw mill is a permitted use too.........Hmmmmm

What are these "permits" and "inspections" you speak of? You don't live far enough out into the country.

 

[Smithdoor]

The full amps on a 5 HP is around 28 amp 240volt you need the higher amp for starting the motor
the 10 Hp will full load is 50 amp for starting you need 100 amps
I have run 10 HP on a 60 amp breaker but would trip from time to time

Dave

Hey Dave,
your statement about a 50 amp service running only a 5 hp motor, simply is not true.
I have a 7.5 hp RPC that is wired to 50 amp single phase service that starts and runs unloaded 10 hp motors without tripping the breaker.
that is twice the capacity you stated.

 

[Wireaddict]

I'd be afraid to make a Y-delta transition with a motor connected to a an electronic VFD because of voltage spikes that could destroy the VFD output as any other hard contact between a VFD & motor might.

Are you still considering using a 10 hp RPC/idler? Since your surface grinder will only use 60 Hz. that's a consideration. I have one machine, a Sheldon lathe, that's wired for straight 480V, 3-phase so I use an RPC & a 6 KVA [open delta (primary & secondary)] step-up transformer to run it. Since I didn't have any 3-phase motors to try out I bought a new RPC but would've preferred to experiment some. Incidentally, the lathe runs great with this setup; when I run it for several hours the transformer gets maybe 30 degrees warmer than the rest of the shop or warm to the touch.

 

[uncle harry]

John, you raise a good point about not switching all of the motors off. I wonder if adding a 1/2 hp motor to the mix that always runs, as an idler, would be the key. Hmmmmm.

Maybe you could use the coolant pump as the "added" idler by adding a 3-way valve to the coolant pump output. Assuming that there is a contactor for the coolant pump, you could use a dpdt center-off switch for the contactor coil as well as the bypass valve coil. One pole would control the contactor only in both "on" positions while the other pole would control the bypass valve in the "idler" mode. This all assumes that the pump has enough "idler" horse power.

 

[Smithdoor]

In Fresno CA the permit is around $100
The meter ring is $200
Wire and other parts need $300
The cost of contractor is $1,000
The power company to bring the power to bring the power to meter was 10,000

you what see of up grade a meter to 400 amp 1 phase if power company is too high

Dave

What are these "permits" and "inspections" you speak of? You don't live far enough out into the country.

 

[Wireaddict]

I use a RPC to drive a 6 KVA 3-phase [open delta (primary & secondary)] step-up transformer to power a Sheldon lathe which has a straight 480 VAC motor & it works great. When I use the lathe for several hours the transformer gets about 25 degrees F above the shop temperature. If I had a 7.5-10 hp 3-phase motor to experiment with I would've tried to make my own idler/RPC but instead I bought a RPC & tranny to save time.

 

[Wireaddict]

Oops---I didn't see my post from last night so I repeated part of it then couldn't remove the one from tonight. Sorry!

 

[Scruffy]

I run my 15 hp pause converter on a 50 amp breaker and haven't tripped a breaker in 2 yrs of use. And yes I have used all 15 hp several times.
Thanks ron

 

[uncle harry]

Not an ideal setup but, being an experimenter, I'd try this, too. Rather than using a starter or spin-up motor the first thing I'd try is add a cap [not sure what size but I've seen info on this on the 'net] between one of the power leads & the third motor lead through a NC contact from a contactor to start the motor with no load. I'd connect this contactor coil to an on-delay timer set for more than enough time for the motor to get up to speed. I'd use a second contactor with 3 NO contacts between the 3-10 hp motor leads & the load-side disconnect switch &/or other protection equipment. The intent of the timer-contactor wiring is to allow the motor to start & accelerate unloaded, then apply the derived 3-phase power to your loads. To try it out I wouldn't even use a timer & probably just a NO push-button switch to the starting cap; I'd only want to check the impact of starting the motor on the lighting, AC & other equipment. You might find that you don't need an auxiliary motor & everything else to get it rolling.

One more thing I'd try is to add about a 10-20 uF, 350-450 WVAC "motor run" type cap across the 2 motor leads that you're applying the 240 VAC to; this'll improve power factor somewhat & reduce the motor current. This applies to the motors you'll be supplying, too. Hope this helps.

This approach is just what I did for my rpc. It's only a 3 HP 3 ph motor and is started with a delay timer to bring it up to speed. After the time out the start contactor is switched out & a 3 pole 3 PH contactor engages to supply the resulting 3 Ph to an outlet for various machines (in principle & actuality since I've never used it). I have since employed 3 dedicated VFD units for 2 lathes & a Bridgeport KO. It is there if I need it for any other impulse purchases that I might let "follow me home". Every so often I hit the start button to hear it run.