220 V 1Ph to 600 V 3Ph Help Needed

I have read many threads from this and other sites and I have gained some knowledge but not enough to feel confident about investing in hardware yet. I received (for free) a large lathe that requires 600v 3Ph. I have 100 amps of 220 going to my garage. I believe I need to purchase a rotary phase converter and a transformer to create 3Ph then step it up to the required voltage. The machine manual recommends 30 amp feed. There are 3 motors in the machine, an 11Kw spindle motor, a lube pump motor and a rapid feed motor. There is also a small transformer that creates control voltages. Changing to a lower voltage would not be a reasonable proposition. I am making the following assumptions;

30 amp x 600v = 18KVA so I believe a 20 KVA 220 - 600 transformer is required.
18KVA x 1.5 = 27 KVA so I believe I need a 36 hp phase converter.
36 x 750 = 27000 watts or 123 amps so I believe my amperage may be limited but this seems excessive to me based on the actual current draw of machines I have owned in the past.

Another way to look at this is total machine Hp (17) requires 23 amps at 600V or 14KVA. Could I use a 15KVA transformer and a 25hp phase converter which I could feed with 85 amps?

And then of course there is inrush current, isolation vs auto transformer, step up vs back feeding a step down transformer and many other unknowns. Any pointers would be greatly appreciated.

Glenn

you can feed a 20hp with about 85A
I have done this all, auto transformer and a 20hp spindle to drive a 10HP cnc mill that says 63A at 230V
biggest thing is having a big enough rpc to drive it, without it the voltages spike all over.
also check the voltages now and again, here in canada it goes up and down like crazy off the 240V.

Common problem for us in Canada. I run a 10 hp Phase Perfect to generate three phase feed a 30 kva transformer wired backward to boost to 600 all on a 40 amp breaker this will run a 10hp 600 volt motor motor but it is marginal. The limiting factor seems to be the phase converter.
Bob

My experience ( not expertise ) tells me the 100 amp input is marginal at best. There will be losses along the way and starting up a large old machine takes some reserve. If you are also running lights, air, etc on the 100 amps you don't have all of it available. The transformers are also generally oversized a little more than your example. You might make it work but I'd oversize the rpc and transformer so if you have problems it is only the wiring that needs to be swapped. Keep in mind that some rpc will be sized by the largest motor they will start and others by how much hp they can handle. An Am rotary 25 hp won't be adequate ( 30-40 would ) but a 25 hp Kay would. Both would want more than 85 input amps.

I'd also prefer an isolation step up transformer but will let others guide you there. You could also consider a motor swap. I just bought a NOS Marathon Black Max 10 hp 230v three phase motor ( $2500 new ) for $350 including shipping. Motor deals are out there and even with new starters might cost less than a transformer and eliminate the input amp problem. Dave

Thanks gentlemen. I just stumbled on an RPC and transformer pkg on Kijiji that is being used to start and run a 15hp motor at 600v. I will take a look at it tomorrow and see what supply amperage is being used. I find that things nominally run at far less amperage than the max rated startup peaks and the motor in the lathe has a current limiting start circuit on it. The lathe is in my garage and there will be no other loads other than lighting and it’s all LED. I will reply again after I see the RPC.
Glenn.

Make sure you have disconnect switches or contactors between your phase converter and your transformer - starting the phase converter with the transformer connected creates a very high current draw at startup. Best to start the phase converter all by itself, then connect the transformer, then start the lathe.

Thanks Guru, will do.

metronorth said:

Thanks gentlemen. I just stumbled on an RPC and transformer pkg on Kijiji that is being used to start and run a 15hp motor at 600v. I will take a look at it tomorrow and see what supply amperage is being used. I find that things nominally run at far less amperage than the max rated startup peaks and the motor in the lathe has a current limiting start circuit on it. The lathe is in my garage and there will be no other loads other than lighting and it’s all LED. I will reply again after I see the RPC.
Glenn.

Click to expand...

That the ADX american rotary on there im guessing?

It is. I purchased it today and will pick it up on Monday. It’s larger in real life than the pictures suggest.

metronorth said:

It is. I purchased it today and will pick it up on Monday. It’s larger in real life than the pictures suggest.

Click to expand...

decent unit, remember the motors alone weigh like 200+ lbs they work pretty decent. just need to wire it up and go.

It will need to be strapped down well before driving it home.

these few equations will help to guide you in the future
1 HP =746 watts
watts = volts times amps
amps = watts divided by volts

none of this includes efficiency or other loss considerations that will eat a small percentage of your supply amps

do not forget to calculate the input amps to determine if your electrical service can handle the load

also as you mentioned lathes usually dont run at full motor load,
but starting current will always be the same for a given motor, particularly with a heavy connected load (big chuck)

as the guru mentioned
do not forget to determine the input rush for your transformer, it can be amazingly high when stepping up
(it is the result of the magnetizing current in the txr windings. the same as a motor. it will continue to be high until the core is magnetized and creates an impedance. same as a motor and usually shorter than a motor since there is no inertia to overcome) . a circuit breaker is much more tolerant of short over current events than a fuse
and i also recommend disconnects/contactors between rpc, transfmr, and load

finally be sure the wire/conductors you use are rated for the full load amps of the eqpt. you are feeding. even though you expect less at normal use

After getting advice from members here, I decided to upgrade the service to my garage to 125 amps. But there’s always a catch! When digging out the original feeder cable, I found it buried at 12” or less with no proper conduit protection from the 24” depth into the house or garage. Ok, no problem, I was going to dig 24” deep and do it right anyway but the trench was shared by the gas line feeding the garage and it was also buried 12” or less below grade with no trace. I bought the house 3 years ago and our lawyer recommended title insurance to protect us from these types of surprises so it looks like I will be delayed until things sort themselves out.
Typical.