It's finally time to power up the ole Bridgeport!

[Cadillac STS]

When I first got my Bridgeport and powered it up it just blew the circuit breaker. Couldn’t figure it out for a while. Turns out the spindle brake was set on and the motor couldn’t turn. Turned off the brake and everything was fine!

 

[Izzy]

I haven't gotten power to it to test out my breakers yet haha if y'all think I'll be ok with a 5hp roto phase I'll contact that guy and get my machine running!

 

[Chipper5783]

If you want to go cheap, for the purpose of testing you do not need the transformer. You can run that 440V motor on 240V. Motor shops routinely run motors at reduced voltage when testing them (generally it is much higher voltage and larger motors than what you are considering, but the concept is the same). Of course you still need the RPC.

You can't run a low voltage motor from a higher voltage source (i.e. a 240V motor on 440V would not be good). There is no problem running a 440V motor at 240V - however, you must not exceed the motor nameplate full load current. That 4HP motor will be totally gutless (perhaps less than 50%), but you'll still have more capability than most mini-mills. Of course you still have to sort out the requirements for the table drives (which you said were DC) - but at least you will know that the main motor is good.

You will have a control transformer and it will have multi taps, so you'll need to move the tap connection so that your control power (which is single phase anyway) is the correct voltage for the coils. I always use the "real" power (which I set up on L1 & L2, with L3 being the generated leg) on the control transformer - not sure if that matters.

Your other question is whether that 5HP RPC is going to be adequate? That is a good question. I also have a 5HP RPC and I have two machines with 5HP motors: an air compressor and a lathe. The air compressor runs with no problem. The lathe has a 2 speed motor (3/5 HP) will trip the RPC if on the higher speed settings or with a heavy chuck or several starts close together. It has a manual speed switch - I don't change it on the fly.

I also have a 3 phase transformer 240-600V on my little milling machine (6kVA). It also has a 2 speed motor, which is 2.2 kW on the high speed (about 3HP), it struggles to start on high speed (sometimes it goes, sometimes it trips the RPC). This little mill has separate contactors for each speed so I hit the low speed button, then the high speed button.

If you are getting that 5HP RPC at a fair price - go for it and get your machine going. If it does not work out, you won't have trouble selling it on a fair price (may be a small loss).

Let us know how it works out. David

 

[Izzy]

@Chipper5783 thanks! I'll contact the seller for the rpc! My only 3phase machine is my mill. The control panel transformers are already setup for 440 3phase so all I gotta do is hook up 440 3phase and it will all work. The transformers in the control panel feed the DC motors.

 

[warrjon]

Someone was telling me the transformer may stall the rpc due to it's size? Is that a possibility? Id hate to buy something I can't use...

You really only need 4KVa to easily run a 3kW motor as the mill does not start under load.

They are referring to inrush current and a 25KVa transformer this will be around 60 amps.

I would put the stepup transformer before the RPC and run the RPC at 440volts, this way the mains will be handling the inrush. Or add relay operated current limiting resistors that are switched out once the TX is on.

 

[warrjon]

You could run a VFD into the setup TX in place of the RPC and have over current control as the VFD will ramp the voltage up significantly lowering the TX inrush current. Don't know about the US but Down under my 4KW VFD was $200 and a RPC was $1500

 

[Izzy]

im from canada. im getting both the transformer and phase converter for 400. its hell trying to find industrial type stuff in my area there was literally only one other RPC for sale in my entire province.... it was also a 5hp but was asking 600. its next to impossible to find a sinlge phase transformers at that high of a voltage normally anything over 220 here is 3 phase. i knew this thing would be alot bigger than i need but its literally the smallest 220/480 transformer i could find.... is it possible to have a shop lower the Kva rating?

 

[warrjon]

To give you an idea of how big a 25KVa TX is - I have a 10KVa TX on the pole outside my house feeding 3 houses from the HV. If I were you I find out just how big this 25KVa TX is, do you need a crane to move it.

Here is a pic of a 25KVa TX
https://www.indiamart.com/proddetail/25-kva-three-phase-transformer-13476189248.html

If you do go this way the 3 phase TX can still be put in the single phase, just use 1 phase of the TX.

If I were you I would seriously look at VFD's. My mill is 5hp with 110Vac power feeds running off a TX inside the mill cabinet. I have rewired my mill so everything runs and the original switches operate the mill. I do not use the coolant so this is disconnected. I have disconnected the main contactors as the VFD runs the motor directly.

Our single phase is 240V, I put a 240V power lead on the mill, changed the input tap (My TX was multi tap) from 415V to 220V. Then wired 240V directly out to the VFD, so the main power switch on the mill turns the VFD off.

I rewired the forward/reverse switch to the VFD so it controls F and R.

The motor was star only, so I had to find the star connection in the motor and bring it out to the terminal box, easy to do this took less than an hour including re-lashing the motor windings. If you are unable to do this any motor shop should do it for a reasonable cost.

 

[Izzy]

i cant run a VFD because the motor is wired into a control panel in the back of the machine, power does not go directly to the motor. it goes through a set of contactors, fuses, and motor starters thats why i cant run a VFD. its not that i havent looked into it i thoroughly have when i first bought the machine the problem is this isnt your basic mill its a series 2 its a little more complicated. the panel needs to see 440 3phase and from my research a VFD is not a power source its a motor controller. correct me if im wrong but from what i can gather is the contactors wont work properly with power coming from the VFD the VFD has to power the motor directly correct? here is the transformer in question. add states 25kva. but i honestly dont have the slightest clue about that kinda **** tho it'd be like telling your wife the lawn mower has 500hp she'd believe it haha

 

[Izzy]

i had a motor shop look at the motor and its permnently wound for 440 volt and changing to 220 would require a new motor or a re-wind and that alone puts me well over the cost of a phase converter and rpc setup. then id stall have to buy all new fuses, contactors, and motor heaters so not only would that be exponentially more expensive it would also be alot more work. the conclusion ive drawn is the cheapest easiest possible route is the one im taking i just need a little help figuring out the details. heres the transformer in question, its the little guy.