[dws_engineering]

Hello,
Have just installed a 3 phase generator for my workshop as have been running a rotary inverter for years.
The generator is 40kva and produces 55amps per phase,
when connected up to everything in the workshop e.g, big milling machine, bridgeport interact, all works fine.
However, when connected to the bridgeport vmc and the m/c turned on, the voltage on the generator goes from 400v to 450v and hasnt done the vmc much good as wires started smoking. No damage was done thank goodness. But does anyone know why this happens? All the other machines are fine.
Does it need a 3phase filter or diodes in the line?

any help would be great.
thanks
Dave

[Al_The_Man]

Obviously excessive current is the cause of the wires heating up.
Is this with the VMC powered up but not running?
Did you take a current reading on each phase when this happens?
It sounds like the excessive current is possibly causing the generator to compensate somehow.
Is there a misconnected ground somewhere maybe?
Al.

[dws_engineering]

Obviously excessive current is the cause of the wires heating up.
Is this with the VMC powered up but not running?
Did you take a current reading on each phase when this happens?
It sounds like the excessive current is possibly causing the generator to compensate somehow.
Is there a misconnected ground somewhere maybe?
Al.

Hello,
The machine was switched on and powered up when i noticed something wasnt right and quickly turned it off. I didnt leave it on long enough to take a reading incase something expensive was damaged.
It was the generators own dial that went up by 50volts.

Am now scared to plug back into generator to find the cause. Its strange why all the other machines are fine while plugged into generator. And the fact the vmc works fine while plugged into the rotary inverter.

cheers
Dave

[Geof]

Does the vmc draw the same current on all legs of the three phase? My guess is that something badly unbalanced the load on the generator and interfered with the voltage control.

Did you have all the machines connected and drawing power when this happened. If the answer to this is no I would consider powering up the ones that do work fine, all together, and checking the current draw on each leg. Then add the vmc into the picture and see what it does to the current draw. Measure the current one leg at a time so you can just turn the vmc on for a couple of seconds, enough to get an ammeter reading on each leg. My theory is that having a decent sized balanced load on the generator before connecting a possibly unbalanced load will stabilize things and allow the generator to maintain the correct output voltage.

[dws_engineering]

Does the vmc draw the same current on all legs of the three phase? My guess is that something badly unbalanced the load on the generator and interfered with the voltage control.

Did you have all the machines connected and drawing power when this happened. If the answer to this is no I would consider powering up the ones that do work fine, all together, and checking the current draw on each leg. Then add the vmc into the picture and see what it does to the current draw. Measure the current one leg at a time so you can just turn the vmc on for a couple of seconds, enough to get an ammeter reading on each leg. My theory is that having a decent sized balanced load on the generator before connecting a possibly unbalanced load will stabilize things and allow the generator to maintain the correct output voltage.

I had all the machines powered up and spindles running when i turned the vmc on. And i tried turning the vmc with nothing else on and still the same result.

Will try measuring each phase later. I may try swapping two of the phases around and see what that does.
many thanks
Dave

[Al_The_Man]

I would power off as much as possible in the VMC, breakers etc, and see what the results are, if you can get it come on and stabilized, then bring various systems on line one at a time?
Al.

[dws_engineering]

I would power off as much as possible in the VMC, breakers etc, and see what the results are, if you can get it come on and stabilized, then bring various systems on line one at a time?
Al.

Very good idea. When i get time to get the generator out again ill try that. Let you know how i get on over the weekend.
Thanks

[dws_engineering]

For anyone else with this problem,
A three phase filter has sorted out the problem

[petextr]

HI i recently bought Bridgeport interact 2 and i don't have 3 phase line in my garage ,and i wont run this machine from 3 phase converter ( transwave ) but i don't know what power bridgeport have motor 2hp plus other electronics control and tv. i need some advice if anyone did this before

[dws_engineering]

Hello,
i run my other machine which is an interact 2 mark 2 from a transwave rotary inverter.
These machines dont like static converters if thats what you have,
I'm running the controll and screen from mains 240v, this is done by wireing in the controll to a 13amp plug. remember you need to change the voltage on the switch to 240v instead of 110v on back of controll.
If you have an interact 4 you may need a mains filter as my vmc needed one as the spindle drive and boards created spikes in the electric when run from a generator.

hope this is of some use.
Message me if need any help.
cheers
Dave

[claya]

For anyone else with this problem,
A three phase filter has sorted out the problem

I am thinking of using a 3phase generator to determine the size of phase converter we need for a VMC. (47kva @ 136amps) How has the generator worked out. Any suggestions?

[Jim Dawson]

The easiest way to figure out what RPC that you need is to look at the nameplate amps on the machine. The spindle is the high current user so if you take the spindle HP and multiply by 1.5 you should be well within the safe operating range. Every 3 phase motor that is added to the circuit (coolant pumps, hydraulic pumps, ect.) adds to the starting capacity of the RPC

On a CNC machine tool phase balance is important, so install a CNC rated RPC.