South Bend Nordic 15 electronics

I have a Nordic 15 I bought lightly used. Since I do not have 3 phase power to my shop I hooked up my static 7hp phase converter, eager to see this baby run for the first time in my shop. Then things got exciting. Long story short the transformer and the contactor coil are smoked. I checked all my connections to make sure I didn't cross something up. Everything was correctly hooked up. My neighbor is an electrician so I had him take a look. He said the phase converter caused the issue by outputting unbalanced voltages. Needless to say, I am not happy. I have a knowledge of electricity but 220v single phase is as far as it goes. My question is, now what can I do fix this? I have ordered a new coil for the contactor but what can I do with incoming voltage and the transformer to make sure I don't have a repeat oh sh*t moment. I'm open to all options. First time post, so if this is in the wrong group please direct me to the correct one.

You fucked up.

The static phase converter is really just a starter. It does not output 3 phase power. It just has some capacitors that let you start a 3 phase motor and when it's running it will stay running. The only way you can use it is to hook it directly to a motor through a drum switch or something simple.

It will not play nice with things like contactors and transformer. You need to fix the damage you did and use a rotary phase converter.

How many HP is the motor? If it is 3hp or below, I would rip out all the electrics, and put in a VFD. But, I have some experience with them.

allan

Ewlsey: Noted. Thank you for the reply. Dummy question: will a rotary have any voltage spikes? Just trying to gather info.

Kitno455: It's a 5hp motor. Could I use a vfd rated for 5hp though? I have a vfd that runs my bridgeport. It's rated for 5hp max. Maybe get one that's rated a bit higher?

A rotary phase converter is basically the same a static phase converter except it uses a dedicated motor to generate the 3rd phase. So it uses some capacitors to start and run a motor like your static, but then it uses the motor as a kind of generator to create a 3rd phase. It will not have voltage spikes if done correctly.

ewlsey said:

A rotary phase converter is basically the same a static phase converter except it uses a dedicated motor to generate the 3rd phase. So it uses some capacitors to start and run a motor like your static, but then it uses the motor as a kind of generator to create a 3rd phase. It will not have voltage spikes if done correctly.

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Is this something I can build? Or better bought?

Larger VFDs often require derating for use on single phase inputs. So, you have to buy a larger VFD than you need, just to get the bigger input capacity.

allan

Sharkfindustries said:

Is this something I can build? Or better bought?

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Google American Rotary, mine has been flawless for over 10 years, 2 friends bought American Rotary as well and have had no problems. I run 3 cnc's on mine with no trouble at all.

And my .02 ,if your lathe does NOT have a clutch use a rotary converter at least 200% of motor HP. IE my 18" has a 7.5 HP motor and for reliable starting I'm running 15 HP worth of converter, which is 200% of motor.

Just an observation. by the time you replace the transformer, contactors and verify that everything else is good, then purchase a good Rotary phase converter, you might be spending more than a VFD cost. a VFD replaces all of it. And is much simpler to wire up and maintain. all you need is to wire up your controls. and as a bonus, you get variable speed.

Just something to think about.

Stay safe and have fun.

Joe.

RPC's are really nice if you have multiple pieces of gear to run. With a large enough unit you can actually have it feed a 3 phase panel and split it out from there, provided you don't run so much at once that you exceed the RPC's limits.

For a single device, the VFD route probably makes more sense unless its a massive motor that you're trying to power. The phase converter cap boxes work for "dumb" devices like motors, but they don't play so well on things with electronics and controls.

kitno455 said:

Larger VFDs often require derating for use on single phase inputs. So, you have to buy a larger VFD than you need, just to get the bigger input capacity.

allan

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I wish people would stop propagating this nonsense.

JustinB said:

I wish people would stop propagating this nonsense.

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I'll quote from a Yaskawa manual:

Using VFDs specifically designed for single-phase use is not always practical as manufacturers may offer
single-phase models only in low horsepower ratings. Therefore, it may be necessary to apply a three-phase VFD in
larger capacity single-phase situations. When applying single-phase power to a three-phase VFD, there are several
constraints that need to be considered.

Standard Pulse-Width-Modulated (PWM) VFDs use a 6-pulse diode rectifier because of its simplicity and low cost
structure. The 6-pulse rectification results in 360 Hz DC bus ripple when used with a three-phase 60 Hz supply.
However, under single-phase use, the DC bus ripple becomes 120 Hz and the VFDs DC bus circuit is subject to
higher stress in order to deliver equivalent power. Additionally, input currents and harmonics increase beyond those
encountered with three-phase input. Input current distortion of 90% THD and greater can be expected under
single-phase input, compared to approximately 40% with three-phase input as indicated in Figure 2.0. Therefore,
single-phase use requires the three-phase VFD power rating be reduced (derated) to avoid over stressing the
rectifier and DC link components.

Other drive makers manuals say something similar. Care to give your sources?

allan

That note applies only to 3 phase input VFDs that are only being supplied with single phase.

If you buy a VFD that is specifically designed to accept only a single phase input, no derating is required.

ewlsey said:

That note applies only to 3 phase input VFDs that are only being supplied with single phase.

If you buy a VFD that is specifically designed to accept only a single phase input, no derating is required.

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Certainly. Do you know any such VFDs at 5hp?

allan