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230v to 380v VFD - Euro Motor Questions

BHolcombe

Aluminum
Joined
Apr 15, 2019
I recently brought a Graule Radial arm saw in from Germany. The motor/controller is a bit confusing as it has a lot to say but doesn't quite clear up what the machine is wired for. It needs a bunch of stuff repaired but one of the head scratching areas is the voltage.

I've seen other listings for these saws, with dual voltage listed 230v/380v, however the tag is typically placed on an area of the saw that has been replaced with a new part on this machine and the tag was not saved.

Anyone with experience in this would be greatly appreciated.

If it is 380v, what kind of VFD will be needed?

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Note that a VFD first converts input AC voltage to DC. AND that the DC voltage can be greater than the nominal AC voltage.
MOST good VFDs allow programing for V/Hz relationship.

So....

If the VFD output is set to follow a 380/50 or 380/60 relationship, the motor wired wye will function fine on just about any nominal 240 V input. (set Freq. out Max to achieve desired motor rpm)

Rotor speed may not be per data plate at rated voltage, but it will be "correct" per seen VFD output.
 
Note that a VFD first converts input AC voltage to DC. AND that the DC voltage can be greater than the nominal AC voltage.
MOST good VFDs allow programing for V/Hz relationship.

So....

If the VFD output is set to follow a 380/50 or 380/60 relationship, the motor wired wye will function fine on just about any nominal 240 V input. (set Freq. out Max to achieve desired motor rpm)

Rotor speed may not be per data plate at rated voltage, but it will be "correct" per seen VFD output.
This will work up to about 40hz. Then torque drops.
 
Most 400V (380-480V) VFD's sized for the output current would work, but would need to have an input voltage higher than the output and 3 phase unless running in a derated mode using a higher output VFD (see individual VFD deratings). There are some VFD's that step up the voltage and are single phase input 220V. How well they work and durability is a question.
 
So, sounds like it might be best to run from the RPC, to a step up transformer.

I like the promise of those ATO step up inverters, but I’m wondering about their quality simply because no other manufacturer seems to offer this on anything outside of small motors.

Might be worth taking the risk and seeing, since it will be easier and way less expensive than any other approach.

As an aside, I’m looking into having the motor rewound for 240v 3ph. This will also be expensive but for the simple fact that it is going to make things less complicated I may do it if I can find someone who will do the work.
 
If the motor's junction box doesn't have all six wires brought out, the rewire job (on a UK/European motor) should be only to find the (hidden inside the motor) star point and separate those three wires to bring them out. Can be a relatively simple DIY job if you are happy with a soldering iron and some insulating sleeve.
 
Mark,

If I change this to delta, would it run on 220v 3ph 50hz?

This certainly would make life much easier.

I’m just a bit confused because Europe’s 220 is single phase wye.
 
Well, here’s what’s under the controller. Six wires in total, but one appears to be a ground and another appears to be a neutral.

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If 3 coming out of the motor are connected together, them break that connection and check for continuity to the three phase wires.

It is unusual for the star point of the 3 wires to be connected to neutral.
 
There are definitely five wires on the supply connection, which normally implies three phases plus neutral plus ground. The ground connection can be eliminated by checking between the wires and the metalwork, should be the green/yellow one! on the other connections, if there are three wires (plus the one going to the supply) joined together, that's the star/Wye point, which needs separating into individual ends.

if those aren't obvious, you need to disconnect the chocolate block/connection block and map out the connectivity between each pair of ends. If you don't have a multi-meter, this is a good time to get a cheap one, failing that, a battery and torch bulb can be used.
 
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There is a manual for newer versions (dual voltage) of this saw that may be helpful but schematic is in German, might also email the company. VFD voltage doublers are more common in the smaller 120 to 240 models, although Phase Perfect does sell single phase 240 to 3 phase output 480. Cost of voltage doublers at the higher voltage is less cost effective/practical vs. 3-phase step up transformer. A Phase Perfect (Simple models are on sale) could be used with a step up transformer as an alternate, but gets pricey.
 

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Thanks, gents! This is very helpful!

Looks like I may have to open up the motor and see what the terminated connections look like. So far, I see three motor leads, two for the overload, and a ground.
 

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Inside the motor
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Five of these go into insulation, I don’t see any type of overload switch and the yellow/green is connected to a ground.
 
Sounds good, I’ll go ahead and do that. Thanks for your guidance!

I assume I’ll have to reapply electrical insulating varnish, and the wrap/cord. What is the wrap and cord made of?

Edit, I found McMaster sells fiberglass tape made to absorb insulating varnish, and sells aerosol insulating varnish.
 
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