Dead speed controller on Sieg SX2, can I just use an off the shelf VFD ?

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BruceCook

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Hi all, a couple of nights ago I went to switch on my mill, it twitched and then the fault light came up. I spun it a couple of times & got it to run twice, but it sounded very rough. I've looked at the mechanical components, and those look fine, so I'm guessing the roughness is one of the windings not being properly energized by the 3 phase inverter in the controller.

Looking at it it seems that the Motor is OK (a 500W 3-phase 230 volt "dc" motor) 5.5 Ohms showing between U, V, W.
I've seen a number of posts where the controllers in these give up the ghost, I've taken a look at the 6 IGBTs and testing in-situ they all look to be ok, so I'm guessing it's one of the other components & given I'm in the middle of a project I don't really want to stop and try to figure the board out.

The replacement controller from the manufacturer is $500, and frankly at the price I would prefer something more robust. Looking at ali express I see a number of "industrial" 750W 250v 1 to 3 phase VFD units at the $70-80 mark, which seems like a reasonable option I could have in 2 weeks. The bonus with these is that they have a number of additional interfaces I could play with in future.

The only issue I see currently is it looks like the motor has a hall effect unit - there's a 6-wire shielded signal cable to the motor & I can't find reasonable documentation on the VFDs (or the motor) to work out if it can be hooked up. or indeed if it's actually required. I am quite comfortable with electronics, but no specific experience with these motors.

Aside from the caviet emptor implied by the source (I'll have a fire extinguisher at the ready) is there any reason one of these off the shelf VFD units wouldn't work ?
 
BruceCook said:
Hi all, a couple of nights ago I went to switch on my mill, it twitched and then the fault light came up. I spun it a couple of times & got it to run twice, but it sounded very rough. I've looked at the mechanical components, and those look fine, so I'm guessing the roughness is one of the windings not being properly energized by the 3 phase inverter in the controller.

Looking at it it seems that the Motor is OK (a 500W 3-phase 230 volt "dc" motor) 5.5 Ohms showing between U, V, W.
I've seen a number of posts where the controllers in these give up the ghost, I've taken a look at the 6 IGBTs and testing in-situ they all look to be ok, so I'm guessing it's one of the other components & given I'm in the middle of a project I don't really want to stop and try to figure the board out.

The replacement controller from the manufacturer is $500, and frankly at the price I would prefer something more robust. Looking at ali express I see a number of "industrial" 750W 250v 1 to 3 phase VFD units at the $70-80 mark, which seems like a reasonable option I could have in 2 weeks. The bonus with these is that they have a number of additional interfaces I could play with in future.

The only issue I see currently is it looks like the motor has a hall effect unit - there's a 6-wire shielded signal cable to the motor & I can't find reasonable documentation on the VFDs (or the motor) to work out if it can be hooked up. or indeed if it's actually required. I am quite comfortable with electronics, but no specific experience with these motors.

Aside from the caviet emptor implied by the source (I'll have a fire extinguisher at the ready) is there any reason one of these off the shelf VFD units wouldn't work ?
Click to expand...

This is an interesting question, so I’ll be following this thread.

However, these machines (and their close relations) use PWM DC drives, and while VFD does use PWM to create the variable frequency AC output, the output is sinusoidal so I don’t think it would be directly compatible unless you change the motor as well as the controller. That said, my background is process engineering so I very well could be mistaken.
 
Edit: No you can't use a VFD to power a brushless DC motor- one or both will burn up. Brushless DC motors resemble steppers and require special drives.
You would need an oscilloscope to properly troubleshoot your controller

We have a repair person here in the states named Pete- you might want to email him:
his website is www.olduhfguy.com

Personally I would change the motor to a brushed DC type and power it with a KB electronics controller (KBIC or KBLC series)
The cost could be very low if you can pick up a motor cheaply- cannibalize an exercise treadmill for example
The KB controllers use both current and voltage feedback and have good load regulation over a wide speed range
Some lathes used them as OEM
 
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Brushless DC is NOT the same as 3 phase. Yes there are physical visual similarities like they both have 3 power wires and if you reverse any 2 the motor runs in the opposite direction. But that is where the similarities end.

In a brushless dc motor the rpm is equal to the frequency. So if you were to feed it 60hz you would have 60 rpm. If you need your motor turning 2000 RPM then it would need 2000 Hz no VFD can do this. Some of the controllers are capable of outputting 15,000 Hz or more to get very high RPMs for certain applications. Like a high speed spindle. A VFD WILL let all of the magic blue smoke out of any brushless DC motor.

*** WARNING ***
Semi technical stuff to follow in mt best version of layman's terms.

A brushless DC motor is expecting DC power that is why it has permanent magnets and not inductive. In an AC motor the polarity of the windings and the rotor are flipping back and forth between North and south at the voltage goes back and forth between positive and negative. In the brushless DC the magnets are permanent so they will not switch polarity so as the positive part of the AC cycle starts the motor would try to start spinning in one direction then at the negative part of the cycle came the motor would try to reverse direction. This would give the equivalent of a locked rotor condition.

There are 2 types of brushless DC. There is sensored, witch is what you have and there is sensorless. Sensored is best when starting against a load and/or maintaining a precise RPM. Sensorless is great when there is minimal and/or predictable starting load and precise RPM is not needed.
The brushless DC controller is doing a lot of things that a VFD can not do. In a brushless DC motor it is putting DC power to only one set of windings at a time. The hall effect sensors are looking at the magnets and feeding back to the controller where the rotor is in relation to the coils, The controller can then determine the correct moment to turn off this winding and switch on the next winding. This is especially important during startup to be sure that the correct winding is energized at the correct time.
 
before doing anything else, if you haven't already done it.. check and tighten any spade type wire connector.. squeeze them so the mate firmly.. if they are on free wires (not on a board or switch) replace them with a better form of connector.. my mill started faulting replaced the power cord connectors to good wire-nuts, problem solved.. I take it that is Oz dollars on the price for a new controller.. about 350 LMS price..
 
Hi all, noticed some things not making sense. First does the mill you have look like the one you will find if you run a search for "Sieg SX2" then click on the LMS link? The one at that link says it's a 350 watt motor. It also looks just like my H.F. mill and it too has the 350 watt motor. When I take a look at the top of the motor I can clearly see the screw caps for two brushes. I'm certain mine has a brushed DC motor in it.

A brush-less dc as they call them to the best of my knowledge are 3 phase permanent magnets. I have an homemade exercise bike I made from a BLDC motor and it makes a great 3 phase alternator.

Anyhow are you sure your mill has a 3 phase motor? Do you get the same ohm reading on all three wires? It should be quite low on all three.

Also I believe the speed of a BLDC motor has to do with the frequency and the number of polls the motor has, not just the frequency.
 
Maybe Australia gets imported a completely different version but in any case if you decide to order a replacement controller make sure it's for your market and not for the US as we run split phase here at half the voltage (115 instead of 230)
 
tghsmith said:
before doing anything else, if you haven't already done it.. check and tighten any spade type wire connector.. squeeze them so the mate firmly.. if they are on free wires (not on a board or switch) replace them with a better form of connector.. my mill started faulting replaced the power cord connectors to good wire-nuts, problem solved.. I take it that is Oz dollars on the price for a new controller.. about 350 LMS price..
Click to expand...
Also take a close look at the board and components, any burnt spots? Bulging capacitors? Maybe a mosfet that overheated due to a loose or bad heat sink connection? If you find something you might be able to fix it.
 
DeltaCharlie said:
Also take a close look at the board and components, any burnt spots? Bulging capacitors? Maybe a mosfet that overheated due to a loose or bad heat sink connection? If you find something you might be able to fix it.
Click to expand...
After re-reading your OP it does look like you do have a BLDC 3 phase motor and you have already taken a close look at the IGBTs (I call them MOSFETs) but would not know without looking up the data sheet.

The only other idea I can come up with is perhaps you can find a different 230 volt BLDC controller from or for something else that could be made to work at a much lower price.
 
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