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

[VicHobbyGuy]

I don't know if this will help: I converted my 7x lathe to a brushless motor. This is the controller for it: https://www.aliexpress.com/item/1005004661918827.html
Not cheap, but a lot less than $500.
This was the 'kit' with the motor and controls: https://www.aliexpress.com/item/1005004383853835.html

No wiring diagram with it - it was 'plug and play' with idiot-proof (more or less) connectors .

 

[BruceCook]

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.

Ah, thanks, that is the information I was looking for, and as usual the easy option isn't what it seems

I had assumed that a VFD that used the back emf for position feedback would be able to work without using the secondary positional sensors, although I did wonder about the differences in motor design being an issue & that the use of IGBTs instead of mosfets for the drivers was just a shortcut way to power the windings when true sinusoidal output wasn't required.

Now to take a look through google land to see if I can find a reasonable quality driver for that motor, unfortunately there's not a lot of information about that specific motor, I wonder if it's an in-house Sieg creation, or a badge engineering job.

Thanks again for the detailed response.

 

[BruceCook]

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.

Hi DeltaCharlie, I had a brain fart when posting the model, it's actually an SX2P, I see from the sieg range that some of the models come brushed as well as brushless, the model I have is brushless.

The drivers 6P7NC60HD are IGBT which are different to mosfets, generally used in applications where high current, high speed switching, hard switching and low internal resistance is required. You'll see these used in high power applications such as welders.

Armed with my slighly lower level of ignorance, I'll take a look around for a suitable DC brusless motor controller, thanks to yourself and other for setting me straight.

 

[mksj]

Seems like a common problem, there are less expensive options for a replacement control board in Australia and UK. There are BLDC motors and controls for less, but getting the motor to fit is usually more of a challenge with a gear head mill.

SIEG SC3 / SX2 Control Board 220-240V

used on SC2-112, SC3-112, SX2-142, SX2P-69, SU1-131

www.ausee.com.au

SX2-142 Main Control Board - Arc Euro Trade

Main control board for the SX2 Mill. Programmed for use with the SX2-95 brushless motor.

www.arceurotrade.co.uk

 

[BruceCook]

I don't know if this will help: I converted my 7x lathe to a brushless motor. This is the controller for it: https://www.aliexpress.com/item/1005004661918827.html
Not cheap, but a lot less than $500.
This was the 'kit' with the motor and controls: https://www.aliexpress.com/item/1005004383853835.html

No wiring diagram with it - it was 'plug and play' with idiot-proof (more or less) connectors .

That certainly looks like it's in the ballpark. The lack of wiring diagram is annoying (I find that with a lot of products from aliexpress) and would probably make it problematic to interface with my existing motor, but that whole kit with motor come in cheaper than a new Sieg control board and would give me a 350 watt upgrade to boot. The way the SX2P motor is mounted means switching it out would be straight forward too.

Thanks for the pointer, it's certainly an option.

 

[VicHobbyGuy]

That certainly looks like it's in the ballpark.

With my Sieg 7x14 lathe, the brushless controller wouldn't fit in the stock 'box'. Making a bigger box was part of the upgrade project. I had some coated hardboard and used epoxy fillets to join up the face and sides. 3D printing a box would have been a possibility, but this was before I bought a 3D printer.

 

[BruceCook]

Seems like a common problem, there are less expensive options for a replacement control board in Australia and UK. There are BLDC motors and controls for less, but getting the motor to fit is usually more of a challenge with a gear head mill.

SIEG SC3 / SX2 Control Board 220-240V

used on SC2-112, SC3-112, SX2-142, SX2P-69, SU1-131

www.ausee.com.au

SX2-142 Main Control Board - Arc Euro Trade

Main control board for the SX2 Mill. Programmed for use with the SX2-95 brushless motor.

www.arceurotrade.co.uk

Fortunately my mill is belt drive with the motor mounted on a sliding plate, so it might just be a case of switching the belt pulley over and mounting the new motor on the new plate, or at worst fabricating an new plate for the motor.

Thanks for the links, I'll check them out.

 

[BruceCook]

With my Sieg 7x14 lathe, the brushless controller wouldn't fit in the stock 'box'. Making a bigger box was part of the upgrade project. I had some coated hardboard and used epoxy fillets to join up the face and sides. 3D printing a box would have been a possibility, but this was before I bought a 3D printer.

I'm not adverse to replacing the control box with an of-the-shelf box from an electrical supplier. On my lathe that sits on the back, out of the way in any case.

 

[BruceCook]

So.. With the supplied information I've found this at about 1/4 the cost of a replacement unit, it looks like it meets the spec and with the added bonus of an easy to install control panel & the ability to run the mill in reverse.

My only challenge will be working out the Hall sensor wiring, which I should be able to do by applying a voltage & spinning the motor with a scope on the outputs. I should be able to trace Vcc / gnd on the original board.

https://www.aliexpress.com/item/1005005669580752.html?spm=a2g0o.productlist.main.85.6520ci6wci6wFU&algo_pvid=fa91f40d-1aba-44db-8c4e-8d12ee541263&algo_exp_id=fa91f40d-1aba-44db-8c4e-8d12ee541263-42&pdp_npi=4%40dis%21AUD%21141.91%21110.69%21%21%2196.78%2175.49%21%402103201917276917805215729e9c78%2112000033958725074%21sea%21AU%213008240567%21X&curPageLogUid=TxicaGRLk1QF&utparam-url=scene%3Asearch%7Cquery_from%3A

 

[DeltaCharlie]

So.. With the supplied information I've found this at about 1/4 the cost of a replacement unit, it looks like it meets the spec and with the added bonus of an easy to install control panel & the ability to run the mill in reverse.

My only challenge will be working out the Hall sensor wiring, which I should be able to do by applying a voltage & spinning the motor with a scope on the outputs. I should be able to trace Vcc / gnd on the original board.

https://www.aliexpress.com/item/1005005669580752.html?spm=a2g0o.productlist.main.85.6520ci6wci6wFU&algo_pvid=fa91f40d-1aba-44db-8c4e-8d12ee541263&algo_exp_id=fa91f40d-1aba-44db-8c4e-8d12ee541263-42&pdp_npi=4%40dis%21AUD%21141.91%21110.69%21%21%2196.78%2175.49%21%402103201917276917805215729e9c78%2112000033958725074%21sea%21AU%213008240567%21X&curPageLogUid=TxicaGRLk1QF&utparam-url=scene%3Asearch%7Cquery_from%3A

The thought cross my mind that the motor you have might not be designed for 230 volts input, the input to the original controller was 230 but there might be some or a lot of step down. One simple thing you could do to get an idea of what voltage the motor was designed for would be to set the belt drive to high and chuck up a corded drill to spin the mill over fast. Take a volt meter set it to AC and see what the output across two of the motor wires is. It should put out something like 80% voltage of what the motor was designed to run on.

Hope this helps