Can anyone help me with ideas for driving a med/large dc spindle drive motor, please?

[Mortattoo]

Hi Guys,

Thanks for the ideas, it is a great help! So I have a 230-110 transformer and the parts to rectify that after the drop down. I also have capacitors big enough to smooth this out. That part SEEMS to be simple enough (famous last words).

The pulse width modulation regulator on the other hand has me scratching my head again, i'm afraid....Can anyone give me a link to a module that might give me an idea of what i'm looking for?

I have used PWM with smaller motors using a micro controller to product the pwm and an H-bridge to control the power. Is that basically (although a much bigger version) what i am looking for?

Also, can i use a nice big shunt resistor to limit the current for the field winding, if there isn't enough resistance already? I have some pretty large ones knocking about from a servo motor braking circuit.....

My biggest fear here, if i'm being honest, is that i do something daft and damage the motor....It is not something I can afford to "scrap". If i can get all the parts together, can i "test" this with lower power to make sure i have a working solution before I go "full" power? Or is there any advice for this to make sure i don't do any serious damage?

Thanks again for all the help, any advice is greatly appreciated.


Cheers,

Mort

[Muzzer]

Do you have any DC bench power supplies? 30 - 60V at perhaps 10A? That might be enough to get it spinning.

You probably don't need to worry too much about smoothing the voltage at this stage, so a variac and bridge rectifier might suffice.

[Voicecoil]

To check what current the field winding will draw, firstly check it's DC resistance with a DMM, then apply the law of Mr Ohm to get the current - this will give you an idea whether you need to add anything in series for safety.
As far as PWM drive modules go, there used to be a guy from Hungary on fleaBay who made some good ones at a reasonable cost (around £100 or so) though I can't find him at the mo - COVID issue I wonder??? - we swapped a few emails and he knew his stuff. Otherwise go to Inverterdrive.co.uk, you will find a selection of drives there. The principle is just as you have described only bigger - you'd be talking of between 2 and 4 paralleled 600V+ MOSFETs top and bottom, or a pair of big chunky IGBTs. Provided you have a big variac there shouldn't be any reason why you can't test the setup at a lower voltage - and if you had a real monster you could even use it for speed control!

[Mortattoo]

Hi Guys,

I will follow your suggestions as best i can!

I need to get started by figuring out the connections. The panel is marked up as three phase with 6 brass bolts for connection, which i why i thought it was a three phase motor in the first place (i guess it's a standard fitting rather than one made for each type of mill). Once i have figured out the three connections I will start on the power supplies. Will start on about 60v up to about 110v (depends on what i can get to work from the pile i have stashed).

Next up will be getting or making a PWM drive. I have a dozen 47N65C3 MOSFETs (650v 47A continous, 141A spike) and will try to make up a simplified PWM for a bit of control. I am not sure i even have the skills to get this to work but at least I will be learning something new and therefore it is never a wasted effort. The interdrive ones are great i reckon, but again, budget doesn't strech that far right now....possibly something to aim for if I don't get this working as is, but that might be a while down the line.

I don't have a variac that would come even close to large enough for this application so i will have to figure out that as we go. Or maybe find one on the "bay" as it would be a great addition to the bench anyway.

For now, I have already learnt a lot, thanks very much for your help and advice. Any further thoughts or advice is gratefully recieved!

Cheers,

Craig

[EddyCurrent]

Have a look here; https://inverterdrive.com/group/DC-T...Input%7c230Vac

[Mortattoo]

Have a look here; https://inverterdrive.com/group/DC-T...Input%7c230Vac

Thanks for the link but I just don't have the budget for this at the moment. I guess the motor would need something around the size of a Parker SSD 512C but at £400 it just isn't practical right now.

Cheers,

Mort

[Voicecoil]

If I have a spare mo. I'll have a think about what would be the best driver for those things - BTW, do you want reversing on the spindle?

[Mortattoo]

Thanks Voicecoil,

Yes, i want reversing but i am aware that this is an added complication that can be addressed at a later date. If there is an easy way to do it, great. If not, I can live without it.

Cheers,

Craig

[Voicecoil]

Those Infineon FETs are likely a good choice, I've found their devices reliable in SMPS applications. They do however have a pretty huge input capacitance so you'll need a driver chip with plenty of beans like the ONSemi FAN7191. Going back to my original suggestion, rectifying & smoothing the mains to give ~325V @ abou 5KW will need some biggish capacitors which will draw hellish charging current spikes from the mains - using smaller caps that don't charge all the way when under load might make Powergen rather happier, but will of course reduce your available power - on which subject does the Bridgeport have pulleys connecting the motor to the spindle? Obviously at lower voltages you will get lower motor RPM.

[Doddy]

Going back to my original suggestion, rectifying & smoothing the mains to give ~325V @ abou 5KW will need some biggish capacitors which will draw hellish charging current spikes from the mains

I genuinely don't know the answer to this: Would it not be worth trialling without caps at first - the inductance of the motor windings will provide a hefty current stabilisation without throwing energy into expensive high voltage, high capacitance, high ripple caps?