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ZeroCount
25-02-2009, 01:26 AM
Hi, I've been making my brain hurt looking at stepper motors, torque ratings,
etc. but I've noticed something a bit odd.

It appears that to get the best performance from a stepper it should be driven at ~20 times its rated voltage, or 32 times the square root of the coils inductance in mH (this makes more sense considering the step input voltage / current curve of an inductor).

Looking at several motors in the 1.8 to 3Nm range this would equate to a driving voltage of around 60 to 100V, but most (cheap) drivers seem to have output voltage limits of around 35 - 48V, which would imply not getting the best from the motors.

Anyone know of any drivers with higher voltage capability available in the UK that don't cost an arm and a leg?

I know drivers are available like the MCP MSD980 - 7.8A @ 90V, but 105+VAT per axis is too steep for me at the moment. :(

I look forward to any information you can share.

ZeroCount
25-02-2009, 12:21 PM
Thanks for that, I've been trawling EBay looking for bargains, but I hadn't thought to try the non-UK versions of the site.

Following the link you gave I found a much more reasonable 3 axis driver kit that does 60V @ 5A, but nothing higher.

Time to hit the books again to try and find out how much lower voltages hurt performance :(.

ZeroCount
25-02-2009, 09:38 PM
5A is fine for most sensible steppers up to around 12Nm, it's the voltage I want higher, to play it safe with voltage spikes on the mains supply I'd have to drop to 10+% below the max voltage, or invest in a regulated supply. And that would drive the cost up again :(.

I thought on imports the tax was just paying the VAT? (Unless I get it sent marked as a gift :D).

Gary
26-02-2009, 08:40 AM
Voltage makes a differnece to top speed performance, but do you need it?
You mention 1.8-3 Nm, so you are within the Nema 23 range, so look for a motor that is as high current as possible, to keep the inductance as low as possible.
There are disadvantages to high voltage as well; the motor will get a lot hotter, and will make a lot more noise.
In my experience for a nema 23 motor 40-50 V is fine, and going up to 70 V will only give you a performance increase at the higher speeds. (Over 300 RPM)
Do you want to pay 50-60% more for 15-20% more performance?
What torque and speed do you need?
Nema 34 motors are different, and these really need high voltage to get the best from them.

ZeroCount
26-02-2009, 11:33 AM
Thanks Gary, food for thought there. I agree higher current, lower inductance motors have lower voltage requirements as well.

Slightly confused as to higher voltages causing more noise :confused: why would this be?

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The more I learn about this hobby, the brighter the light of knowledge grows, the deeper is the pit of ignorance revealed...

Gary
26-02-2009, 12:07 PM
I am not sure why it makes more noise, will have a look into it and post later.


Thanks Gary, food for thought there. I agree higher current, lower inductance motors have lower voltage requirements as well.

Slightly confused as to higher voltages causing more noise :confused: why would this be?

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The more I learn about this hobby, the brighter the light of knowledge grows, the deeper is the pit of ignorance revealed...