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General Mach Discussion / Re: Mill Spindle Speed Control - DC Motor
« on: August 21, 2017, 05:19:59 AM »
Hi Keith,
yes the whole shooting match off on 10A circuit. Don't know what its like where you are but in New Zealand its not uncommon for a 10A circuit
to be a lot more heavily loaded. I work as a technician fixing welders and even little inverter welders regularly draw 30A. I know its not ideal
but that's what happens with very few if any ill consequences. The circuit feeding my mill is 2.5mm square and I'm not uncomfortable at running at
25A continuously. As it turns out you have to be doing something pretty extreme to draw that sort of juice.
I know the name plate says 12A but that is in fact the peak, not rms. It is however 12A peak per phase, and of course there are three of them! The
full load amps (FLA) referred to the 230V input is 28A! The rms doesn't sound quite so bad, 19.8A ...LOL
Of course the reality is that I seldom get anywhere close to max current and therefore max torque. Also lets imagine I'm driving a facing tool at high
torque but often modest speed, say 1000 rpm. Under that circumstance the voltage at the motor terminals will be about 1/3 rated ie 100V. The DC link
voltage is 320V (230VAC rectified and smoothed) and consequently the effective PWM of the link voltage to the terminals represents a transformation
of 3:1. If the phase current is 12A per phase the link current required to feed that phase is 4A. You can see where I'm going here, those occasions where
I require max torque often coincide with modest speeds and the effective transformer action of the PWM buck regulators means everythings kool.
I have three 5 phase 23 size steppers with genuine Vexta 230V drivers. According to the name plate they can draw heaps of current but in practice I've
never seen the draw more than an amp, thats roughly 230W...where could all that power go...little 23 size steppers couldn't absorb that much except briefly!
The 1/8 hp coolant pump draws more on average than one of the axis drivers.
The upshot is that I have to really bore into a piece of stainless with a 16mm tool to start drawing decent current from the plug and a that stage my mill
is 'a humming and'a jumpin' and can't really take any more, its not 250 kg but probably 150kg.
If you think I'm being a bit cavilier about it wait until you see someone plug in a single phase plasma cutter and start cutting, it makes my mill look liteweight!
Craig
yes the whole shooting match off on 10A circuit. Don't know what its like where you are but in New Zealand its not uncommon for a 10A circuit
to be a lot more heavily loaded. I work as a technician fixing welders and even little inverter welders regularly draw 30A. I know its not ideal
but that's what happens with very few if any ill consequences. The circuit feeding my mill is 2.5mm square and I'm not uncomfortable at running at
25A continuously. As it turns out you have to be doing something pretty extreme to draw that sort of juice.
I know the name plate says 12A but that is in fact the peak, not rms. It is however 12A peak per phase, and of course there are three of them! The
full load amps (FLA) referred to the 230V input is 28A! The rms doesn't sound quite so bad, 19.8A ...LOL
Of course the reality is that I seldom get anywhere close to max current and therefore max torque. Also lets imagine I'm driving a facing tool at high
torque but often modest speed, say 1000 rpm. Under that circumstance the voltage at the motor terminals will be about 1/3 rated ie 100V. The DC link
voltage is 320V (230VAC rectified and smoothed) and consequently the effective PWM of the link voltage to the terminals represents a transformation
of 3:1. If the phase current is 12A per phase the link current required to feed that phase is 4A. You can see where I'm going here, those occasions where
I require max torque often coincide with modest speeds and the effective transformer action of the PWM buck regulators means everythings kool.
I have three 5 phase 23 size steppers with genuine Vexta 230V drivers. According to the name plate they can draw heaps of current but in practice I've
never seen the draw more than an amp, thats roughly 230W...where could all that power go...little 23 size steppers couldn't absorb that much except briefly!
The 1/8 hp coolant pump draws more on average than one of the axis drivers.
The upshot is that I have to really bore into a piece of stainless with a 16mm tool to start drawing decent current from the plug and a that stage my mill
is 'a humming and'a jumpin' and can't really take any more, its not 250 kg but probably 150kg.
If you think I'm being a bit cavilier about it wait until you see someone plug in a single phase plasma cutter and start cutting, it makes my mill look liteweight!
Craig