[joeavaerage]

Hi,
if you want more speed and more 'authority' use a much higher voltage driver, 80V is the current norm among the 'big boys drivers',
and use an 80V supply, don't mess around.

Craig

[tjbaudio]

Hi,
if you want more speed and more 'authority' use a much higher voltage driver, 80V is the current norm among the 'big boys drivers',
and use an 80V supply, don't mess around.

Craig

I take it that's a vote for keep the steppers and upgrade the control. More current and more voltage.

[joeavaerage]

Hi,
yes a little more current so that you can exploit the current rating of your servos would be nice.

Voltage on the other hand does not improve the torque but rather delays the onset of torque reduction with speed.
All steppers lose torque the faster they go. Inductance is a good indicator how bad that torque reduction will be.

For example a 1mH 23 size stepper with a 72V driver may retain 45-50% of its holding torque at 1000rpm.
A near identical 2mH 23 size stepper might have 15-20% of its holding torque at 1000rpm.
An 8mH stepper probably won't even get to 1000 rpm, and could have as little as 5% of its holding torque at only 500rpm.

Low inductance steppers are highly regarded for CNC purposes but they tend to be high current units with only moderate torque
specifications, and so only ever bought by people who know what they want. Most manufacturers make high torque units but with
commensurately high inductance and sell to people who don't understand inductance. Don't be duped......you want the lowest inductance steppers
you can get.

Your existing 2.2mH (when wired in parallel) are probably OK. With a good high voltage driver and preferably a high current
linear supply, you'll get the gest out of the steppers you've got.

Craig

[tjbaudio]

Thanks Craig. If the rule of thumb from Gecko 32 * SQRT (L) = VMAX holds true that puts me at a 48V psu. 80V sounds high to me on such a motor. I don't want over the top speed at the expense of excessive heating. My Z is going to be pretty low RPM anyway, 100 RPM would get me 25ipm. It's a very small machine!

A KL-5042 digital is $29. That would handle the 48V and the 4.2 A of my existing motors. That looks like my minimum cost upgrade.

Now to look at what minimum plus a couple of bucks gets me.

[joeavaerage]

Hi,

If the rule of thumb from Gecko 32 * SQRT (L) = VMAX holds true that puts me at a 48V psu. 80V sounds high to me on such a motor. I don't want over the top speed at the expense of excessive heating.

Rubbish. Firstly that's Geckos Rule of Thumb....and I'm not quite sure that thumbs have much say in Physics. The higher the voltage the faster you go....that's Physics.
Current is what causes heating, not voltage.

A stepper has low resistance windings typically 1 Ohm or so. Thus for rated current of 3A you need only apply 3V. The high voltage is the 'Force' the current through the
winding in the shortest possible time and once the rated current is flowing the drive uses pulse width modulation to reduce from 80 (or 48 or 36 etc) down to 3V necessary
to maintain rated current only. Despite the high voltage power supply the stepper on average sees only 3V. The heating is 3V times 3A =9 Watts.

I have Vexta 5 phase steppers on my mini-mill and they run through 10:1 low lash (<2 arc min) gearboxes using Vexta drivers. The drives are direct off-line 230VAC, and
that gets rectified and buck regulated to 150VDC and that DC voltage is applied to the steppers via a PWM circuit. They whizz around at 2400 rpm and haven't missed a step in six years,
except if I do something stupid. Voltage doesn't hurt steppers....excess current does.

Quite frankly paying $29 to get another lousy 12V.......save your money.

If speed is not your issue then get higher torque steppers with as low inductance as you can afford.

Craig

[tjbaudio]

Quite frankly paying $29 to get another lousy 12V.......save your money.

If speed is not your issue then get higher torque steppers with as low inductance as you can afford.

Craig

Thanks for the extra info. What I was thinking is the $29 get's me is going from 8.8mH and 2.1A to 2.2mH and 4.2A. If I'm understanding you right that 8.8mH with the low voltage is killing my speed and torque. I'm also seeing that going from a 50V controller to 80V controller doubles the cost.

I have been looking for stronger steppers with lower inductance. Most I see are 3mH or higher and would still need a new controller. I did find a 570oz-in with 2.5mH but it needs 5A $40 plus $35 for a 50V5.6A controller. That's tempting for my Z. I think I also made a mistake when I bought the ball screw. I did not realize it was .5 inches per turn. I may need to look at that setup as well. It was working ok till I needed more torque for drilling ops.

I also have seen several places that claim higher voltage just gets me more speed for rapids. Actual cutting speeds in metal are not high enough to get the benefit of high voltage. Since this is a minimill I don't have the rigidity and horsepower to cut fast or deep. Feed and speed calculations put me under 10ipm for most of my cuts unless I'm doing wood or plastic.

I do appreciate your time. I don't like to quibble over such small cost items but like many, I have been out of work for most of the last year. I'm just trying to get my hobby to put some stuff up on etsy type sites to earn some extra $$.