could some one explain the following

[derkiow]

I am trying to size up a transformer for my drivers pacsci ms6410's.Going of the following info what current spec do i use? rms or average current (ie 45 volts times rms current equals va rating or 45volts times average current equals va rating) when buying a transformer """""""The average current load of the 6410 is a function of the motor
used as well as motor speed and torque. To optimize the power
supply design, the supply current can be measured using a DC
current meter when the motor is producing the highest shaft
power. If it is difficult to make this measurement, assume the
maximum average load current equals the selected phase current.
Thus, if the DIP switch is set for 5 Amps RMS, assume the
maximum average power supply current is 5 amps.
The average transformer secondary current equals the sum of the
average currents for all 6410s powered by the supply. Because
the transformer supplies pulses of current to charge the “bus”
capacitor(s) on the other side of the diode bridge, the rms current
is higher than the average current. The transformer should have a
rated secondary rms current of at least 1.8 times the average
current.


Example The transformer used to supply three 6410 drive modules, each
set for 5 Amps rms should have a rated secondary rms current of
1.8 * (5 + 5 + 5) = 27 amps or greater.
Note: It is generally not advisable to significantly oversize the
transformer because this will increase rectifier surge current
during turn on, as well as capacitor ripple current.""""""""
derkiow

[vger]

derkiow,

Looks like some pretty good drivers.

Take that desctription on line at a time...

Basicly it boils down to....

Choose a transformer with a current capacity that is 1.8 times the total current settings of all the 6410's that it will be powering.

What are the specs on the steppers you are going to be using with these drives?

Steve

[derkiow]

K32HMHK - LNK - NS - 00 pacsci stepper motors 2 stack bipolar 6.1 amps and 3.4volts ,,, 1580oz/in ....derkiow

[derkiow]

so a the transformer i would be looking for would 45volt at 27amp which equals 1215va is that correct ....derkiow

[vger]

That looks about right. You could probably get by with 1000 VA if you want.

Steve

[Alexthehun]

Originally Posted by derkiow K32HMHK - LNK - NS - 00 pacsci stepper motors 2 stack bipolar 6.1 amps and 3.4volts ,,, 1580oz/in ....derkiow

Looking at your spec: 6.1A at 3.4Volts=21Watts. So why would you need a 1000VA for 3 or even 4 of these?

What has been overlooked: the stepper driver acts as a dc-dc converter: making a high current/low voltage suply from a high voltage low current.
In other words at 34 V feed the current would only be 610mA! (times number of drives you want to use=total current requirement) A LOT less than 27 Amp, even if you want to include this 1.8 factor.

[vger]

I believe derkiow's quote was from the manual on the drives (page 4 of appendix C to be exact). Transformer current capacity will have a direct effect on load regulation as well. These drives also have electonic damping to help eliminate midband resonance issues. It would be interesting to know just how much power is required to damp the natural oscilations of the motor/mechanical system.

Steve

[derkiow]

Thanks for the replies , so what size transformer do i need the max 1215va or a lot lower as alexthehun suggests. I worked out that 45v ac on the secondary would equate to 75v dc allowing for the factors given in the driver manual for safe operation ,, can these motors handle 75volts at 5amps (or 7.1amps with micro stepping ) or is the statement wrong..... help...derkiow

[vger]

Derkiow,

I would not run them right at their limit (75V) because line voltage fluctuations could produce a problem. Suppose the transformer is rated right at 45V and that rating is with an input voltage of 117.5 V. And you plug it in to your outlet which happens to be running 122.3V and your DC bus then it up to almost 80V and the magic smoke appears.

Alex does have a point... The total power required should be much lower than the example in the manual. However, the manual shows the drive itself disipating about 27 watts of power when running at 5 amps (about 80 watts for 3 drives). With both coils energized (as they are all the time in full step mode) you have about 40 watts per motor (120 watts for 3 motors). So using this method, and using the 1.8 multiplier, say 360 watts total. Although that seems logical, I would be tempted to go with the manual and use something closer to what the manufactuer suggests.

Here is a link to one that might work for you...
Amveco - AA59902-042 - Transformers - Power Products - Allied Electronics

There are 2 primary windings allowing you to run it from 120 or 240 V and 2 secondary windings (connect them in parallel) that will give you 42 V at 23.6 amps. There are probably cheaper solutions avaliable.

Steve

PS... The drives regulate the current by chopping the power at a 20 Khz rate. Yes the full voltage is applied to the motor, but only in very short pulses such that the average current is whatever the drives are set at.

[derkiow]

Thank's again for your input ,,, found the following transformer here in the uk
.....1kVA 230V 2 x 40V toroidal transformer...... for 63 GB pounds plus vat and delivery......totals at around 89 GB pounds.......ps have emailed the drivers manufacturers to see what they have to say on the subject.....derkiow