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Messages - joeaverage

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3891
General Mach Discussion / Re: CS Labs CSMIO/P-A
« on: August 07, 2018, 02:49:00 AM »
Hi,
these three phase 200V drives are for the Yanks. There is no need for you to follow suit.

Your converter outputs three 230V-to-neutral phases or 400V line-to line. You should be getting a drive and a servo to accommodate that.

For instance the Allen Bradley numbering goes:
MPL-A430H    where the A stands for 230V and
MPL-B430H    where the B stands for 400V operation. Note that it is common to state the AC line voltage for which the servo/drive is matched
when in actual fact they will operate at the DC Link voltage and the DC Link voltage derived from a 400VAC supply is 560VDC.

Craig

3892
General Mach Discussion / Re: CS Labs CSMIO/P-A
« on: August 06, 2018, 07:28:01 PM »
Hi,
thats not going to be easy...how do you intend the load your existing spindle to rated output?
I would be less concerned about your existing spindle, its likely to have a power factor of 0.8, not
great but not too bad either. Likewise your single to three phase converter is likely to be very good.

The trouble comes when you fit a servo drive, they have a simple rectifier input and could draw much
more current than you think. Without one to test and some means of loading it to rated output
you won't know.

Given that the current is drawn in pulses even supposed 'real rms reading' meters are not really that good.
Thus you would need some good gear to make effective measurements. By that stage you already have
your drive and servo....its a bit late to decide you don't want it after all.

Clearly you have made some allowance for increased current draw at the time you fitted your converter, I would
think you can afford to box on. If it proves that the current draw is excessive then you will just have to back
off your demand....which you can set by taking a lighter cut...OR...setting a realistic current limit by programming
your drive.

Your 100A supply and 50-60A breaker should allow you to proceed safely. As I have said before its actually really hard
to load up motor that much, you may find that all of these precautions are uneccessary.

Craig

3893
General Mach Discussion / Re: CS Labs CSMIO/P-A
« on: August 06, 2018, 03:19:50 PM »
Hi Mick,

Quote
I don't understand why we are getting 4397w when the motor is rated at 3000w

Nor do I but you provided the torque and speed figures. The shaft output is just that, it has no bearing on the electrical
means by which it was generated and the calculation is exactly as Isaac Newton proposed.

My guess is that the torque figure supplied was somewhat higher than its 'rated torque' The motor does not just stop when its gets
to its rated torque, if the drive produces yet more current the motor will produce yet more torque and therefore power to the load. Over a period
of time you might expect it to overheat. The 'rated' output is more about a thermal condition rather than an absolute limit.

There are two figures of merit that apply to servos which can be relied on to produce accurate numbers. The first, called the torque constant or Ka
is in so many 'Nm per Amp' Thus if a motor is supplied 10A and its Ka is 0.95 Nm/a then its torque at that operating condition is 9.5Nm.
The second is called the back EMF constant or Kv in so many 'Volts per 1000 rpm' or some other equivalent units. Thus a motor spinning at 2000 rpm
with a Kv of 100 V/1000rpm will have a back emf of 200V. If our supply is 230V, the motor cannot run much faster as the back emf is close to defeating
the applied voltage.

The two numbers relate very much to the design and construction of the motor. In general we want Ka to be high, that is a motor than can produce
a lot of torque from a small current. For instance you might decide to have a high number of turns in the stator so that it produces a strong magnetic
flux for a given current and choose high strength rare earth permanent magnets  for the armature.

Both of these however increase Kv also, and as we have seen its the back emf that determines the motors top speed for a given input voltage.
You came across an example yesterday where a servo produced high torque up to 2600rmp and then seemed to die. The Kv figure is such that the servos top
speed with 230V input is 2600 rpm. To get it to go faster you have to artificially manipulate its Kv, which can be done, within limits, with field oriented control
with a technique called field weakening.

Craig

3894
General Mach Discussion / Re: CS Labs CSMIO/P-A
« on: August 06, 2018, 04:58:50 AM »
Hi Mick,
kool, it sounds then that you have taken some precautions against overloading your supply.

Just a few thumbnail calculations:

current (assuming unity power factor) =5000 (W)/ 230 (V)
                                                       =21.7A rms

21A doesn't sound too bad does it? But remember this embodys the assumption that unity power factor, ie perfect power factor applies.
We all know that there is never a perfect power factor. I would be prepared to guess that the converter you have is good, even very good, it
would certainly account for their popularity. Lets assume that your converter has a power factor of 0.95, most industrial electricians would regard
that as very good indeed.

current (assuming 0.95 power factor) =21.7 / 0.95
                                                      =22.9A

Still pretty fair, only 23% of the current available from your 100A domestic supply.
The real trouble now comes when three phases generated by your converter are applied to your servo drive. You recall the circuit diagram that I posted
earlier, the three phase version is very similar and suffers the identical power factor problem.

I repair welders for a living, inverter welders particularly. Day after day I see for instance a single phase stick welder producing 100A at 20V into
our load bank and yet 20A indicated current coming from the single phase supply. We'll do the energy balance to determine the effective power factor of this
situation:

input power (indicated)= 230 (V) X 20 (A)
                                 =4600 W
output power( actual)= 20 (V) X 100 (A)
                               =2000 W

Power Factor (effective)= 2000 / 4600
                                  =0.438

Just about all single and three phase off-line rectifiers suffer this power factor degradation. There are circuits to correct it, I suspect your converter uses them
but your proposed servo drives do not.

Thus lets now calculate the current required by your servo drive referred back to the single phase supply assuming this power factor:

current (single phase equiv)= 5000 (W) / 230 (V) / 0.438 (power factor effective) / 0.95 (power factor converter)
                                        =52.24A rms

Lets put that number into perspective. Firstly its one half of the rated supply of your domestic network connection. Secondly it near the circuit breaker
rating and this is just rated current, not any overload or inrush current.

You can see now that the power factor, which is far from an easy measurement, affects so dramatically the required input current. I've seen power factors
as low as 0.3 but 0.4 to 0.5 are the norm for reasonably made off-line rectifiers of simple type. You can also see my concern that you might cause your electrical
installation harm or risk fire or injury unless you understand the demands of your servo drive.

Craig
                                       

3895
General Mach Discussion / Re: CS Labs CSMIO/P-A
« on: August 05, 2018, 08:49:28 PM »
Hi,

the first motor:

power =2600 X 2 X PI / 60 X 19
          =5172 W

the second:
power = 3000 X 2 X PI / 60 X 14
          =4397 W

So despite the first motor dying at speed, in the field weakened operating condition, it is still the more powerful motor.

Hey, all these high power motors are wonderful things but you have to squeeze the electricity to run them
through your domestic supply. Not withstanding what looks to be a really impressive single to three phase converter
you will still have to supply it something like 60A to produce 5kW output. Will your domestic supply and cabling
accommodate such high currents?

Craig

3896
General Mach Discussion / Re: CS Labs CSMIO/P-A
« on: August 05, 2018, 05:31:51 PM »
Hi,

Quote
Strange it says that in the Manual but the torque graph shows 19nm up to around 2600rpm then drops to 9nm at 3000rpm

Its called 'field weakening', a clever technique for extending the rev range of a motor which would otherwise top
out a a lower speed due to lack of voltage. This is a pretty radical reduction though.

Craig

3897
General Mach Discussion / Re: CS Labs CSMIO/P-A
« on: August 05, 2018, 02:37:26 PM »
Hi,

Quote
If I continue to use the single to three phase converter then I have loads of options including 3 phase

You have a single phase to three phase converter of 6kW output?

Can you provide some details, maybe a shot of the nameplate?

Craig

3898
General Mach Discussion / Re: CS Labs CSMIO/P-A
« on: August 05, 2018, 08:44:19 AM »
Hi Hood,
who cares whether its 2.2kW or 3kW, Mick is never going to run 5-6kW from a single phase supply.

Craig

3899
General Mach Discussion / Re: CS Labs CSMIO/P-A
« on: August 05, 2018, 07:54:29 AM »
Hi,

Quote
It happily powers the 6kw spindle motor on the lathe. My preference would be not to use it and have everything single phase.

Don't think its going to happen, unless you are prepared to spend some serious money on a high current single phase connection
and suitable high current circuitry 5-6kW is beyond single phase. Hood is of the opinion that 3kW is achievable where my contention is
closer to 2.2kW. As to which if either of us is right does not change that we are in agreement that 5-6kW is beyond single phase.

Yes the two servos would perform almost indistinguishably below 2000 Hz where they are both capable of near identical torque.
The older Allen Bradley design likely has a greater moment of inertia and may therefore take a little longer to accelerate. Most likely
the rotating mass of the lathe is going to predominate in the moment of inertia calculation however.

Craig




3900
General Mach Discussion / Re: CS Labs CSMIO/P-A
« on: August 05, 2018, 07:35:01 AM »
Hi Mick,
the Allen Bradley with the DSD-030 shows 8Nm at 3000rpm.

angular frequency= 3000 x 2 x PI / 60
                         = 314.1 rad/sec
power =frequency x torque
         = 314.1 x 8
         = 2513 W
         =2.5kW

The BCH2MM152 shows 5Nm at 3000rpm

power = frequency  x torque
          =314.1 x 5
          =1570 W
          =1.5 kW

So firstly the power output of the Allen Bradley servo is 2.5kW not 3kW and secondly when is 5Nm ever 'nearly the same' as 8Nm?
You may note that the low speed torque of the Schneider servo is a little higher, in fact closer to 8Nm, than its ultimate torque, 5Nm, at rated speed,
but it does not mean its more powerful, I rather suspect that change occurs by virtue of the transformation effect of the drive rather than any
characteristic of the servo.

Craig

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