Re: [Emc-users] An interesting video on motors

[nk]

2020-12-24 18:43 skrev andy pugh:
On Tue, 22 Dec 2020 at 16:37, Nicklas SB Karlsson  
wrote:


As I understand it is an IPM Internal Permanent Magnet motor, have
principal picture in old course literature from university. Would 
guess

it is used because full torque is seldom used and iron losses will be
lower for lower magnetic losses


The video suggests that by changing the phase of the magnetic field
relative to the rotor they can effectively switch between reluctance
(for high speed, low back-emf) and PM (high torque) modes.


Reluctance is much higher in path of magnets so it is much easier to 
increase flux in between magnets there it is iron which have much lower 
less Reluctance. Never heard about increasing flux for IPM, only 
flux-weakening to run at higher speed. To get reluctance effect there 
should be flux between magnets, uncertain about this, have a tried a 
reluctance motor, it had two operating points, one rotating backwards at 
slower speed less efficient.


For those not familiar with magnetic circuits reluctance fulfill same 
purpose in magnetic ciruits as resistance do in electric circuits though 
circuits are less perfect, in particular I do not think there are any 
insulator, only conduct magnetic flux better than vacuum. Magnetic 
fields are generated by currents or magnets, then flux depend on 
magnetic field and reluctance=1/permeance.


If I think right the motor will have higher inductance in between 
magnetics and this will increase cross coupling which vill make it 
harder to keep magnetic flux on desired level.


Nicklas Karlsson


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Re: [Emc-users] Checking vfd hookup question?

[Jon Elson]

On 12/24/2020 11:43 AM, Dave Cole wrote:

Automation Direct sells braking resistors.
https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/vfd_accessories/braking_units_-a-_resistors 


Looks like the cheapest one is about $30.
I've used stovetop elements from eBay for about $12 or so.  
If they are good enough for

Haas in mass manufacture, they ought to be good enough for me.

Jon


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Re: [Emc-users] Checking vfd hookup question?

[Dave Cole]

Automation Direct sells braking resistors.
https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/vfd_accessories/braking_units_-a-_resistors
Looks like the cheapest one is about $30.
But unless you are hitting the brakes constantly, they usually don't get 
hot.
A 300 watt (continuously rated) would be good for a 2+ kw drive if you 
aren't using it constantly.
The problem with using a stove element is that you will need to protect 
the terminals.   A 240 input drive has about a 350v DC bus voltage.

You don't want to get shocked with 350 VDC!

Dave

On 12/24/2020 11:06 AM, Jon Elson wrote:

On 12/24/2020 02:18 AM, Chris Albertson wrote:
"All the time?"    When you have a hard requirement like this is when 
some
detailed engineering can pay off.    Assume you are reversing at 50% 
duty

cycle and burning 1KW 50% of the time.   Where I live this can cost 12
cents per hour.  This is $89 per month if you actually do run "all the
time".  Or $1,000 per year.  Or maybe you are usig a lower value 
resister

and burning 4KW with your brake?   That is $4K per year
The VFD only turns the braking resistor on when the DC link voltage 
rises above some limit due to energy returned from the motor during 
deceleration.  I never detect any warming on mine except during rigid 
tapping cycles.
A better way is to use a battery inside the power supply.   a 100 
amp-hour

lithium battery would cost possibly $400.

You are going to need a 340 V battery bank, and a charger for it.

Jon


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Re: [Emc-users] Checking vfd hookup question?

[Jon Elson]

On 12/24/2020 02:18 AM, Chris Albertson wrote:

"All the time?"When you have a hard requirement like this is when some
detailed engineering can pay off.Assume you are reversing at 50% duty
cycle and burning 1KW 50% of the time.   Where I live this can cost 12
cents per hour.  This is $89 per month if you actually do run "all the
time".  Or $1,000 per year.  Or maybe you are usig a lower value resister
and burning 4KW with your brake?   That is $4K per year
The VFD only turns the braking resistor on when the DC link 
voltage rises above some limit due to energy returned from 
the motor during deceleration.  I never detect any warming 
on mine except during rigid tapping cycles.

A better way is to use a battery inside the power supply.   a 100 amp-hour
lithium battery would cost possibly $400.
You are going to need a 340 V battery bank, and a charger 
for it.


Jon


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[Emc-users] Back to the6040 and trying to make LCNC control the spindle

[Gene Heskett]

Greetings all,

I got no response of any kind yesterday from the motor.

So this morning I powered it up and immediately did a set on pd0013 which 
restores factory defaults.  But the jumper that controls which POT, the 
front panel or the electronic on in the 7i76D is used. That now makes it 
run FWD only at up to about 395HZ.

But despite checking d044 and friends for default settings, and having 
the proper connections to FWD/REV and COM, there is not any dc power on 
the FWD/REV terminals, therefor its not detecting the direction commands 
from LCNC.
PD001 and PD002 are both set to 1, meaning external terminals.
PD023 is set to 1, meaning REV run is enabled.
PD044 is 02
PD045 is 03 but I've now printed the booklet some bigger than theirs and 
I see that fwd/rev s/b 5, not 3.
Now it runs FWD only but both axis direction buttons start it. Maybe both 
need set to 5 and I need to swap leads on the motor?

That was confusing to the max as I am using the original motor cable 
which comes from the 4 pin motor, but the 4th pin has no connection, and 
its jumpered thru a 5 pin plug, only 3 were used and by the time I had 
rang it out and screwed it to the UVW terminals I wasn't convinced my 
name was still Gene.

There is a table above that list of explanations on page 36. The English 
is good, but not explicit enough. So if anyone has an answer, pipe up 
please.

Thanks.


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] Checking vfd hookup question?

[Gene Heskett]

On Thursday 24 December 2020 03:18:24 Chris Albertson wrote:

> "All the time?"When you have a hard requirement like this is when
> some detailed engineering can pay off.Assume you are reversing at
> 50% duty cycle and burning 1KW 50% of the time.   Where I live this
> can cost 12 cents per hour.  This is $89 per month if you actually do
> run "all the time".  Or $1,000 per year.  Or maybe you are usig a
> lower value resister and burning 4KW with your brake?   That is $4K
> per year
>
> A better way is to use a battery inside the power supply.   a 100
> amp-hour lithium battery would cost possibly $400.  Then the braking
> energy goes into the battery and then a few seconds later the battery
> is used to run the spindle in the forward direction.   The battery
> needs to be sized so that the energy transferred each cycle is small
> (maybe 1%) of the total capacity.The power supply only has to
> supply power to
> overcome friction.   Most of the energy to accelerate the load comes
> from the brake.
>
> This is exactly how a hybrid car works.   They are most efficient with
> batteries that work at about 400 volts or more.
>
> THis said, I doubt anyone is actually going to run a 7.5KW motor at
> max performance forward reverse cycles for hours on end.   But if you
> do running a stove element is not cheap.
>
> It is really not very complex to brake with a battery as long as the
> battery is very large relative to the current.  A double H-bridge is
> all you need.
>
>
You make a very good argument. Using my GO704 with a stock PMDC motor as 
an example, but running on around 127 volts instead of the nameplate 90 
volts, administered by one of Jon's pwm-servo amps, with the reverse 
sequence controlled by some limit3 in the hal file, I block the reversal 
and program a quick stop by zeroing the input to a limit3, which dumps 
the motor back into the psu, running it up to about 170 volts as it does 
so. But the stop is sensed by a oneshot watching an encoder signal, and 
when 10 millisecs has passed, with no encoder, it finally allows the 
reverse to get to the controller, the requested speed input to the 
limit3 is restored, and that ramps it back up to the S speed set, using 
up that excess charge in the psu. only when the charge in their 
considerable number of microfarads is used up does it resume drawing 
power from the powerline. And the reversal time, even at 3000 rpm is 
less than 400 milliseconds. That peak at 170 volts is well above the 
voltage rating of those caps, but it is such a short duration that the 
average heating from their leakage has not damaged them in close to 5 
years.  And at tapping speeds of say 500 rpm in low gear, the overtravel 
at the bottom of a G33.1 is well under a full turn. Jons pwm-servo is 
set to limit the currant at 17 amps, not quite double the nameplate 9.7 
amps, and the current limit makes the iron in the motor chirp for a 
small fraction of a second. NO other excitement. When I am tapping a 
hole big enough I have to peck the tap, I have a 4 second wait at the 
top of the routine, long enough to clean the tap with an air hose and 
give it another drop of cutting oil. I have tapped 7/16xUSS holes in 
1/2" alu that way.

Pretty good for a cheap machine with plastic gears that is permanently 
out of tram because the post isn't vertical. The bolt holes are far 
enough off I can't fix it without reaming the holes thru the post to the 
next mm up. A reamer I didn't have the last time I had it apart. But 
that is a different story. The point is, that I am recovering that 
energy from the motor, and using it to restore its speed in the other 
direction, and its equally as effective at the opposite M4 to M3 
reversal at the top of the stroke.

I am using a similar bit of hal trickery in the rpi4 config on the 
Sheldon with a resistorless vfd. I rigid tap there at 100 rpms, and with 
a nearly 40 lb 8" chuck mounted, the over travel there is .24 turns. 
Much worse at higher speeds of coarse. Its a permanent part of my axis 
display.

> On Wed, Dec 23, 2020 at 9:23 PM Scott Harwell via Emc-users <
>
> emc-users@lists.sourceforge.net> wrote:
> >  THE Huan Yang 7.5 requires 1000 watt at 75 ohms.
> >
> >
> >
> >
> > On Wednesday, December 23, 2020, 8:17:03 PM CST, andrew beck <
> > andrewbeck0...@gmail.com> wrote:
> >
> >  Just to tag in.
> >
> > I need a braking resistor for my cnc mill spindle it's a 7.5kw vfd.
> >
> > Needs to rigid tap all the time etc


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] Checking vfd hookup question?

[Chris Albertson]

"All the time?"When you have a hard requirement like this is when some
detailed engineering can pay off.Assume you are reversing at 50% duty
cycle and burning 1KW 50% of the time.   Where I live this can cost 12
cents per hour.  This is $89 per month if you actually do run "all the
time".  Or $1,000 per year.  Or maybe you are usig a lower value resister
and burning 4KW with your brake?   That is $4K per year

A better way is to use a battery inside the power supply.   a 100 amp-hour
lithium battery would cost possibly $400.  Then the braking energy goes
into the battery and then a few seconds later the battery is used to run
the spindle in the forward direction.   The battery needs to be sized so
that the energy transferred each cycle is small (maybe 1%) of the total
capacity.The power supply only has to supply power to
overcome friction.   Most of the energy to accelerate the load comes from
the brake.

This is exactly how a hybrid car works.   They are most efficient with
batteries that work at about 400 volts or more.

THis said, I doubt anyone is actually going to run a 7.5KW motor at max
performance forward reverse cycles for hours on end.   But if you do
running a stove element is not cheap.

It is really not very complex to brake with a battery as long as the
battery is very large relative to the current.  A double H-bridge is all
you need.



On Wed, Dec 23, 2020 at 9:23 PM Scott Harwell via Emc-users <
emc-users@lists.sourceforge.net> wrote:

>  THE Huan Yang 7.5 requires 1000 watt at 75 ohms.
>
>
>
>
> On Wednesday, December 23, 2020, 8:17:03 PM CST, andrew beck <
> andrewbeck0...@gmail.com> wrote:
>
>  Just to tag in.
>
> I need a braking resistor for my cnc mill spindle it's a 7.5kw vfd.
>
> Needs to rigid tap all the time etc
>
-- 

Chris Albertson
Redondo Beach, California

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