Re: [Emc-users] Brake resistor question

[Viesturs Lācis]

Thanks for all the responses!
I got some insight, where to start.

Viesturs


2014-04-17 19:31 GMT+03:00 Jon Elson :

> On 04/17/2014 08:56 AM, Viesturs Lācis wrote:
> > Hello!
> >
> > I have three chinese servo drives in the waterjet machine and they are
> > constantly faulting with "overvoltage" error. Since I have not yet added
> > any braking resistors, it seems obvious that I should do so.
> > The question is: how do I determine appropriate resistance and rated
> power
> > values for the resistor?
> > Motor parameters are here:
> > http://www.cutting.lv/fileadmin/user_upload/tg-motor.pdf
> >
> > Currently max current in motors is set to 1,4A, which makes me think that
> > actual motor power is 500W.
> >
> 560 V at 1.4 A is a reasonable guess. That would be 400 Ohms.
> A 100 W vitreous ceramic resistor works well, they take
> momentary
> overloads easily. You could probably go a little lower on the
> resistance without trouble. But, it is unlikely the motors will
> generate much more than their continuous rating while
> being decelerated.
>
> Jon
>
> Jon
>
>
>
> --
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Re: [Emc-users] Brake resistor question

[Jon Elson]

On 04/17/2014 08:56 AM, Viesturs Lācis wrote:
> Hello!
>
> I have three chinese servo drives in the waterjet machine and they are
> constantly faulting with "overvoltage" error. Since I have not yet added
> any braking resistors, it seems obvious that I should do so.
> The question is: how do I determine appropriate resistance and rated power
> values for the resistor?
> Motor parameters are here:
> http://www.cutting.lv/fileadmin/user_upload/tg-motor.pdf
>
> Currently max current in motors is set to 1,4A, which makes me think that
> actual motor power is 500W.
>
560 V at 1.4 A is a reasonable guess. That would be 400 Ohms.
A 100 W vitreous ceramic resistor works well, they take 
momentary
overloads easily. You could probably go a little lower on the
resistance without trouble. But, it is unlikely the motors will
generate much more than their continuous rating while
being decelerated.

Jon

Jon


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Re: [Emc-users] Brake resistor question

[Gene Heskett]

On Thursday 17 April 2014 11:56:00 Eric Keller did opine:

> Haas uses electric stove elements.  I suppose they had an engineer sit
> down for 10 minutes to figure out the resistance.  They will certainly
> take a significant amount of wattage

Along those same lines, replacement water heater elements could be used in 
those higher voltage environs.  The mica sheets wound with the flat 
nichrome from old bread toasters might also be a suitable source.  Shield 
those from swarf obviously.  Ditto for old electric clothes dryers.
 
> On Thu, Apr 17, 2014 at 9:56 AM, Viesturs Lؤپcis 
wrote:
> > Hello!
> > 
> > I have three chinese servo drives in the waterjet machine and they are
> > constantly faulting with "overvoltage" error. Since I have not yet
> > added any braking resistors, it seems obvious that I should do so.
> > The question is: how do I determine appropriate resistance and rated
> > power values for the resistor?
> > Motor parameters are here:
> > http://www.cutting.lv/fileadmin/user_upload/tg-motor.pdf
> > 
> > Currently max current in motors is set to 1,4A, which makes me think
> > that actual motor power is 500W.
> > Experienced guy suggested braking resistor with 100-150 ohm
> > resistance. But how do I determine correct rated power? Or is it that
> > I just take the biggest power available as it cannot be too high?
> > 
> > Viesturs
> > 
> > --
> >  Learn Graph Databases - Download FREE O'Reilly Book
> > "Graph Databases" is the definitive new guide to graph databases and
> > their applications. Written by three acclaimed leaders in the field,
> > this first edition is now available. Download your free book today!
> > http://p.sf.net/sfu/NeoTech
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> > https://lists.sourceforge.net/lists/listinfo/emc-users
> 
> 
> -- Learn Graph Databases - Download FREE O'Reilly Book
> "Graph Databases" is the definitive new guide to graph databases and
> their applications. Written by three acclaimed leaders in the field,
> this first edition is now available. Download your free book today!
> http://p.sf.net/sfu/NeoTech
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Cheers, Gene
-- 
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 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 
US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS

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Re: [Emc-users] Brake resistor question

[Gene Heskett]

On Thursday 17 April 2014 11:32:36 Viesturs Lācis did opine:

> Hello!
> 
> I have three chinese servo drives in the waterjet machine and they are
> constantly faulting with "overvoltage" error. Since I have not yet added
> any braking resistors, it seems obvious that I should do so.
> The question is: how do I determine appropriate resistance and rated
> power values for the resistor?
> Motor parameters are here:
> http://www.cutting.lv/fileadmin/user_upload/tg-motor.pdf
> 
> Currently max current in motors is set to 1,4A, which makes me think
> that actual motor power is 500W.
> Experienced guy suggested braking resistor with 100-150 ohm resistance.
> But how do I determine correct rated power? Or is it that I just take
> the biggest power available as it cannot be too high?

The latter here. I am using much lower R's than that, and there would be a 
limit to how many strokes I can use for a g33.1 on my lathe.  But its more 
than a single usage to tap a hole would need. My resistors are 6 of the 20 
watt 8 ohm power r's from the shack, and do get warm.  The high speed set 
(I stage them with a wcomp module) loads a 1hp treadmill motor with a 2x2 
network, giving 8 ohms & 80 watts, sandwiched between some alu angle, then 
as the speed dies it drop to 4 ohms at 40 watts air cooled, with the last 
stage being a dead short from about 125 spindle revs to stopped.

Two reasons for the application staging,
 1. don't exceed the motors nameplate or circuit breaker amps for fear of 
damaging the PM field magnets, and
 2. Don't unscrew the fan/pulley from the motor shaft.  It is loctite'd in 
place and screwed on much tighter than factory, but since its 3 or 4 lbs of 
iron, could rip up things in the box very easily should it come loose.

> Viesturs
> 
> -- Learn Graph Databases - Download FREE O'Reilly Book
> "Graph Databases" is the definitive new guide to graph databases and
> their applications. Written by three acclaimed leaders in the field,
> this first edition is now available. Download your free book today!
> http://p.sf.net/sfu/NeoTech
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> https://lists.sourceforge.net/lists/listinfo/emc-users


Cheers, Gene
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 
US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS

--
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Re: [Emc-users] Brake resistor question

[Kirk Wallace]

On 04/17/2014 07:25 AM, Kirk Wallace wrote:
> On 04/17/2014 06:56 AM, Viesturs Lācis wrote:
>> Hello!
>>
>> I have three chinese servo drives in the waterjet machine and they are
>> constantly faulting with "overvoltage" error. Since I have not yet added
>> any braking resistors, it seems obvious that I should do so.
>> The question is: how do I determine appropriate resistance and rated power
>> values for the resistor?
>> Motor parameters are here:
>> http://www.cutting.lv/fileadmin/user_upload/tg-motor.pdf
>>
>> Currently max current in motors is set to 1,4A, which makes me think that
>> actual motor power is 500W.
>> Experienced guy suggested braking resistor with 100-150 ohm resistance. But
>> how do I determine correct rated power? Or is it that I just take the
>> biggest power available as it cannot be too high?
>>
>> Viesturs
>
> Some VFD manuals have sections covering braking resistors. Some resistor
> modules have sensors or protection devices of some type.
>
> The Ohms and voltage values will set the current going through the
> resistor.
>
> V = I * R
> or
> V / R = I,
>
> let's say 240V / 100 Ohms = 2.4 Amps.
>
> Watts = V * I or 240 * 2.4 Amps = 576 Watts.
>
> If you go higher in Ohms, you will get less braking. The VFD's braking
> circuit will likely have a maximum current rating as well as the motor.
>
> One of my shop-made braking modules (four gold colored resistors) is
> bolted to the back of my VFD here:
> http://www.wallacecompany.com/cnc_lathe/HNC/00024-1a.jpg

Another thing that comes to mind, without a braking resistor, you 
essentially have a resistor of very high Ohms. When you call for braking 
the motor turns into a generator and the generated voltage goes into the 
VFD's braking circuit which at this point presents no load, so the 
voltage goes too high. If you configure the VFD settings to slow down 
over a longer time, less voltage goes to the braking circuit and you can 
avoid the over voltage alarm.

If you want faster braking, set the VFD to a shorter braking time, but 
also add some braking load by reducing the braking resistance. Since we 
are starting with nearly infinite Ohms, any reduction will help quite a 
bit. You can reduce Ohms and braking time up until the current limit of 
the braking circuit and motor. Once you have the Ohms value, you can 
calculate the Watt rating for the resistor. If the resistor gets hot, 
increase the braking time or add a heat sink.


-- 
Kirk Wallace
http://www.wallacecompany.com/machine_shop/
http://www.wallacecompany.com/E45/

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Re: [Emc-users] Brake resistor question

[Eric Keller]

Haas uses electric stove elements.  I suppose they had an engineer sit down
for 10 minutes to figure out the resistance.  They will certainly take a
significant amount of wattage


On Thu, Apr 17, 2014 at 9:56 AM, Viesturs Lācis wrote:

> Hello!
>
> I have three chinese servo drives in the waterjet machine and they are
> constantly faulting with "overvoltage" error. Since I have not yet added
> any braking resistors, it seems obvious that I should do so.
> The question is: how do I determine appropriate resistance and rated power
> values for the resistor?
> Motor parameters are here:
> http://www.cutting.lv/fileadmin/user_upload/tg-motor.pdf
>
> Currently max current in motors is set to 1,4A, which makes me think that
> actual motor power is 500W.
> Experienced guy suggested braking resistor with 100-150 ohm resistance. But
> how do I determine correct rated power? Or is it that I just take the
> biggest power available as it cannot be too high?
>
> Viesturs
>
> --
> Learn Graph Databases - Download FREE O'Reilly Book
> "Graph Databases" is the definitive new guide to graph databases and their
> applications. Written by three acclaimed leaders in the field,
> this first edition is now available. Download your free book today!
> http://p.sf.net/sfu/NeoTech
> ___
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> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>
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Re: [Emc-users] Brake resistor question

[alex chiosso]

Hi , Viesturs.

I found this 
documentthat
may be useful .
I do believe that 100W should be ok for a 500W motor .
Of course the calculation is related to the energy that have to be
dissipated during the braking phase.
So also acc/dec time can influence too.

Alex


On Thu, Apr 17, 2014 at 4:25 PM, Kirk Wallace
wrote:

> On 04/17/2014 06:56 AM, Viesturs Lācis wrote:
> > Hello!
> >
> > I have three chinese servo drives in the waterjet machine and they are
> > constantly faulting with "overvoltage" error. Since I have not yet added
> > any braking resistors, it seems obvious that I should do so.
> > The question is: how do I determine appropriate resistance and rated
> power
> > values for the resistor?
> > Motor parameters are here:
> > http://www.cutting.lv/fileadmin/user_upload/tg-motor.pdf
> >
> > Currently max current in motors is set to 1,4A, which makes me think that
> > actual motor power is 500W.
> > Experienced guy suggested braking resistor with 100-150 ohm resistance.
> But
> > how do I determine correct rated power? Or is it that I just take the
> > biggest power available as it cannot be too high?
> >
> > Viesturs
>
> Some VFD manuals have sections covering braking resistors. Some resistor
> modules have sensors or protection devices of some type.
>
> The Ohms and voltage values will set the current going through the
> resistor.
>
> V = I * R
> or
> V / R = I,
>
> let's say 240V / 100 Ohms = 2.4 Amps.
>
> Watts = V * I or 240 * 2.4 Amps = 576 Watts.
>
> If you go higher in Ohms, you will get less braking. The VFD's braking
> circuit will likely have a maximum current rating as well as the motor.
>
> One of my shop-made braking modules (four gold colored resistors) is
> bolted to the back of my VFD here:
> http://www.wallacecompany.com/cnc_lathe/HNC/00024-1a.jpg
>
>
> --
> Kirk Wallace
> http://www.wallacecompany.com/machine_shop/
> http://www.wallacecompany.com/E45/
>
>
> --
> Learn Graph Databases - Download FREE O'Reilly Book
> "Graph Databases" is the definitive new guide to graph databases and their
> applications. Written by three acclaimed leaders in the field,
> this first edition is now available. Download your free book today!
> http://p.sf.net/sfu/NeoTech
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Re: [Emc-users] Brake resistor question

[Kirk Wallace]

On 04/17/2014 06:56 AM, Viesturs Lācis wrote:
> Hello!
>
> I have three chinese servo drives in the waterjet machine and they are
> constantly faulting with "overvoltage" error. Since I have not yet added
> any braking resistors, it seems obvious that I should do so.
> The question is: how do I determine appropriate resistance and rated power
> values for the resistor?
> Motor parameters are here:
> http://www.cutting.lv/fileadmin/user_upload/tg-motor.pdf
>
> Currently max current in motors is set to 1,4A, which makes me think that
> actual motor power is 500W.
> Experienced guy suggested braking resistor with 100-150 ohm resistance. But
> how do I determine correct rated power? Or is it that I just take the
> biggest power available as it cannot be too high?
>
> Viesturs

Some VFD manuals have sections covering braking resistors. Some resistor 
modules have sensors or protection devices of some type.

The Ohms and voltage values will set the current going through the 
resistor.

V = I * R
or
V / R = I,

let's say 240V / 100 Ohms = 2.4 Amps.

Watts = V * I or 240 * 2.4 Amps = 576 Watts.

If you go higher in Ohms, you will get less braking. The VFD's braking 
circuit will likely have a maximum current rating as well as the motor.

One of my shop-made braking modules (four gold colored resistors) is 
bolted to the back of my VFD here:
http://www.wallacecompany.com/cnc_lathe/HNC/00024-1a.jpg


-- 
Kirk Wallace
http://www.wallacecompany.com/machine_shop/
http://www.wallacecompany.com/E45/

--
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[Emc-users] Brake resistor question

[Viesturs Lācis]

Hello!

I have three chinese servo drives in the waterjet machine and they are
constantly faulting with "overvoltage" error. Since I have not yet added
any braking resistors, it seems obvious that I should do so.
The question is: how do I determine appropriate resistance and rated power
values for the resistor?
Motor parameters are here:
http://www.cutting.lv/fileadmin/user_upload/tg-motor.pdf

Currently max current in motors is set to 1,4A, which makes me think that
actual motor power is 500W.
Experienced guy suggested braking resistor with 100-150 ohm resistance. But
how do I determine correct rated power? Or is it that I just take the
biggest power available as it cannot be too high?

Viesturs
--
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