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Old October 10th 19, 06:29 PM posted to rec.crafts.metalworking
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Posts: 1,571
Default ReWind the Transformer

Some years (10+) back I partially unwound the power transformer for my
power supply on the Hurco mill so that I could stay within the safe
margins for the servo drivers I chose. Sadly the servo drivers did not
hold up. I replaced them with same more than once before finally
upgrading to something that could handle a lot more.

I've got one servo motor that is getting pretty hot. Its also got the
most load on the machine. The Y-axis motor. Its a belt drive and it
has to sling around the weight of the table and the saddle. It gets hot
enough after a few hours to give a 1st degree burn. Not quite enough to
make instant skin death, but its hot. You would suffer injury if you
wrapped your hand around it and held on.

I have considered a couple options including converting it from a belt
drive to a direct drive. A direct drive would have much less parasitic
load. There may be an issue with the ballscrew itself, but I'm holding
out. I have loosened the gibbs slightly, and I have made sure the ball
nut and the gibbs are getting plenty of oil from the automatic oiler.

I am wondering if I increase the voltage by rewinding a few wraps back
onto the transformer to bump the voltage back up to the original 90(+/-)
VDC instead of the current 78VDC. If the voltage is higher the current
should be lower at the same load requirements. Will that result (within
reasonable limits) in a slightly cooler motor?

I'm also considering wrapping a heat sink around the body of the motor
with a generous slathering of heat sink compound. I believe I can make
a bendable heat sink that could be warped to fit the motor.

In all the years I have owned this machine i have always had issues with
the Y axis. Its burned up servo drives, and a while back the motor
cooked. I do mean cooked.

Actually I am considering doing all of the above. My only real issue
with any of these things is that making the axis direct drive will
result in that huge motor (and protective cover) sticking out in front
of the machine in the way of daily operation.

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Old October 10th 19, 07:34 PM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Nov 2006
Posts: 1,354
Default ReWind the Transformer

On Thu, 10 Oct 2019 10:29:22 -0700, Bob La Londe wrote:

Some years (10+) back I partially unwound the power transformer for my
power supply on the Hurco mill so that I could stay within the safe
margins for the servo drivers I chose. Sadly the servo drivers did not
hold up. I replaced them with same more than once before finally
upgrading to something that could handle a lot more.

I've got one servo motor that is getting pretty hot. Its also got the
most load on the machine. The Y-axis motor. Its a belt drive and it
has to sling around the weight of the table and the saddle. It gets hot
enough after a few hours to give a 1st degree burn. Not quite enough to
make instant skin death, but its hot. You would suffer injury if you
wrapped your hand around it and held on.

This is a horizontal mill? The Y axis is vertical? Does it have a
counterweight or air spring to coutner the weight of the table?
That would be the first thing I'd consider.
I have considered a couple options including converting it from a belt
drive to a direct drive. A direct drive would have much less parasitic
load.

I really doubt the belt makes any difference.

There may be an issue with the ballscrew itself, but I'm holding
out. I have loosened the gibbs slightly, and I have made sure the ball
nut and the gibbs are getting plenty of oil from the automatic oiler.

I am wondering if I increase the voltage by rewinding a few wraps back
onto the transformer to bump the voltage back up to the original 90(+/-)
VDC instead of the current 78VDC. If the voltage is higher the current
should be lower at the same load requirements. Will that result (within
reasonable limits) in a slightly cooler motor?

No, it will make no difference. The drive gives the motor the current
required to deliver the torque needed to stay in position. Higher
voltage to the drive MIGHT actually make it worse.
I'm also considering wrapping a heat sink around the body of the motor
with a generous slathering of heat sink compound. I believe I can make
a bendable heat sink that could be warped to fit the motor.

If this is a DC brush motor, that will have little benefit. It is the
rotor (armature) that is producing all the heat. Possibly forced air
cooling to the motor will help. If it is a brushless motor, then heat
sinks of forced air cooling will help a lot, as all the hear is generated
in the stator.

In all the years I have owned this machine i have always had issues with
the Y axis. Its burned up servo drives, and a while back the motor
cooked. I do mean cooked.

And, if you can't hold your hand on it, then you are COOKING it now!

Jon
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Old October 10th 19, 09:11 PM posted to rec.crafts.metalworking
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Posts: 1,571
Default ReWind the Transformer

On 10/10/2019 11:34 AM, Jon Elson wrote: On Thu, 10 Oct 2019 10:29:22
-0700, Bob La Londe wrote:

Some years (10+) back I partially unwound the power transformer for my
power supply on the Hurco mill so that I could stay within the safe
margins for the servo drivers I chose. Sadly the servo drivers did not
hold up. I replaced them with same more than once before finally
upgrading to something that could handle a lot more.

I've got one servo motor that is getting pretty hot. Its also got the
most load on the machine. The Y-axis motor. Its a belt drive and it
has to sling around the weight of the table and the saddle. It gets hot
enough after a few hours to give a 1st degree burn. Not quite enough to
make instant skin death, but its hot. You would suffer injury if you
wrapped your hand around it and held on.

This is a horizontal mill? The Y axis is vertical? Does it have a
counterweight or air spring to coutner the weight of the table?

No, no, and no. I'd guess that table and saddle at around 1000 lbs.
Conventional XY movement.

That would be the first thing I'd consider.
I have considered a couple options including converting it from a belt
drive to a direct drive. A direct drive would have much less parasitic
load.

I really doubt the belt makes any difference.



Any? mechanical power transmission always has some associated loss in
usable power. The timing belts on this machine are pretty darned tight.
I matched the deflection on the Y up with the deflection on the Z.
They are the same center to center distance, and the Z has no issues.


There may be an issue with the ballscrew itself, but I'm holding
out. I have loosened the gibbs slightly, and I have made sure the ball
nut and the gibbs are getting plenty of oil from the automatic oiler.

I am wondering if I increase the voltage by rewinding a few wraps back
onto the transformer to bump the voltage back up to the original 90(+/-)
VDC instead of the current 78VDC. If the voltage is higher the current
should be lower at the same load requirements. Will that result (within
reasonable limits) in a slightly cooler motor?

No, it will make no difference. The drive gives the motor the current
required to deliver the torque needed to stay in position. Higher
voltage to the drive MIGHT actually make it worse.


I considered there might be an issue with back EMF at higher voltage,
but generically total power is a function of amps*volts. Its my
understanding that DC motors typically have a sweet spot, and it was
originally powered at 90VDC. My thought was in addition to requiring
maybe less current for operation it might also be its "sweet spot."

I'm also considering wrapping a heat sink around the body of the motor
with a generous slathering of heat sink compound. I believe I can make
a bendable heat sink that could be warped to fit the motor.

If this is a DC brush motor, that will have little benefit. It is the
rotor (armature) that is producing all the heat. Possibly forced air
cooling to the motor will help. If it is a brushless motor, then heat
sinks of forced air cooling will help a lot, as all the hear is generated
in the stator.



Do you think the heat might have an affect on the field of the permanent
magnets? Its not an open motor, so forced air through the motor is not
an option. Of course air could be blown over the motor, but that would
not directly cool the rotor.



In all the years I have owned this machine i have always had issues with
the Y axis. Its burned up servo drives, and a while back the motor
cooked. I do mean cooked.

And, if you can't hold your hand on it, then you are COOKING it now!



I am aware.
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Old October 10th 19, 09:48 PM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Apr 2008
Posts: 2,061
Default ReWind the Transformer

On Thu, 10 Oct 2019 13:11:46 -0700, Bob La Londe
wrote:

On 10/10/2019 11:34 AM, Jon Elson wrote: On Thu, 10 Oct 2019 10:29:22
-0700, Bob La Londe wrote:

Some years (10+) back I partially unwound the power transformer for my
power supply on the Hurco mill so that I could stay within the safe
margins for the servo drivers I chose. Sadly the servo drivers did not
hold up. I replaced them with same more than once before finally
upgrading to something that could handle a lot more.

I've got one servo motor that is getting pretty hot. Its also got the
most load on the machine. The Y-axis motor. Its a belt drive and it
has to sling around the weight of the table and the saddle. It gets hot
enough after a few hours to give a 1st degree burn. Not quite enough to
make instant skin death, but its hot. You would suffer injury if you
wrapped your hand around it and held on.

This is a horizontal mill? The Y axis is vertical? Does it have a
counterweight or air spring to coutner the weight of the table?

No, no, and no. I'd guess that table and saddle at around 1000 lbs.
Conventional XY movement.

That would be the first thing I'd consider.
I have considered a couple options including converting it from a belt
drive to a direct drive. A direct drive would have much less parasitic
load.

I really doubt the belt makes any difference.



Any? mechanical power transmission always has some associated loss in
usable power. The timing belts on this machine are pretty darned tight.
I matched the deflection on the Y up with the deflection on the Z.
They are the same center to center distance, and the Z has no issues.


There may be an issue with the ballscrew itself, but I'm holding
out. I have loosened the gibbs slightly, and I have made sure the ball
nut and the gibbs are getting plenty of oil from the automatic oiler.

I am wondering if I increase the voltage by rewinding a few wraps back
onto the transformer to bump the voltage back up to the original 90(+/-)
VDC instead of the current 78VDC. If the voltage is higher the current
should be lower at the same load requirements. Will that result (within
reasonable limits) in a slightly cooler motor?

No, it will make no difference. The drive gives the motor the current
required to deliver the torque needed to stay in position. Higher
voltage to the drive MIGHT actually make it worse.


I considered there might be an issue with back EMF at higher voltage,
but generically total power is a function of amps*volts. Its my
understanding that DC motors typically have a sweet spot, and it was
originally powered at 90VDC. My thought was in addition to requiring
maybe less current for operation it might also be its "sweet spot."

I'm also considering wrapping a heat sink around the body of the motor
with a generous slathering of heat sink compound. I believe I can make
a bendable heat sink that could be warped to fit the motor.

If this is a DC brush motor, that will have little benefit. It is the
rotor (armature) that is producing all the heat. Possibly forced air
cooling to the motor will help. If it is a brushless motor, then heat
sinks of forced air cooling will help a lot, as all the hear is generated
in the stator.



Do you think the heat might have an affect on the field of the permanent
magnets? Its not an open motor, so forced air through the motor is not
an option. Of course air could be blown over the motor, but that would
not directly cool the rotor.



In all the years I have owned this machine i have always had issues with
the Y axis. Its burned up servo drives, and a while back the motor
cooked. I do mean cooked.

And, if you can't hold your hand on it, then you are COOKING it now!



I am aware.

Greetings Bob,
Your DC brushed motor consumes current based on the torque
requirement while the voltage is related to speed. So higher voltage
will help it go faster but will not lower the current required. If you
could change the torque requirement that would help. Can you change
the gearing so that the motor spins faster? Years ago I ran into this
exact problem on a home made 4th axis. And the solution was to speed
up the motor while lowering the torque.
You are correct that total power is voltage times current.
Unfortunately supplying more voltage to the motor will not cause it to
draw less current.
Eric
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Old October 10th 19, 10:15 PM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Aug 2012
Posts: 1,571
Default ReWind the Transformer


On 10/10/2019 1:48 PM, wrote:
On Thu, 10 Oct 2019 13:11:46 -0700, Bob La Londe
wrote:

On 10/10/2019 11:34 AM, Jon Elson wrote: On Thu, 10 Oct 2019 10:29:22
-0700, Bob La Londe wrote:

Some years (10+) back I partially unwound the power transformer for my
power supply on the Hurco mill so that I could stay within the safe
margins for the servo drivers I chose. Sadly the servo drivers

did not
hold up. I replaced them with same more than once before finally
upgrading to something that could handle a lot more.

I've got one servo motor that is getting pretty hot. Its also got the
most load on the machine. The Y-axis motor. Its a belt drive and it
has to sling around the weight of the table and the saddle. It

gets hot
enough after a few hours to give a 1st degree burn. Not quite

enough to
make instant skin death, but its hot. You would suffer injury if you
wrapped your hand around it and held on.

This is a horizontal mill? The Y axis is vertical? Does it have a
counterweight or air spring to coutner the weight of the table?

No, no, and no. I'd guess that table and saddle at around 1000 lbs.
Conventional XY movement.

That would be the first thing I'd consider.
I have considered a couple options including converting it from a belt
drive to a direct drive. A direct drive would have much less

parasitic
load.
I really doubt the belt makes any difference.



Any? mechanical power transmission always has some associated loss in
usable power. The timing belts on this machine are pretty darned tight.
I matched the deflection on the Y up with the deflection on the Z.
They are the same center to center distance, and the Z has no issues.


There may be an issue with the ballscrew itself, but I'm holding
out. I have loosened the gibbs slightly, and I have made sure the

ball
nut and the gibbs are getting plenty of oil from the automatic oiler.

I am wondering if I increase the voltage by rewinding a few wraps back
onto the transformer to bump the voltage back up to the original

90(+/-)
VDC instead of the current 78VDC. If the voltage is higher the

current
should be lower at the same load requirements. Will that result

(within
reasonable limits) in a slightly cooler motor?

No, it will make no difference. The drive gives the motor the current
required to deliver the torque needed to stay in position. Higher
voltage to the drive MIGHT actually make it worse.


I considered there might be an issue with back EMF at higher voltage,
but generically total power is a function of amps*volts. Its my
understanding that DC motors typically have a sweet spot, and it was
originally powered at 90VDC. My thought was in addition to requiring
maybe less current for operation it might also be its "sweet spot."

I'm also considering wrapping a heat sink around the body of the motor
with a generous slathering of heat sink compound. I believe I can

make
a bendable heat sink that could be warped to fit the motor.

If this is a DC brush motor, that will have little benefit. It is the
rotor (armature) that is producing all the heat. Possibly forced air
cooling to the motor will help. If it is a brushless motor, then heat
sinks of forced air cooling will help a lot, as all the hear is

generated
in the stator.



Do you think the heat might have an affect on the field of the permanent
magnets? Its not an open motor, so forced air through the motor is not
an option. Of course air could be blown over the motor, but that would
not directly cool the rotor.



In all the years I have owned this machine i have always had

issues with
the Y axis. Its burned up servo drives, and a while back the motor
cooked. I do mean cooked.

And, if you can't hold your hand on it, then you are COOKING it now!



I am aware.

Greetings Bob,
Your DC brushed motor consumes current based on the torque
requirement while the voltage is related to speed. So higher voltage
will help it go faster but will not lower the current required. If you
could change the torque requirement that would help. Can you change
the gearing so that the motor spins faster? Years ago I ran into this
exact problem on a home made 4th axis. And the solution was to speed
up the motor while lowering the torque.
You are correct that total power is voltage times current.
Unfortunately supplying more voltage to the motor will not cause it to
draw less current.
Eric



I have been looking for a band-aid (rather than surgery) for this
application. I think that might just be the band-aid I need. Right now
its a 1:1 belt drive. I will have to think about that some. It would be
nice to keep the motor inside the knee where it is now.


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Old October 10th 19, 10:29 PM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Jan 2018
Posts: 18
Default ReWind the Transformer

On 10/10/2019 2:15 PM, Bob La Londe wrote:



I have been looking for a band-aid (rather than surgery) for this
application.* I think that might just be the band-aid I need.* Right now
its a 1:1 belt drive. I will have to think about that some.* It would be
nice to keep the motor inside the knee where it is now.



My bandaid solution would be to clamp a heat sink with fins to the servo.

Paul
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Old October 10th 19, 10:50 PM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Jan 2008
Posts: 80
Default ReWind the Transformer

Higher voltage means more power but less time. The sweet spot you
mentioned is in there somewhere. Winding the transformer back to
normal first will give you an answer of some sort.

Hul

Bob La Londe wrote:
Some years (10+) back I partially unwound the power transformer for my
power supply on the Hurco mill so that I could stay within the safe
margins for the servo drivers I chose. Sadly the servo drivers did not
hold up. I replaced them with same more than once before finally
upgrading to something that could handle a lot more.


I've got one servo motor that is getting pretty hot. Its also got the
most load on the machine. The Y-axis motor. Its a belt drive and it
has to sling around the weight of the table and the saddle. It gets hot
enough after a few hours to give a 1st degree burn. Not quite enough to
make instant skin death, but its hot. You would suffer injury if you
wrapped your hand around it and held on.


I have considered a couple options including converting it from a belt
drive to a direct drive. A direct drive would have much less parasitic
load. There may be an issue with the ballscrew itself, but I'm holding
out. I have loosened the gibbs slightly, and I have made sure the ball
nut and the gibbs are getting plenty of oil from the automatic oiler.


I am wondering if I increase the voltage by rewinding a few wraps back
onto the transformer to bump the voltage back up to the original 90(+/-)
VDC instead of the current 78VDC. If the voltage is higher the current
should be lower at the same load requirements. Will that result (within
reasonable limits) in a slightly cooler motor?


I'm also considering wrapping a heat sink around the body of the motor
with a generous slathering of heat sink compound. I believe I can make
a bendable heat sink that could be warped to fit the motor.


In all the years I have owned this machine i have always had issues with
the Y axis. Its burned up servo drives, and a while back the motor
cooked. I do mean cooked.


Actually I am considering doing all of the above. My only real issue
with any of these things is that making the axis direct drive will
result in that huge motor (and protective cover) sticking out in front
of the machine in the way of daily operation.

  #8   Report Post  
Old October 11th 19, 02:01 AM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Apr 2008
Posts: 2,061
Default ReWind the Transformer

On Thu, 10 Oct 2019 14:15:20 -0700, Bob La Londe
wrote:


On 10/10/2019 1:48 PM, wrote:
On Thu, 10 Oct 2019 13:11:46 -0700, Bob La Londe
wrote:

On 10/10/2019 11:34 AM, Jon Elson wrote: On Thu, 10 Oct 2019 10:29:22
-0700, Bob La Londe wrote:

Some years (10+) back I partially unwound the power transformer for my
power supply on the Hurco mill so that I could stay within the safe
margins for the servo drivers I chose. Sadly the servo drivers

did not
hold up. I replaced them with same more than once before finally
upgrading to something that could handle a lot more.

I've got one servo motor that is getting pretty hot. Its also got the
most load on the machine. The Y-axis motor. Its a belt drive and it
has to sling around the weight of the table and the saddle. It

gets hot
enough after a few hours to give a 1st degree burn. Not quite

enough to
make instant skin death, but its hot. You would suffer injury if you
wrapped your hand around it and held on.

This is a horizontal mill? The Y axis is vertical? Does it have a
counterweight or air spring to coutner the weight of the table?
No, no, and no. I'd guess that table and saddle at around 1000 lbs.
Conventional XY movement.

That would be the first thing I'd consider.
I have considered a couple options including converting it from a belt
drive to a direct drive. A direct drive would have much less

parasitic
load.
I really doubt the belt makes any difference.


Any? mechanical power transmission always has some associated loss in
usable power. The timing belts on this machine are pretty darned tight.
I matched the deflection on the Y up with the deflection on the Z.
They are the same center to center distance, and the Z has no issues.


There may be an issue with the ballscrew itself, but I'm holding
out. I have loosened the gibbs slightly, and I have made sure the

ball
nut and the gibbs are getting plenty of oil from the automatic oiler.

I am wondering if I increase the voltage by rewinding a few wraps back
onto the transformer to bump the voltage back up to the original

90(+/-)
VDC instead of the current 78VDC. If the voltage is higher the

current
should be lower at the same load requirements. Will that result

(within
reasonable limits) in a slightly cooler motor?

No, it will make no difference. The drive gives the motor the current
required to deliver the torque needed to stay in position. Higher
voltage to the drive MIGHT actually make it worse.

I considered there might be an issue with back EMF at higher voltage,
but generically total power is a function of amps*volts. Its my
understanding that DC motors typically have a sweet spot, and it was
originally powered at 90VDC. My thought was in addition to requiring
maybe less current for operation it might also be its "sweet spot."

I'm also considering wrapping a heat sink around the body of the motor
with a generous slathering of heat sink compound. I believe I can

make
a bendable heat sink that could be warped to fit the motor.

If this is a DC brush motor, that will have little benefit. It is the
rotor (armature) that is producing all the heat. Possibly forced air
cooling to the motor will help. If it is a brushless motor, then heat
sinks of forced air cooling will help a lot, as all the hear is

generated
in the stator.


Do you think the heat might have an affect on the field of the permanent
magnets? Its not an open motor, so forced air through the motor is not
an option. Of course air could be blown over the motor, but that would
not directly cool the rotor.



In all the years I have owned this machine i have always had

issues with
the Y axis. Its burned up servo drives, and a while back the motor
cooked. I do mean cooked.

And, if you can't hold your hand on it, then you are COOKING it now!


I am aware.

Greetings Bob,
Your DC brushed motor consumes current based on the torque
requirement while the voltage is related to speed. So higher voltage
will help it go faster but will not lower the current required. If you
could change the torque requirement that would help. Can you change
the gearing so that the motor spins faster? Years ago I ran into this
exact problem on a home made 4th axis. And the solution was to speed
up the motor while lowering the torque.
You are correct that total power is voltage times current.
Unfortunately supplying more voltage to the motor will not cause it to
draw less current.
Eric



I have been looking for a band-aid (rather than surgery) for this
application. I think that might just be the band-aid I need. Right now
its a 1:1 belt drive. I will have to think about that some. It would be
nice to keep the motor inside the knee where it is now.



I hope it works. Where is the encoder for the Y axis? If it's on the
ballscrew then you can probably get away with changing the pulley
ratio. If it's on the motor, then you will need to tell the control
what the new ratio is. Or move the encoder.
Eric
  #9   Report Post  
Old October 11th 19, 03:07 AM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Aug 2012
Posts: 1,571
Default ReWind the Transformer

On 10/10/2019 6:01 PM, wrote:
On Thu, 10 Oct 2019 14:15:20 -0700, Bob La Londe
wrote:


On 10/10/2019 1:48 PM,
wrote:
On Thu, 10 Oct 2019 13:11:46 -0700, Bob La Londe
wrote:

On 10/10/2019 11:34 AM, Jon Elson wrote: On Thu, 10 Oct 2019 10:29:22
-0700, Bob La Londe wrote:

Some years (10+) back I partially unwound the power transformer for my
power supply on the Hurco mill so that I could stay within the safe
margins for the servo drivers I chose. Sadly the servo drivers

did not
hold up. I replaced them with same more than once before finally
upgrading to something that could handle a lot more.

I've got one servo motor that is getting pretty hot. Its also got the
most load on the machine. The Y-axis motor. Its a belt drive and it
has to sling around the weight of the table and the saddle. It

gets hot
enough after a few hours to give a 1st degree burn. Not quite

enough to
make instant skin death, but its hot. You would suffer injury if you
wrapped your hand around it and held on.

This is a horizontal mill? The Y axis is vertical? Does it have a
counterweight or air spring to coutner the weight of the table?
No, no, and no. I'd guess that table and saddle at around 1000 lbs.
Conventional XY movement.

That would be the first thing I'd consider.
I have considered a couple options including converting it from a belt
drive to a direct drive. A direct drive would have much less

parasitic
load.
I really doubt the belt makes any difference.


Any? mechanical power transmission always has some associated loss in
usable power. The timing belts on this machine are pretty darned tight.
I matched the deflection on the Y up with the deflection on the Z.
They are the same center to center distance, and the Z has no issues.


There may be an issue with the ballscrew itself, but I'm holding
out. I have loosened the gibbs slightly, and I have made sure the

ball
nut and the gibbs are getting plenty of oil from the automatic oiler.

I am wondering if I increase the voltage by rewinding a few wraps back
onto the transformer to bump the voltage back up to the original

90(+/-)
VDC instead of the current 78VDC. If the voltage is higher the

current
should be lower at the same load requirements. Will that result

(within
reasonable limits) in a slightly cooler motor?

No, it will make no difference. The drive gives the motor the current
required to deliver the torque needed to stay in position. Higher
voltage to the drive MIGHT actually make it worse.

I considered there might be an issue with back EMF at higher voltage,
but generically total power is a function of amps*volts. Its my
understanding that DC motors typically have a sweet spot, and it was
originally powered at 90VDC. My thought was in addition to requiring
maybe less current for operation it might also be its "sweet spot."

I'm also considering wrapping a heat sink around the body of the motor
with a generous slathering of heat sink compound. I believe I can

make
a bendable heat sink that could be warped to fit the motor.

If this is a DC brush motor, that will have little benefit. It is the
rotor (armature) that is producing all the heat. Possibly forced air
cooling to the motor will help. If it is a brushless motor, then heat
sinks of forced air cooling will help a lot, as all the hear is

generated
in the stator.


Do you think the heat might have an affect on the field of the permanent
magnets? Its not an open motor, so forced air through the motor is not
an option. Of course air could be blown over the motor, but that would
not directly cool the rotor.



In all the years I have owned this machine i have always had

issues with
the Y axis. Its burned up servo drives, and a while back the motor
cooked. I do mean cooked.

And, if you can't hold your hand on it, then you are COOKING it now!


I am aware.
Greetings Bob,
Your DC brushed motor consumes current based on the torque
requirement while the voltage is related to speed. So higher voltage
will help it go faster but will not lower the current required. If you
could change the torque requirement that would help. Can you change
the gearing so that the motor spins faster? Years ago I ran into this
exact problem on a home made 4th axis. And the solution was to speed
up the motor while lowering the torque.
You are correct that total power is voltage times current.
Unfortunately supplying more voltage to the motor will not cause it to
draw less current.
Eric



I have been looking for a band-aid (rather than surgery) for this
application. I think that might just be the band-aid I need. Right now
its a 1:1 belt drive. I will have to think about that some. It would be
nice to keep the motor inside the knee where it is now.



I hope it works. Where is the encoder for the Y axis? If it's on the
ballscrew then you can probably get away with changing the pulley
ratio. If it's on the motor, then you will need to tell the control
what the new ratio is. Or move the encoder.
Eric


Yeah, that's no big deal. I can set the PPI pretty easily. The math is
simple too once you have done it once or twice.

  #10   Report Post  
Old October 11th 19, 04:43 PM posted to rec.crafts.metalworking
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Posts: 16
Default ReWind the Transformer

On Thursday, October 10, 2019 at 10:29:27 AM UTC-7, Bob La Londe wrote:
Some years (10+) back I partially unwound the power transformer for my
power supply on the Hurco mill so that I could stay within the safe
margins for the servo drivers I chose. Sadly the servo drivers did not
hold up. I replaced them with same more than once before finally
upgrading to something that could handle a lot more.

I've got one servo motor that is getting pretty hot. Its also got the
most load on the machine. The Y-axis motor. Its a belt drive and it
has to sling around the weight of the table and the saddle. It gets hot
enough after a few hours to give a 1st degree burn. Not quite enough to
make instant skin death, but its hot. You would suffer injury if you
wrapped your hand around it and held on.

I have considered a couple options including converting it from a belt
drive to a direct drive. A direct drive would have much less parasitic
load. There may be an issue with the ballscrew itself, but I'm holding
out. I have loosened the gibbs slightly, and I have made sure the ball
nut and the gibbs are getting plenty of oil from the automatic oiler.

I am wondering if I increase the voltage by rewinding a few wraps back
onto the transformer to bump the voltage back up to the original 90(+/-)
VDC instead of the current 78VDC. If the voltage is higher the current
should be lower at the same load requirements. Will that result (within
reasonable limits) in a slightly cooler motor?

I'm also considering wrapping a heat sink around the body of the motor
with a generous slathering of heat sink compound. I believe I can make
a bendable heat sink that could be warped to fit the motor.

In all the years I have owned this machine i have always had issues with
the Y axis. Its burned up servo drives, and a while back the motor
cooked. I do mean cooked.

Actually I am considering doing all of the above. My only real issue
with any of these things is that making the axis direct drive will
result in that huge motor (and protective cover) sticking out in front
of the machine in the way of daily operation.


I think changing the motor drive ratio is the best solution. However if one wants to get heat out of a brush dc motor i would get a non contact temperature sensor ($30 at harbor freight) and find the hot spots. The hot spots are the place to apply cooling. If the motor has plain bearing than most of the heat is being rejected though the shaft to the housing. If they are ball bearing then the heat is likely from convection of the air internal to the motor to the housing.

If you put a fan on the output shaft that blows over the motor housing you attack to heat sources. You cool the motor shaft and you cool the motor housing with force air which provides much more cooling than a static heat sink. If one need more cooling wrap copper tube around the motor and pass cold water though it.


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