Low cost power supply
Posted by
David Howland
on 1999-09-15 12:23:24 UTC
A good source for DC power supplies is: Marlin P. Jones & Assoc. Inc. http://www.mpja.com (800) 652-6733 and the latest catalog is 99-06
As you know the concept I have been exploring might draw me into an electrical design, integrating the servo amplifier and digital interface components on one board in an effort to retrofit mills without steppers, however, I do not beleive that makes any since when others have already created reasonable sub systems which do the job nicely and end up producing work which is not damaged by sloppy concepts.
What contributions I will make, if no one has already done so, is to design the kind of power supplies that are required, as long as what I develop reduces the costs below what might be available from surplus. I've noticed that it is easy to find surplus power supplies in voltages up to 48 VDC, but if you need higher voltage and higher current, even chaining surplus power supplies together ends up costing more money than I think might be done with an electrical design and surplus power supply components.
Therefore, if this is of value to anyone, I will be happy to supply a schematic diagram and a bill of material with parts sources and present prices for the components for a higher voltage supply that might meet the needs for servo amplifiers and large steppers. Several members have upgraded stepper drivers and power supplies and might have the power supply and cost information to compare against the value of such an effort. One source for large Electrolytic capacitors in the bay area is RA Enterprise. I may be there on Saturday. If anyone wants anything, let me know the price limit you have in mind and I'll let you know the details of what I see there.
For a large power supply to come in at a reasonable price, the expensive items include the transformer and the large capacitors. To put this concept in perspective, you can buy power supplies from MPJ
Unregulated: 48 VDC 10 Amps for $147.85 each, therefore two = 96 VDC at 10 Amps for $295.70
You can buy 24 VAC 10 Amp transformers for $18.00 and 4 of them run you $72.00
The next expensive components are large electrolytic capacitors. If you can score those for under $50, your are on your way to getting the costs under control. I'll look at the large electrolytic caps while I'm at RA on Saturday.
What are the specs for a DC supply that meet the requirements for Servo and Stepper use? What have members paid to obtain this sort of power? If 96 VDC at 8 Amps can be built for $200.00 in components (including fans, enclosure, line filter and the rest) and 4 hours of labor, will that get the job done?
David Howland
-----Original Message-----
From: Jon Elson [SMTP:jmelson@...]
Sent: Tuesday, September 14, 1999 11:42 PM
To: CAD_CAM_EDM_DRO@onelist.com
Subject: Re: [CAD_CAM_EDM_DRO] Low cost Servo Controller
From: Jon Elson <jmelson@...>
Note, also that you will need an external +/- 12 Volt DC power
supply,
about 1/2 A for the +, and .25 A for -, for each amplifier. One big
supply is fine. You will also need a DC power supply for the servo
power. I'm using a 15 Amp, 68 Volt unregulated supply for my setup,
but your motors determine what is appropriate. You will also need
a card cage for the 4.5 x 6" cards (standard Vector board format).
I used some 22/44 contact wire-wrap sockets for the board to plug
into. I used some 1/8 x 1/2" bus bar (armature bar) to connect
ground
and servo power to all the amps. I ran the bar between 2 rows of
pins,
and soldered 4 pins to each bar. For the motor output, I bent 4 pins
together, and stuffed them into a crimp-type male 1/4" quick
disconnect
terminal. I then soldered the terminal to the pins. There are 2 of
these terminals for each motor. Finally, you need a good DC tach
to provide velocity feedback for the servo loop. I got 3 really nice
DC tachs from C&H surplus in Pasadena, CA. Unfortunately, those
are all gone. I'm looking for some more, and if I find a suitable
source,
I'll let everyone know. The trick here is it must have minimal
ripple
at constant speed. Some small ironless-rotor DC servo motors, like
Maxon and Escap are made exactly the same as their tachs, and will
work fine.
The final gizmo to construct is the power up/down control. I use a
setup with a small relay and a big contactor to ramp the servo supply
up and down. When the CNC control commands the servos to
come active, the first relay connects a resistor to charge up the
caps
located on the amp cards. When enough time has elapsed, a simple
delay circuit closes the direct connection to the DC power supply
with the big contactor. When the control tells the servos to power
down, the small relay opens, which cuts power to the contactor, as
well as connecting a dump resistor (same actual resisitor as the
charging one) to the amps, draining the on-board cap, and also
burning off any back-emf coming from decelerating motors.
I'm having some slight problems with burning contacts on the small
control relay, so we might try a bigger one with more contact gap.
My phone at home (with the recorder) is (314) 965-5523.
I'm usually here in the mornings (central time) and evenings, and of
course
on weekend. On weekday afternoons, I am at Wash U., at (314)
935-6547.
Jon
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To Unsubscribe, read archives, change to or from digest.
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bill,
List Manager
As you know the concept I have been exploring might draw me into an electrical design, integrating the servo amplifier and digital interface components on one board in an effort to retrofit mills without steppers, however, I do not beleive that makes any since when others have already created reasonable sub systems which do the job nicely and end up producing work which is not damaged by sloppy concepts.
What contributions I will make, if no one has already done so, is to design the kind of power supplies that are required, as long as what I develop reduces the costs below what might be available from surplus. I've noticed that it is easy to find surplus power supplies in voltages up to 48 VDC, but if you need higher voltage and higher current, even chaining surplus power supplies together ends up costing more money than I think might be done with an electrical design and surplus power supply components.
Therefore, if this is of value to anyone, I will be happy to supply a schematic diagram and a bill of material with parts sources and present prices for the components for a higher voltage supply that might meet the needs for servo amplifiers and large steppers. Several members have upgraded stepper drivers and power supplies and might have the power supply and cost information to compare against the value of such an effort. One source for large Electrolytic capacitors in the bay area is RA Enterprise. I may be there on Saturday. If anyone wants anything, let me know the price limit you have in mind and I'll let you know the details of what I see there.
For a large power supply to come in at a reasonable price, the expensive items include the transformer and the large capacitors. To put this concept in perspective, you can buy power supplies from MPJ
Unregulated: 48 VDC 10 Amps for $147.85 each, therefore two = 96 VDC at 10 Amps for $295.70
You can buy 24 VAC 10 Amp transformers for $18.00 and 4 of them run you $72.00
The next expensive components are large electrolytic capacitors. If you can score those for under $50, your are on your way to getting the costs under control. I'll look at the large electrolytic caps while I'm at RA on Saturday.
What are the specs for a DC supply that meet the requirements for Servo and Stepper use? What have members paid to obtain this sort of power? If 96 VDC at 8 Amps can be built for $200.00 in components (including fans, enclosure, line filter and the rest) and 4 hours of labor, will that get the job done?
David Howland
-----Original Message-----
From: Jon Elson [SMTP:jmelson@...]
Sent: Tuesday, September 14, 1999 11:42 PM
To: CAD_CAM_EDM_DRO@onelist.com
Subject: Re: [CAD_CAM_EDM_DRO] Low cost Servo Controller
From: Jon Elson <jmelson@...>
Note, also that you will need an external +/- 12 Volt DC power
supply,
about 1/2 A for the +, and .25 A for -, for each amplifier. One big
supply is fine. You will also need a DC power supply for the servo
power. I'm using a 15 Amp, 68 Volt unregulated supply for my setup,
but your motors determine what is appropriate. You will also need
a card cage for the 4.5 x 6" cards (standard Vector board format).
I used some 22/44 contact wire-wrap sockets for the board to plug
into. I used some 1/8 x 1/2" bus bar (armature bar) to connect
ground
and servo power to all the amps. I ran the bar between 2 rows of
pins,
and soldered 4 pins to each bar. For the motor output, I bent 4 pins
together, and stuffed them into a crimp-type male 1/4" quick
disconnect
terminal. I then soldered the terminal to the pins. There are 2 of
these terminals for each motor. Finally, you need a good DC tach
to provide velocity feedback for the servo loop. I got 3 really nice
DC tachs from C&H surplus in Pasadena, CA. Unfortunately, those
are all gone. I'm looking for some more, and if I find a suitable
source,
I'll let everyone know. The trick here is it must have minimal
ripple
at constant speed. Some small ironless-rotor DC servo motors, like
Maxon and Escap are made exactly the same as their tachs, and will
work fine.
The final gizmo to construct is the power up/down control. I use a
setup with a small relay and a big contactor to ramp the servo supply
up and down. When the CNC control commands the servos to
come active, the first relay connects a resistor to charge up the
caps
located on the amp cards. When enough time has elapsed, a simple
delay circuit closes the direct connection to the DC power supply
with the big contactor. When the control tells the servos to power
down, the small relay opens, which cuts power to the contactor, as
well as connecting a dump resistor (same actual resisitor as the
charging one) to the amps, draining the on-board cap, and also
burning off any back-emf coming from decelerating motors.
I'm having some slight problems with burning contacts on the small
control relay, so we might try a bigger one with more contact gap.
My phone at home (with the recorder) is (314) 965-5523.
I'm usually here in the mornings (central time) and evenings, and of
course
on weekend. On weekday afternoons, I am at Wash U., at (314)
935-6547.
Jon
--------------------------- ONElist Sponsor ----------------------------
GRAB THE GATOR! FREE SOFTWARE DOES ALL THE TYPING FOR YOU!
Tired of filling out forms and remembering passwords? Gator fills in
forms and passwords with just one click! Comes with $50 in free coupons!
http://www.onelist.com/ad/gator1
------------------------------------------------------------------------
Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the discussion of shop built systems in the above catagories.
To Unsubscribe, read archives, change to or from digest.
Go to: http://www.onelist.com/isregistered.cgi
Log on, and you will go to Member Center, and you can make changes there.
For the FAQ, go to http://www.ktmarketing.com/faq.html
bill,
List Manager
Discussion Thread
David Howland
1999-09-15 12:23:24 UTC
Low cost power supply
gary@x...
1999-09-16 08:16:44 UTC
Re: Low cost power supply
David Howland
1999-09-16 11:22:11 UTC
RE: Low cost power supply