RE: Low cost power supply

A Great Surplus Store in the San Jose, Calif area:

RA Enterprise Sat 9:00 A.M. to 3:30 P.M. M - F Don't know?
691 Walsh Ave, Santa Clara, CA (cross street Layfette)
(408) 986-8286

They carry a fair amount of electronic equipment especially non main stream test equipment for who knows what. They are getting somewhat picked over as more and more people have discovered them. Some of the best stuff is more and more difficult to locate there. I cleaned out most of the rotary encoders and large servo and step motors and they don't seem to be restocking. I also picked up some complete 1 and 4 axis tables complete with everything out to the power plug and data connectors. Others have been working over that stuff pretty hard as well, but they do have about 20 feet of assemblies which have linear slides and leed screws (not ballscrews) of various small sizes, which have been removed from who knows what. All of the big steppers are gone, and probably those with shafts extending out the front and back.

One item RA has in large amounts can be identified in McMaster-Carr. From catalog 103, on page 675 you will see Hardened and Ground Solid Shafts and Support Rails. What RA has in large amounts is similar to the 12 (mm) Metric Shafts, however RA has no support rails. The 12 (mm) shafts they have exceed 5 ft in length and have 4.0 mm tapped holes spaced on one side, (they holes do not go all the way through the shaft). The McMaster-Carr part number which is similar to what RA has is 6499K81 on page 675 of catalog 103, however these 12 (mm) shafts are longer than 1200 (mm). I do not remember what RA charged, but I know I bought 20 of them for less than the price of one in McMaster-Carr. RA does not have the mating components, and the open sleeve bearings from McMaster-Carr are $20 each in Frelon, and $23 in recirculating ball, or $44 in recirculating pillow block.

Anyone know a surplus source for 12 mm open bearings? I am designing my Home made DRO around these 12 mm slides. When I've got it running, I'll post the details including the source code. I have a new idea on DRO concepts I hope to make work.




-----Original Message-----
From: gary@... [SMTP:gary@...]
Sent: Thursday, September 16, 1999 8:17 AM
To: CAD_CAM_EDM_DRO@onelist.com
Subject: Re: [CAD_CAM_EDM_DRO] Low cost power supply

From: gary@...

David, Do you have an address and telephone number for RA enterprises??

GaryP
--------------------------------------

David Howland wrote:

> From: David Howland <dhowland@...>
>
> 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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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
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For the FAQ, go to http://www.ktmarketing.com/faq.html
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