508,088 active members
3,583 visitors online
Register for free
Login
IndustryArena Forum > WoodWorking Machines > DIY CNC Router Table Machines > 1st Build, will this be a decent Design?
Page 8 of 8 678
Results 85 to 96 of 96
  1. #85
    Junior Member
    Join Date
    Jun 2010
    Posts
    3897

    Re: 1st Build, will this be a decent Design?

    Fair enough. I don't know the DMM range. My experiences have been with different brands.
    Do you know what the black cubes on the bottom chassis are? Could they be filter inductors? Or just some fancy sort of connector?

    Cheers
    Roger

  2. #86

    Join Date
    Jan 2005
    Posts
    10429

    Re: 1st Build, will this be a decent Design?

    Quote Originally Posted by RCaffin View Post
    Fair enough. I don't know the DMM range. My experiences have been with different brands.
    Do you know what the black cubes on the bottom chassis are? Could they be filter inductors? Or just some fancy sort of connector?

    Cheers
    Roger
    The Black cubes I manufacture are just terminal Blocks that whole package is 4 low 60v volt 20A Ac Servo drives with built in Breakout Board a plug and play package I used to build
    Mactec54

  3. #87
    Junior Member
    Join Date
    Jun 2010
    Posts
    3897

    Re: 1st Build, will this be a decent Design?

    Hi Mactec

    Very nice stuff! Very nice assembly too.

    To explain a little bit (for others maybe):
    An SMPS switches the supply through to the output at a very high on/off rate. The average of the mark/space ratio is what sets the output voltage. The output of the switching stage is inductively filtered to produce a DC voltage with a saw-tooth waveform superimposed. The key point here is that the control circuitry looks at the filtered output as it rises and falls, and uses the levels it sees to control the switching. This is how every SMPS from a tiny wall-wart to a multi-kilowatt supply works. For that matter, it is also used at the grid level.

    If you put a big cap across this output directly, smoothing the ripple out, the control circuit cannot see the varying voltage the way it should, and the switching is upset - badly. However, if you put an inductance AFTER this monitored output stage and feed that into a big cap, then the control circuit will still see the varying voltage but the output will be much smoother.

    My spindle PS does not have this output filtering, and many other 'simple' SMPS packages don't either. However, it would appear that some SMPS units do have this output stage filtering (the more expensive ones!). If the filtering is good enough, then there won't be lots of RFI on the supply lines into the motor power drivers, As modern power drivers are also SMPS units, you don't want them being upset by RFI on the input lines which could confuse the control circuits.

    I was a bit too sweeping in my previous statement about not putting a cap on the output of any SMPS supply.

    The problem then is to find out whether the SMPS you are considering buying has output filtering to reduce the RFI. Very often this information is not given in the specs. You may have to ask the manufacturer - or buy the supply and measure the output voltage with a CRO.

    Cheers
    Roger

  4. #88
    Registered
    Join Date
    Aug 2009
    Posts
    215

    Re: 1st Build, will this be a decent Design?

    CRO
    It doesn't need to be a Cathode Ray Oscilloscope... any digital scope should work for the task, also.

    Of course - no matter which type you have - watch out for grounding issues!
    https://youtu.be/xaELqAo4kkQ

  5. #89
    Gold Member
    Join Date
    May 2005
    Posts
    3864

    Re: 1st Build, will this be a decent Design?

    Quote Originally Posted by RCaffin View Post
    The bit which puzzles me is that 2 of the trannies were <40 quid each, but the slightly higher voltage version with the same powwer rating was 122 quid. Something a shade strange there.

    The advantage of a tranny/diode/cap PS over an SMPS one is that you cannot blow up the tranny by dumping reverse charge from deceleration into it, but you can blow up the SMPS that way. A second advantage is that the RFI from the SMPS can send your driver mad: such drivers are not built to handle that sort of incoming RFI.

    YMMV.

    Cheers
    Roger
    The issue of blowing up a SMPS, from high bus voltages, is probably the best reason to avoid them. The alternative is to look for DC SMPS specifically designed for servo / stepper duty. The other advantage is that transformer based supplies are dead simple to repair which for me is a big deal.

  6. #90
    Junior Member
    Join Date
    Jun 2010
    Posts
    3897

    Re: 1st Build, will this be a decent Design?

    Ah well, these days 'CRO' = oscilloscope.
    I gave away my last genuine CRT-based oscilloscope some 20 years ago. Very good Tektronix one too.

    Cheers
    Roger

  7. #91
    Registered
    Join Date
    Aug 2009
    Posts
    215

    Re: 1st Build, will this be a decent Design?

    I still have... I think it's back under the old LaserJet 5mp, in the closet... a Tektronix AN-425. It's more-or-less in mint condition; so I think it was a stockpiled-spare that one of the branches of the armed forces here was keeping... I'm afraid that I haven't pulled it out since I got my first Rigol, though...

  8. #92
    Junior Member
    Join Date
    Jun 2010
    Posts
    3897

    Re: 1st Build, will this be a decent Design?

    I think I started with a Tek 556 with 1A1 plug-ins, but the nuvistors died, so I graduated to a Tek 475. I gave that one to a friend when it developed a problem - he had the bits to repair it, and now I have a Tek TDS 220. I had to repair the front end BNC connectors : a known fault with the BNC connector design.

    I don't recognise the AN-425 though.

    Cheers
    Roger

  9. #93

    Re: 1st Build, will this be a decent Design?

    Thanks to everyone involved in this thread, I received my Toroidal PS this afternoon, it's been out of stock for two weeks but this is my set-up and after testing it I'm getting 69VDC final output so I'm more than happy with it. I just need to tidy it up a bit as it looks a bit messy at the moment, this layout is just for testing purposes.

    Thanks again for all your input, I got there in the end and saved over £100 so I'm happy!

  10. #94
    Junior Member
    Join Date
    Jun 2010
    Posts
    3897

    Re: 1st Build, will this be a decent Design?

    Hi Phil

    Put that diode bridge on a heatsink, PLEASE!
    At 10 A and 1.8 V across the bridge, it will be dissipating 18 W.

    Cheers
    Roger

  11. #95

    Re: 1st Build, will this be a decent Design?

    Hi RCaffin,

    I found this Heatsink in an old computer parts box I had, is it ok, do ya think?

    One thing I've noticed is the Capacitor is holding a charge for an unthinkable amount of time, when I initially tested it I had a resistor to help discharge the capacitor, and it did it in around a few hours. I've since removed the resistor, I knew the Capacitor would take longer to discharge, however, I didn't think it would take more than a day.... so far it's taken 5 days and it's only at 37V now (from an initial 69V.) so it's only dis-charging at around 6V a day!!??? I'm starting to think I should have left the resistor on but I just thought it wouldn't work as it's bridging the +/- Outputs which didn't seem logical to me..?

  12. #96
    Junior Member
    Join Date
    Jun 2010
    Posts
    3897

    Re: 1st Build, will this be a decent Design?

    That will help for sure. It would help if you could lift the heat sink 5 - 10 mm up in the air: get better air circulation.

    As for the discharge rate - that sounds really wrong to me. Those electrolytics have an internal discharge or leakage of their own.
    I would want to check the AC input lines: it sounds as though they still have volts on them. How that could happen is another matter!

    Yes, you should have a discharge resistor across the cap anyhow. A 10 k power resistor would be fine.
    I would also add a fuse on the AC input, just on general principles. It is OK to switch the AC input, but do not switch the DC output: that can damage the motor drivers.

    Eventually you may want to bolt the toroid to a metal base plate: it too will get warm and need to dissipate heat. The insulation provided is adequate for that (but check the specks anyhow).

    Cheers
    Roger

Page 8 of 8 678

Similar Threads

  1. GME's New 80/20 CNC Build - My Design
    By GME in forum DIY CNC Router Table Machines
    Replies: 401
    Last Post: 11-09-2019, 07:14 PM
  2. First half-decent machine build attempt
    By _AR_ in forum Vertical Mill, Lathe Project Log
    Replies: 19
    Last Post: 03-16-2013, 05:16 AM
  3. Design and Build
    By Eddymeister in forum DIY CNC Router Table Machines
    Replies: 34
    Last Post: 08-18-2011, 09:33 AM
  4. Build Inexpensive CNC with decent tolerances-Share your input
    By Andy990 in forum DIY CNC Router Table Machines
    Replies: 23
    Last Post: 12-26-2009, 05:49 AM
  5. What CNC design did you build first?
    By soundmotor in forum DIY CNC Router Table Machines
    Replies: 2
    Last Post: 04-29-2006, 03:05 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •