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Linear Power Supplies And The Propeller — Parallax Forums

Linear Power Supplies And The Propeller

idbruceidbruce Posts: 6,197
edited 2017-04-28 12:51 in Propeller 1
Hello Everyone

Several years ago, I salvaged a nice multi-tap transformer, from a damaged Harmon Kardon receiver, which I would like to use for this project (forums.parallax.com/discussion/166498/discussion-laser-direct-imaging-of-pcbs-and-the-propeller). This transformer has 7 leads exiting the transformer housing, which are as follows:

Bundled Together
BLUE, BLUE, BLACK

Individual
GREEN

Individual
GREEN WITH FUSE

Individual
RED

Individual
WHITE

The red and white individual wires go to the primary side of the transformer. With a 120V applied to the primary side, I can get a wide array of many different voltages through various combinations, but these are the combinations that interest me, and their outputs:
BLUE and BLACK: 30V
BLUE and BLACK: 30V
GREEN and GREEN WITH FUSE: 7.5

As mentioned, I would like to use this transformer in a project, and this project involves stepper motor drivers and a Propeller Project Board. The stepper drivers have a max input voltage of 45V and the Propeller Project Board has a max input voltage of 16V. So I am thinking that with each of the combinations listed above, I would rectify and smooth each of the output voltages, and use them as follows:
BLUE and BLACK: Stepper driver power supply
BLUE and BLACK: Stepper driver power supply
GREEN and GREEN WITH FUSE: Propeller Project Board power supply

After 7.5V has been rectified and smoothed, is there anything else that I would need to do to the output voltage to make it acceptable for the Propeller Project Board?
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Comments

  • kwinnkwinn Posts: 8,697
    Shouldn't need anything else. That will provide about 10.5V in to the 3.3V switcher.
  • idbruceidbruce Posts: 6,197
    kwinn

    Thanks for the input.

    When it comes to smoothing the rectified 7.5V for the Project Board, is there any special size capacitor that you would recommend?
  • kwinnkwinn Posts: 8,697
    If you're only powering the Propeller board then a 1,000uF or so should be fine. No harm in going a bit higher though. Even a 10,000uF 16V electrolytic is not all that big or expensive. In either case they should be low ESR and include a 0.1uF to deal with the switching regulator current spikes.
  • frank freedmanfrank freedman Posts: 1,975
    Meter the thing out, odds are the blue/black/blue are a center tapped winding which you could use as a 60V for higher voltage needs.

    Your comment about various combinations makes me think you want to meter it out to see how many separate windings there are and how they are connected. They don't sound isolated from your initial descriptions. Your initial description makes me wonder if the green wires are tapped off the blue so that the connections could be blue/green/black/green/blue as a single secondary winding. The original purpose of that could be to give power to possibly a low and high negative supplies as well as a low and high positive supply for the various analog stages in the receiver/amp. Use grain of salt, this is only idle speculation.
  • idbruceidbruce Posts: 6,197
    edited 2017-04-28 18:53
    @kwinn

    Thanks once again for your input. I have quite a few capacitors laying around from salvage, and I probably have a 10,000uF 16V electrolytic. I will have to look. Anyhow thanks.

    @Frank
    you could use as a 60V for higher voltage needs

    After rectification, that would be nearly double the max input voltage for my stepper drivers :) So that one is a non-starter :)
    Your initial description makes me wonder if the green wires are tapped off the blue so that the connections could be blue/green/black/green/blue as a single secondary winding. The original purpose of that could be to give power to possibly a low and high negative supplies as well as a low and high positive supply for the various analog stages in the receiver/amp. Use grain of salt, this is only idle speculation.

    Idle speculation.... I will say that is exactly what I was thinking. The other possible voltages, are of little value to me at this point, however that may change with the wind :)

    =============================================================
    The wind changed.....

    Instead of making my own laser driver from a LT1121 regulator, I simply purchased a driver off ebay. That driver requires a 12V input, and I suppose it would be wise for me to see if I can get anywhere near 12V out of one of those taps.
  • kwinnkwinn Posts: 8,697
    +1 - That's an excellent suggestion Frank. Using a common center tap with multiple windings calls for a different design than separate windings. Best to ohm out the windings and figure out which are connected and which are not.
  • idbruceidbruce Posts: 6,197
    Those voltages must be bleeding through with the power turned on, because it appears that the blues are center tapped and the greens must but be a separate winding.

    BLUE & BLUE 0.6 Ohms
    BLUE & BLACK 0.5 Ohms
    BLUE & BLACK 0.5 Ohms
    GREEN WITH FUSE & GREEN 0.5 Ohms
    GREEN WITH FUSE & BLUE 0.0 Ohms
    GREEN WITH FUSE & BLUE 0.0 Ohms
    GREEN WITH FUSE & BLACK 0.0 Ohms
    GREEN & BLACK 0.0 Ohms

    With the power turned on, I get all kinds of different voltages :)
  • kwinnkwinn Posts: 8,697
    What you need to do is measure the resistance between each wire and every other wire and put the readings in a table similar to the attached spreadsheet. Use the lowest ohms scale on the meter.
    xls
    xls
    xfmr connections.xls
    6K
  • idbruceidbruce Posts: 6,197
    kwinn
    What you need to do is measure the resistance between each wire and every other wire and put the readings in a table similar to the attached spreadsheet. Use the lowest ohms scale on the meter.

    I am not really sure why that was necessary, because it includes all the information provided above, but okay, here it is :)
    table.jpg
    389 x 103 - 14K
  • frank freedmanfrank freedman Posts: 1,975
    Just for grins, do you remember the HK model you salvaged it from? you may find out exactly what you have if you can get a Sams on it. May take some digging since so much has become throwaway anymore. If resistance does not give you enough info, see what an inductance meter says.......
  • idbruceidbruce Posts: 6,197
    edited 2017-04-29 10:34
    @frank and kwinn
    If resistance does not give you enough info, see what an inductance meter says.......

    Are you guys seeing something that I do not see? Because to me, it appears that the greens are a totally separate winding, since....
    There is zero resistance between either of the greens to black, blue 1, or blue 2

    And that the two blues are center tapped with the black because....
    1. There is 30V from black to blue 1.
    2. There is 30V from black to blue 2.
    3. There is 60V from blue 1 to blue 2 (although I did not say this before, but hinted to it)

    This leads me to believe that when the primary is connected to 120V....
    1. The two greens are a secondary 7.5V winding
    2. The two blues are a center tapped secondary 60V winding

    Am I missing something?
  • kwinnkwinn Posts: 8,697
    idbruce wrote: »
    @frank and kwinn
    If resistance does not give you enough info, see what an inductance meter says.......

    Are you guys seeing something that I do not see? Because to me, it appears that the greens are a totally separate winding, since....
    There is zero resistance between either of the greens to black, blue 1, or blue 2

    And that the two blues are center tapped with the black because....
    1. There is 30V from black to blue 1.
    2. There is 30V from black to blue 2.
    3. There is 60V from blue 1 to blue 2 (although I did not say this before, but hinted to it)

    This leads me to believe that when the primary is connected to 120V....
    1. The two greens are a secondary 7.5V winding
    2. The two blues are a center tapped secondary 60V winding

    Am I missing something?

    To me the zero resistance implies a dead short which is why I am questioning this. If the two greens and two blues are independent windings there should be infinite resistance (over range display) between any green and any blue wire. Are you perhaps putting zero for the over range reading?
  • idbruceidbruce Posts: 6,197
    edited 2017-04-29 14:25
    kwinn
    To me the zero resistance implies a dead short which is why I am questioning this.

    Now I understand :)

    Okay I am using a Fluke 112 for these readings and the actual reading for any green to any blue is "0L". The owners manual states that "0L" represents an input which is too large for the range, so I am assuming this means infinity, since there is no mention of or symbol for infinity :)

    Just to double check, I performed a continuity check between:
    the greens and the blues - result - no continuity
    the greens and black - result - no continuity
    the blues and black - result - continuity

    I apologize for the confusion, because I should now the infinity symbol for my own darn meter :) In my defense, I normally use the continuity setting when searching for 0 resistance or shorts, because it has an audible indicator (BEEP) :)

    EDIT: In reality that is no defense :) Because I know 0 ohms represents a short... Just wasn't thinking properly. :)
  • kwinnkwinn Posts: 8,697
    edited 2017-04-29 17:20
    idbruce wrote: »
    .........

    Just to double check, I performed a continuity check between:
    the greens and the blues - result - no continuity
    the greens and black - result - no continuity
    the blues and black - result - continuity

    I apologize for the confusion, because I should now the infinity symbol for my own darn meter :) In my defense, I normally use the continuity setting when searching for 0 resistance or shorts, because it has an audible indicator (BEEP) :)

    EDIT: In reality that is no defense :) Because I know 0 ohms represents a short... Just wasn't thinking properly. :)

    No problem. I thought the zero might be an oh for overload but it is safer to check. That verifies that your earlier post with the voltages are correct. One 7.5V green winding, and one 60V blue with a black center tap. That's a fairly common transformer winding.
  • idbruceidbruce Posts: 6,197
    edited 2017-05-01 02:00
    I am beginning to think that the multi-tap transformer for my power source is not my best route or the easiest route.

    The Pololu DRV8825 High Current Stepper Motor Drivers (https://pololu.com/category/154/drv8825-stepper-motor-driver-carriers-high-current) requires 8.2V to 45V to operate.

    The 100mW 405nm Blue Violet Purple Laser Diode Module (ebay.com/itm/100mW-405nm-Blue-Violet-Purple-Laser-Diode-Module-12VDC-TTL-Stage-Lighting-/191350524506?hash=item2c8d614a5a) requires 12V to operate.

    The Propeller Project Board USB (https://parallax.com/product/32810) requires 5V to 16V.

    I am beginning to think that a linear power supply, with an output of 13.5V, might be just the ticket for the sake of simplicity.

    For example, I would only need a transformer with one winding and enough VA to handle the whole project. Unregulated 13.5V would go to both the stepper drivers and the Propeller Project Board, while a regulated 12V branch circuit would go to the laser driver module.

    However, a linear power supply, with a 13.5V output, would only be beneficial, if I can drive the machine load at a pace of at least 5mm/sec.

    EDIT: There will be (2) stepper motors that require 0.5A per phase, so 2.0A should cover both the steppers and the Propeller Project Board. And I would imagine that 1.0~1.5A should be sufficient to drive my laser diode, which is not the one included with the driver module. So I estimate that I will need approximately 3.0~3.5A of current. Actually 2.5A is probably a more realistic figure.

    EDIT: I now see that if I use a 7812 regulator for the laser, I should have a linear supply that outputs around 14.5V.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2017-05-01 02:20
    I'm really shocked that nobody in this forum has shown you how to wire up a full-wave center-tapped power supply! Here's a diagram:

    full-wave_center-tapped.gif

    This is Novice ham license stuff from the 1960s.

    -Phil
    full-wave_center-tapped.gif
    440 x 147 - 2K
  • idbruceidbruce Posts: 6,197
    Phil

    I appreciate your input on this matter.

    I must be honest though, I have had that information for years: hammondmfg.com/pdf/5c007.pdf

    For CNC machinery, with stepper drivers, I have always seen people use the "FULLWAVE BRIDGE Capacitor Input Load" circuit within that document.

    Is there any major difference between the two, besides less components?
  • jmgjmg Posts: 15,148
    idbruce wrote: »
    ...
    EDIT: There will be (2) stepper motors that require 0.5A per phase, so 2.0A should cover both the steppers and the Propeller Project Board. And I would imagine that 1.0~1.5A should be sufficient to drive my laser diode, which is not the one included with the driver module. So I estimate that I will need approximately 3.0~3.5A of current. Actually 2.5A is probably a more realistic figure.

    EDIT: I now see that if I use a 7812 regulator for the laser, I should have a linear supply that outputs around 14.5V.

    To power a pump recently, I needed 24V at 2.5A, so I checked into laptop power packs.
    Found a universal one that has a rotary selector for 12/15/16/16.5/18/18.5/19/19.5/20/22/24V, 100W 100~240VAC
    and it came with a series of connector-adapters.
    From memory, ~ US$20, I was quite impressed.
    Compact, light, and plenty of rating headroom, and easy to replace in the future.
  • idbruceidbruce Posts: 6,197
    jmg
    To power a pump recently, I needed 24V at 2.5A, so I checked into laptop power packs.
    Found a universal one that has a rotary selector for 12/15/16/16.5/18/18.5/19/19.5/20/22/24V, 100W 100~240VAC
    and it came with a series of connector-adapters.
    From memory, ~ US$20, I was quite impressed.
    Compact, light, and plenty of rating headroom, and easy to replace in the future.

    I previously thought about a laptop supply, but changed my mind, because I have noticed that smps don't last that long when hooked up to an inductive load. I have gone through quite a few of PC PSUs in the past. It seems like the linear supplies last forever, as long as they are fused.

    However, I will say that they do offer smps specifically for CNC use, so I would imagine there is special circuitry for the inductive loads.

    I just remembered while I was typing my post, that I have a 13.8V 2.5A linear power supply laying around that is just collecting dust :) It might be the perfect ticket. Here is a similar one to the one I have, only mine is the Cat. No. 22-120, instead of the Cat. No. 22-120a: https://ebay.com/p/RadioShack-Micronta-22-120a-Regulated-12-volt-DC-Power-Supply-Converter/1601471854
  • kwinnkwinn Posts: 8,697
    idbruce wrote: »
    Phil

    I appreciate your input on this matter.

    I must be honest though, I have had that information for years: hammondmfg.com/pdf/5c007.pdf

    For CNC machinery, with stepper drivers, I have always seen people use the "FULLWAVE BRIDGE Capacitor Input Load" circuit within that document.

    Is there any major difference between the two, besides less components?

    Very little difference between a single winding and full wave bridge and a center tap winding with single diodes for comparable transformers.

    The center tap circuit typically has higher IIR losses in the transformer due to using twice the number of turns but smaller gauge wire.

    The bridge circuit has a higher loss across the diodes since the current has to go through two diodes to the load.
  • idbruceidbruce Posts: 6,197
    kwinn
    Very little difference between a single winding and full wave bridge and a center tap winding with single diodes for comparable transformers.

    The center tap circuit typically has higher IIR losses in the transformer due to using twice the number of turns but smaller gauge wire.

    The bridge circuit has a higher loss across the diodes since the current has to go through two diodes to the load.

    Okay, so now, what if you have a center tap full wave bridge, with the ground capped... How does that compare?
  • DigitalBobDigitalBob Posts: 1,486
    Bigger is better. Transformers are cheap enough from surplus houses, eBay etc. So I would go with a 10 amp 48v or better full wave rectifier mega caps for the steppers. And run the prop off a wallwart small power supply.
  • Peter JakackiPeter Jakacki Posts: 10,193
    A SMPS will do fine for heavy inductive loads but why don't you just do the obvious and filter the output with a series diode, a choke, a TVS diode, and a big cap for those surges or something similar?

    There's no good reason to use big old transformers although the center tapped variety were excellent for generating plus and minus supplies, just hang another 2 diodes and cap in reverse with the circuit from Phil. I'm shocked he neglected to mention that variation :)
  • idbruceidbruce Posts: 6,197
    @DigitalBob
    Bigger is better. Transformers are cheap enough from surplus houses, eBay etc. So I would go with a 10 amp 48v or better full wave rectifier mega caps for the steppers. And run the prop off a wallwart small power supply.

    I would have to respectfully disagree. Bigger is not always better, but almost always, it will be more expensive, and sometimes, much more expensive :)

    I have a 48V 20A PSU that I built for my wire bending CNC and it wasn't cheap. If I really wanted or needed speed, then I would go with a higher voltage, but this specific project has a set pace.
  • idbruceidbruce Posts: 6,197
    Peter

    Here is the THING.... At this point, my new machine is just an experiment to see how successful it will be, and I have already invested $300, plus looking at additional expenses. So I am really trying to cut costs, at least until I get some worthy results. As mentioned a few posts back, I had forgotten about an old Micronta 22-120 I had laying around, and I believe that will be just about perfect for this project.

    However, as always, I do appreciate your input and sharing your knowledge.
  • kwinnkwinn Posts: 8,697
    idbruce wrote: »
    kwinn
    Very little difference between a single winding and full wave bridge and a center tap winding with single diodes for comparable transformers.

    The center tap circuit typically has higher IIR losses in the transformer due to using twice the number of turns but smaller gauge wire.

    The bridge circuit has a higher loss across the diodes since the current has to go through two diodes to the load.

    Okay, so now, what if you have a center tap full wave bridge, with the ground capped... How does that compare?

    If the center tap is not connected and a bridge rectifier is used then you have the same situation as a single winding full wave bridge.

    With the center tap as the common connection you have a plus and minus power supply.
  • idbruceidbruce Posts: 6,197
    I just remembered while I was typing my post, that I have a 13.8V 2.5A linear power supply laying around that is just collecting dust

    Okay so I got to poking around and took the power supply out of the box. To my amazement, the housing was riveted together. Then I pondered, "how do I know that it is a linear power supply?". I then surmised that there must be a schematic in the owners manual, because I knew it was linear (besides the fact of it being heavy from the transformer size).

    Upon opening the owners manual, I did indeed find a schematic :) In addition to the schematic, there was quite a lengthy description about the circuitry of the power supply. :) Truly impressive as far as owner's manuals and simple linear power supplies go, at least according to what I read. There is a complete list of all the components utilized, and the detailed description explains the function of every component used.

    I tried to locate the manual online, so that I could link to it in this thread, but all I could find was the schematic, which doesn't seem that impressive, compared to the schematic with a detailed description :)
  • idbruceidbruce Posts: 6,197
    edited 2017-05-01 13:26
    kwinn
    With the center tap as the common connection you have a plus and minus power supply.

    I had forgotten all about that, however I do remember reading something about it many moons ago.

    When I was asking about a comparison, I was more or less talking about the losses that you were previously talking about.
  • kwinnkwinn Posts: 8,697
    Lets compare two transformers with identical VoltAmp ratings and primary windings. Transformer A has a single winding that outputs 7.5VAC, Transformer B has a center tapped winding that puts out 7.5VAC between the center tap and each end of the windings, and a total of 15VAC. To fit twice as many windings the wire used for transformer B needs to be half the cross sectional area of the wire in transformer A. That wire will have twice the resistance of the wire in transformer A.
  • DigitalBobDigitalBob Posts: 1,486
    Bruce
    I have a few CNC setups one is an old Hurco it has three servo motors. That sucker has a mega transformer 480 volt to I think 60 volt I could look at the VA if you need it. And another setup using Anaheim automation steppers I think each stepper is 8 amps they each have their own transformer. Just a matter of opinion I like reserve power for servo's for those high torque surges. Same for stepper
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