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24v control/test box

  1. Oct 28, 2011 #1
    Hey, all. I've got a project that I need to do for work, but I'm not sure where to start. I need to design and build a box that will run on and put out 24 VDC, but also be able to put out +/- 10 VDC. The current does not go above 2 amps. It will also need to have test points to monitor the signals on the pins of a 12 pin connector. It's a breakout box combined with a power supply and control function, I guess.

    My main problem is the power supply. How do I pull +/- 10 VDC from +24VDC with a common ground?
     
  2. jcsd
  3. Oct 29, 2011 #2

    berkeman

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    Can you just use an off-the-shelf lab power supply? You can get them with multiple outputs, and you can use a couple of them if it's easier to get all of the output voltages that you want.
     
  4. Oct 29, 2011 #3
    Depend on how good you are with electronics, you can design the converter with ICs or buy existing modules. I have trouble finding 24 to 10 volt. Here is just an example of a 24 to 12 converter.

    http://www.trcelectronics.com/Meanwell/dc-dc-converter-sd25.shtml


    You have to spend some time digging yourself. You can look for 24V to 12V ISOLATED converter that have output voltage adjustment down to 10 volt. You can hook an isolated converter to get -10V out of a +10V converter, just swap the output leads. Make sure to get an isolated output or else if you create some smoke, I don't know you!!!!

    Happy hunting.
     
  5. Oct 31, 2011 #4
    Thank you for the responses. I am currently using multiple power supplies to generate the signals I need, including using a dual power supply/pot setup for my control signal, but I would like to be able to do all of it from just one 24V source instead of using the 3 supplies that I'm using now. All of the signals I need are +24V except for the +/- 10V control which is what gave me trouble last time.

    I did not have the control circuit isolated last time, but I did not see any smoke, just some strange voltages and current spikes but thank goodness for safeties on the power supplies. So the control circuit needs to be isolated to avoid ground loops and other such gremlins? I'll check around for a converter.
     
  6. Oct 31, 2011 #5

    cepheid

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    Yeah you can look for a DC-DC converter, which converts voltage in the same way as a switched-mode power supply. Vicor is one brand I've used in the past. Advantages of these things are that they are stable, can handle a lot of power, produce isolated outputs, and are generally much more efficient than linear power supplies (like voltage regulators). The latter step down voltages by basically wasting power.

    Disadvantages of the DC-DCs are that they are expensive and, being switching supplies, can produce a lot of electronic noise
     
  7. Oct 31, 2011 #6
    What I mean isolated DC to DC converter means the output and input are isolated. Say the output is +10V and 0V, You can ground the +10V side and take the 0V terminal as output. That will give you -10V. Yes, you have to worry about ground loops, but that's another subject.
     
  8. Oct 31, 2011 #7
    With good pcb layout practice and careful grounding, it is really not a problem. At the beginning before I was in charge of the EE designing mass spectrometers, the company used all linear supplies and it's like a big tall rack full of supplies. I changed it all to switcher and we have no problem. We had very sensitive electronics like Faraday Cup amp that measure at 10ee-12 Amp range and various pulse counting and control circuits, but we never have problem. Just by good EMC design.

    A lot of times, the Faraday Cup amp has to be floated at some voltage. I actually put a DC to DC converter on the pcb with the amp together right next to each other. I use noise cancelling technique to cancel the noise and it worked just fine!!!
     
  9. Oct 31, 2011 #8
    I still need to control the voltage through the whole range of +/- 10V. It controls a linear force motor through a pcb that I did not design and for which I do not have the schematics. The command signal does not actually power the motor as the control current never exceeds 5mA. When I tried this last time using only a regulator , potentiometer, and a polarity switch, it would not function. A poster on another forum suggested I isolate the circuit using optocouplers as the circuit would function with the control on a seperate power supply, but not with everything on only one. I am, however, not familiar with optocouplers and would not know where to begin. The isolated DC/DC converter idea is something I can actually do, so I will try that and hope for the best, I guess.
     
  10. Oct 31, 2011 #9
    So just plugging an isolated DC/DC converter in between the control circuit and the power circuit should work? I've found one here http://www.milelectronics.com/products/series-p.htm [Broken]
    Will this work? It meets the specs that I am looking for. +24VDC input with a +12V output and 150V isolation between the two.

    Found a dual converter here, too. http://products.cui.com/CUI_VASD1-S2...df?fileID=2862 [Broken]
     
    Last edited by a moderator: May 5, 2017
  11. Oct 31, 2011 #10
    I thought you need 2A!!! I would have found one for you if you can use 1Watt supply!!!

    Yes, if it is good enough for you, it'll work.
     
  12. Oct 31, 2011 #11
    I have ordered the dual converter. I hope it works this time. Don't see why it shouldn't. I'll check back in a few days to tell you how it went. Thanks for the help!
     
  13. Nov 2, 2011 #12
    The isolated converter works like a charm. Thanks for all the help!
     
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