Multiple output power supply (4? 5?)

Discussion in 'Power Electronics' started by hroldan, Oct 12, 2016.

  1. hroldan

    Thread Starter New Member

    Oct 12, 2016
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    Hi, I'm getting lost on what I'm doing. I just built another cnc laser cutter but instead of using several power adapters for the laser, motors, shield, etc, I want to use one power supply/adapter. I have some options (24V, 36V and also one from an old printer providing 32V and 16V). I need to feed:
    • Laser driver #1. It has it's own current regulator (LM317) for safety, lasers die otherwise. Each of the two already calibrated and with it's own heat sink. I just need to provide 7.5V.
    • Laser driver #2. Same as #1. Just need to provide 7.5V.
    • GRBL Shield (Arduino), I need to provide 12V at 500mah (will also work with 9V)
    • Cooling fans. 3 of them, 12V each rated 0.09A
    Tried connecting the fans to the GRBL shield (12V all of them) but then both motors turn it affects the cooling so I need a separate power for the fans and the Shield. I don't see a problem feeding the fans with 12V together because there is no load (as in with the stepper motors).

    Basically while not perfect, I'm thinking on using 4 LM317 to regulate the voltage into 4 outputs: 7,5V, 7,5V, 12V and 12V. Then the laser drivers take care of the rest with their own LM317. I know it's not perfect but I have too many power adapters and I plan to use some instead of buying more stuff. I know each LM317 will take a bit of power doing it's job but it's ok. My best pick is one HP power adapter with two outputs: 32V at 940ma and 16V at 625ma.

    I will appreciate any light. Tried writing my attempts and more details but it appeared confusing at the end. Thanks in advance.
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Yes a single power supply could be used with multiple voltage regulators to deliver the desired voltage needed for each specific component.

    Be aware that attempting to drop from a larger supply voltage to a lower voltage with an LM317 (or any linear regulator) may/will dissipate quite a bit of heat and could require large heatsinks,etc...
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    You don't say what the current requirement is for each of the lasers, but you already are up to 0.77 A with the fans and the GRBL. This rules out using only one source supply output. I don't see any problems with your approach. It is simple, low risk, low noise, and reuses one common part rather than have different part types for each output. If the laser currents aren't to high, I'd use the 32 V for the GRBL because steppers are grouchy, and the 16 V for everything else.

    ak
     
  4. hroldan

    Thread Starter New Member

    Oct 12, 2016
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    Thanks Mcgyvr, will take care of having enough power on the source and heat sinks. I was playing around with LM317 last night and already building it
     
  5. hroldan

    Thread Starter New Member

    Oct 12, 2016
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    Thanks AnalogKid, each current regulator (LM317 based) feeds from 300 to 900 to the lasers, depending on the laser (been using IR, red and violet). Each laser driver is fixed to the laser needs. -Yes I also think 32V should be enough for the motors and the fans (if done properly), in fact I've been using a power adapter feeding 12V at 500mah to the motors with no problem at all.

    I'm facing a problem now: I just built two voltage regulators feeding 12V and also 16V (for testing) using one LM317 and adjusting the variable resistors, and I'm getting the needed output. After calibration the circuit went nuts and starting deliver higher voltages. I learned the circuit shouldn't be measured with no load :) ok, solved. I fixed that but after a bit of time the voltage goes up and down (slightly).

    • Is it because of the heat on the LM317?
    • Or heat on the variable resistors?
    • Heat on all the components?
    • I read recently no variable resistors should be used, just one fixed and one variable (not two)

    Thanks
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Are you using the recommended input/output capacitors? (specifically output ones)
     
  7. hroldan

    Thread Starter New Member

    Oct 12, 2016
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    Ehhh... yes? :facepalm: sorry it was my bad.

    Thanks mcgyvr for your post. I will update to contribute in case anyone finds this useful and thus avoid my mistake:

    Using the LM317: I did use the capacitors on the laser drivers (Lm317 as current regulator yes for the lasers) feeding them 12V. But I didn't use them in the case of voltage regulators, that's my mistake. Then, about the central matter of the thread (my question) on using Lm317 to create multiple voltage outputs, that's where I messed up :( . I didn't use capacitors, so the voltage was the desired but for moments, then started going up, or down, etc.

    My solution: used the 7812 as voltage regulator. In this case I get 12 volts perfectly avoiding the use of LM317 as voltage regulators. It was only LATER that I found readings in the line of Mc advice, using capacitors. So now as an update of my situation, it works, but as follows:

    I have a power supply from an old HP Officejet 6000. This provides 16V 625mA --- AND --- 32V 940mA. I'm using only the 16V output. From there it goes to 2 different 7812, so I get 1 + 1 = 2 individual 12V outputs. I have another one there using a 7809, so I get an extra output of 9V

    In short:
    • 1 x 12V
    • 1 x 12V
    • 1 x 12V
    That's 3 outputs with 3 diff voltages. TWO 12V feed individual sets of LM317 as current regulators for the lasers. And the extra 12V feeds another LM317 (yes individual) to drive the Arduino Shield (motors) with different current settings. Everything works perfectly and there is very little heat. I'm also using cooling fans (3), one for each laser and the extra for the heat sinks.

    So the old HP power supply is now giving 3 different voltages using 7812 and I'm limiting the current using LM317, yes, with capacitors. Hope this helps someone in the future. Thanks for the time and observations.
     
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