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IndustryArena Forum > CNC Electronics > CNC Machine Related Electronics > High voltage power supply, low voltage perihperals
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  1. #1
    Join Date
    Mar 2013
    Posts
    10

    High voltage power supply, low voltage perihperals

    Hi all,

    I've got my CNC setup with a 48v PSU powering he controller board with steppers and a 12v PSU powering my 3 proximity sensors (NPN Inductive). What I'm doing at the moment (which is working) is connecting all the + and - leads of the sensors together with the + and - of the 12v power supply respectively. I then plug the output line from NPN sensor to the breakout board (Gecko 540). I was then told I had to connect the ground of the 12v to the ground of the 48v PSU. That's all working fine but having two power supplies hooked up like that is bothering me.

    I had 3 other ides which I'm not quite sure how to implement:

    1.) Connect the 3 sensors in series. Not their output lines... just the power lines. If I understand that correctly, 3 sensors (rates at 10v-30v) connected in series with 48v supplies should supply 16v to each sensor. Will that work? It would eliminate the 12V PSU which would be advantageous.

    2.) Remove the 12V power supply and buy/create a circuit that steps the 48V down to something in the 30v-10v range. I would keep the common wiring as is and just connect the + lead from all sensors to this circuit. I've got a bunch of small time components on me, I think most of the voltage regulators are 12v/5v but I have plenty of resistors, capacitors and diodes that I hope I can whip something up with. I'm not quite sure how to do that though.

    3.) Buy a relay for each sensor. This option is the most confusing for me. I have a 12VDC relay lying around with 4 pins. It doesn't have a second voltage on it like some of the others I've seen so I'm guessing it takes 12VCD as input and can only switch 12VDC. I'm guessing I need something that takes 12VDC and switches on 48VDC? This is the option I'm most sketchy on.


    I'm really hoping option one works but I don't want to try it in case I blow something up. Which do you think is a good option?


    Thanks.

  2. #2
    Join Date
    Dec 2012
    Posts
    199
    Hello,
    Your connection as described looks ok to me.
    You need to have the - of both powersupplies together.
    If your sensor is a three wire sensor, then the switching wire is related to the others.
    The NPN inductive sensors pull down the output when active.
    Your option 1 in that case will BLOW something on the breakout board, so don't try.
    Option 2 will do the job in a nice way, but take care, most of these 12volt regulators can't handle 48V on the input.
    DC DC HRD Voltage Converter 24V 36V 48V Step Down to 12V 3A Switch Power Module | eBay
    something like this might do the job
    I would not advice option3 the relay will introduce an extra point of disturbance.
    Regards,
    Toin.

  3. #3
    Join Date
    Sep 2010
    Posts
    1765
    agree mostly with Toinvd; to add to his YOU WILL BLOW UP INTERFACE BOARD WITH DOOR #1: Consider what voltage will be on the output pin of the top most series sensor: its 12v PLUS the 12v from middle one PLUS the 12v from the bottom one.... I assure you the interface board is not rated at 36v or higher. Also, you cannot gaurantee all 3 will present same load on vs off so they will NOT divide the 48v by 3 each....

    it is 100% common on machines to have multiple power supplies like this; you should not be trying to eliminate the 12v one.

    many folks, including many low cost drive mfgrs, will tell you that you MUST have the - side of both supplies tied together; I would not do that, it should not be required and just asks for trouble with more noise and future defects that do not have to happen.

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