DIY Power Supply Wiring Questions


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    Default DIY Power Supply Wiring Questions

    Hi,

    I have 3 ATX Power supplies on hand and I want to run them in series to get 36V for a diy CNC Plasma Table I am building.

    I read through the entire thread on daisy chaining them, and read other sites and articles, but I am unclear on four points.

    I understand that all power supplies after the first in the series must have the (-) ground disconnected from the case. I have done this and checked it with a multimeter to ensure there is NO continuity between a black wire and the case. DONE.

    I have also read that I need a resistor between any one black wire (ground) and any one red wire (+5V). This is not demonstrated in the image below that I found on the daisy chaining thread....

    Q1: Is the load resistor on the 5V only needed during testing when no driver is connected? Can it be omitted once the power supply 36V is connected to the drivers. Do the drivers provide the load during operation that the load resistor provides during testing?

    Q2: If the resistor cannot be eliminated, do I need 3 resistors, one per power supply?

    On my main power supply, I joined one black wire and one green wire. As I understand it, this allows it to turn on.

    Q3: Do I need to do the same on the the other two power supplies also?

    Q4: Do the three Powwer Supply Metal Cases need to be electrically insulated from each other or can they be connected?

    Thank you for your help.

    -Mike


    DIY Power Supply Wiring Questions-atx-series-jpg

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    Attached Thumbnails Attached Thumbnails DIY Power Supply Wiring Questions-atx-series-jpg  


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    Default Re: DIY Power Supply Wiring Questions

    Caution: I do not know these particular PSs, so my answers are a bit generic.

    Is the load resistor on the 5V only needed during testing when no driver is connected?
    No. It is needed to load the +5 V line as that is the one used to control the whole system. And it must stay there. You should use a power resistor for this as it will get hot.

    If the resistor cannot be eliminated, do I need 3 resistors, one per power supply?
    Yes, 3 quite separate power resistors are needed.

    On my main power supply, I joined one black wire and one green wire. As I understand it, this allows it to turn on.
    Do I need to do the same on the the other two power supplies also?

    Don't know. You could experiment.

    Do the three Powwer Supply Metal Cases need to be electrically insulated from each other or can they be connected?
    The cases should all be earthed for safety. The difference between the -ve arm of the 12 V supplies and ground should not be big enough to matter.

    Cheers
    Roger



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    Default Re: DIY Power Supply Wiring Questions

    Excellent. Thank you Roger. Everything is very clear now, except for the connecting power supply cases one to another.

    I asked: Do the three Powwer Supply Metal Cases need to be electrically insulated from each other or can they be connected?
    You responded: The cases should all be earthed for safety. The difference between the -ve arm of the 12 V supplies and ground should not be big enough to matter."

    My interpretation: "I can bolt all three supplies together; but, it does not matter" Yes? No? Ideally which is best or is it irrelevant?

    Obviously this means the master power supply which still has the black line connected to the case will in effect be touching all three cases.

    Reference the earth safety:

    All three power supplies have a US 110VAC line coming in. The green wire in on all power supplies is connected directly to the metal case and I DID NOT sever them.

    On the two additional power supplies, the earth ground connects to the case, but stops there because I have severed the black (-) ground connecting the circuit board from the case.

    On the main power supply, the black line is not severed, so there (-) ground black line meets the safety ground coming in from the wall.

    Isn't this amazing. A man in the middle of America is receiving help from a man in Australia, at the speed of light. If I may say, "good on ya mate!" Thanks Roger,

    -Mike



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    Default Re: DIY Power Supply Wiring Questions

    Hi Mike

    what current do you need from the power supplies ?

    this is what I would do

    DIY Power Supply Wiring Questions-atx-series-jpg

    the 5 ohm resistors provide the minimum 1 A load to the +5V output

    the diodes prevent the 12V output of one PSU being reverse biased by the others (they may not all startup together every time !)

    the 1N5401 is OK for currents upto 3A or P600A is OK upto 6A


    John



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    Default Re: DIY Power Supply Wiring Questions

    Hi John,

    Amperage requirements may vary.

    My steppers: 3V, 3A, 3.5mH, 270oz. in.
    My Drivers: 4A, 42V

    As of now, I am set to use 3 of the steppers (already purchased) at 36V and 3A.

    Other options I am exploring:
    1. Purchasing another stepper and driver for the other side of the gantry.
    2.Running the steppers at 4A to get more out of them? I don't know if this is BAD or not. I have read about it, but I have been sipping out of a fire hydrant as I learn CNC.
    3.Since the stepper VMAX is 59V I am also exploring over volting the drivers by adding another ATX 12V for 48V. The Drivers I am using are labeled TB6600, but they are NOT TB 6600s. They are TB67S109AFTG chips. The drivers are very popular for those that have them. I got mine on ebay, but they are located here also. The technical data says their true working limit is 47V, but this is based on "temperature". I thought a good heat sink and some fans might allow me to run the 48V. If this turns out to be an acceptable idea, this will increase the amperage also.

    With my current plan, 3A I will need a 6.1A supply. If I decide to go with four total steppers at 3A (two steppers to move the gantry), I will need 8.2A.
    If I operate the drivers at the 4A, 3 steppers will require an 8.2A supply and 4 steppers will require a 10.9A supply

    I made a 10ohm 10watt purchase of resistors from ebay this morning. Do I need to change to 5ohm? It was only $1.22 (US) nfor 5 delevered, so it is not a big deal if I need to order the 5ohm also.

    Can you recommend diodes I need for 8.2A and perhaps 10.9?

    Thanks John,

    -Mike



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    Default Re: DIY Power Supply Wiring Questions

    BTW, the drawing was excellent!!!! Thank you John.



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    Default Re: DIY Power Supply Wiring Questions

    All three power supplies have a US 110VAC line coming in. The green wire in on all power supplies is connected directly to the metal case and I DID NOT sever them.
    On the two additional power supplies, the earth ground connects to the case, but stops there because I have severed the black (-) ground connecting the circuit board from the case.

    This is all good.

    I made a 10ohm 10watt purchase of resistors from ebay this morning.
    Two 10 ohm resistors in parallel make a (20 W) 5 ohm resistor. No problems.

    I suspect that sooner or later you will have to buy or make a power supply just for the steppers. Using ex-PC suppliers is OK for a temporary lash up, but it is a bit messy. The fortunate thing is that you do NOT need an expensive switched mode PS for the morors: a simple (large) transformer, diode bridge and large capacitor is ideal. Better, in fact, than a switched mode PS which can actually create some problems.

    A man in the middle of America is receiving help from a man in Australia, at the speed of light.
    Chuckle. A year or two ago I was sorting out why a factory in the USA was losing CNC machines once a week, at vast repair expense. Or maybe that was two different factories ...

    Cheers
    Roger



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    Default Re: DIY Power Supply Wiring Questions

    Hi Roger

    thats what makes web sites like CNCZONE with members helping each other




    Hi Mike

    don't go over 3A for the motors you have - depending on the manufactures data sheet you look at
    you will find they will run at 70 or 80 C - too hot to touch


    just incase you end up with four 4Amp motors you will need to look for diodes that can pass16 or 20A

    the reverse voltage only needs to be 30V or so

    first web search result for axial Schottky 16a Diodes

    https://www.amazon.com/dp/B01FVEZT00/ref=biss_dp_t_asn

    a pack of five made by littlefuse Part Number DST2045AX

    DIY Power Supply Wiring Questions-dst2045ax-jpg

    it will be better if you stick to the Operation Range of supply voltage
    once you go over 47V the greater the chance the board will fail

    when you try to stop or decelerate a heavy part of your machine the motors will be driven by the moveing mass and the motors become generators that can raise the supply voltage - its one of the things switchmode power supplies don't like about stepper motor drivers

    with only 3V differance between the operation maximum and the absolute
    it may pay to limit the supply to 36 to 40V even though it can limit the maximum speed of your machine


    John

    PS
    you can try using the 10 ohm resistors with the power supplies you have , they may work OK

    if you need to use 5 ohm resistors just connect another 10 ohm resistor in parallel with your existing resistors

    Last edited by john-100; 02-17-2017 at 06:02 PM. Reason: add PS


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    Default Re: DIY Power Supply Wiring Questions

    Ok, I have all the power supplies now. The resistors are enroute from China.

    Two questions:

    1. Do I NEED the diodes? Can I have a switch disconnect from the drivers until all the power supplies are on or some other work around? Reason, the diodes are spendy and I am doing this project for the almost free aspect.

    2. Will the amperage draw be 31 AMPS? I have 4 power supplies. The input of the power supplies is 9 amp for two of them and 6.5 amp for two, totaling 31 Amps for four if I decide to go 48V instead of 36V. This is too much for the breaker and the cost of operation would be insane for my max need of 48V DC at 6amps. I am making an assumption that the 31 Amps would be at max draw on all supplies and not the draw I would experience since my draw is MUCH less than the max capability of the supplies.

    Note: Someone gave me some really good heat sink material, so I am thinking of going 48V with the drivers by removing them from their heat sinks and attaching them to the replacement.

    Thank you,

    -Mike



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    Default Re: DIY Power Supply Wiring Questions

    The input of the power supplies is 9 amp for two of them and 6.5 amp for two, totaling 31 Amps for four if I decide to go 48V instead of 36V.
    I may be a shade confused here, but I suspect that what you have written is wrong. I think you are talking about the outputs of the power supplies, not the inputs.
    Where are you putting the breaker? On the DC line to the motor drivers?
    If you are sticking to the idea of a series connection between the power supplies, then you add the volts, NOT the currents.


    Cheers
    Roger



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    Default Re: DIY Power Supply Wiring Questions

    Hi Mike

    the diodes are to protect any power supply that is slower than the other supplies to start up
    if the power supplies were identical you would have a better chance of gettting away without the diodes

    I take it the 31A is the total inrush current / surge current for the four power supplies
    depending on the type of the circuit breaker and the duration of the surge will determin whether the circuit breaker trips

    once started ,you would expect

    the input power taken by the power supplies will be equal to the stepper driver input current X the stepper driver driver input voltage X 1.25
    ( the 1.25 assumes the power supply is 80% efficient )

    but you will find the stepper drivers input current is lower than the 3A you have set the motor current to because you are only replacing the power lost due to the motors coil resistance

    for instance the Gecko G540 can supply 3.5A to 4 motors , that adds up to a total of 14A
    but the G540 only has as an internal 10A fuse !!!!

    the driver input current works out to about 0.7 X the motor current


    John

    Last edited by john-100; 03-02-2017 at 05:02 PM. Reason: add driver input = 0.7 X the motor current


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    Default Re: DIY Power Supply Wiring Questions

    Ok, Got it. John, you are correct, I am talking about the demand for amps from the wall. The outlet only has 20AMP breaker and I also wanted to make sure it was not going to be a some HUGE energy pig. I can work with this. I will look for some cheaper diodes online. If they are going to be expensive I will just spring the extra for the proper turnkey power supply.
    Thank you, -Mike



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