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IndustryArena Forum > CNC Electronics > CNC Machine Related Electronics > 120vac Vs 240vac on Imported power Supplies.
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  1. #1
    Join Date
    Dec 2003
    Posts
    24216

    120vac Vs 240vac on Imported power Supplies.

    Some tests we did with ref to one of the threads pertaining to using 120v or 240v on Chinese origin P.S.
    http://www.cnczone.com/forums/genera...-supplies.html

    This is to try and clarify a little around the questions of connecting the common SMPS power supplies that originate in China, and as to whether the 220v connection can be made in N.A..
    They all appear to be made exactly from exactly the same source, according to the specs and pictures posted.
    We recived one in some equipment and decided to do some investigation as to what differences there may be by using European 240vac (L1 & Neutral) or N.A. 240vac (L1 & L2).
    Upon opening the unit up, the first thing that stood out was the internal fuse was wired into the N terminal, which although would still open on a fault, did not meet the usual safety criteria especially when used in countries such as UK or on 120vac in N.A..
    If using the 240vac supply in N.A. it is advised to use fuses in both L1 & L2 in any event. And also use a fuse in the L1 terminal connection if using 120vac.
    The input to the supply is labeled GND N L , most are aware that in N.A. for the 240v connection there is no neutral when using 240v. the neutral occurs on the 240v centre tap.
    With respect to the two terminals L1 and N, there does not appear to be any internal electrical difference between them,
    the ground terminal is grounded to the case through a circuit board trace that has four 1kv .01uf capacitors from N to Gnd, from L1 to Gnd and from 24v -ve to Gnd and one from the switching circuit to Gnd.
    The unit was hooked up to a 240v supply with L1 and L2 on the L1 & N terminals and a resistive load was supplied that loaded the supply to the maximum rating of 8 amps.
    It ran on test with no problem and supplied a full 48vdc at the rated current. The fan fitted only runs in the event of an overheat of the electronics.
    From the tests, the supply performed as it should and there was no reason evident that would explain why there might be a difference between the two 240vac systems?
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  2. #2
    Join Date
    Jan 2005
    Posts
    15362

    Re: 120vac Vs 240vac on Imported power Supplies.

    Quote Originally Posted by Al_The_Man
    Upon opening the unit up, the first thing that stood out was the internal fuse was wired into the N terminal, which although would still open on a fault, did not meet the usual safety criteria especially when used in countries such as UK or on 120vac in N.A..
    It is obvious there are some differences in manufacture, I have never seen one, with the Fuse on the N terminal, they have always been on the L1 which is correct place for it


    Quote Originally Posted by Al_The_Man
    the ground terminal is grounded to the case through a circuit board trace that has four 1kv .01uf capacitors from N to Gnd, from L1 to Gnd and from 24v -ve to Gnd and one from the switching circuit to Gnd...
    This part is also not the same, as what we have seen, & tested, the case is Grounded, but some of your other connections are very different to what we have seen
    Mactec54

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