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Does this power supply seem safe

Discussion in 'Power Electronics' started by Sander Busch, Jun 28, 2017.

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  1. Sander Busch

    Sander Busch

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    Jun 28, 2017
    I bought this 12.6v 1A power supply off of eBay but it seemed to light so i opened it up and i think that transformer looks a little bit to small. And the whole thing just seemed a bit sketchy. But my electronics knowledge isn't that big yet so I was wondering if some of you would have a look at it.
     

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    Last edited by a moderator: Jun 29, 2017
  2. Bluejets

    Bluejets

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    Oct 5, 2014
    Switchmode power supply transformers are smaller due to the fact they run at a higher frequency than mains transformers. This is the attraction in the first place.
    Just taking a squiz at something in electronics is not the usual way to ascertain ratings.
     
    Last edited by a moderator: Jun 29, 2017
  3. Audioguru

    Audioguru

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    Sep 24, 2016
    A power supply has many detailed spec's. This cheap Chinese junk has no detailed spec's. But it is very cheeeep.
    It is not a charger circuit for a lithium-ion battery.
     
  4. Sander Busch

    Sander Busch

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    Jun 28, 2017
    No i am aware that it is not a lithium-ion charger it is supposed to be used in conjunction with a bms that is also why it supply's 12.6v wich i needed in order to change a 3s li-ion. But my main concern was if the mains part was safe as i am not that experienced in mains voltage.
     
  5. Bluejets

    Bluejets

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    Oct 5, 2014
    Why pull the thing apart then?
    This is how people get zapped.
     
    davenn likes this.
  6. davenn

    davenn Moderator

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    Sep 5, 2009
    once inside the case you are fully exposed to the mains voltage
     
  7. davenn

    davenn Moderator

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    Sep 5, 2009
    curiosity of what is inside ........ surely you have done that ??
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    There seems to some decent isolation on the PCB between primary side and secondary side. That's good.
    There seems to be an overvoltage protection at the input side. That's good, too.

    The quality of the transformer's construction cannot be judged from the photos.

    The quality of manufacturing is poor. See for example how the wires are attached to the PCB:
    upload_2017-6-29_8-7-24.png
    Instead of fitting the wires through the holes and then soldering them, they are soldered flat to the PCB at the bottom. This is not good practise.

    Note that there is no protective earth and no strain relief for the mains wires. This power supply needs to be housed in a non-conducting housing (as the original plastic housing). Care has to be taken that even in case one of the primary wires comes lose it cannot touch the secondary side. The original housing may (or may not) have the required separators built in.

    My opinion: If one is not an expert in such things it is better to keep this kind of power supply closed in the original condition. By opening the housing you not only lose what litte warranty there may be but also risk reassembling it incorrectly which may directly lead to latent danger.
     
    Sander Busch likes this.
  9. Sander Busch

    Sander Busch

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    Jun 28, 2017
    That is true but not if you are carful and make sure that it's not plugged in and you discharge the capacitors then you should be safe. And it's not like that I don't know any thing about electronics else i would not have opend it. I did i because it seemed to light to be true so i would not risk plugging it in before i was sure it wasn't going go up in flames. You never know with these cheap Chinese products. I think it would be more dangerous just to plug it in without knowing if it was safe then opening it. And what is ment by that i am not that experienced was that i wasn't that experienced with how the circuit worked. I do know how to handle mains voltage i have been wiring lamps and sockets many times before.
     
    Last edited: Jun 29, 2017
  10. Sander Busch

    Sander Busch

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    Jun 28, 2017
    Yes but not if it isn't plugged in and all the capacitors i discharged. And you put the whole thing together in perfect order before testing if it works.
     
  11. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir Sander Busch . . . . .

    Well . . .since you done spents your hard earned munneys . . . and bought the farm.
    Why not see what you actually have now ?
    What I am seeing there is the AC line power coming in thru the two red leads and with one side thru a fuse and then going into a small FWB rectifier and then into a Main Filter cap and the full DC oltage is then fed into the 8 pin " power suplpy in a DIP "

    It has the power FET and control electronicsall inside and drives your ferrite based power transformer which seems adequately sized for only 12 watts of power. Then there is one additional ancillary compoent in the form of the side mounted 4 pin DIP just to the side of the transformer.
    It provides a totally isolated, voltage sampling feed back from the secondary of the power transformers derived power supply.
    As the secondary power is being subjected to different loads, it corrects for different loading back at the main power IC DIP by duty cycle adjustments.
    The secondary output voltage is dependent of two op amp sections of an LM358, for corrective voltage corrections.
    Finally there is the 12.6 @ up to 1 amp output at the Red- Black leads.

    If it was mine to evaluate, I would be digging up enough 10 watt power wirewound resistors, for the arranging of them in combinations to initially come up with ~50 ohms to get a quarter loaded down supply.
    Initially DC meter the supplys unloaded voltage output and then see what the loaded pull down voltage is being.
    Then rig up a resistance combination to get ~25 ohms and test it to see how well the output voltage holds up at 1/2 loading.
    Then make a final plunge to 15 or 12 ohms to do a full power and evaluate regulation and leave the load hoked up for quite a time period to detect just how hot the power transformer runs. And see if the output voltage sags.

    If you finally decide to fly the thing, it would be a shame if you did not additionally get those AC line and DC output wiring leads connections up to mil spec and aerospace soldering standards.


    73's de Edd
     
    hevans1944 and davenn like this.
  12. Doug3004

    Doug3004

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    23
    Sep 5, 2014
    Warranty? That's a good one :>D

    When I buy generic Chinese-made power supplies, I assume that they're safe and reliable to about 50% of their current ratings. I haven't burned one up yet. And I've even accidentally shorted out a couple of them, and they even clicked off and on like they were supposed to, and still worked afterwards. I simply avoid running them hard.

    I've bought a couple power supplies from surplus places--that were originally high-cost items from various companies--and all of them look perfect overall. The PCBs are clean with clean edges and holes and sharp traces, the solder bath is complete (no hand-soldering is apparent), the components are laid out densely packed and all the parts are perfectly aligned in all three dimensions. These cost 10X what the same-size Chinese generic ones do however.
     
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