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Power Supply Help

Discussion in 'General Electronics' started by Tech, Jun 9, 2016.

  1. Tech

    Tech Well-Known
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    I had a capacitor fry in my 12v power supply I bought from the parts store, it was recommended in the instructions of a 3D printer I bought. The printer worked for a few days and I got a handful of prints done before it died. The power supply never got hot to the touch during any of the prints, is their anyway to tell if I wired something wrong or it was just a bad power supply? Im not sure if this helps but its labelled rt1 and is located above the AC inputs. Any help would be great!
     
  2. Kyo

    Kyo Master
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    Hard to say what went wrong with the power supply without having it on hand. Wiring is really straight forward on these 12v power supply's. If it was up and working for a while allowing you to get some prints done; I would say it was probably wired correctly. Select proper input voltage? Did you adjust the output voltage? Short any wires to or from the supply? If it was me I would try and trace the problem ( what made the cap blow in the first place ) then replace the capacitor with a new one.. In the off chance it was just a bad supply ( it happens ). Hit up the parts store with a email they will get you sorted right out.

    Just curious, what printer are you working on?
     
  3. Tech

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    I received a email from them they offered to replace it so thats awesome! I did get in touch the makers of the printer kit, I sent him some pictures of the wiring and he said it all looked fine. I did select proper input voltage, I checked the output voltage it was a little bit over 12 volts. I couldn't find any places where wires looked damaged or creased. The printer is a Makerfarm Pegasus 12". I really like it a lot! The reason I asked this is im just curious on what could have caused it to fail. Not a upset customer or anything like that. Where can I source a new capacitor?
     
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  4. Kyo

    Kyo Master
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    New Capacitors can be found at most local electronics stores if you have any in your area. If not digikey , jameco , mouser, bgmicro, are all places to find that kind of thing. I usually go with digikey.
     
  5. Tech

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    From what I could figure out it is a thermistor that keeps going bad in the PSU it had the labeling NTC 5D-15. I took a picture of the inside of the PSU. Any ideas what could be causing them to do this?

    20160616_232747.jpg 20160616_232801.jpg
     
  6. Steve Fox

    Steve Fox Veteran
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    I had one like this. I replaced the thermistor twice and the fuse twice.
    Finally out of desperation, I shorted the fuse with a piece of wire.
    It blew the bridge rectifier and burned a small hole in my workbench.

    I threw it away.
     
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  7. Tech

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    this is the second one that did this. Im not sure if they will keep replacing them for me. So you think if I replace the thermistor in this it will just blow again? Can you recommended a better power supply?
     
  8. Steve Fox

    Steve Fox Veteran
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    I can almost guarantee the thermistor will blow if you replace it.
    Something is overloading the supply or there is a bad component.

    The ones at this price point all look the same to me. They even have some the same assembly idiosyncrasies.
    I have purchased five and three have had issues. This is the only one I couldn't fix.
    One had two bad solder joints and one blew the fuse and worked once I replaced it.
    I haven't plugged the last one in yet.

    I purchased all off eBay in the range of$22-$27 for a 24v 15amp supply.
    All came from China through different distributors in California.
    I also have a couple of 12v ones that are several years old.
    The circuit boards and components look the same in all of them.
    Every one had bent edges on the case from shipping due to poor packaging.
    The 24v ones have one coil that is unsoldered. I wasn't sure if it was supposed to be that way or a bad solder joint, so since it worked, I left it disconnected.
    I think if you want something better, it will cost significantly more.

    The good news is once it works, it lasts a long time.

    You are working on it without a load so that your problem isn't too much current?

    Steve Fox
     
    #8 Steve Fox, Jun 17, 2016
    Last edited: Jun 17, 2016
  9. Tech

    Tech Well-Known
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    oh okay well i'll keep trying until I get one that works. I havent tried one without a load on it. When I get a new one i'll test it out on something else. I never really thought it would be caused from to much current since its what the kit recommends and they said its the one they have been using for years.
     
  10. Steve Fox

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    Could be a wiring issue, a bad motor or any number of things.
    if that's the case, a new thermistor should fix it.
    You don't have to hook anything to them. There is an LED that tells if it is working.
     
  11. Tech

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    Oh okay well I did send pictures of the wiring to the kit provider he said everything looked good. I checked the voltage while it was doing a print it would fluctuate between 12.04v-12.14v that seems to be normal tho right? I did order a pack of thermistors so I will try to fix the ones I have. I planned on getting a new power cord as well just to eliminate that as a problem. by light thats the green led by the voltage adjustment?
     
  12. Steve Fox

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    Yes, the green LED is the one I'm referring to.
    The color varies, I have green, red and yellow.
    The voltage you measured is well within tolerance.
    I wish I could find a schematic for these. There can't be a lot to them.

    When I hook mine up, I try it with no load, then connect one motor and cycle it for a while, add the second, cycle it a while and then connect the other two. All of mine worked until I connected the last two motors. I guess that's when the weaknesses show up.

    I just looked at the pictures you attached. The inside of yours looks just like mine except one of my heat sinks only has one transistor (or whatever it is) on it. I can't recall which has one and which has two.
    That torroid just above the three capacitors is where one leg on mine is disconnected.

    Based on my experience, the third time is charm. The next one they send you should fix the problem, if it is a bad power supply.

    There is nothing more frustrating than getting this far and having to wait for something beyond your control.

    Steve Fox
     
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  13. Tech

    Tech Well-Known
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    Just wanted to update this thread in case anybody else has the same problem. I replaced the thermistor and drilled around a 3in hole in the top of the power suply case and added a computer case fan to push air in. As of now I have printed for a combined total of around 91 hours with no problems. This is much better then before, the previous times I was getting around 10 hours before the power supply would blow a thermistor.
     
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