Buying electronic components from Ebay

Discussion in 'General Electronics Chat' started by cdez, Nov 21, 2014.

  1. cdez

    Thread Starter New Member

    Nov 16, 2014
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    0
    Hello,
    I need several quantity of electronic components for my project, mostly mosfets and mosfet drivers. Because I have a quiet low budget I decided to buy from China/Ebay even if it's risky ..

    I'd like to know your experience on Ebay, if you have a trusted seller in mind I'd like to know.

    I have found this offer for IR2110 very interesting from "gc_supermarket":
    http://www.ebay.com/itm/10PCS-IR211...570?pt=LH_DefaultDomain_0&hash=item4609fbc4c2

    And these IRF3205 N mosfets from "jk_parts":
    http://www.ebay.com/itm/10-x-IRF320...925?pt=LH_DefaultDomain_0&hash=item416381c7d5

    Did you ever bought from these sellers ? What are the risks that these are counterfeits in your opinion ?

    Thanks
     
  2. takao21203

    Distinguished Member

    Apr 28, 2012
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    463
    GC are pretty decent, fully professional, you always get a tracking number on larger orders.

    i always got my orders. A few times things were missing, or shipped less than paid for, but always minor. One time I got a refund, another time I got it reshipped, another time I just didnt want to enquire about it.

    MOSFETs, well, there are several kinds, I have seen one kind with brittle legs, so inferior amalgam was used perhaps some recycled copper with impurities. It doesnt matter just breaks off more easily, when you bend them in any kind.

    Also MOSFETs always have the problem if you work them at the margin very hot, sooner or later some will explode. I dont recommend more than 70C outer temperature measured.
     
    cdez likes this.
  3. cdez

    Thread Starter New Member

    Nov 16, 2014
    9
    0
    Thanks for your answer,
    I need that my mosfets support 25 to 30 amps drain to source, the IRF3205 has 8mOhms Rds(on) so P = 25*25*0.008 = 5 watts, it should be ok with some heatsink I hope. But if the mosfet from ebay doesn't match the datasheet I could have serious problems ...
     
  4. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    You need fairly good cooling for 5 Watts TO220.

    For instance, you can mount them upside down on a PCB, and install a VGA cooler fan, pushing on the metal tabs, with thermal grease.

    A small passive heatsink will quickly overheat and will not be capable to transport off much heat.

    To rely on 0.008 Ohms is more than problematic. I wouldnt put more than 8 Amps through a TO220 MOSFET, so you'd need 4 in parallel.

    You may get away with just one, and small cooler and then some day, it overheats and explodes. Might be only 70C on the cooler, but 140C inside the chip.
     
  5. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    I have purchased several batches of Mosfets from China. Twice I received counterfeit parts. Example: I ordered IRF1404 mosfets that should have a 0.004 ohm Ron resistance. The parts I received had >0.025 ohm Ron resistance. I found I had more success if I email them first asking about the part I was interested in and that I would test the Ron value. Some did not respond back, the ones that did respond and assured me the parts were genuine, and they delivered good parts. The Chinese do not want negative feedback.

    Good luck
     
  6. nigelwright7557

    Senior Member

    May 10, 2008
    487
    71
    I bought some mosfet's from ebay and they blew up too easily.
    Bought some from RS Components and they were fine.

    Do yourself a favour and buy from RS. They aren't that expensive.
    Buy cheap, buy twice !
     
  7. cdez

    Thread Starter New Member

    Nov 16, 2014
    9
    0
    hmm... are you sure ? If TO220's would be limited to 8 Amps then why companies like I&R would be trying to make lowest Rds(on) possible and try to improve characteristics :/ I think it depends on what's inside the mosfet, not the box.
     
  8. NorthGuy

    Active Member

    Jun 28, 2014
    603
    121
    There's no telling if what you're buying meets the specs or not. I buy lots of things on eBay, but I would rather buy FETs on DigiKey.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,534
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    My choice for individual semi's etc is Digikey as well, I have bought the odd, very cheap, already built item from H.K. etc for expediency, if it cashes in, I have not lost much.
    Max.
     
  10. adam555

    Active Member

    Aug 17, 2013
    858
    39
    I buy regularly on ebay from China; but I would not recommend it if you are looking for quality or are in a hurry. Orders usually take about a month to arrive -though I just received an order last week that I placed in June- and a very small percentage get lost in the post; but you won't have problems getting a refund.

    Apart from that, everything else was fine; except for an IC they sent me that was not up to specs... probably a counterfeit.
     
  11. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    They arent limited to 8 Amps but at this current, fairly thick cable already heats up considerably.

    Also consider the MOSFET isnt always continously fully "on", so the average resistance is higher. Depends if you switch slow, or very fast. Well sure you can approach the margins, but you'll see with cheap parts, they'll blow up sometimes before the margin is fully exercized.

    Bonding wire costs money, after all, good 100% copper is more expensive too.

    Great idea isnt it? Use unrefined copper from recycling which has impurities- and costs much less.
     
  12. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    The package limitations of TO-220 cases have been studies. They will handle 8 amps.
    http://www.irf.com/technical-info/designtp/dt93-4.pdf

    John
     
  13. Nootron

    New Member

    Nov 22, 2014
    1
    0
    I buy electronic components from ebay all the time. You will save soooo much on shipping that it simply does not matter if you should ever
    buy from the wrong guy and get ripped off. You have saved so much money over time it doesn't matter.

    I tend to just use common sense. If the auction store has been established and has lots of components and lots of sales in the past
    then I have no problem buying from them. These things are soooo cheap who cares if one accidently buys from a vendor that
    does not act reputably.

    If they can ship 10 diodes clear from China (halfway around the world) for free then companies in the U.S. actually could do the same
    or a rather minimal charge. $4.95 shipping for super light parts doesn't cut it.
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,534
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    The Chinese govt. subsidies the shipping.;)
    Max.
     
  15. ISB123

    Well-Known Member

    May 21, 2014
    1,239
    527
    5$ for shipping is pretty cheap.
     
  16. NorthGuy

    Active Member

    Jun 28, 2014
    603
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    Worth nothing that I almost fried $3K inverter because the $1 connector which I bought on eBay shorted inside. Since then, I became more careful with what I can or cannot buy.
     
  17. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,687
    900
    I started buying some minor stuff from dealers in China a couple of months ago. Got some instrument cases, back-up cameras (2), wide-angle lenses for those cameras, connectors, DuPont cables and so forth. Sometimes I have felt almost guilty. For example, a set of 40-connector male/male DuPont cables for $1.59 + free S&H. So, I bought 2 sets for $3.18 total. It is hard to see where the profit comes from.

    My limited experience has been pretty good. Communication is poor, but I give an "A" to some vendors for trying. In one example, a wide-angle lens was sold as IR only. It was cheap, maybe because of that limitation. I needed visible light, but the picture suggested that the IR feature was due only to a removable cap, which turned out to be correct. Finally, some of the China-based vendors have established fulfillment centers in the US, which expedites shipping a little, but not always.

    I follow three simple rules:
    1) I check to see if the dealer is mostly in electronics or women's undergarments, etc. I only buy from the former.
    2) I exclude any dealer whose sales are all "private."
    3) I do not buy anything I cannot reasonably inspect. Thus, I have not bought any IC's yet. One might think the cameras would not be included under these rules. I did take a little risk, but balanced that against the fact that had I bought from US dealers, they would have been the exact same thing, cost more, and customer service, if any, wouldn't be better.

    Again, my experience has been very limited, but so far I have been happy. I would never spend more than I could afford to lose before buying stateside.

    John
     
  18. ISB123

    Well-Known Member

    May 21, 2014
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    I wouldn't buy any FTDI chips from eBay.Never bought any ICs except ones that were built into the product like stepper drivers,they all work fine.
     
  19. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    From what I've heard the destination country does not get a share of the mail fee, so someone in the USA is subsidizing my EBay shipments.

    I've also heard in China market share is king over profits, so they will sell below cost to buy share.

    I seldom buy components off EBay, mostly mechanical items (protoboards, connectors) or complete modules. The only problems I have had were short shipments, which the sellers have always rectified.
     
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