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  • EEVblog #281 – BK Precision 8500 Electronic Load Teardown

    Posted on May 23rd, 2012 EEVblog 34 comments


    http://www.bkprecision.com/products/dc-electronic-loads.html

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    Teardown Tuesday.
    What’s inside BK Precision’s 8500 300W 120V/30A DC Electronic Load?
    It is also known as the Itech 8512.

    Dave’s DIY Simple Constant Current Dummy Load:

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    • ftransform

      could the transformer have been placed in the front in order to have a more even weight distribution for the unit?

      • codeboy

        That could be it. With the transformer at the back, it likely tombstones… or acts like those Weebles from the 70’s

      • http://www.eevblog.com EEVblog

        Interesting thought. But I think it’s just a physical size thing. Maybe one of those cascading design choices? You make some decision up front that forces you in a particular direction, and it’s too late to go back and change it all.

    • http://adrienj.com AJ

      Haha, love the sped-up whistling.

    • emad

      thank u so much David for that great jop …

      please one episode on how to design an inverter

      because it is too hard to fresh eng. th do that ….

      thank u agaen

    • Wartex

      I have the same unit and while it’s built well, some of the components inside are very crappy. Funny how you omitted that being all “independent”. Also the “RS232″ on the back is TTL and plugging in a serial cable will damage the unit. They could have built in an optoisolated USB interface for extra $20 or just made an IR window with and IR USB cable attachment. That’s tightassery right there for which you chastise other brands. That cable you have doesn’t come with the unit normally, you have to buy it separately as well and it’s a bitch to find in stock.

      Feels like you are becoming a marketing machine for Agilent and whomever else sends free test gear.

      That agilent scope you got screams product placement all day long. What’s next, Coca-Cola with bottle labels facing the camera at all times? Not impressed.

      • http://www.eevblog.com EEVblog

        Forever the complainer and conspiracy theorist huh Wartex? I don’t even know why you bother watching any more.
        You said it yourself, its well built, and that was my general conclusion too.
        You claim there are “crappy components” inside? Please list them, and please be specific with details of why.
        Some have said the Lelon brand caps are crap, others have said they are ok. I have not personally heard bad things about them, and I’m not about to do extensive research to find out just for a 2 second part of a 30 minute video.
        If you have experiences with them them then please detail it, that’s what the blog is about. If I’m wrong or miss something then I will correct the video with an annotation. (go check, I just did)
        I stand to be corrected on everything I say.
        I did not really think about the serial interface in the teardown, it never occurred to me. I often miss mentioning things, it happens.
        Yes, it’s not isolated.
        Yes, I think they should have isolated it internally too. I’ll mention that in a review.

        As for the Agilent scope, it’s my main scope I use, so what am I supposed to do, hide it out of shot? Not use it in videos?
        Should I hide all the equipment in my lab so no one sees it and shoot against a blank wall? lest anyone think it’s all paid product placement?
        Perhaps you missed the fact that it’s mostly hidden behind my head in most front on shots! Oops, I’d better fix that lest Agilent don’t like me any more!

        I run an electronics engineering video blog. I use equipment on camera to a large audience, and I like reviewing them and tearing them down, that’s why people watch.
        I call things as I see them, it’s “off-the-cuff”, so I miss stuff. Even if it wasn’t off-the-cuff, I’d still miss stuff, or have different opinions and experiences to others.
        Gear is going to be used and commented on, and it’s always going to be essentially an advertisement for the company, that’s just the nature of the beast.
        Some of it I pay for, some of it I get for free from either dealers or manufacturers, and some of it is loaned and I have to return it.
        Am I supposed to slander every product I get? What if I find little wrong with it, as is often the case?
        Often it’s hard to find anything wrong with top shelf gear like Agilent, Tek etc, they are top shelf for a reason.
        And I generally won’t bother reviewing gear I know will be shit, because, well it’s shit.
        I do try to find all the negative things I can about a product, but I’m human, I miss stuff, and I also have my own opinions and experiences and knowledge. That’s why the comments and forum exist so people can correct me.

        How about you post a video response and actually contribute something instead of just bitching all the time?
        You have that same bit of gear, lets see YOUR teardown and comments.

        • Wartex

          First of all, thanks for your reply.

          The fact is, if you point out major flaws like unfinished (TTL vs USB) and unsafe comm link in the initial video, companies will stop sending you shit. The resistors in the unit are one hung low for example (at least mine). At $1100 they could have used better parts. The caps are not shit but questionable. In the past you had a healthy dose of bad and good. Now if you find a flaw, you try to rationalize it why they did it. And why not review shitty gear? It’s a great way to teach aspiring engineers what NOT to do.

          Regarding the scope: I never said to hide your gear. All I said is that it feels “placed” in the latest videos compared to the rest of the junk. The fact is that is one expensive piece of gear and if I were you I’d too feel obliged to stick it in the frame as a thank you to the manufacturer. The issue is, that puts you on top of a slippery slope. The same slope that a million of other blogs slid down when manufacturer corrupt the publishers with free shit. Companies that loan do not create an incentive to bias the reviews, the stuff you get to keep does.

          I’m not complaining, this is criticism. I’ve watched your videos since day one, I see a bad trend and I’m giving you feedback. I don’t belong to a local circlejerk so I’m not going to mindlessly nod to everything you say or crawl up your ass. I’m not suggesting you send free shit back, but if I were you I’d give some of it away in contests to prove you are not manufacturer’s bitch. I think you are an alright guy and would hate you to become a product shill. That is all.

          • http://www.eevblog.com EEVblog


            The fact is, if you point out major flaws like unfinished (TTL vs USB) and unsafe comm link in the initial video, companies will stop sending you shit.

            1) I don’t care. If I find a problem I will mention it. If I don’t mention something it’s because I haven’t noticed it.
            2) I think you are wrong. Look at Extech, I have hammered their stuff, they still like me. I showed Agilent’s brand new 3000 scope go up in smoke, and their mulitmeter go haywire, they still like me. I exposed a problem with Fluke’s #1 product, they still like me. I showed how to hack Rigol’s scope, they still like me. And I could go on. Off hand I can’t think of anyone who I’ve mentioned bad stuff about not dealing with me again.


            In the past you had a healthy dose of bad and good. Now if you find a flaw, you try to rationalize it why they did it.

            I don’t think I’ve changed much, but my style has evolved, that’s only natural. If I can think of a reason of why they might do something, then I’ll mention it, because it might be interesting and promotes discussion. Doesn’t mean I’m justifying it. Sometimes I get angry about stuff and call it crap etc, and other times it’s more of a shoulder shrug, it’s kinda random.


            And why not review shitty gear? It’s a great way to teach aspiring engineers what NOT to do.

            Maybe. But I just don’t like reviewing gear I know will likely be a load of shit. That’s my choice.


            Regarding the scope: I never said to hide your gear. All I said is that it feels “placed” in the latest videos compared to the rest of the junk.

            It’s the only digital scope I have in the lab, what do you want me to do with it?!


            The fact is that is one expensive piece of gear and if I were you I’d too feel obliged to stick it in the frame as a thank you to the manufacturer.

            I don’t feel obliged, not in the least. I’m not the same as you.

            If me simply using the thing and having it on my bench pisses you off, wait until Agilent fly me down to Melbourne next month to film upgrading it to 1GHz and touring their cal lab…
            That will make me an Agilent shill in your books I’m sure!


            The issue is, that puts you on top of a slippery slope. The same slope that a million of other blogs slid down when manufacturer corrupt the publishers with free shit. Companies that loan do not create an incentive to bias the reviews, the stuff you get to keep does.


            Only if you let it. I’m not like that, I can’t help myself, I’m stupid enough to bite the hand that feeds me. Just ask any one of my previous employers!
            Once again, perhaps you are forgetting that I posted a video of that exact same scope BLOWING UP IN SMOKE!
            I can’t imagine anything worse I could have done to Agilent than post that video!
            Seriously, the thing blew up in smoke 10 minutes after using it while I was filming the review. And I did actually think for a minute – geeze this company has been great to me, they give me a world exclusive on this scope, and they let me keep it. Should I really post that video?, it could be horribly damaging given the massive publicity this scope release was likely to generate – they’ll never speak to me again!, they’ll sue me!
            But it was only a fleeting thought. So what did I do? I posted the video because that’s what happened, and I thought it was funny. I’ll take my chances thank you very much.
            What would YOU have done?


            I’m not complaining, this is criticism. I’ve watched your videos since day one, I see a bad trend and I’m giving you feedback.

            Thanks, but I think any trend you see is imaginary, and you are reading more into it than is really there.


            I’m not going to mindlessly nod to everything you say or crawl up your ass.

            I’d call you an idiot if you did.
            If I wanted that I’d heavily moderate the youtube and blog comments and the forum, but I don’t.


            I’m not suggesting you send free shit back, but if I were you I’d give some of it away in contests to prove you are not manufacturer’s bitch.

            I was just thinking this morning that I have a spare LCR meter I want to give away.
            Problem is mostly that the gear is really useful stuff that I need myself, I can use in the blog for tutorials etc, and also for physical product comparisons when doing other reviews. I’m almost forced to keep all this stuff for that purpose alone.

      • Henrik Jensen

        I have two of these loads and both included both RS232 and USB interface in the box.
        I have used them a lot (at a low power level) and there have not been any problems, except a few caveats in the user interface.

    • Salas

      Lelon caps have a bad rep

      • Wartex

        Like I said – don’t expect any serious bashing. Now that expensive gear started rolling in for free, all of it will be visible at all times in all videos and none of it will have any major flaws in reviews.

      • http://www.eevblog.com EEVblog

        Please cite.
        Another commenter said they used to have a bad rep but are now quite good.
        I doubt that ITech would build such a generally high quality unit and then skimp on a few caps on the logic power supply.

        • Wartex

          http://www.badcaps.net/forum/showthread.php?t=14610

          http://spectrum.ieee.org/computing/hardware/leaking-capacitors-muck-up-motherboards

          >>>>It is clear now that a faulty electrolyte is to blame for the burst capacitors. The mystery is: where did it come from and which manufacturers used it? Citing Japanese sources, initial reports claimed that major Taiwanese capacitor firms, including the island’s market leaders, Lelon Electronics Corp. and Luxon Electronics Corp., had turned out faulty products. But both companies have denied the accusations.<<<<

          Google "bad lelon caps"

          • http://www.eevblog.com EEVblog

            Thanks.
            I don’t see anything in that thread with evidence about actual bad Lelon caps. Perhaps I missed it?
            But if so, ok, that’s one person who had an issue in a bit of cheap consumer gear.
            Lelon being a “market leader” in Taiwan kinda puts them in the ok category does it not?
            The IEEE article is from almost 10 years ago.
            Yes, a lot of manufacturers got caught up in the bad electrolyte issue at the time.
            I’m still not convinced that those 105C rated Lelon caps in the BK Precision supply would be dubious.

    • Wilfred

      Dave, I wanted to applaud you for mentioning the source of the BK Precision electronic load.

      Then when I logged on I read Wartex’ comments and your response. I see he shares my concern (unease?) about the “possibility” of a slide down the slippery slope. I (like Wartex I think) don’t think you are on it and I don’t even think you will go down it. However, reviewing free stuff means you have to be super careful. It leaves you open to critisism from uncharitable persons, however unjustified you may feel it to be.

      • http://www.eevblog.com EEVblog

        Nothing new there at all, I get criticism all day every day.
        And of course I can’t get away with doing shill reviews even if I wanted to. I have countless clued up viewers who will point out within minutes of the video upload if I missed something, talking BS, or if I’m hiding something etc. That’s what makes my reviews inherently different from consumer and other reviews and bloggers who’s audience are not technically clued up.
        So the problem will always be what I don’t mention, and given that I can’t possibly find every bad or questionable issue with a product, there will always be some people who interpret that as “selling out” or whatever. When the fact is I simply didn’t see it.

    • JohnTech

      Liked the review Dave, Its an interesting product.
      Regarding any such ‘Slippery Slope’,
      The beauty of the internet, If you don’t like it, dont view it.
      Anyways; A leopard does’t change its spots and (like my Ozzy Engieers Mates over here in the UK) I fully expect you to keep saying it how you see it for a long time yet. John.

    • Th3_uN1Qu3

      Lelon are so-so. I haven’t seen any failed ones myself, but there are reports of them going bad in LCD monitors. But, compared to where they would normally live in a monitor, they are not in a high heat position in this unit. I would have liked to see Japanese caps for that price, but oh well.

      Delta Electronics uses cheap caps (Ltec) in a lot of their power supplies. Yet there are very few complaints – they know what they are doing.

      In most cases it’s not the poor quality of the caps alone that kills them, but shit thermal design as well. Some designers expect a cheap capacitor of unknown origin to perform as good as a brand name capacitor, they push too much ripple current thru the caps AND stick them right next to the heatsink of the power diodes (which is always too small and runs crazy hot), and that’s when things start going south. Or it’s all just planned obsolescence, who knows. All i know is that it gives me work.

    • Richard

      What happened to commenting on the actual topic? This topic is about an electronic load teardown. The comments have morphed into a discussion about Dave’s objectivity and subjective comments about some potential yet-to-be substantiated, could be true capacitor quality.

      Dave: the reviews are excellent and hit the key points for design information. I believe this is your only intention. I don’t know if you have been secretly bought out by “The Man”, but that doesn’t seem to get in the way of producing a good review – albeit cursory of this particular topic at this point.

      What I hope is that you take this topic further. For example, it is relatively easy to build a static load (as you have done in an earlier episode). However, turning that into a fast, stable dynamic load is another story. Perhaps take the tear-down a bit further and walk through the schematic to illustrate some of the design choices. Cheers.

    • Th3_uN1Qu3

      I would have commented on topic if i could actually afford one of those load testers. :P

      Agreed on commenting on the schematic, but chances are, with the part number on the MCU erased, there is no schematic to speak of.

      • http://www.eevblog.com EEVblog

        I couldn’t find a schematic for it.

    • http://sven.killig.de/ Sven Killig

      Looks similar built like my BK 1785B PSU where I tried to silence the fan:
      http://www.eevblog.com/forum/product-reviews-photos-and-discussion/photo-and-fan-mod-of-a-bk-precision-1785b
      With it came an IT-E131 TTL/RS232 cable that IS isolated.

    • http://www.kean.com.au Kean

      Hey Dave,

      I’ve got one of the ITECH IT8511’s which I got about a year ago on ebay for a bit over $500.

      It is only rated at 150W, but I opened it up and followed along during the tear down video and it looks identical to yours in terms of all the resistors and MOSFETs. I wonder if the wattage is purely a configuration parameter so they can charge more.

      Anyway, I am glad I opened it up as the transformer had obviously taken some force during shipping and was bent over against some of those unsecured TO-220’s MOSFET’s. One of the feet is also broken – unfortunately ITECH skimped a bit on the feet and handle in comparison to the BK version.

      The part number on the main chip is also ground off on mine. Stupid practice!

      I’ve used it for testing a few PSU designs, but also for battery testing. The controls are a bit weird in places, especially the battery mode with no response unless you press the exact combination of buttons.

      I’ve also got the BK 9130 triple output PSU which is fantastic, but a bit pricey. I could justify buying that as I use it almost every day, unlike the DC load.

      Keep up the great work.

      Cheers,
      Kean

      • http://www.eevblog.com EEVblog

        I assumed it would have had one less current shunt resistor or something at least!

        • http://www.kean.com.au Kean

          Out of interest I popped the cover for another look, as I expected the same. It has the same two big shunt resistors, the same eight RX21 R05 8W load resistors, and the same eight IRPF250N Power MOSFET’s.

          The only differences I noted from your description in the vid was this one uses TL084’s rather than TL074’s, and you have a higher rev VFD PCB (34 vs 33 in mine). Also mine doesn’t have as many test stickers :-(

          So I think the max wattage is probably hardcoded in firmware…

          I have to admit I haven’t tried taking it up to that — well at least I hadn’t until a moment ago. It will actually let me set the constant power up to 200W, or if I set constant current to 30A, it will also max out at 200W. Left it running for 5 mins or so till it got warm, but I wouldn’t want to leave it for extended periods that high.

          Of course the front panel of the IT8511 says “120V/30A/150W”, and 150W is more than enough for my typical (precision) usage. The IT8511 can be got for almost half the price of the 300W BK model.

          BTW, the date codes on the PCB’s are in YYMMDD format, so they are 2010 or 2011 designs – not 2006.

          Kean

    • http://www.vtunneltr.com vtunnel

      Thanks you… Cok guzel bir yazi olmus tebrikler…

    • Tekati

      Freaking Dave,

      Man I hate your reviews. Every time you review something cool I always find myself running out to find and purchase one.

      Half of the stuff on my desk is now there because of you and I am running out of space.

      I actually purchased the BK 8500 from a guy on eBay used for 400.00. Pretty darn good price I think anyway. Already got it and put it to the test and well it performs just as I expected from your review. I just so happened to have a great use for it and thought of plenty more uses for it already that I had never even thought of. Kudos for the excellent review.

      Haters will be haters so don’t ever let them get to you as I can already see they wont. I too have watched all of your videos although I did not find you until about a year ago, I have since watched every video you have produced and seeing as I have watched them one after another I can tell you I have not seen any of this so called slippery slope. Your reviews to me seem just as honest and forthcoming today as they have in the past.

      Keep up the good work is all I can say and I look forward to hating you for making me purchase cool things for some time to come.

    • Dawid

      Hi! I’m designing an electronic load and I wonder what kind of IC is used in BK-P as Current Sense Amplifier on the input shunt resistor? The 120 V (or 300 V in BK-P 8502 model) input voltage is too high for most of IC… I want to also have 120…150 Vin in my dummy load but best IC I’ve found is Linear LTC6101 and it handles only 100 Vcmr

    • Shaun

      Hello
      I’m a design engineer and would love to see a detailed review on this hardware given the experience you have accumulated with it since the tear-down, any plans to post such a video? I’m interested because we are looking at equipping our lab with these and I’d like to know what I’m in for.

      • http://www.eevblog.com EEVblog

        Yeah, eventually. In the mean time, if you need an electronic load and it meets your basic spec, you can’t go wrong with this BK Precision.

    • Ben Lanza

      Looking forward to a review of the BK 8500.

    • Paul

      Hi Dave,
      Can you confirm that the 8500 can be _controlled_ over USB from a controlling PC, but that current and voltage readings cannot be _read_ by the PC over USB?

      The spec sheet seems to indicate that through what it doesn’t say.

      Thanks!

    • Glenn

      Has anyone tested the

      MCH EL3630B DC Electronic load

      Or more info, and insite pictures of this constant current?
      He is 300 watts and for good price on. aliexpress.com.

      Thanks!