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High current DC power supply. Linear or SMPS?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by fastline, Oct 31, 2017.

  1. fastline

    fastline Member

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    Have a product that I would like to offer commercially and will need a pretty substantial AC-DC power supply. Exact specs are not yet known but approx 50-60VDC at 60A. Though it does need voltage regulation, the precision does not need to be all that great, nor does the efficiency because it won't run much. It would remain powered up many hours though.

    My electrical expertise is limited so not sure if I trust myself getting it right, especially a SMPS?

    However, there are LOTS of parts and pieces to this product and must be constructed economically so if I outsource everything, financial success will be limited. Can bare board reliable PSUs be obtained? I have done other, smaller projects but designing the PCB, having them printed, and assembling in house, but I know others are much better at this.

    One angle that I like about inhouse design is control of the project for repair and diagnostic purposes.

    Any thoughts on which direction may be best?
     
    Last edited: Oct 31, 2017
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Have you done the maths?, what country are in? - 60V at 60A is 3600W - more than you can get from a 13A UK socket (which is more powerful than most). This also assumes 100% efficiency from the PSU, and a linear one will be a LOT less than that, and a switch-mode one a fair bit less.
     
  3. fastline

    fastline Member

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    In the USA, and will need to operate on 220-240VAC. Rough target output to the load is 3000W. We may wish to throttle back the output a bit depending on what is feasible. I know this is a pretty serious PSU.
     
  4. dave

    Dave New Member

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  5. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    I have an old linear 60 volt 30 amp supply and when it needs moved I call my son. Without even knowing your product a 60 volt 60 amp linear supply will likely weigh in at over 100 Lbs. I would be thing something in a SMPS as a linear supply that size will be extremely expensive and have substantial weight to it.

    Ron
     
  6. AnalogKid

    AnalogKid Well-Known Member

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    If you can stand 50 V, that is within 48 V adjusted up 10%. You can use what is called a telecom rectifier. In the old days, that's what it was, a big-assed rectifier. Today it is a purpose-built, single output, AC/DC power supply, often 1/4 rack width, good for hundreds to thousands of watts. Also, they usually are current-sharing, so three 1500 W units get you some operating margin plus some redundancy. Because the telecom industry sucks up a lot of these, the cost-per-watt is lower than that of normal industrial supplies. Last one I used was from Unipower.

    ak
     
  7. fastline

    fastline Member

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    I was sort of leaning towards the SMPS as this seems to be the norm today for lighter, cheaper, more compact designs. I guess my only resistance there is a lack of full understanding to design a good one, in which a commercially purchased unit may squash th budget pretty fast.

    Question - with such saturation in the market with SMPS supplies, are there any integrated semiconductors that help to simplify these designs and reduce the part count? I know when looking at some supplies, it seems they design in several features that may be of little use. Once the ideal voltage is determined, we could used a fixed voltage design, but would certainly want certain safety features such as over current or high temp shut down, etc.

    Or maybe some commercial vendors that would be cost effective? Only ones I have looked at is Mean Well so far.
     
    Last edited: Oct 31, 2017
  8. fastline

    fastline Member

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    Thank you! That is the sort of info I am looking for. I think staying within certain "standard" designs will be most ideal.
     
  9. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    If your making a few and you are buying them in then smps's are probably the way to go, as it would be cheaper.
    If your designing yourself than linear would be better unless your experineced with smps's.
    There are companies that sell modules and boards ready made for limited production runs, ie if your making < 100 or so.
     
  10. fastline

    fastline Member

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    Dr Pepper, can you tell me more about the modules and boards? I really think SMPS will probably be the way to go here. An open chassis is fine as it will all be further enclosed. I think we just need to get down to what the board and component costs would look like so we can see how much mark up is in one. I think once we can get out of the "limited production" phase, we can look more at using a commercial unit but keep costs down right now is important.

    I really need to make time to educate more about SMPS as they are in everything today.
     
  11. AnalogKid

    AnalogKid Well-Known Member

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    For fewer than 10 units and more than 1000 W, you cannot build a power supply for less than you can buy one. Linear, switching, Van de Graaff Generator, whatever. No.

    A linear supply is relatively easy to design and build at any power level, but a multi-kW transformer will be huge, heavy, and expensive. Plus, there is all of that heat to get rid of somehow. Is a 3-phase AC input available?

    At your power levels, a switcher is the clear favorite for cost, size, and efficiency. But a multi-kilowatt switching power supply transformer would take an expert months to get right. An intermediate solution could be a supply made up of multiple high density DC/DC converters (Vicor, SynQor, etc.) in parallel, but these things are not nearly as easy to parallel up as the manufacturers say. And you would need a 3000 W power factor correcting front end to reduce the otherwise enormous capacitor bank to something reasonable. And don't forget the heat. Yes, switchers are more efficient than linears, but an 80% efficient 3 kW switcher produces 750 W of heat.

    My vote is to start with something off the shelf. If you really need a higher output voltage, talk to a manufacturer about a modified standard.

    ak
     
  12. fastline

    fastline Member

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    That seems like some fair advice. As much as I would like to DIY these things, I know switchers can just be tricky.

    So, can anyone recommend some reasonable manufacturers to talk with? I don't even want to use the word "China", but I know a ton of electronics come from there and see many big names just acting as the middle man, with a big margin.
     
  13. dknguyen

    dknguyen Well-Known Member

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    Try asking on RCgroups.com under the batteries and charger section. They will probably point you towards server power supplies.
     
  14. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    Looks like you've had all the advice you need.
    Ebay is a source of smps modules in small quantity, meanwell are a semi decent manufacturer of smps supplies for din rail mounting, if you want something very robust and high profile then siemens is another manufacturer, they do a range called sitop dc supplies, but they are a lot more expensive, a 24v 10a meanwell supply would be around 70 notes, siemens double or triple that.
     
  15. AnalogKid

    AnalogKid Well-Known Member

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    I like MeanWell, but I don't think they do kW.

    ak
     
  16. shortbus=

    shortbus= Well-Known Member

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    Just a hobbyist, but for something that is,
    the off the shelf makes more sense. Prevents the need to be UL approved. Which unless I'm wrong, limits the liability issues in a product.
     
  17. AnalogKid

    AnalogKid Well-Known Member

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    Good point. Depending on the intended market, full certs for a multi-kW switcher could be $10k. More for MIL.

    ak
     
    Last edited: Nov 2, 2017
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  18. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    I dont know so much about Ul, here in the Uk we have a similar blurb or CE mark, if you use a product within a product then if said product has a CE mark its makes things easier however you'd still need to document the system to state it complied, I would think your system is similar.
    If you got a siemens unit they would almost certainly be able to supply enough blurb on it to equal its weight.
     
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  19. Rich D.

    Rich D. Member

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    That is a lot of power! Would that be heat, light, microwave, or motion from a motor? Nobody asked how the power is used, but depending on its use a full-time, high-voltage, high-current supply may be expensive overkill.
    If this is an intermittent requirement with a longer resting cycle, say for only a second or less - like on an electronic flash - the input power can be much less than that and stored for rapid release when needed.
    In some instances, the power doesn't even need to be stored electrically, but in hydraulics, or in a weight or flywheel.

    Also, don't underestimate the cost of getting a product certified. Going with a certified supply can greatly reduce the development cost for some projects.
     

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