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Seeking: ~120V DC 20A supply

Discussion in 'Electronic Components' started by David Lesher, Nov 4, 2012.

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  1. David Lesher

    David Lesher Guest

    Three of us are working on an electric car conversion. We're
    now working on the "home" charger for it. For that, we are
    seeking a digitally controllable switcher supply with ~120V
    output, at up to 20-30A. At these power levels, 240VAC supply is
    more likely.

    Obviously new this will be $$$$, but I wonder if anyone knows of
    a surplus candidate.

    We currently ^H^H^H presently have a 48V 750W supply with remote
    sense but would prefer something the charge controller can
    directly manage [We now use a D-A to fake the sense input into
    giving us our desired output...] as well as being able to charge
    the whole string at once.

    {Question: If you have 3 EE's is that 6E, or (EE)^3?}
  2. John S

    John S Guest

    That's beside the point. Can you help with the requirement?
  3. David Lesher

    David Lesher Guest

    We want to *build* an electric car for the same reason people
    enter the NYC Marathon, walk on the Serengeti, go to the Moon,
    and many other challenges.

    There are many people who may buy one; that holds no interest
    to us. As engineers who alas seldom get to actually create, we
    decided to do just that.
  4. Joerg

    Joerg Guest

    A good candidate might be a multi-kilowatt VF drive and then hack it.
    Sometimes called VFD, other times just "drive". Even big ones have
    become quite inexpensive. They come for inputs of 120VAC, 207VAC,
    230VAC, 240VAC, 277VAC, and so on. You'd have to remove or disable the
    bridge at the oupt so you get DC, and then also hack the control
    circuitry so it doesn't scribe a sine.

    Another good candidate could be a huge UPS. One of those server room
    versions. There are companies that routinely switch them out almost like
    the batteries, one of the reasons being (like with VF drives) that the
    electrolytics in there have a finite life span. This would also need to
    be hacked.

    Afraid there is no market for what you are looking for, so not likely
    surplus gear. What's wrong with faking signals for the sense lines? I do
    that all the time.

    For a loner type nerd that would be a crowd :)
  5. Jamie

    Jamie Guest

    I think if you are going to work with that level of voltage you should
    incorporate some sort of ground fault sensor to terminate the output
    immediately if some one comes in contact with it, even if it is floating.

    It does not take much to stop the heart.

  6. mike

    mike Guest

    Presumably, you have a high-current variable supply to run
    the motor. Can you stick in a relay to flip it around
    to take rectified line input and charge the battery?
    3 EE's are useless. It's like having three watches.
    One watch and you know what time it is. Three and you're never
    quite sure. They can't agree on anything.
  7. Xantrex and Sorensen (now ametek) made exactly the sort of monster power
    supplies you need. I think xantrex dropped out of the power supply
    business, but the tiny bench ones were just rebadged units from the TTI,
    in the UK.

    check test equipment dealers. The really old sorensen stuff will be 1980s
    goofy linear power supplies with SCR preregulation. Those will be giant,
    and probably stuffed with obsolete parts. The newer ones are real
    switching power supplies.
  8. tm

    tm Guest

    What kind of regulation do you need? Current limiting? 120 volts at 30 amps
    is 3600 watts at the load. The input power will be higher, say 20% higher.

    That is definitely 240 volt territory. You are looking at inverter welder
  9. Guest

    Followups set to sci.electronics.components.

    Isolation transformer, Variac, bridge rectifier, stepper motor?

    The real classic way is a phase angle dimmer made of a a bridge
    rectifier followed by an SCR; turn the SCR on sooner in the half-cycle
    for more current. Use a microcontroller to pick the turn-on point and
    you have a digital input. (You could argue that this is a switching
    supply, but it isn't what is normally meant by "switching".)
    The power supplies I have used in the past with this kind of juice have
    been from Sorensen (formerly a tentacle of Raytheon, now owned by
    somebody named Ametek) and Zivan (an Italian company with US sales).
    The Sorensen ones are general-purpose supplies and are usually available
    with both front-panel knobs and remote control. Zivan makes ones that
    are specifcially designed to be battery chargers for traction
    applications; the controller is already built in. I don't think the
    Zivan had any kind of data bus; it did have a few discrete inputs and
    outputs for things like start/stop, status, and remote sense. It came
    with a temperature sensor you could put somewhere in your pack to both
    tailor the charge rate and act as a safety. It also had a blinkenlight
    to indicate charge states and problems.

    One Sorensen supply I used had to send about 48 V at 10 A down several
    hundred feet of wire to some DC-DC converter bricks that output 5 V and
    12 V. Something in this setup broke the regulation in the Sorensen; it
    would still put out something but it wasn't related to where the knobs
    were. At least they fixed it reasonably quickly under warranty, and
    the repaired unit seemed to work OK. I think it had a data bus, but in
    the prototype stage, the operator just tweaked the front-panel knobs to
    get "enough" input voltage at the DC-DC bricks.

    The Zivan charger I used did just fine at charging a series string of
    twelve 12 V lead-acid batteries (144 V), but for some reason, had a
    high leakage to ground on the AC input. It would sometimes pop GFCI
    outlets or breakers, even when everything was otherwise sound. Non-GFCI
    outlets/breakers were fine. Other people who had used Zivan chargers
    reported similar problems. I suspect it may have been designed to a
    European standard that allows higher leakage current.

    I have seen Sorensen power supplies show up at used and surplus
    electronics dealers. A Zivan probably won't show up used in these
    places, but a group of electric car home-brewers might be a good place
    to look. Both are available new, which might help set an upper bound
    on time or money for a home-made solution.

    Some other random things that you probably have already thought of:

    Put a simple (maybe electromechanical?) timer somewhere to shut off the
    charger as a last ditch defense against overcharge... it depends on the
    pack size, but if you haven't gotten the battery charged in (say) 8
    hours, you're probably not going to. This is more important with a
    home-made charger; commercial chargers often have something like this

    Give a little thought to interlocking the charger power (AC input must
    go away before DC output can be disconnected), or select a charge plug
    that can stand being disconnected under load. Also, interlock the
    "ignition" of the car and the charger input... the first electric car
    charger probably got dragged down the street a few days after the first
    electric car was invented. The "ignition" interlock also helps prevent
    overloading the charger by trying to run the drive motor while the
    charger is connected.
    A really wide shoe?

    Matt Roberds
  10. One and one half pairs of double Es.

    No apostrophe needed where this one is.
  11. David Lesher

    David Lesher Guest

    That does not leave much left now, does it?

    Not what we have in mind. We need a switcher supply.
  12. David Lesher

    David Lesher Guest

    Hardly, the motor controller deals in hundreds of amps, more at
    peak. Further, we'd have to run its cooling pump. And a relay
    to switch the output? Huge.
  13. David Lesher

    David Lesher Guest

    Yes, current limit. But that term basically describes the
    control input; power supplies limit output, and the consequence
    reduces both voltage and current furnished to the load.
  14. David Lesher

    David Lesher Guest

    As you should. You should have said "Selenium bridge rectifier..."`

    It sounds like no one has seen what we need; and/or the 750W 48V max
    supplies are not that bad after all.
    There is a separate charging controller processor. It has lots
    of AD inputs and measures every cell while charging. If any cell
    gets too high in voltage, or too warm; charging terminates with
    an error report. At $135/cell, you do not want to cook any.
    There are numerous interlocks, both hardware & software.....
  15. P E Schoen

    P E Schoen Guest

    "David Lesher" wrote in message
    You might want to read this thread, and I have several posts as PStechPaul:

    It is an open source design so you might be able to scale it down for your
    smaller needs. There have been many suggestions and ideas thrown around. If
    you are not too concerned about power factor, a simple full wave bridge
    might be OK, and if you need a higher voltage, a doubler circuit may be the
    way to go. If you do not mind having high ripple content, you could dispense
    with a capacitor filter (which causes poor power factor), and use the raw
    rectified output. Then you can make a simple buck converter that will
    regulate the portion of the waveform above the battery voltage for charging.

    Good luck on your electric car. All we need is a major advance in battery
    technology or some other small efficient means of converting or storing
    energy, and they will be very cost effective and "environmentally friendly".

  16. amdx

    amdx Guest

    You should ask about this on the electric car forum.

  17. Joerg

    Joerg Guest

    I assume temperature is the #1 culprit. It gets quite toasty in those
    boxes and they save every penny because the market is so tough since
    China entered it.

    Then there is always the question what quality grade of capacitor they
    have put in.
  18. Joerg

    Joerg Guest

    Sure it does. You have a big fat switcher that can be precisely
    controlled and you don't have to stack several telco switchers. Stacking
    switchers is always a white-knuckle scenario.

    The control circuitry is easy, what's difficult are the ferrite
    transformer, the big semiconductors and the layout (for good EMC). The
    latter are all done. I don't think you will find the perfect solution
    with your desired control gear on a silver platter for this job.

    UPS and VFDs _are_ switching supplies. For the UPS kind you just have to
    make sure that it is a true power conditioner type and can work sans
  19. David Lesher

    David Lesher Guest

    Looking at the page, I've not found
    the circuit description or schematics.

    From reading mentions of GFCI's, it sounds like this design is
    not isolated. We have debated that issue, and for now at least,
    we want isolation.

    I don't know if the other 2 folks have seen the thread, but I
    will point it out to them.
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