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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

    The switcher in the VFD's I know are switching rectified line
    voltage to create 3 phase; there are thus six sets of power
    semis. The control function is to vary the frequency while
    firing the semis in sequence. The output is 3phase AC, but
    hardly sine waves.

    I can't see what that has in common with a high power multi-tens
    of KHz switcher, with a transformer suitable at the frequency &
    power level.
    While I've not repaired any VFD's, I've read a bunch of spec sheets
    while seeking one. None I saw alluded to a HF transformer.
    The UPS's I have scraped have real, 60 Hz, transformer iron.
     
  2. David Lesher

    David Lesher Guest

    We want isolation. That means a transformer. At 60 Hz, that is huge,
    but at 100 KHz, far less so.
     
  3. Joerg

    Joerg Guest

    Modified sine or the ancient six-step? That must have been a real cheapo
    VFD. The ones I dealt with had a real clean sine wave coming out. You do
    not have to buy three-phase, they also come single-phase.

    Well, it's been a while but the ones I saw had that in there. Plus a
    bridge which you'd have to disable or bypass.

    If you mean a big ferrite transformer, all the ones I looked at had those.


    Wow, those must be from the days of Fred Flintstone :)

    Fast forward 40 years and check out a modern "real" UPS in detail:

    http://www.freescale.com/files/dsp/doc/app_note/AN3113.pdf
     
  4. P E Schoen

    P E Schoen Guest

    "David Lesher" wrote in message
    There is another thread where someone showed a 3kW charger. Here are the
    specs:
    http://www.ev-power.cz/docs/GWL-Power-POW-PFC_1-8kW-Spec.pdf

    The thread is:
    http://www.diyelectriccar.com/forum...ion-vw-polo-ac-industrial-motor-78701p12.html

    Meanwell makes battery chargers up to 1000W standard, and possibly up to
    3000W special:
    http://www.meanwell.com/product/inverter/inverter02_2.html

    Maybe you can use three chargers.

    Paul
     
  5. Joerg

    Joerg Guest

    Not necessarily. I just sim'd another converter, a step-up to 28V.
    Including magnetics losses it clocks in at slightly above 97%. When the
    boards come back they are usually about where the sim said.

    I still think Mike Engelhardt should get a Nobel prize for LTSpice.
     
  6. Guest

    I've actually done this to charge a traction battery pack. The only
    difference was that instead of a stepper motor, a student kept an eye on
    the multimeter and cranked the Variac down as the battery charged up.
    Works fine, if a bit labor-intensive.
    Zivan makes exactly what you need, if you don't mind buying the charge
    controller and power supply all packaged into one unit. If you want to
    roll your own controller, Sorensen probably makes what you need for the
    power supply.
    I just remembered another manufacturer of telecom-type supplies, Valere.
    Same problem as you have now, though; for most of their products, the
    world ends at 54 V. They do have a few that are available in 125 V DC
    output; they are the style where you buy a shelf and then buy modules
    to plug into it. Usually you can get some kind of data bus to the
    shelf.
    Watchdog timer driving the I/O pin that goes to the big contactor?
    Yow! At cell voltages of popular chemistries, and a 120 V pack, you've
    got somewhere between about 33 and 100 cells, or $4,455 to $13,500 in
    all.

    Matt Roberds
     
  7. David Lesher

    David Lesher Guest

    With a selenium stack? I hope not...
    But we don't want to blow oogobs of $$ on fullpriced new...
    The 750W ones are $30 each, so we can tolerate some design pain
    at that delta-$
    Not the BIG contactor; charge isolation one.
    It's on the lower end but still the biggest investment...
     
  8. Guest

    No, just a plain old square brick rectifier bridge with Si diodes,
    something like 600 V, 35 A. I found a piece of random sheet metal lying
    around the shop and bolted the bridge to that for a heatsink. Heat sink
    grease was in short supply, so we used a little wheel bearing grease
    instead. Worked fine, if a bit greasy-smelling when warm.
    Understood. I was trying to supply some brand names that might be good
    keywords for Ebay, Craigslist, etc.
    Are the outputs full floating? You could *try* stacking three of them,
    but as mentioned elsethread, that's generally a bit of a gamble with
    switchers.

    Matt Roberds
     
  9. Jasen Betts

    Jasen Betts Guest

    I've got an 3 year old one here with a 50Hz transformer.
    the device weighs about as much in iron and copper as it does
    in lead. the badge says "Dyn-a-mix" which is the importer's
    mark.

    It's just a little one. 1200VA output, 230Wh of battery.
     
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