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I'm in over my head, would someone kinly throw me a life ring?

Discussion in 'Electronic Basics' started by Greg Postma, Apr 28, 2005.

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  1. Greg Postma

    Greg Postma Guest

    I don't know enough about electronics/electicity to know if I am in the
    correct place to seek some help, but if not, please pardon my intrusion.

    In the past, I have help clients locate many diverse (read obscure)
    devices,products, vendors, technologies,etc.......

    Today,I was asked by a client to help him find an inverter that would
    convert a 76vDc input to a 110vAc out put. The current draw would be
    about 500ma. I know just enough about electricity to know what an
    inverter does, but I've never sourced them before. Thie client has an
    EAU of 3-5000 units. I've googled (76vdc invert,etc) and found great
    sources for inverters to run the coffemanker while you are driving,
    however the device I seek has not been found.
  2. Did you find this one?

  3. Norman Webb

    Norman Webb Guest

    Intrigues me what situation would use 76Vdc (not a multiple of 6, 12, 24
    Is it possible to tap a lower DC voltage and use an off the shelf 12vdc to
    110vac inverter.


    Greg Postma wrote in message ...
  4. Greg Postma

    Greg Postma Guest

    Ya know, the numbers didn't add up, (but what do I know) so after dinner
    I called the guy to get more information. The source of the DC power is
    6-12v batteries (in series) so the voltage could be anywhere from 72vDC
    (6x12) up to 79.2vDC (6x13.2). He picked 76 volts "cuz it's in the middle".

    So knowing what I now know, I'm looking for an inverter that can handle
    72-79.2vDC input and 110vAC output. The output current will be about 10
    amps @ 110vAC. I hope this cleared this matter up.

    Some times a client will ask me for a mouse, so I find him a mouse, ship
    him a mouse, bill him for a mouse and then I get a nasty email calling
    me names, telling me that I shipped the smallest moose the client has
    ever seen. I guess today,I've been looking for mouse when the client
    wanted a moose.
  5. Greg Postma

    Greg Postma Guest

  6. John Smith

    John Smith Guest

    You said "The current draw would be about 500ma. " and now you're saying
    "The output current will be about 10 amps @ 110vAC.". This obviously
    doesn't add up.

    Besides your spec being ambiguous, just do as others have suggested, and use
    one of those 12v batteries: why go from 72V?
  7. John G

    John G Guest

    There was a thread not long ago similar to this.
    Is it a need to boil a coffee pot in a train engine that prompts this
  8. John Smith

    John Smith Guest

    Then go back to steam engines, and just use the fire :)
  9. Greg Postma

    Greg Postma Guest


    The device I seek is not for me. One of my clients (who has employed my
    services many times in the past) asked me to find a source for an
    inverter using 76Vdc in and 110Vac out. He said he would need about
    500ma. I sent my first plea for help shortly after I spoke with him.
    In my second post, I said "Ya know, the numbers didn't add up, (but what
    do I know) so after dinner I called the guy to get more information. The
    source of the DC power is 6-12v batteries (in series) so the voltage
    could be anywhere from 72vDC (6x12) up to 79.2vDC (6x13.2). He picked 76
    volts "cuz it's in the middle". After speaking with him,and offering the
    same suggestion I received "Just grab 12vDc off one of the batteries and
    use a commercial inverter" I was informed that the ONLY source of power
    was the 72Vdc. There is no access to any other power.

    So.... here we are. I'm still looking for a source of an inverter to go
    from 72vDc to 110vAc at about 10 amps. As for the location of where this
    is to used, I've got no idea. Could be for making coffee in a locomotive
    or powering a microwave oven in the space shuttle for all I know. I
    really don't know or care what my clients do with the products I locate,
    design or manufacture. Like wise, I don't care what they do with
    information I provide when I am doing basic research..... It's really
    nunna my business.....

    Hope I didn't sound ungrateful for the suggestions made by the group and
    I also hope that I didn't sound snobbish or boorish. I just thought
    that this project would be simple and it is starting to seem like the
    wheel has to be re-invented<g>.

    So if any of you kind, bright, energetic, good looking folks have any
    ideas that might help locate this elusive "grail" I would be most thankful.

  10. John Fields

    John Fields Guest

  11. Greg Postma

    Greg Postma Guest

    John, You are correct, originally I asked for 500mA and then after
    further questioning of my client, I learned that he misspoke. His
    initial request for 500mA will not meet the needs of his project. After
    discussion, he informed me that his needs are more like 5-6 amps and I
    made the call for 10amps as a safety factor.

    So the requirements for the device are nominal 72vDc in, nominal 110vAc
    60hertz out, with a capacity of 10amps out. I hope that this clarifies
    the needs of this project.

    Thanks for your patience
  12. John Fields

    John Fields Guest

    Almost. Does he need a sinewave output or can he settle for a modified
    sinewave or a square wave?

    Also, and I apologize for not asking earlier, does your client have
    efficiency constraints?
  13. Wayne

    Wayne Guest

    Another "gotcha" to consider. You should also find out if the DC supply
    (battery bank) is big enough to power your inverter for the required amount
    of time, whatever that is. This is a simplified version of a more
    complicated question, but you need to know how long the AC device will
    demand current. If the load is 1 Amp for 24 hours, this requires a minimum
    24 Amp-hour set of batteries. In this scenario, 12 Amp-hour batteries would
    not hold enough charge to power the system for the required time.
  14. Rich Grise

    Rich Grise Guest

    Then either:
    A: Hack the coffee pot to run off 72-79VDC
    B: Get three more 12V batteries, put them in series, and in series
    with the 72V, for 108-120 VDC and run the coffeepot on DC.

  15. Greg Postma

    Greg Postma Guest

    Ya know, I think I like this group<G>
    Very Innovative thinking........
    I mentioned this idea to my client and after he stopped laughing like
    fool, he said he thought that I'd come up with a solution like a 3000
    milealong extension cord.....
    But I like your idea better Rich
  16. Would it be possible to tab in between the battery pile and use a
    standard 12 or 24 V converter. Probably a lot cheaper than something
    crafted for a specific application.

    In addition, 10 A at 110 V is quite a bit of power to sustain from batts
    for any length of time. Even with 76 V input, taking into account the
    inevitable losses (converters usually have efficiencies of 70-80%), he
    will load the battery with almost 20 A. Your client will need rather
    large batts and thick cable, too.
  17. Rich Grise

    Rich Grise Guest

    It's a train.

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