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Need PWM controller for current source to charge 48v lead acid.

Discussion in 'Electronic Design' started by Sjouke Burry, Dec 19, 2012.

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  1. Sjouke Burry

    Sjouke Burry Guest

    Why not regulate the generator to output the correct charge voltage?
    No conversion losses, only slight modifications to the
    generator control hardware.
  2. Yzordderrex

    Yzordderrex Guest


    I have a small diesel engine spinning a DC generator. I need a control chip that will take approximately 60v that generator puts out and charge the lead acid bank. Bank is 16 27M Die Hard deep cycle wired in 4x4 configuration. It is my intention to control diesel speed to give me a little headroom for charging the battery pack. I will use external mosfets to get about 50A of charging current, so just looking for the control chip.

    Any ideas would be helpful.

  3. mike

    mike Guest

    that generator puts out and charge the lead acid bank. Bank is 16 27M
    Die Hard deep cycle wired in 4x4 configuration.

    It is my intention to control diesel speed to give me a little headroom
    for charging the battery pack.

    I will use external mosfets to get about 50A of charging current, so
    just looking for the control chip.
    What's the fully charged voltage of your battery?
    Looks like you have barely enough voltage.
    Crank the engine speed down 5%. And regulate it by current
    and voltage. Probably less lossy than the best switcher
    you can build that will run off that little headroom.
    High technology is not always the best answer.

    You want to run the engine at maximum efficiency whatever
    the charge level. That may not be the same speed over
    the whole charging range.

    And it only takes 10 milliohms of cable to lose half a volt.
  4. Guest

    Gee, that's a GREAT idea. Maybe you should tell the car manufacturers
    about that. ;-)
  5. Nico Coesel

    Nico Coesel Guest

    I'd use a microcontroller. That puts everything under one software
    controlled loop. In that case it's also easy to have the diesel start
    and stop automatically.
    Running a diesel at maximum effiency is at near full power (or at
    least near maximum torque). So a switcher if most likely to provide
    the best fuel economy.
  6. linnix

    linnix Guest

    But can it be removed with no tools? If so, I would throw a fit as well. It would be open invitation for car thieves and broken windows.
  7. Guest

    Rather than have the thief take a crowbar to your dash?
  8. mike

    mike Guest

    Up to here, that statement agrees with my "understanding".

    So a switcher if most likely to provide
    The conclusion is the part I contest.
    I define efficiency as the ratio of energy imparted to the battery
    divided by the gallons of diesel fuel used.

    The switcher reduces the generator current which reduces the torque.
    It makes little sense to run at higher speed at reduced torque
    and also lose 10% in the switcher.

    This all depends on the facts presented...60V and 4 batteries in series.
    IF there are other unstated loads or considerations or...or...
    the optimal solution might be completely different.

    Best you can do is solve the problem as disclosed.

    I've given the OP the benefit of the doubt and assumed they
    know that a 48V lead acid battery doesn't charge at 48V.
  9. Yzordderrex

    Yzordderrex Guest

    I didn't want to get into too many details here - but you guys (being engineers) leave me no choice:) Thanks for all the design input, but I'm reallyall set. I'm just looking to do a 50 amp current source using a buck converter. I've been designing power conversion gear since the 70's. I find the manufacturer search engines to be a little lacking, and Digikey not muchbetter.

    The generator I believe has permanent magnets on the stator with a wound rotor and slip rings. (They sell em on Ebay for 4 or 5 hundred bucks. Peopleuse them as motors on motorcycles and lawn mowers and so forth.) I'm driving it with a Chinese diesel that is rated for 6HP. I have all set up, just have to buy the timing belt. I've geared it to run at the most efficientspeed. I will eventually charge 32 batteries when fully up and running.

    I am also doing 48vdc to 120vac converter/inverter, and PV array chargers. All this is being done in my spare time as I am General Contractor for my house that this is all going to power. Utility wanted $17k to string wiresto my house. Roof going on today and windows next week. Hopeful to be inwith some kind of electricity by the end of the year. Picked up 2kW worthof panels and the state and fed is going to kick in $2400 in rebates.

    I am in-between jobs now so a little reluctant to call my usual TI or LT reps. I've actually referred to this newsgroup as my design team on numerousoccasions. I've been hanging around here for probably 10 years and gotten a lot of good design advice.

    Thanks for all the design advice. Hope this tome has shed some light on project. Tim was the clear winner with supplying part numbers. Tim has been a very good ally over the years as well as John and some others. Thanks to all for the input - I'll be sure to follow up with my design.

  10. Mark

    Mark Guest


    I know this is true for some alternators, because most motorcycle
    charging systems work this way, a simple shunt regulator at the
    output. But I've always wondered about this. My assumption is that
    this can work only if the output Z is pretty high. In a sense the
    alternator is always loaded at it's maximum current to keep the output
    voltage down. The question is WHY would anybody design it this way.
    Seems very wasteful of power and operating the alternator at max
    current 100% of the time can't be good for the life of the windings,
    in fact burnt out alternators is a common problem on some bikes. So
    again, WHY are the designed this way?

  11. Les Cargill

    Les Cargill Guest

    Nissan offered a continuously variable transmission on the Murano.
  12. Jasen Betts

    Jasen Betts Guest

    All altenators, even ideal altenators, have an inherent current limit,
    due to the field strength limit.
    they behave like lossy current transformers.
  13. Nissan has been using Jatco CVTs in some of their models:

    I've driven a couple of them a fair bit, and they're pretty good.
    There have been some issues reported with reliability, but I've not
    seen it personally.

    Best regards,
    Spehro Pefhany
  14. Rocky

    Rocky Guest

    Maybe not US manufacturers. But these are available with CVT.
    Mercedes A & B class
    Audi A4 - possibly other Audis
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