Dc to Dc generators

Discussion in 'Electrical Systems' started by John Kane, Jun 12, 2013.

  1. John Kane
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    John Kane Junior Member

    Has anybody used a dc to dc generator, I am looking at using one and would like some feedback
     
  2. jonr
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    jonr Senior Member

    I use small ones. It's like an inverter but it produces DC output. Just stay within the rated watts or amps.
     
  3. viking north
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    viking north VINLAND

    I assume it's a dc motor driving a dc generator --possibly converting a low voltage dc into a higher voltage dc, 12v to 24 or 36v or the inverse. In either case there will be( I squared R )power loss(heat) thru the copper windings so you'll end up with less power regardless.
     
  4. jehardiman
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    jehardiman Senior Member

    They are called motor-generator (M-G) sets, and can be DC-DC or AC-DC or DC-AC depending on how they are wired. Normaly they are reversible, and a Viking pointed out, they work better at higher volatges (i.e. power = I^2 R V=IR so higher voltage for power means less amprage and less loss.)

    http://en.wikipedia.org/wiki/Motor-generator
     
  5. CDK
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    CDK retired engineer

    It was called a "dynamotor" and had one rotor with double windings, each with its own collector.
    I still have one in my shed, made by ITT, for nostalgia reasons only. The specs on the faceplate say that for even Watt you put in, exactly half a watt comes out, so they are rightfully extinct now.

    DC to DC conversion is now done by chopping the DC into slices at high frequencies, feeding that to a suitable transformer and rectifying the output again. The efficiency is near 95%, maintenance is zero, savings in investment, weight and volume are huge.
     
  6. John Kane
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    John Kane Junior Member

    Sorry I was not clear. What I am looking at is a Diesel engine generator 24v-6,000w that generates a 24v current to be applied to a 24v battery bank. It is rated at 94% efficiency.
     
  7. CDK
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    CDK retired engineer

    That is a completely different animal.
    For use as a battery charger the output should be about 28V and it needs a temperature sensing input to prevent boiling in hot climates and/or small battery banks.
     
  8. John Kane
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    John Kane Junior Member

    Yes I understand it will be 28v charging and it will be feeding lithiums-lifep04. Has anybody used this system?
     
  9. CDK
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    CDK retired engineer

    A few forum members have been experimenting with LiFePO4 batteries, but not at such power levels. For propulsion, 24V is not suitable because currents (and losses) are too high to be practical. System voltages usually are between 84 and 200 V.
    My advice is to gather information about electrical propulsion systems first, then suitable batteries and chargers. The latter are quite complicated microprocessor controlled devices; these batteries require much more monitoring than lead/acid and get easily damaged.
     
  10. John Kane
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    John Kane Junior Member

    I am not looking to use this system for propulsion but to subsidies the house system. The propulsion system will be a minimum of 72v possibly up to 125v.
     
  11. CDK
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    CDK retired engineer

    So 24V it is then....
    That are 8 cells if you use the latest LiYFePO4 types, available in capacities up to 1000 Ah. Because they must be monitored both during charging and discharging, you need a controller circuit between your diesel generator and the battery bank. Grid powered chargers are commercially available, but I doubt there is an off the shelf solution for this application right now.
     

  12. jonr
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    jonr Senior Member

    The regulators on 12V truck alternators can be modified to make them output 28VDC. But be careful - these alternators may claim 250 amp capability but then overheat when doing it continuously. Plus they are more efficient at low rpms/output. So consider using two or more.
     
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