High amperage voltage converter - possible?

Discussion in 'The Projects Forum' started by RogueRose, Jun 14, 2015.

  1. RogueRose

    Thread Starter Member

    Oct 10, 2014
    189
    4
    I need to make an adjustable voltage controller that is capable of delivering high current for peaks of maybe 3-5 seconds. The supply voltage is from a LiPo pack of whatever voltage is best for this project so we are looking at multiples of 3.7 (7.4 - 11.1 - 14.8 - 18.5 - 22.2 - 25.9 - 29.6) Voltage needed is 12 - 20 (but ideally 7.8 to 26.5 if that is possible). Current draw is really difficult to determine as differnet applications require more/less current. Many apps are in the 15-25 range while others are 35-50 maybe sometimes hitting 60-65 for short peaks.

    Is this project possible with these kinds of current demands?










    i
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,767
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    Is it acceptable for the supply voltage for any application to 'sag' (say, from 12V to 10V) during the 5 sec period? Or must it be closely regulated at a fixed voltage? The former might be manageable with a capacitor bank; whereas the latter would likely require an expensive solution.
     
  3. RogueRose

    Thread Starter Member

    Oct 10, 2014
    189
    4
    I would suspect that most applications will be fine with a voltage sag. This will be used with power tools and some other motor driven appliications if that helps figure out what is needed.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Hmm, after checking out supercap prices it looks like a capacitor bank solution would be more expensive than just using a big array of LiPo batteries. There are, of course, safety issues with using such an array (i.e controlling charge and discharge rates/voltages and cell balancing).
     
  5. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    One area this hits is an electronic load: This http://www.testequipmentdepot.com/b...tm?ref=gbase&gclid=CP3C1buPksYCFcMSHwod1kAAsA is one such example. 60 V, 30A

    e.g.( 240 A, 150 V) http://www.dc-electronic-load.com/Maynuo-M9717-DC-Electronic-Load,3.6kW,240A,150V-p08169607.html

    Electronic loads have applications testing batteries, so it may be of more use to you.

    Certain specially designed power supplies have the ability to do what's called series/parallel operation, so you can double the voltage or double the current of two IDENTICAL power supplies.
     
    Last edited: Jun 15, 2015
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,515
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    That, and the caps are good for zillions of charge/discharge cycles. They are on transit buses because they work (and because the bus has a ton of room). Your OP has a wide range of output requirements. Taking one set of values, 65 A x 20 V x 5 s = 6500 W-s. To have a constant voltage during the output pulse, one approach is a large capacitor bank charged up to some higher voltage, and it discharges into an output regulator. The higher the peak capacitor voltage, the smaller the amount of capacitance needed.

    The total energy in a capacitor (in watt-seconds) is 1/2CV^2, one-half capacitance times the square of the voltage. So a capacitor array charged up to 50 V and discharging down to 25 V (5 V output regulator headroom) over 5 seconds equals:

    .5xCx2500 - .5xCx625 = 937.5 x C

    For 6500 W-s, you need 6500/937.5 = 6.933 F. 7 farads at 50 V is a large capacitor array, but it can be built with catalog-standard parts for about $175 from Digi-Key.

    ak
     
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