Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Upgrading a 12V Alternator to Produce a higher output Volts

  1. Jun 26, 2015 #1
    Hi could anyone please help with this:-
    I have a 12V 90Ah automobile alternator.
    is there a way to increase the output volts beyond the 14/13.8v to say 192v?
  2. jcsd
  3. Jun 26, 2015 #2
    How much power and what "quality" of the assembly and the requlation of the 192V, full time use - etc... The down and dirty way for 100-200 W is to buy a car inverter and then a simple rectifier will give ~160Vdc -- a transformer between the Inverter and rectifier could provide higher voltages. So we would need more details of what you are trying to do.
  4. Jun 26, 2015 #3
    Step up transformer? Turn ratio about 16.
  5. Jun 26, 2015 #4


    User Avatar

    Staff: Mentor

    I pinged the OP to see if that's maybe a typo, and should be 19.2V...
  6. Jun 26, 2015 #5

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    think about your basics

    voltage is rate of change of flux
    which is in proportion to RPM
    and its field will make enough flux to produce 15 volts at idle.

    192/15 = around 13

    so you could spin it 13X idle RPM if it'll stay together...
    or you could rewind it with more turns

    try a search on
    lundell alternator high voltage

    here's a couple of my early hits



    remember your car alternator is a three phase machne

    so that suggestion of an external transformer isn't bad.
    A military surplus three phase 400 hz transformer and reasonable RPM sounds plausible to me.
    Last edited: Jun 26, 2015
  7. Jun 26, 2015 #6
    Since he do not post AC or DC -- 13.6 and 14V are the typical DC Voltages - what is an alternators typical V before the rectifier (IDK) ?
  8. Jun 26, 2015 #7
    This post is incredibly vague.
  9. Jun 26, 2015 #8
    Hi there,

    no not a typo.
    I need to generate enough power to charge an array of 16x12V DC deep cycle batteries(192v connected in series 120AH)
  10. Jun 26, 2015 #9
    I have an array of 16x12vDC batteries connected in series giving me my 192vDC required for my power unit.
    as I am off the grid, I need to find a mechanism to charge these batteries as I have no AC to use an AC charger. Hence was toying with the idea of using a vehicle alternator.
    load would vary but would never be at 100% as I have built in a 25% reserve using a 30KW inverter drawing its source from the DC array.
  11. Jun 26, 2015 #10

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    a sinewave clipped at Vout + a couple diode drops

    found this on youtube

    a fellow running one at ~30 volts for a HHO generator


    as you can see it's capable of substantially more voltage, how high would the peak be ?
    Last edited: Jun 26, 2015
  12. Jun 26, 2015 #11

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    you'll want a higher voltage rectifier pack

    the stator iron will get hot at that flux level and frequency
    and you'll not get full 90 amp output current

    you'll have to experiment
  13. Jun 26, 2015 #12
    please can you give me more info on this.
    I am assuming that I can use a 12vDC alternator with a step up transformer to provide my 192vDC?
  14. Jun 26, 2015 #13
    The max. power being generated by your alternator is constant. You can play with the voltage at the expense of current. So charging time will be quite high.
  15. Jun 26, 2015 #14
    OK more info helps... first the string of 16 batteries is not a small investment and if not charged properly you will shorten their life - so IMO I can not see the logic in trying to do this on the cheap. If they are 12V Lead Acid - they will need to be charged at 13.6-14 VDC each x 16... 224 V ! - so a commercial purpose built charger would be better. - Are you going to use the alternator - while in the vehicle? Or some alternate mechanical source? - how will this be controlled. The alternator has a limit of ~ 1KW, - so you will max out at 5A charging current.
    There are a number of other ways to address this - I am guessing you already have the AC inverter to go from the batteries to your "house" - if not I would parallel the beatteries, allows charging direct and there are a number of cheap 12 VDC to 120VAC inverters. This is a good case for solar - due to the cost of running an engine.
  16. Jun 26, 2015 #15
    I have the inverter and the battery bank. I also have an AC motor running at 2800rpm .375kw (on a separate circuit drawing from the power provided by the inverter) to drive my Alternator. I also have a comparator under and over voltage control unit that starts and stops the AC motor.
    your plan for a commercially built charger has given me an idea. I will invest in a smaller inverter at minimal cost say a 3kw unit which will then be powered by a separate 12vDC battery connected to the alternator. This inverter will then provide AC to the commercial AC charger which will then provide the charge needed for the primary array.
  17. Jun 26, 2015 #16
    Huh? As I read this you have Battery -> Inverter -> AC Motor -> Alternator -> Back to the Battery? -- Regardless - if the alternator is 90A - you only need a 1000W Continuous inverter ( be sure to look for continuous rating - many vehicle inverters are rated for peak.)
  18. Jun 26, 2015 #17
    will do so. thank you and all others who commented. it is appreciated.
  19. Jun 26, 2015 #18

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    Why stop there ? Keep going and run the whole US power grid from your single 12v battery.... oh i forgot you're off grid....

    Are you aware just what you have written ? Surely it is not what you are thinking ?
  20. Jun 26, 2015 #19
    Haha is this a perpetual motion machine we are talking about?
  21. Jun 26, 2015 #20
    Not sure I understand you.
    this is what I have in place already:-
    30kw inverter receiving input from 192v battery array. this feeds my home with 30kw of AC 220v power.
    I then have on a separate circuit my 220v AC motor which drives my 12vDC 90ah alternator. I need this to re-charge my batteries, hence the thread,
    based on suggestions from Windadct, a secondary circuit with a separate inverter will power up a commercial AC charger which will charge my 16 batteries.
    my single battery is required to power the second inverter only.
    am I missing something. all circuits are separate.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Upgrading a 12V Alternator to Produce a higher output Volts
  1. Alternator output (Replies: 16)