NEED HELP: Measurements and DC to DC Conversion

adam1984adam1984 Solar Expert Posts: 72 ✭✭✭✭
I also put this post in the beginners corner by mistake:

i have built a great DC generator using parts similar to that of a wind turbine. It runs great, and i am able to generate 660VDC out of the "box". it is essentially a box with 2 leads (4/0 cable) coming out. Here is my question:
I am setting it up in a hybrid system, with the "Box" taking the place of solar panels. I am thinking of using the new Xantrex 600Vdc 80A charge controller (XW mppt 80), however the max voltage is 600Vdc. So here is my dilemma. I am not sure they make resistors/potentiometers that can handle this voltage. The second problem is, since there are no 600Vdc loads i know of, i am having a hard time figuring out the wattage and current. Is there any way i can step this voltage down below 600 so it will be able to go through the XW charge controller. Basically this is a battery charger, and i am using a GVFX3648 hybrid outback inverter in this system, with a 48V bank. Or is there an easier way to have this system set up? I have the "Box" going into the XW charge controller, that running to the batteries, and the bank going to the GVFX. I just can seem to figure out how to take a current measurement without it under load, or how to find a load that can handle 600VDC. keep in mind the system isnt hooked up yet, i first need to figure out the wattage, current, and how to lower the voltage below 600Vdc. THANKS IN ADVANCE!

Comments

  • AntronXAntronX Solar Expert Posts: 462 ✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    Can you rewind your generator to output lower voltage? It would be a lot harder to make DC switching converter to handle this kind of input. You could experiment with feeding unrectified AC from your generator through power transformer to step voltage down before rectifiers. Or use 3 transformers if your source is 3 phase AC. What exactly you have in that "box" ?
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    Use a grid tie inverter that can handle 660VDC and backfeed the GVFX? Or just reduce the RPM of the generator so that the voltaje drops below 600V. As soon as you connect a load it's bound to drop a little further too.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    Your info on the generator is not very detailed. Just saying it can produce 660 vdc does not say much.

    As you say it is similar to wind turbine I assume it is a three phase PMA.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    "a box with 2 leads (4/0 cable) coming out" that produces 660 VDC?
    What is it and how does it work? 660 V with 4/0 cable? Very mysterious.
    Is it something driven by an engine, or does it produce this voltage on it's own?
  • adam1984adam1984 Solar Expert Posts: 72 ✭✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    First off thank you to everyone.
    Here is what would have been helpful if i reread my post:

    It is a 6kw 3 phase PMA ran through a rectifier to produce DC voltage of about 660Vdc.
    I do understand that lowering the RPM's will lower the voltage below the 600, which is able to go into the charge controller.
    Here is what i dont understand:
    If it is a 5kW generator, and it produces 660V, does that mean (theoretically, not taking into account losses) should have a current of 5000/660 = 7.57A?
    And also, if i lower the RPM's, am i losing more power, or should the current increase, meaning lowering the RPMs to reach 600V would give me 5000/600= 8.33A?
    Also, it does produce voltage on its own.
    Thanks again.
  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    Simple version -

    Voltage in a generator is dependent on
    # of turns of wire on rotor/armature
    RPM

    Current in a generator is dependent on
    wire gauge (size)
    motive force to spin generator
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • adam1984adam1984 Solar Expert Posts: 72 ✭✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    So am i correct in saying that since current is dependent on wire gauge, that current wont change at all with the rpms? Or is this correct:

    A 5kW generator, and it produces 660V, does that mean (theoretically, not taking into account losses) should have a current of 5000/660 = 7.57A?
    And also, if i lower the RPM's, am i losing more power, or should the current increase, meaning lowering the RPMs to reach 600V would give me 5000/600= 8.33A?
  • BB.BB. Super Moderators, Administrators Posts: 29,366 admin
    Re: NEED HELP: Measurements and DC to DC Conversion

    Unfortinatually, the answer is "it depends"... Depends on the design of the alternator and the design of the load.

    More than likely, if 7.57A is the maximum output of the alternator at X,XXX RPM, then the output current at a reduced RPM will be 7.57A or a bit less like 10% +/- (alternators usually have a fairly flat current curve once they hit a minimum RPM from what I recall).

    Here is an example of the output of a large vehicle alternator.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • adam1984adam1984 Solar Expert Posts: 72 ✭✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    Great thanks everyone. one more quick question regarding charge controllers. The XW MPPT80 can handle 600Vdc. Is there anything special about solar panels that make the charge controller function, or as long as the DC voltage and current are within the specs, does it matter whether its a generator, turbine, or pv module as the input? I ask because im not sure if a solar charge controller can work with solar panels only or wind turbines or alternators of the same dc voltage and current.
    THANKS!
  • BB.BB. Super Moderators, Administrators Posts: 29,366 admin
    Re: NEED HELP: Measurements and DC to DC Conversion

    MPPT type charge controllers are actually pretty neat... The can take a wide range of input types and output useful power to charge a battery bank...

    One of the things that has been done with the small MorningStar 15 amp MPPT charge controller (a very nice one in its own right)--They connect it to a 24 or 48 VDC battery bank and use it to efficiently charge a 12 volt (or 24 volt--but you need a 32-48 volt or greater input voltage) battery bank.

    The issue with using other sources--Such as various forms of Wind or Water turbines is that the controller tries to maximize Pmaxpower=Vmp*Imp equation--so the controller will vary the amount of current it pulls from the energy source to optimize its output (when maximum charging current is called for).

    For some devices, such as a horizontal axis wind turbine, when the charge controller needs less power (battery is fully charged), the controller will cut back to near zero current...

    For many HAWT and Hydro-Turbines, running without an electrical load can cause them to over-speed--and they can also over voltage too.

    There are a few charge controllers out there that are setup to also monitor the turbine's speed so they can add loads to prevent over-speed. The new Midnite Classic charge controller has the optional components to support this additional function...

    People here might be able to help you more if you can better describe your loading requirements for your turbine.

    The additional hardware/programming required to modulate the load so as to control turbine speed is not cheap.

    If your turbine is otherwise governable--Then you don't need those functions and can probably get use a "simpler" MPPT charge controller or a MPPT controller that has a user programmable maximum current/power output (to prevent overloading your turbine/power source).

    It is actually not a simple/easy thing to set this up and account for all of "boundary conditions"... For example with your turbine, you want, for example 7 amps at 600 volts... However, if the output voltage falls to 60 volts, the charge controller will try to draw 70 amps from your alternator.

    Obviously, a made-up worst case example--but you do have to worry about how the MPPT controller behaves vs the capability of your turbine.

    So, you have to look at the output current capabilities of the alternator, and how programmable the MPPT controller is...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • phred01phred01 Solar Expert Posts: 35
    Re: NEED HELP: Measurements and DC to DC Conversion
    adam1984 wrote: »
    First off thank you to everyone.
    Here is what would have been helpful if i reread my post:

    It is a 6kw 3 phase PMA ran through a rectifier to produce DC voltage of about 660Vdc.
    I do understand that lowering the RPM's will lower the voltage below the 600, which is able to go into the charge controller.
    Here is what i dont understand:
    If it is a 5kW generator, and it produces 660V, does that mean (theoretically, not taking into account losses) should have a current of 5000/660 = 7.57A?
    And also, if i lower the RPM's, am i losing more power, or should the current increase, meaning lowering the RPMs to reach 600V would give me 5000/600= 8.33A?
    Also, it does produce voltage on its own.
    Thanks again.
    Just a few thing to throw into the pot If u want to make a poor man's load use a series string of 6 110v globes(same wattage say 100w). Have a number of these
    & add them one @ a time so as to avoid lower resistance when the filaments are cold. Second point is if u want to reduce the voltage without rewinding the generator use 3 transformers ahead of the diodes (one on each phase). NB if u half the voltage the diodes current will double. Hope this helps
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion
    adam1984 wrote: »
    First off thank you to everyone.
    Here is what would have been helpful if i reread my post:

    It is a 6kw 3 phase PMA ran through a rectifier to produce DC voltage of about 660Vdc.
    I do understand that lowering the RPM's will lower the voltage below the 600, which is able to go into the charge controller.
    Here is what i dont understand:
    If it is a 5kW generator, and it produces 660V, does that mean (theoretically, not taking into account losses) should have a current of 5000/660 = 7.57A?
    And also, if i lower the RPM's, am i losing more power, or should the current increase, meaning lowering the RPMs to reach 600V would give me 5000/600= 8.33A?
    Also, it does produce voltage on its own.
    Thanks again.

    PMA have a complicated volt-current-rpm relationship. The 660v is likely at high rpm's with little to no load. You can get some idea of V-I-rpm from this link:

    http://www.hydrogenappliances.com/pmacurves.html

    Just guessing, if it is 660 vdc open circuit, then it probably about 120 vdc at rated load of 5kW. That would be 42 amps. The high voltage limit is based on rectifier diodes breakdown voltage rating. The high current limit is based on PMA wire diameter and current rating/heat sinking of the rectifier diodes.

    Wire in PMA should be about #8 or #10 wire gauge if you can see it through vents in case.

    At 42 amps the rectifiers will dissipate about 80 watts so they need good heatsink with good air flow across heat sink.

    A fuse should be used to prevent burning out PMA wire or diodes.

    As example, an inverter-generator, like a Honda or Yamaha, has a PMA that will produce over 300 vdc at rectifiers output with ECO off at 3800 rpm's with no load. At rated load the rectifier output drops to about 180 vdc. With ECO on and a light load the engine with reduce its rpm's to maintain about 190 vdc at rectifier output. As load is increased, the engine rpm will increase, to maintain the 190 vdc at rectifier output which is about minimum voltage necessary, with some inverter losses, to achieve the 170 volt sinewave peak by the PWM sinewave inverter.
  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion
    phred01 wrote: »
    ..... Second point is if u want to reduce the voltage without rewinding the generator use 3 transformers ahead of the diodes (one on each phase). NB if u half the voltage the diodes current will double. Hope this helps

    This is only correct with 50/60 hz If you have a wind or hydro generator, it's AC frequency is "wild" and all over the place 30 hz to 400hz or higher.
    Transformers only have a limited power band, and you can find military style transformers 50-400Hz that would work with most wild AC.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • NEOHNEOH Solar Expert Posts: 74 ✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    1) SWP does make a 3-Phase Step-Down Transformer for their High Voltage Whisper 200 & Whisper 500 Wind Turbines. So, this appears to be a viable option.

    2) 400 Hz? That seems very fast. 400hz x 60sec/min / 4 poles = 6,000 RPM. Those blades are really spinning!

    3) I do not follow the logic that: At 60 Volts (ie Low Wind Speeds and Low Power) that the MPPT Charge Controller will attempt to pull 70 amps. There simply is not 4,200 watts of wind power available at Low Speeds. This would cause the Rotor to stop rotating which would produce 0 watts (Minimum Power!) and that is exactly the opposite logic of what the MPPT would actually do. I think, the MPPT will lower its Max Power Point Target down (as voltage lowers) to about 420 watts, at 60 volts and pull only 7 amps (approx) keeping the Rotor turning - maximizing the power produced. MPPT attempts to "Walk-Up" either side of the Power Curve and stay at the Peak Point / MAX power (whatever that dynamic value currently is at the moment) and it never wants to "Walk-Down" either side of the power curve towards 0 Watts (MIN Power). I don't think the "70 amps at 60 Volts" condition will ever occur with this PMA and MPPT.
  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion
    NEOH wrote: »
    1)...
    2) 400 Hz? That seems very fast. 400hz x 60sec/min / 4 poles = 6,000 RPM. Those blades are really spinning!.....

    That's for a 4 pole alternator. 9, 12, 18, 24 are common numbers, till you know how many poles are used, best to guess safely.

    Can you have a 4 pole, 3 phase configuration ??
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • NEOHNEOH Solar Expert Posts: 74 ✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    Yep - 4 Poles per Phase x 3 Phases = 12 Coils. Very common. I think all of your numbers are Coil Counts. They are all divisible by three. Each phase only uses 1/3 of the coils therefore a 12 Coil - 3 Phase PMA has 4 Poles per Phase. Which why I used 4 to calculate the RPMs from your 400Hz Frequency. Even using 24 Coils (8 poles per phase) that computes to 3,000 RPM which is still way too fast.
  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    OK OK, it's your parts. I'm just pointing out that it's "wild" AC, and I haven't a clue what Freq it's going to hit, but, that whatever it does run, your components need to work too.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • adam1984adam1984 Solar Expert Posts: 72 ✭✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    Well im getting the charge controller next week. I was able to lower RPM's and have the voltage output at 435V. The charge controller can handle 80A and 600V. It is made for solar panels, however i am going to try running the PMA through it. Since it is DC voltage, and is stable, and obviously at 0Hz, im not sure why it would have any trouble with the solar controller. I am hoping this works, and will let you guys know what i come up with. The PMA produces its own power, however it does need an AC generator to start, but once it is running, it will produce power on its own.
    Thanks,
    Adam
  • Ralph DayRalph Day Solar Expert Posts: 886 ✭✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion

    ''The PMA produces its own power, however it does need an AC generator to start, but once it is running, it will produce power on its own.''

    Am I missing something, or does this sound like this:

    http://themagniworkreview.blogspot.com/

    Just curious. What's spinning the PMA?

    Ralph
  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    Re: NEED HELP: Measurements and DC to DC Conversion
    adam1984 wrote: »
    .....The PMA produces its own power, however it does need an AC generator to start, but once it is running, it will produce power on its own.
    Thanks,
    Adam

    Are you sure it's a PMA ? Perm Magnet and moving wire = voltage.

    INDUCTION Generators need a "tickle" to get them going, I hope someone is not pulling a fast one on you.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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