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6kw solar design from used equipment design.

Discussion in 'Power Electronics' started by Engineer_Paul, Aug 23, 2018.

  1. Engineer_Paul

    Engineer_Paul

    8
    0
    Sep 5, 2017
    I have some new parts and used parts. I have a background in CNC, control systems, but only fixing drives not much in the way of building from parts. I am thinking of designing a MPPT charger, and having it automatically determine the best point from measurements instead of me programming that point. I am looking at using something such as audrino or pi zero for that, as it does not need too much to test and calculate the max power point. The using something such as an IGBT for the switching element to take the output from the panels and convert it to the proper charging voltage. Then I am not sure if I want to try 48v or 120v for the batteries, as I know (20) 6v in series will be 120v, but that brings up a few other things that few mention. One is how does voltage equalization work, as there are devices available to equalize 4 batteries in series and they are cheap. However I don't know if they are any good. Also in another thread someone was talking about using 120vdc to 120vac that is easy to do with a simple switching and regulator module that outputs 4 signals and reads the output voltage such as ( DC-AC pure sine wave inverter SPWM board EGS002 EG8010 + IR2110) as can be found on ebay, and there are sample circuits on their website if you want to go with 370vdc and direct filtering of the output, or use a transformer and a lower voltage along with some MOSFET's in groups of 4 in the H bridge circuit. I was thinking of just getting a used transformer if I am going to do that and rewind so it will have a lower voltage primary. Also multiple primary windings or even water cooled if not enough room and just use copper tubing that is covered with an insulated braid.

    Just in case there are others using this post to help their own project I will mention that water cooled with a flow switch can easily take a 3/8 copper tube and make a conductor that can easily handle 400amps or more continuously. I say this because it heats up slightly with 500amps going through it from experience. Also in high power control IGBT's are often used such as in welding and submerged arc supplies as opposed to the hockey puck SCR's of the past. The SCR's work with AC input and IGBT's MOSFET's and so forth can easily convert DC to AC at moderate frequencies at a few KW to about 200KW.

    What I am not sure of us how to balance charging voltage on a number of batteries in series without wasting power. I was thinking of a voltage comparator for each battery voltage, and reference it to the overall voltage. If more than 1/n it should draw power from that section and put it to the overall voltage, if that one voltage is less than 1/n it would take the total voltage and charge that one section at a faster rate. I wonder if there are any better ways, such as using a transformer with a winding for each battery and a bridge rectifier to each battery. Then all would be forced to be the same, as this is the same way that all computer power supplies work. They reference one voltage and all of the others track according to that one output voltage.

    A few cautions for anyone that might also be thinking of this, and that is a safe inverter is one that has a transformer between the input and output for isolation. Even if grounded at one point, the possibility of DC getting out to a motor is a very costly mistake and also possibly deadly. Other thing is to use fuses and interlocks for safety not only of people, but to protect the equipment. I have seen what it looks like when a transformer shorts on 480v 3 phase, and if it happened in a home and not an open area chances are people will die from the smoke, sparks and flames. Also I have seen what 1000Amps at 200volts does it burns through inches of steel, so going without protection for yourself, others and the equipment is asking for problems. These things were from plasma arc cutting, and the 1000amp was when one of the (3) 4/0 cables somehow became pinched in a cable carrier. I fixed these and many other problems over the years of machine service in Southern California, Arizona, Mexico, and even other parts of California.

    I see no problem re purposing transformers to other usages as new ones are quite expensive and more so if custom. Also just because something was once used to generate RF power does not mean that it can't be changed to make AC power from DC power, just have to apply proper filtering.
     
  2. Bluejets

    Bluejets

    3,517
    713
    Oct 5, 2014
    mmmmm....
     
  3. kellys_eye

    kellys_eye

    4,281
    1,144
    Jun 25, 2010
    seconded
     
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