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MPPT charge controller

Discussion in 'Power Electronics' started by juliantech5, Jul 3, 2018.

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  1. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    They are both options. I'm not familiar enough with these devices or your detailed requirements to be able to choose between them.

    That's because switching regulators have a theoretical maximum efficiency of 100% (voltage in * current in = voltage out * current out, noting that current in will differ from current out) and there are a variety of issues (aside from quiescent current) which introduce losses. In comparison, the efficiency of a linear regulator is essentially determined by the inverse of the ratio between the input and output voltages.

    As an example, a switch mode regulator could require 10V at 100mA in order to drive a load of 5V at 180mA. The efficiency requires you compare the input and output power, and in this case you'll get 90%. That extra 10% is lost in various forms which don't help the regulation.

    An equivalent linear regulator would require 10V at 180mA to supply 5V at 180mA. The efficiency is 50%. In this case any losses in the regulator cause part of the losses we know we are causing anyway.

    BTW, both examples ignored any power need to actually operate the regulator.

    As long as you're not getting your power from a solar panel, these regulators are probably fine to operate a circuit from a lower voltage. However, they're probably not ideal to charge a battery (although, for a single charge cycle, you could do it).
  2. juliantech5


    Jul 3, 2018
    Ah ok, looking at the datasheet it seems to do the job with some extra legroom regarding minimum voltages and mA. Do you know anyone experienced in circuit design for this sort of devices? Thanks
  3. Engineer_Paul


    Sep 5, 2017
    Interesting, and I will say that it takes some engineering to do it, and there are many factors that work in a vacuum that do not need to be considered here on earth. #1 is cooling, as the only way to cool in space is by radiation or conduction to a cooling unit. Then there is the radiation that causes electronics to not perform as expected. One thing it does is turn things on when you are telling them to turn off with a pull down.

    As for your circuit it needs to be many different things. That is because it is not practical to get 3.3 volts from a 3.7 v battery, so that voltage will need to be boosted to at least 8volts then can be regulated back to 3.3 with a buck converter. Next is the charging it is required that the batteries can handle a vacuum, and the temperature range. There are off the shelf IC's that can do the battery management, and that will need to be driven by another converter that takes the solar output and makes the voltage compatible with the battery management.

    I would not think of using standard lithium batteries for space application, as they need cooling and other things that will cause them to fail. Keep in mind Boeing had battery failures on one of their latest jets because of this cooling issue.

    About me I have worked as an engineer in machine design, and have worked with vacuum equipment. One of the things I have done is air cool motors in a vacuum chamber for robotic motion. Built the control system, and made the whole system work. I just did not do the layout or welding on the chamber or plumbing for the vacuum. I did all the water, air, and gasses, plasma torch and controls. At the moment I am not able to work full time, and can't do much physical work due to back and other problems. My guess is that you might be working for some place such as Space X that hires people without lots of experience that is still quite young. I do find it interesting to see 3 or more that have a hard time with things that are quite basic. I know this because I have seen and talked to them when I was working on a project to do some work on some satellite parts for Aerojet. I have the experience to do things quickly and I am older, but younger don't know the materials and how things in the natural world work, but have the ability to do physical things that people like myself can't do anymore.

    Most important for you right now is having a vacuum chamber to do testing with wires going to the outside to simulate the power from the panels, and a load that needs to be something such as a resistor bank outside the vacuum. Less than that and you will not have a clue even with a FLIR to know what will happen when the thing starts working for the first time. I know how to use computer programs for simulation, but they only do a fraction of what is needed to make this one fly.
  4. juliantech5


    Jul 3, 2018
    Hey Paul, Interesting.
    Quite a bit has happened since I wrote that post back in the day, I was actually doing the project on my own out of curiosity and general aerospace interest, posted on some other forums and now we are a couple people working on software, hardware, marketing and such.
    You can find more information at our website and our github though we already have a working prototype satellite that is undergoing testing, managed to design all the systems with a little more research. If you'd like to help in any aspect we are completely open source and appreciate all support.
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