Electronics > Power/Renewable Energy/EV's

Open Source MPPT Solar Charge Controller- Wifi enabled

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evjim:
Hi, I am working on an open source solar charge controller using the TI SM72442 IC. I am designing for a 100VDC maximum open circuit input and a 65 amp current limit. It can charge batteries from 12 to 48 volts. It will incorporate the ESP8266 wifi chip for remote status view and programming.

I originally started this project using the BQ24650 because it is an all in one chip for MPPT. It does not need a separate H bridge driver. But it is limited to 30volts open circuit and cannot communicate with a microcontroller. The SM72442 has I2C and readable registers that show the status of Vin, Vout, Iin, & Iout. Most often solar charge controllers are located in a not so commonly accessed area. So the homeowner may not know the battery state of charge is low or there is an error. Having wifi connectivity allows the user to more easily monitor the system.

I'm working on the project in KiCad. It is my first project in KiCad as I usually use a closed source EDA tool.
Here is my github page of the project:  https://github.com/junglejim8/opensolar
Would be cool to get feedback or collaborators.
The schematic is nearly complete, I am working on the BOM, will move to layout in a week or so.

Question:
-I am trying to source an inductor for the project. It must be at least 0.8uH, But Ideally more like 3-10uH to keep input and output capacitance values lower. The design documents allow for a 60% peak to peak ripple current. So I need to find a power inductor with Irms 65 and Isat >85amps. I like coilcraft because they have interactive tools for predicting inductor temperature. But unfortunately none of their inductors offer this current rating for prolonged use.

Can I reliably parallel power inductors to double the current? If I use two of the same part will they share current equally?

Codebird:

--- Quote ---Can I reliably parallel power inductors to double the current? If I use two of the same part will they share current equally?
--- End quote ---

No. They are low resistance parts, at least the good ones, so a variation of even less than an ohm could result in seriously unequal sharing. Remember that at low load, when you aren't drawing enough current to bring the panels down to MPPT, your buck converter is going to be continually on - and your inductors become basically resistors.

You might be able to use lower-inductance, higher-current parts and put them in series? But 85A is a lot to ask of a buck converter, you might have to look into some sort of multiphase buck, or else a specially-wound giant of a toroid.

evjim:
Thanks, yea Coilcraft also replied saying they did not recommend it. They also suggested putting higher current capable inductors in series.

I have found this inductor  on digikey. It seems a lot heftier than the coilcraft ones I found. But they do not show any temp rise information. I would still need to limit Ipeak to about 70 amps. Might be worth lowering my ambitions and set a rms current of 50 amps or so.

w1ntermute0:
I just started thinking about building one of these.  It doesn't look like there's a reasonable off the shelf version with WiFi.  I was originally thinking of building one using a Raspberry Pi since it has built in WiFi and would allow for a lot of flexibility but maybe I can work with you on yours.  I'm mainly a mechanical engineer but I have some experience with software/electronics well.  Maybe I can help with an enclosure among other things.

Here's two projects I was looking at:

Looks Great but does not use MPPT:
http://www.instructables.com/file/FZIT4MII2TQVGML/

Looks promising but doesn't include a circuit to control/monitor the load:
http://www.freechargecontroller.com/

I'd like to be able to monitor Solar volts/amps, battery volts, load amps (with ability to switch load off when battery gets low).  Having cool charts/graphs/stats in the local web interface and/or the ability to relay to one of the online IoT sites that does graphs would also be good.  Although these are often installed out of the way, I kind of like the LCD screen also.

Let me know what you think,
wm

Codebird:
There's an old project of mine from a year or so ago. It actually kind of sucks - it'll only do 10A, and it's hardly professional, but perhaps the design might give you something of an inspiration. It's not a charge controller, it's purely the MPPT part - something you're supposed to be able to put inline between your panel and a PWM charge controller or passive load device. The intention was for it to be cheap enough that you could fit one to every 100W panel. In practice it's unpredictable and unstable, but it does work under the right conditions.

https://birds-are-nice.me/ipfs/QmeHTKsAWhaKeygAqRBkAUkt5t2e9NPZcHT2ZcuyZcXcwy/

There are certain fundamental laws of physics that force you to trade between inductance, current handling, and physical size. You can't have all three: If you want a 65A inductor with lots of inductance, it's going to have to be huge. No getting around it.

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