Tripple MPPT with one Pro Micro

Project5k:
I think this is the point when i birth a new global variable: AFTER_CHANGE_WAIT_TO_SETTLE_DELAY (well probably something a little shorter, but you get the idea.

I would call it BUCK_STABILIZE_DELAY, but long and descriptive is always better than short and ambigous :slight_smile:

Before frying more components, you should limit the current somehow to avoid that while testing :slight_smile:

couka:
I would call it BUCK_STABILIZE_DELAY, but long and descriptive is always better than short and ambigous :slight_smile:

A buddy of mine suggested that commenting as much as possible was a great time saver when programming, he said that it didn't matter how silly it might seem, any comment that can help you remember or figure out something is a good comment, especially if anyone else ever sees your code.

couka:
Before frying more components, you should limit the current somehow to avoid that while testing :slight_smile:

Yea, and I know better(hanging head in shame) I've got some nice large (high Watt low ohms) power resistors, I'll put one or a couple of those in on the + line coming from the test supply. I shoulda done that from the start so that as the current draw increases the applied voltage would fall, thus "softening" the supply to make it act more like a PV panel rather than an infinite current source. a dumb thing I did, in my haste to try and see it work, costs me again.

waiting for parts, (i ordered my low ESR caps and a couple different FET's to play with) and my back hurting, I haven't spent any more time on the code, but i haven't forgotten about reworking it to have the single mppt search alg. I did spend a few min reading about how to code for storing data to the SD card, and how to transmit that data to a website so i can see the graphs from my phone.... cool stuff.

Project5k:
edit: i think i blew my 2104 as well, the Lo out is high, and responds to the enable(SD) pin, but i cant get the HO to do anything, both whilst feeding the in pin a 5vpp sqrwave @15kHz, i have more on order, they just aren't here yet.

What are you using for your 12V supply?
Do you have a scope to view the waveforms?
Why 31kHz?
Thanks.. Tom.. :slight_smile:
Tom.... :slight_smile:

TomGeorge:
What are you using for your 12V supply?
Do you have a scope to view the waveforms?
Why 31kHz?
Thanks.. Tom.. :slight_smile:
Tom.... :slight_smile:

on the test bench i have a few variable voltage brick supplies, like this:
48v adjustable power supply
yes, its a Tektronix TDS 3032
31kHz because that's the lowest "above audible frequency" my arduino mega 2560 will produce across 3 pins simultaneously.

Project5k:
on the test bench i have a few variable voltage brick supplies, like this:
48v adjustable power supply
yes, its a Tektronix TDS 3032
31kHz because that's the lowest "above audible frequency" my arduino mega 2560 will produce across 3 pins simultaneously.

That power supply , did you adjust the current limit way down for prototyping?
Tom... :slight_smile:

It's not a lab supply, unfortunately.
It has a potentiometer for adjusting the voltage, but no current limit.

@Project5k
I would suggest you get a cheap lab power supply.

A simple 0-30V 0-5A one from eBay for 40-50$ should do fine for this and most projects.
I use one of these in my workshop for most electronic projects and charging (car) batteries as well. :slight_smile:

yea.... lab supply.... sure..... maybe someday.... I'm from the oldschool, I remember the days of using a 100W incandescent lightbulb in series with the power line(AKA a tech killer) when testing the degausing coil on CRT tv's....

you're right, that would be a smart move, but I'm sure that I'll be fine just so long as I think my stuff through... and keep a good limiting resistor inline :slight_smile: or maybe I can get that for my birthday in a few months.

Good news, a pile of parts came in today, low ESR caps, some high voltage FET's, more 2104's, asstd. electrolytics, and proto boards. It's gonna be a busy Friday night.

Just a little update, i was able to spend a little time on the bench today, and was able to rebuild the circuitry for my synchronous buck converter, and it worked! so after playing with it a bit with the power supplies on the bench, i ran a set of wires from one of my solar inputs to the circuit. Driving it through the range of PWM from 0 to 99.9(the limit of my bench signal generator) i was able to see a small current multiplication through my circuit.

Unfortunately, the only panels that were getting any sun, weren't fully radiated, and were still in parallel, so my open circuit voltage was 23v, and not the 46v i plan to have upon final implementation. The higher OC voltage should give me a little more current multiplication, and lower the PWM% from the 90 or so i was at on the bench to get max out current with today's testing.

tonight i plan to build the buck converter circuits on actual circuit boards, and not just on a testing breadboard.

oh, i guess i have 3 of em to build... teehee

one thing that i haven't worked out yet is power supplies, the arduino likes 9v, supposedly i can go higher, but the last time i tried to run it from 12v, it was a bit glitchy. the ir2104 FET driver wants more like 11v to make sure to fully turn on the lower fet.

so..... i guess i could have a 9v supply for the arduino, and then power the ir2104 from the battery. I've got a few little 1 inch by 2 inch buck converter boards, i could use one of those to power the arduino from the battery. I'll have to measure what the idle current draw's are to see how much of the battery the arduino and baby buck will eat up over night....

any thoughts?

so i started gathering up 3 bins worth of parts, so i could start assembling my 3 buck boards, and i got to thinking.... I've only tested this thing with 12-14v in, and things seemed almost too good to be true, so i decided to test with a more realistic input voltage, 44V. well, some things started showing up... The upper fet started getting warm, and both the input and output caps started warming up... so i shut everything down, reset my input voltage to 24, and things warmed up, not not nearly as much.

Upon further investigation, i could see really high spikes on the input voltage, like in the order of double the input voltage.... so, for the fet, i'm thinking i'm exceeding the source/drain voltage of the fet, which is 55v.

the other thought on the caps is ESR, i did get low esr caps, but they are rated at 35v.

SO..... in the interest of experimentation, on the input side, i strung 3 caps in series to up the voltage rating, and then paralleled a second string(using 6 caps total, and then on the output i put 2 in series, and added a second parallel string. (less total capacitance, but a high enough voltage total)

My thinking is 1) parallel strings should lower the effective ESR, and the parallel string helps offset the loss of effective capacitance from putting them in series.

well, the caps still got pretty warm, and the high side fet did too, but not as fast...

so my questions are,

  1. Is my thinking right on the caps, and the ESR, do i just go with more? switching at 31200Hz is pretty low in the SMPS world, so i would think that there would be more playroom...
  2. would the spikes on the input be able to heat the fet, without instantly killing it, and would a higher voltage rated fet solve this( and is it worth the higher RDSon???
  3. as the caps were heating up, i noticed that i was pulling way more input current that i was making out.... I'm wondering if all this extra input current could be attributed to the caps?

There seems to be something fundamentally wrong with your Buck converters and/or power source.

Instead of a thousand words, show us your schematic and scope measurements. (Input- and output voltage and -current, gate voltages)

Also, if 44V is a realistic input voltage, why did you use 35V caps?

There's only 3 ways a FET can get warm that I know off: too much current, being in the linear range (high Rds) or current through the body diode.

couka:
There seems to be something fundamentally wrong with your Buck converters and/or power source.

i agree.

couka:
Instead of a thousand words, show us your schematic and scope measurements. (Input- and output voltage and -current, gate voltages)

scope images are a real pain for me, my scope only has the ability to save images to a 3.5 floppy, and i dont have anything that can read a 3.5 right now...so I'd have to take a photo with my phone of the scope screen.

couka:
Also, if 44V is a realistic input voltage, why did you use 35V caps?

I not so smart :frowning: actually i always figured that i could put them in a series parallel configuration to achieve the voltage and capacitance i need.

couka:
There's only 3 ways a FET can get warm that I know off: too much current, being in the linear range (high Rds) or current through the body diode.

seems logical.... definately not over current, IFRZ44'S are rated for 55A, and at most I'm running 1.5A in, so its gotta be that i'm not getting the FET all the way on...

Unless you have found a big batch of very cheap, very special capacitors series-parallel will have much worse ESR than a single cap of the correct rating. Even if that cap has a lower datasheet ESR.

If you exceed the voltage rating on the FET it is likely to just simply explode by avalanche breakdown. But if it is just spikes maybe you just get away with a little heating.

Project5k:
so I'd have to take a photo with my phone of the scope screen

Nothing wrong with that... I do that even though my scope has a USB-port.