This is why it's a good thing that I never went to electrical trade school.

I don't know, I just thought it was neat.

I'll save you 15 minutes:

Dude charges up giant capacitors, verbally wanks about lots of volts, watts and amperes, compares his many volts and amperes to a thunderbolt and wanks some more, dumps the energy into a speaker, blows the speaker.

Visual amazement: not much, even in slomo
Lesson learned: overpowered stuff goes bang
Coolness factor: do you like big caps, lots of watts and lots of amperes? Then none.

With unlimited time, I would love to do lots of these little projects with ESP32s

I been thinking about getting a device like this! Now I can make it! Oh boy

lol it's pretty simple, you just follow the instructions in the dfm8001 datasheet - SCRIN + GND to your solar panel, BAT + GND to your battery. Tie all three VFC pins to the BUCK pin to configure for lipo. Tie both MPPT pins to GND for a shitty solar panel. Tie L_EN, H_EN (unless you wanna use it instead of the RT9080), PRIM_U, PRIMBAT, and DCSC to GND. Leave all other pins floating. I think it's $6 on digikey.

Well, it's a start at least. That DFM module was the selling point of the project for me. It's neat to have something run on solar

oh that's missing the DFM8001 solar harvesting module + solar panels that give it the indefinite indoors feature.

Thanks! :)

I either lost the schematic or never made one, but this one for the newer STM32U3 version is pretty much identical, just with an STM32U3 instead of the STM32L4:

https://i.imgur.com/r15uMNC.png

i think i actually omitted physical pullups on the switches. the max17055 is only so I can track exactly how low-power it is.

this is the pin layout I used on the L4, mirrored, because I deadbugged it upside down:

https://i.imgur.com/vEPDjOL.png

I did it on perfboard and plotted the layout in photoshop, this is the closest to the end before it was all done:

https://i.imgur.com/aDK4pHn.png

That's very neat! Any chance for the schematics?

That's awesome. Great work. I need to get my charger/tester setup done . I run 100% off grid for electricity, so you would think i have this sorted already 🤣 i really need to get my shit together.

Oh my god you just tickled my autism. I WOULD LOVE TO TELL YOU ABOUT MY BATTERY TESTER.

https://imgur.com/a/ZbfAtUk

Unfortunately it is quite a mess because of the number of times I've taken it apart, expanded it, etc:

https://i.imgur.com/mHeF1gA.jpeg

Originally it was all in that black plastic box on the left with the screen. Then I learned two things - 1) if you try to switch an ao3400 mosfet at 20khz to turn a 1 ohm load into a 2A CC load, it will explode. and 2) if you try to put a TP5100 charger in an enclosed space and run it at 2A, it will not.

So the little floating midair circuit board next to the black box is the TP5100 board, heatsunk, and powered by a PD trigger board so it gets its own 9V while everyone else gets 5V. It gets shut on/off by a GPIO wired to its CS pin, but otherwise, it is permanently powered and connected to the battery pins.

The big green circuit board is my attempt at making a much bigger CC load. Here is a rough schematic of whats going on:

https://i.imgur.com/H1qFbui.png

Basically I use a switch to select between high current or low current mode. High current can go from 600mA to 6A. Low current can go from 600mA to 6mA. Then I use a 20 turn trimpot to dial it in, by hand. Dialing it in with the ESP32 would require a DAC, and the S3 doesn't have one, and I trust this manual control more anyway.

Then each side of that switch feeds a pair of 3Peak LMV321B-TR op-amps. They're SMD parts I ordered off digikey, but I've gotten good at deadbugging them. The high-I opamp is wired to a 0.1 ohm, 3W shunt and an IRLZ44N mosfet screwed to a massive CPU heatsink (I used a hand tap to drill a screw hole in the aluminum and then just screwed the mosfet on), the low-I is wired to 10 ohm 1/4w shunt and another little bitty AO3400 mosfet. I have only tested it up to 5 amps, but at 20 watts, the heatsink barely gets warm, and the fan is completely unnecessary.

GNDs are kept separate until the last possible point, to avoid wifi noise from the ESP32 interfering with measurements.

While the ESP32 can't dial in a precise current, it can control the whole thing on or off, thanks to a pair of AO3400 mosfet drains wired to each opamp's output. Whenever the ESP32 wants, it can sink them to ground to turn off a discharge cycle.

Inside the ESP32 black box is also a TP4054, with a series of resistors wired from its PROG pin to different GPIOs. With all floating, the TP4054 does not charge, despite being permanently powered and wired to the battery. By grounding combinations of GPIOs/resistors, I can select a charge current from 600mA down to 30mA.

Battery wires are 18ga, soldered to the battery for maximum connection. Bit of a pain to switch batteries, but way more reliable than any kind of removable connector.

It's ugly, but it works. I've tested 12Ah battery packs at 5A discharge 2A charge, and I've tested 30mAh earbud lipos at 30mA discharge, 30mA charge, all with the same... mess. Oh and it uploads all the data over wifi to my Grafana server for graphing.

Nice. Can you tell us about your battery tester?

Is that what we call a monolithium?

https://www.youtube.com/watch?v=-Y23nfAOiXQ

I've certainly shorted a few batteries by accident and turned their wires into high current fuses a few times, which lets out a lot of smoke and a bit of glowing hot metal out of the wires, but I've never seen a battery itself do that in all my years. The key is to just work with them fully discharged, solder them to the charger, assemble it, THEN charge it.

Honestly, I had a battery from 2021 go up in smoke on me... And I hadn't even done anything with that, the manufacturer made a mistake somewhere. No spicy pillow as a warning, nothing. Even if something physical cuts off the power - if the chemical reaction has started, it's extremely difficult if not impossible to stop it.

I used to feel the same way. BigCliveDotCom talked me into it a couple years ago. Battery chemistry has gotten way safer over the years, good chargers with protection circuits can be had for pennies, and the 18650's especially are in steel cans giving them a little bit of armor, and they often have a CID in one end (giving it a vent-like appearance) that will physically cut the circuit off via physics (not electronics) if pressure builds up. It's not 2016 anymore for lipos, that's for sure.

Then again you can also go the LiFePo4 route - those are becoming more easily available, and they're even safer, albeit about half the capacity.

Yeah you shouldn't if you don't know what you're doing. If you do on the other hand...

Honestly, sounds like a recipe for a house fire. I'm all for DIY solutions and I would love to work on a project like this for an old laptop of mine, but batteries is a line I avoid crossing. When they go up in flames, you're thoroughly fucked.

crunchy compute?

ha. i think its cool they did this, but they cant really think this is anything but art... right?

At one point I was running BeOS on a Pentium 75 with 16MB RAM, later upgraded to a K6-2 266 with 128MB. Those machines, particularly the K6-2, felt faster than anything else I've ever used, and was better at certain things than any other computer I've ever used.

Weird that we used to have to use paging memory but Windows still felt way faster back then.

Eight megabytes and continuously swapping. ;)