Marc's Public Blog - Electronics Hacking

Why we live in a sad world where I had to make my own powerbanks

So there we are, now I have to go back to using raw batteries, even to power USB things like my outfit LEDs, which basically means I need to build powerbanks with raw batteries (which means the batteries get counted as 20 batteries, and not powerbanks, and then I plug in the powerbank module and they become powerbanks after I'm already past airport security)

So now, I'm forced to make my own powerbanks again

As part of looking for new batteries, I found foxbuying.com which made custom Li-Ion packs of multiple form factor and voltages and the support person I talked to was amazing in how much they cared and were willing and able to talk tech. As part of that, they gave me recommendations of powerbank ICs to look for on aliexpress, which was very helpful for my search.

Considering if Lipo Batteries would work, the devil I knew

Given all of this, it's kind of a miracle that I used them for more than 5 years without any issues (even if my circuits did have fuses and I was religious about using low voltage alarms).

I didn't have a lot of luck finding nice lipo packs that weren't too big, and I found this one:

6S 88.8Wh

but the issue is that it had no BMS, so I checked if I could find small balancers I could just connect forever, and by the time I got them, I realized they were huge and even their balancing plug is not the same size as the one on batteries.
As part of the BMS boards I found on aliexpress (thanks to foxbuying.com), one of them supported lipos and balancing packs, which would have been great, but sadly it was configured with undocumented micro resistors on the back that I Was not equipped to adjust:

this could have worked if I could have changed the board to 4S since almost all my lipos are 4S

turns out after days of back and forth on aliexpress support, I Was told the boards could be used with straight batteries without the balance connector, but still limited to 3S

Too bad it was not configurable for 4S or 6S as I did get it to output 20V for my laptop

So I gave up on lipos.

Trying Powerbank Boards and Picking Li-ion Batteries

I tested lipos while I was waiting for the foxbuying lithium packs to arrive (I bought 2P/7Ah 3S, or 84Wh, from which I was able to get around 70Wh of real capacity).

This other board I received from aliexpress turned out to be the first winner: it supports 2S to 6S, can charge at 60W and also has a USB-A output which is a win for me since my LED outfit does use USB-A

of course, it can make any USB voltage up to 20V and charge a laptop or a phone

The problem with those boards is the poor documentation and I couldn't get that board to charge my batteries, until I saw this on the back:

needed some help from google

the tiny 2/3/4/5/6 solder traces are just right of the display

and finally got the power to flow the other way

added some shrink wrap to protect it

I did built my LED outfit to support multiple voltages and work from raw batteries or USB-PD from 12 to 20V:

and USB-A for my pants and shirt

I can also use the USB-C as output for other LEDs

While going production, finding the right multi battery cables was hard, so many had insufficient wire gauge that was disclosed nowhere in the product

even this male male connectors melted the inside wire

the outside still works, but 0.1 ohms shows poor and cheap wiring

And then, even the foxbuying batteries were not able to deliver the 8A they were rated for. I don't actually need the 8A, but the anti short protection BMS kicks in very late and allows the battery to overheat and melt its shielding. Here, discharging at 8A, I got 78C on this connecting bar that overheated enough to melt the shield

I'll be honest the battery was warm enough to burn my finger, not good...

and this happened on a partial short that was not enough to trigger the BMS short cutoff, not good

and the short was due to this bad soldering point that failed

The best of aliexpress, poor manufacturing and no quality control

While looking for those, aliexpress also recommended IP2366, there are plenty of options and they are small and efficient, it was just hard to find quality boards that arrived undamaged, and none of them came with a case or box, which is still an ongoing issue for me (I'm not much of a 3d case designer).

Then, these boards finally arrived, and those were china at its best, great features, cheap, and 3 broken out of 4 :

shipped with broken screens

shipped with broken button, support wanted to ship me a new button for me to surface mount solder

pretty when it works

So I got a refund for the broken ones, took one week of arguing with the sales person, bought more, and 3 more were broken:

how is that even possible?

the new version with a bigger screen is nice, this is the only one that worked but good luck putting it in english but the IP2366 chip is cool

I had to use google translate to finally find the menu in chinese

and this other bigger screen one was also broken

Those boards were great until I realized that if I unplug the battery to change it, they will not work or initialize until I plug USB charging power and reset the battery info on the screen (how many cells). OMG, so stupid... It was nice and pretty, but useless if it won't work after a battery change. After sales support did not agree that the board should remember last setting and work after a battery change, sigh...

I tested the one non broken board I got to charge 4 batteries in parallel:

starting at 9.9V

after 10H charging, 317Wh charge to 12.6V for 4 batteries (80Wh per bat)

And that's another board's documentation, positive on the negative point. WTF?

Turning Batteries into Stable 5V, 8A RC plane UBEC with 5.2V output

So I asked google gemini for help and it suggested RC BECs, which I didn't consider even though I have plenty. The big plus is I wanted to them output 5.25V to end up with more than 5V at the rPi3a after wire losses, otherwise the rPi would slow down and even reboot. Of course ESCs are designed for exactly that and plenty offered 5.25V output, but few had more than 3A output, until gemini offered this one, an 8-16A UBEC with 5.2V output, yes!

tried it under load at 4A and with poor wiring got 4.85V (more on my microcontroller with better wires)

Thanks to this Ubec that works all the way down to 6V, I did a test with 2 7A/3S foxbuying packs and I'm now able to get 65Wh per battery pack:

works all the way down to 6V, 130Wh discharge

and 160Wh to recharge in 6H

While the foxbuying batteries are not super sturdy and as safe as powerbanks, I already knew that going back to my own battery packs would be less safe, but I also need to be honest that while they are very compact and light, it's disappointing their melt their thin outer shield while delivering the 8A they are rated for:

In comparison, these packs were clearly built with more safety and path redundancy in mind (there was a better sleeve around them I already peeled off before this picture and much better path for electrons to travel):

The foxbuying folks did recommend to put my own fuses but I'm using cable doublers, triplers, or quadruplers and I would have to put fuses on each and every branch of these cables, which is a bit too much for now, I might do that later, but I really wish this was part of each battery's BMS, as it should be as adding all the external fuses is splitting cables, more connections, more places that can short, break, or go wrong. For now, I'm going to hope they won't get damaged during use or travel.

And in the meantime solid state battery powerbanks that do not catch fire if you pierce them: https://heybmx.com/ , are still banned.

But as something more positive, some vendors understand the problem and are offering workarounds:

The daughter board looks like this:

and the back looks like this, input for 12V power from the motherboard and Vret to make 3.3V

Then, because I was reckless, I swapped M2 cards while the PC was powered, thinking they were hot swappable like Sata, but they sure are not. Eventually I caused a partial failure of the board. Gemini helped me debug the linux errors from the cards plugged in itand confirmed my guess that the voltage regulator on the board was now partially damaged and gave power, but not enough to be reliable under load.
A new daughterboard is only $20, but that's 2 week shipping from China while my new server would be down. So, it actually knew the daughterboard, it knew where to buy it from and the shipping delay, and it also knew how it was made before I gave it my picture. It confirmed that the best course of action would be to desolder the 100 component that was an inductor, and I could just unsolder it and connect a new 3.3V source to it.

After helping me find a new 5A Vreg on amazon, it looked at the picture of the board, and it confirmed the top pad, is the one feeding 3.3V to the rest of the board. It suggested I use flux to help unsolder the SMD component after I declined the suggestion to use a hot air gun that would be too likely to remove other components, some of which had to be useful:

yes, it looked ugly, but the inductor was removed safely, I then cleaned the flux

Then I happened to have the right female connector in my collection of cables and plugs (happy it does come handy at least a few times), and soldered in the new Vreg:

I had to move it on the other side so it would fit with the case closed

And there you go, I literally fixed the daughterboard and the PC works again! Yeah! I honestly was impressed by Gemini's knowledge of existing boards and its ability to read pictures I sent it, identify the components and confirm test points and how to verify I was adding the new power source in the correct place.

Back to work!

so these batteries that do not look great (and they are not), are legal, but powerbanks are not.

So you're going to tell me, why don't you put those unsafe looking batteries in an enclosure? Great question, when I did that airport security wanted me to open the enclosure to see the battery inside and its readings. How about you make it professional and write the battery reading on the other side, and then add a plug to connect your things to it? Well, that's exactly what a powerbank is and those are not allowed anymore (past 2, which is a useless number for me).

See the problem? I need exactly 5 powerbanks to run my LED outfit, LED backpack, and spare charger for phone and camera. This is with no spares, often I need a 6th for a long night. This does not count powerbanks for my laptop if I end up in a plane without working power. Now you see how it's easy to get to 10 or more and why the new '2 max' really f'ing sucks.

So what are the other options?

Does it surprise you that airport folks said those batteries looked like shit? Of course they did, and that's why I worked hard to replace them with powerbanks that looked a lot better.

Seriously, fuck, this sucks, now I need to replace 10 powerbanks that were not cheap and carry less safe ones because of this idiocy. Welcome back to the past, self made crap that will not look better or be safer, but somehow is legal

And because they really suck, they also banned solid state battery powerbanks that do not catch fire if you pierce them: https://heybmx.com
And 1 month later, it's done:
>>> LED Panels Battery Self Made Powerbanks <<<

History of the LED outfit:

So, why a version 8? Well, the flexible panels in v7 were nice and light, but the flexible part made them break repeatedly. The chip solder points in the back would eventually fail, causing different kinds of failures on the panels, and I had to replace them in the field (even carry spares with me). This was not a long term solution, never mind that my spares were running out and it was probably impossible to buy matching panels today.

When I said things broke, I often had to repair the outfit while at festivals. Initially repairing panels was a lot of work, and required a soldering iron. Version 7 was designed to allow easier panel replacement with just a screwdriver, but I still needed to prepare the spare panels at home (soldering them before they were needed), and I broke almost 10 in 1.5 years. This was not sustainable:

Another issue was that I would lose pixels as they would eventually fall off on the other side, and the plastic cutting board I used as a diffuser and protection layeer, helped, but was not sufficient. My favorite vendor, Hongren Su from Azerone, had a new GOB coating to protect the pixels and and even make them water proof, but he didn't have anymore legacy style panels, just new PWM panels which were not supported by the rpi-rgbpanels library that I use. Those new panels are better in theory since they self refresh at 2khz or so, but they all need a separate incompatible driver, which is a huge pain in the ass. By sheer luck, Kingdoc9 on github had the same problem and somehow managed to use a coding AI to make a driver for a few chips. Total hero!

At the same time, adafruit made an active-3 low profile board which is not ideal since it covers the CPU, hinders cooling and points the connectors up, but it's better than the electrodragon low profile passive 3 board:

And still at the same time (talk about me being lucky), Hongren Su from Azerone, nicely offered to make a custom metal frame for me, with 5 degree bend, which solved both the problem of panels breaking due to repeated flexing, but also significantly simplified mounting of new panels as I only had to slap them on and the magnets did the rest (and boy those magnets are strong):

new versus old, piece of wood used to stir paint, and 3mm screws with limited reach

trying both boards

Now another vexing failure point I had, was the ribbon cables from front panels to rear ones. I used a trick to only drive the front panels with a Raspberry Pi and had ribbon cables to pick up the signal coming out of the front panels, and feeding it to the rear panels. This was a great idea, it ran the rear panels for free, I didn't have to have a 2nd rPi in the rear and saved on power.
But, as there is always a but, wearing the panels, put stress on the ribbon cables and they would eventually break. I did put straps that would get the stress and in theory prevent those failures, but they still happened, worse by then it was the HUB75 plug on the panels that would fail. That was very annoying as it caused my rear panels to have display bugs after the plugs were losing pins and there was nothing I could do short of replacing the entire panel:

note the straps to protect the HUB75 cables

this was supposed remove stress from the HUB75 plugs, but didn't do well enough

there are the HUB75 plugs that would fail

with the new setup, 2 computers (really 4 with the ESP32s), no more ribbon cables front to back

One other build optimization is I did what I should have done a long time ago, which was to use the fat power cables to send power around. Those cables even have ends that plug directly into my 20V-5V DC-DC converter. Why did I not do that earlier and insisted on using JST 2 pin cables everywhere (which I had to solder on each new panel). As an added bonus, those big power cables are thick enough that a single one going across to the back (the only connection between the 2), is enough. In the process I also removed 2 straps between the mid and top panels, as they were unsightly and now unnecessary:

So the new build runs both screens independently:

while both sides are setup to display the same thing, they render independently. This is not a problem of course

Now, I had to write a fair amount of ESP32 code (I used gemini for help), so that the 2 chips would coordinate, the front one would be master (selected by switch) and the rear would listen for a broadcast, become slave, and send its IP to the master. The master would then send a UDP command to the slave to update the pattern every time the master changed. End result:

This is how it works with remote control:

Same communcation panel to panel;

People sometimes ask me if I can "just add" a graphics on the fly. In real life I have to use gimp to shrink the graphic to 128x192 or close to it and convert to gif, it takes a little while:

The new driver is not as fast as the old driver in pushing data to the panels (yet), so I had issues with tearing in some animations as the panel refresh was happening half way through a slower frame push to the panels. I had to fix this by implementing double buffering, and you see the before vs after (left panel vs right panel):

Now, the only problem I have left is increasing the panel refresh from the Pi3as, so that they hopefully allow the panels to refresh faster and not show these half refresh screens. Never a dull moment :)

0.004s

0.002s

0.001s

0.001s

this will more or less fit :)

nothing really looked wrong, but the power supply was dead

So I ripped out the power supply, connected a 2.5mm jack female, and now any external 5V power supply will do the job:

new fan spinning on happy switch

back online

The solution was to find the right dimming/blinking controller, which was quite hard to locate (didn't want to build my own). Uper right is most of the ones I found, they were too big, did dimming but not blinking, also they were USB based, so I have to solder JST connectors. Lower right is a better version, still USB only, although at least it had flashing. And then I finally found the right ones, bare wires, easier to just solder in my JST connectors, and they support flashing and blinking: