Marc's Public Blog - Electronics Hacking

They are of course not all the same real usable capacity, and I've learned not to trust vendor capacity claims anymore either, due to the amount of sellers that plain lie on amazon. The good news is that Neither Xtar nor EBL lied about their cell capacity as long as you understand that the actual energy you can output will be lower due to conversion losses and some safety buffer to give the cell longer longevity.

https://docs.google.com/document/d/1z9o7O5o70SxJnQwKHJD8JdlPdScZZ1o09scHqUlDxeE/edit?usp=sharing

Here is a quick summary without pictures:

New Xtar: Rating: 4.15Wh, Charge: 5.5Wh, 3.45Wh Usable discharge at 1A

Old Xtar: Rating: 3.3Wh, Charge: 5.3Wh, 2.7Wh Usable discharge at 1A

10.6Wh to charge 2 batteries, or 5.3Wh charge per battery

EBL 3.3Wh rating, Charge: 4.3Wh, 2.7Wh usable discharge at 1A

Summary:

Deleepow 3.4Wh rating, 3.8Wh charge, 2.4Wh usable discharge at 1A

Summary:

Just like last year, Illuminaughty was about as far across the playa as a camp can be, so it was nice when we arrived :)

Ran into a bunch of people will cool gear:

Very cool hat:

Impressed that the newer panels can bend pretty well

a lot of work went into these patterns

Anthony had a lot of cool gear he built, I was very impressed:

Obligatory group picture:

Thank you to Chuck for organizing this year again, it was lots of fun.

And if you want even more details and history >>> See this full article on the why and evolution of my LED outfit <<<

For all these years, my outfit has relied on a fanny pack filled with batteries, and with an unslightly tether from the fanny pack to the panels, bringing 2 feeds with 5V (as backup and to spread out the amps over 2 wires). That system worked for many years and would survive the failure of one of the 2 5V connections, or even the 16V connection meant to feed the rPi from its own power source stepped down to 5V on the panels (so that it doesn't see a voltage dip on the remote 5V rail when the display sare fairly bright). All in all, it worked, but the fanny pack tether and wires were cumbersome, and some security folks didn't like all the wires.

After switching to a new neopixel controller that is directly USB powered, it made more sense to power the panels locally and put the batteries on the panels:

For comparison, the old panel on the left only has the rPi and a small 16B to 5V converter and than relies on that tether cable to the white box on the left which has the DC-DC step down and the ESP32:

finished design with padding, power routing from 3 lipos or 2 USB attery packs

While this was not new for v6, made sure the camera still worked, it turns out to not be super reliable on batteries, but when it works, it's a crowd favorite:

The new version works like the old one, but with batteries directly attached to the panels, which in turn makes them much heavier, but oh well. Video with Lipos and DC-DC converter:

However, the more interesting upside is that I could also replace the 16V lips that get stepped down to 5V, with 5V USB Battery packs. the reason I never did that at the time is that the entire system takes way more than the maybe 2.5A you can get from USB packs on a good day. A somewhat cumbersome workaround to this problem is to use 2 USB battery packs with 2 independent outputs each, meaning 4 independent 5V busses able to put out up to 2.5A depending on the battery pack. So, I split my power system in 4:

In total it means the whole thing uses about 3A at 5V, or 15W, which means 180Wh for 12h. In theory 2x 99Wh battery packs would work for 10H, but in real life, the first battery pack gets a lot more load since it runs the rPi, so it only really lasts about 7H before I have to replace it. Not ideal, but still nice that I can run from USB instead of lipos if needed:

Video of the USB version:

After some unfortunate feedback soon after I built the new version, I added a makeshift back cover with duct tape, mostly to hide the "scary" electronics, while still giving me accesss to them since this is still a prototype that needed occasional work and tweaks:

Since the original design with lipos, the good news is that lipo chargers have finally become much smaller. They are now small enough that I can simply leave one in my travel backpack forever:

Now I don't need this "custom made" battery box ;) which worked for its time, but didn't allow bigger batteries being an issue during 12H festivals (2 batteries wasn't enough), and was an issue during airport inspections when they wanted to "see inside the box":

I however found out over time that some airports really didn't like to see the panels in X-Ray with batteries attached. All airports were fine with the panels on their own, and the batteries on their own, but if I left the batteries in the outfit, which honestly is a lot more convenient to me, some airports really freaked out in totally irrational ways and now complained about "too many wires" "looks like a bomb" and all that good stuff. The 2 airports that delayed me enough that I barely made my flight (bangkok and Ontario, CA), literally said they would have been fine if I had packed the batteries together and still carried everything I was carrying, just not plugged in (of course everything was off, and plugged in is actually safer since you don't have loose power connectors that could somehow short).
So I'm not interested in missing a plane due to this and honestly nonsensical and irrational reactions (after all, no one said fear was rational or logical), so I eventually made a "battery pack" that I can more easily slide in and out before and after each flight:

Oh yes, it's still home made looking, could somehow get/make a box for it, but if I do they'll want to open it to see inside, going back to the original box I had earlier, so I'm not sure there is a good way to win this. Also if I make it look too much like one battery instead of 3, they'll complain it's 290Wh (over the limit) instead of 3x 98Wh (under the limit).

And to show how things evolved, this was the v3 outfit with neopixels and only 24x32 instead of 128x192, but much brighter. I did use v3 a couple of times again at day festivals, as it can be made bright enough to work in full daylight, but after doing this a few times (and that required extra batteries), I decided not to bother anymore, and skip the LED panel during day hours (I still have LEDs on arms and legs that can be made bright enough if need be):

Separately, I often have to explain to people, that my outfit is actually a scaled down version of the RGBPanels you see on stage. Once you have the display, it can scale up:

And another question I get is "how long does it last?". 2 batteries of my old 5Ah 4S lipos, was a bit short for an all night 12H festival (EDC), but back then I was also powering the LEDs on my arms and legs, which took an additional non trivial amount of power. For wiring ease, the LEDs are now on a separate battery, which allows the main system to run longer. I also upgraded the batteries from 5Ah to 6.7Ah. As a result, I found out a bit after the fact that actually 2 batteries would have been enough, since I put 3 as per my old setup, I ended up with a full runtime of just under 19H (I stopped the test before the batteries were totally drained since it's not great for them to do so). As I'm writing this, I now realize that with just 2 batteries, I could last 12.5H, which is still more than enough (and it would remove some weight, so I may want to consider that.

310Wh out of my 3 batteries, more than I thought, and almost 19H

because all meters have measurement errors, recharging pushed back in 20.4Ah instead of 21.2Ah which doesn't quite add up, but close enough

Version 5 was a bit upgrade with my P2 run rPi run RGB Panels for a resolution of 128x192 per side. The oldest part of the outfit at this point were actually the Neopixel strips I've had for about 5 years, and despite being more reliable WS2813B with backup data line, the PCB traces would break and the chips solder points would eventually break too. The amount of time I've spent fixing and replacing LED strips is more than I'm willing to talk about, but there was just no good alternative, until now.
In the past, flexible LED strands with wires between each pixel did not have enough density, maybe one pixel every 5cm, which was not acceptable for my use. And after many years of waiting, a company finally made P15 flexible strands, one LED every 1.5cm, which looks much better and is even a bit more dense than my previous strips that were P16.6.
Here there are: https://www.aliexpress.us/item/3256804447608449.html . Update, don't buy these, they are shit and broke within hours. See at the bottom

While I was at it, I added a small programmable 16x32 panel to my fanny pack, because why not (the existing fanny packs didn't have sufficient storage, so I ended up decking out mine), and here is the end result:

I have no idea how reliable the strips will be, and unfortunatley they are WS2811 without the backup data path that WS2813 had, but time will tell. I'm bringing it to EDC and we'll see what happens :)
Update: these broke within hours, they were crap.

Version 6.5.1: Ray Wu Strips

It ended up being more solid, but the flexing and occasional pulling on the bare strips that were attached with safety pins (I didn't want to glue or sew because it would then be unwashable), eventually caused the strips to fail, although it was more slowly. It worked for 4 festivals in Europe and required some resoldering, but it was not terrible. Still, it wasn't a long term solution either.

Version 6.5.2: Full LED Tubing Protection

This is now going to burning man, I hope it will hold, especially with lots of biking :)

once I got the servo validated, I connected it to an ESP8266 as a wifi controller

Here is the basic end result:

The one downside of the ESP8266 is at least the one I have with the firmware I'm using, does not have super reliable Wifi connectivity, so my server keeps track of it being there or not, and can remotely power cycle it as needed. Not ideal, but it works...

There are predators (hawks at least), so I had to add a full net around the area:

cute chickens

This is the door in action after I added a switch to control it locally and wrote code on my home controller to talk it is via wifi:

The last thing I wanted to add was a water level monitor, especially because I had issues with the dispenser leaking, and ending up without water, is bad obviously. My first plan was a predictable total failure;

looks wonderful, but it's not meant to stay in the water and the board, failed

2nd try with pins

oh look, lots of metal ended up in the water, of course!

So yeah, all those classes in middle school about electrolysis are not just to bore you, it is a real thing, and sending current to sense the water through conductors causes ions to move and metal too:

So, I tried again with new conductors and changed my code not to check for water constantly but only 20 seconds every hour. That's thankfully enough that it mostly stopped the issue I had:

And obligatory cute chickens and chicks videos:

Sometimes, I'm also a bit of an overachiever, and analyzed the actual lights in power draw vs amount of light coming out since all the specs online are a lie:

But despite the downsides, it gave me a chance to upgrade them over the year to better ones, including color changing ones which have somewhat held up so far:

Oh yeah, I also got firefly lights, and here is the end result:

Thinkpad P73 vs P70, not a win all around: only one 2.5" drive instead of 2, and a badly designed power system

P70 vs P73, they look pretty similar

*Update*: it seems if that if you get a cheaper nvidia chip with the P73, it is then configured to accept 135W power supplies as the minimum required. That said, it will still refuse to work with any regular 90W power supply or external battery back, unless you force it with the center pin resistor swap.

While I have no plans to use windows on that machine, I thought I'd just try it out to see how it does on power. This is where I was impressed, windows can idle at less than 10W for more than 11H runtime, while I'm lucky if I can get linux at 15W. This is definitely a place where linux should do better, of course, it's not as if Lenovo put any work into making linux more efficient on their hardware either:

*Update* : with tlp and using the nouveau driver just enough to turn off the nvidia chip, I'm now able to tune the laptop down to 10W, almost matching windows.
See tlp issue 494 for details on how to setup tlp to run in low power mode when power is plugged in.

Another disappointment is that the P73 is mostly the same size and weight than the P70, but it has less room for storage. It has a bunch of empty spaces that aren't used for anything, and it can't use two 2.5" SATA drives anymore, like the P70 could. Worse, the now single 2.5" slot uses a lenovo only ribbon cable that does not ship with the laptop and basically means you cannot even add a 2.5" drive without that special ribbon cable, which isn't in stock yet. Well done... Ah yes, the battery is also not hot swappable, even if it is replaceable (unlike a Mac laptop where everything is sealed shut).

this shows the unobtanium lenovo cable for the now only single drive that fits, along the unused space

Ok, stop complaining, just buy a bunch of 170w or 230W power supplies and move on with your life

Tricking the P70 and P73 into accepting a power supply it wouldn't otherwise use

For the P70, I built this power supply adapter with a resistor bridge to tell the laptop how big it should think the power supply, is:

It's basically a configurable version of this. Yes, lenovo, I thank you for the hours I wasted opening up power supply plugs and replacing the center pin resistors:

Here's how the P73 responds:

- 230W works fine   4.6k => I have seen power supplies work with 170W but fail at 230W, so the laptop does draw more
- 170W works ok     1.9k (1.8k also ok)
- 130W rejected     1k
- 90W  rejected     550 

The rejected power supplies will be used to charge the laptop if it is shutdown, but they will not be used in any way otherwise. On the P70 the laptop would at least use the power supply to keep the laptop alive, and use half battery half external power supply. Not so with the P73, it just ignores it entirely.
This is utter bullshit as I have plenty of 90W power supplies, including 12V car converters, or a 90W external 20V battery pack I can't use anymore.

You can go read my Hacking a thinkpad slim tip adapter to output more than 90W (required to charge a Thinkpad P70) page for details, including this nice battery pack I couldn't use anymore:

*Update* : so, actually with some serious tlp hacking (basically I told it to force battery mode even if a power supply is plugged in), I've managed to throttle the laptop enough, even when plugged in, so that it only uses 20W. At that point, I'm actually able to use my old external battery pack, as well as a 90W power supply, as long as I lie to the laptop and pretend they are 230W power supplies with the resistor trick. In my tests with windows, it was not possible to throttle the laptop enough when plugged in, not to have it overwhelm a smaller power supply (not that 90W is small for a laptop that normally uses 20-30W when it's not charging batteries).
If you scroll to the bottom of the page, you'll also see a terrible buffer lipo hardware hack I did that allows to use the battery pack with higher amp draws, but it's a bit ridiculous (and bulky).
See tlp issue 494 for details on how to setup tlp to run in low power mode when power is plugged in.

Without the tlp hack or the buffer lipo hack, when I lie to the laptop and tell it is connected to a a bigger power supply, manage power draw with what I run, and disable battery charging in software, but the laptop will still draw the power supply for over 100W when you plug it in for a fraction of a second, and refuse it if the voltage drops.
Obviously this would not be a problem if the laptop simply had a 90W power supply mode where it throttle things down and turned off battery charging. This is mostly what the P70 does.

In the meantme, on top of hacking my power supplies, I also made this for my laptop, it looks silly and makes the thinkpad not look like a professional laptop, but well, that's lenovo's fault:

this takes any power supply and replaces the center tip resistor with a 1.9k one to emulate a 170W power supply

From talking to Lenovo, they don't think that this is really a problem, so since I'm an engineer, I made my own external battery pack, but I otherwise recommend to road warriors to avoid thinkpads from now on, given the backward power design in this one.

Making a Thinkpad P73 compatible external battery pack

Prototype with 150W step up converter which takes my 16V lipo to 20V while delivering enough amps to make the laptop happy:

it works, and the laptop thinks it's connected to a 230W power supply thanks to the center pin resistor.

Here's a quick demo:

Version 2 was to have a way to recharge the battery pack while it's being used. I've used this to use the battery pack as a buffer to absorb peaks from the laptop without tripping an external power supply, including in a car limited to 100W or a plane power supply limited to even less:

this works in theory, but the lipo charger is quite slow and wouldn't keep up for long, but I made a better version shown lower down

Lenovo's P73 airplane mode simply stops using the external power supply and reverts to batteries. Sigh...

Making a battery pack to act both as buffer for a smaller power supply, and as emergency external power (even power the laptop from 12v)

version 1 was a bit bigger than I wanted, 90W power supply shown for scale

here, the 90W power supply is recharging the battery at 2.5A while it's being discharged at 3A on the output side, using the battery as buffer

I made version 3 a bit smaller, with a built in 12V lipo to act as buffer for a smaller power supply. Yes, it's a beautiful piece of art, I know :)

Pushed to the extreme, I can now use my original external battery pack again by having it recharge my lipo+150W step up that can output more amps than the ravpower pack can. Of couse, it's inefficient, the ravpower pack outputs 20V that gets down converted to 12V by the H605 Air lipo charger, which charges the built in 3S lipo in the box, and then gets up converted back to 20V without the amp limitation (the phone used to control the lipo charger also inside the box):

The really cool thing is that by using tlp, it's actually possible to tune the laptop down to very low power use, even when plugged in, something that windows probably can't do:

7.3W with the screen off (and around 10W with wifi off and the screen on low dim) is not bad for a laptop that big

4S Lipo vs 4x 18650 or 26650 batteries

That said, as I recently found out that 16650 (or better 26650) batteries are both lighter and smaller. The only thing the lipos do, is offer a better discharge rate, but while that's useful for a high power RC plane motor that can empty the batteries in 10mn, it's not needed for a laptop:

26650s are 195 Wh/kg while the lipo I gave was 184Wh/kg. The 3rd battery listed is supposed to be 260Wh/kg which is much nicer, that said, it looks like those samsung batteries are actually smaller than 26650s, lighter, and yet offer the same 5Ah at 3.6V. If so, that's very impressive.

As of this writing, I have however not found 26650 battery holders that hold 26650 protected cells that are a bit longer. This seems to the be only one available, and it's too short to hold the batteries: https://www.amazon.com/gp/product/B074GVPWSH

A few months later, I ended up cutting them and taping them to make them longer. It doesn't work great, but it was enough for a few tests. In the end, I found that somehow I wasn't getting enough amps out of them, which surprised me, so they didn't work that well compared to a lipo:

Conclusion

Jon, presenting the miniconf as per how many

Raspberry Pi running the car

This year's dingo car, controlled by the rPi

All done

Andy presenting the software side of the car

We then trained our cars' neural network by manually driving them arount the track:

and before long, I got my car to drive around on its own

Here is a video of my car driving on its own, including how it learned to drive:

During the miniconf, I also gave a talk on my recent LED panel/ESP32 work and brought my recent RGBPanels:

I knew that this could void the warranty on some parts of the car. I was ok with that. Tesla wants me to buy a powerwall, but I think powerwalls are stupid.

I'd need to spend $30 to $40K in powerwalls to get the same amount of energy I already have in my car and I already paid for. Sorry, but I'm not spending that much for something I may need once every few years. Load shifting my solar in california is otherwise a straight loss, and PG&E forces some silly rules about not allow using powerwalls for time of use power arbitration if you accept the buying credit for them. You get penalized for helping take the peaks off the grid, yeah bureaucracy!
If tesla sold a powerwall that would allow using your car as a battery source for emergencies only (car batteries are not designed for daily cycling like powerwalls), I'd be super interested, but they do not, so I decided to make my own answer.

I knew that I could probably only get 2-3000W out of my car, honestly for emergency use (a couple of fridges and essential equipment), that's good enough. Sure, it wouldn't power all my house lights, or even my furnace for heating (which happens to use over 1000W just to run the fans), but eh, it's for emergency use only, so good enough.

Plugging into the standby 12V battery

My plan was to connect a big GLA 12V battery in parallel with the car's battery, so that it could absorb big peaks and buffer a it longer in case the car's battery recharge didn't kick in quickly enough. I did however confirm that the car's DC-DC system only recharges the standby battery at a slow rate, so it was not adequate for my need.

Plugging into the cigarette lighter adapter

Tapping into the car's DC-DC system

The 2 white holes are where the clips that you need to release. are located. You can also see the black and red tap points:

The Nut on top of the positive bolt under the seat

Building it up without resistor and protection relay

If you do not see a spark, you may just be able to connect the inverter dirctly to your car with just wires (although if that doesn't work, it will trip the DC-DC converter in the car, and require a full car reset to bring it back online).

Building it up

Originally I tried those:

What happens is:

This shows the current meter shunt connected to the bypass relay (which is powered by the connectors on the inverter side). You then see the thick 100W resistor connected in parallel with the relay. This allows current to flow more slowly and ramp up the connection:

I tested a 1300W microwave which worked without issues, so did my fridge and other devices. The pure sine wave inverter is very important for a microwave, but a cheaper inverter worked well enough for my fridge and basic loads.

Since we're talking about currents of 100A or more, we need to talk about wire gauge. The inverter I got came with 10AWG cables of about 1m. These cables are insufficient for 100A (never mind 200A), but in real life will mostly work for short distances and as long as you don't use the full power continuously (which could technically heat up the cable enough to melt its insulation and cause a short eventually). In my tests with 100A, I lost 0.7V due to inadequate wiring:

Given that the car outputs 13.5 to 14V, this drop is not big enough to matter since the inverter works all the way down to 10V or so, but be mindful of potential heat. Here is the end result:

Keeping the DC-DC system awake

Backfeeding your house

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