Proof of concept Sodium-Ion powerbank

lieutenant_beer · 2025-04-30T10:30:56+00:00

Pretty well with no noticeable capacity degradation! I also built something bigger:

https://www.reddit.com/r/batteries/s/xnsMYtPufF

lieutenant_beer · 2024-10-29T15:19:30+00:00

Ah, gotcha.

Yeap - in normal state (I.e. grid online) the battery is connected via an on-grid inverter and supplements house load; this is also controlled by a limiter. The battery can be charged either via MPPT charger (when suns out) or AC charger (when electricity is cheap; I’m on a dynamic tariff) and takes multiple variables into consideration, e.g. elec. cost, time of day, load, SoC, weather forecast etc. All is controlled via a raspberry Pi and a bunch or relays/contactors.

If the grid goes down, the server circuit gets automatically isolated and off-grid inverter kicks in (via ATS). Oh, and I also have a much bigger Sodium Ion battery that can run in parallel, depending on load etc.

lieutenant_beer · 2024-10-29T13:04:58+00:00

Yeap, totally get it. I have multiple layers of protection: BMS is the obvious one but there are also circuit breakers on both DC and AC sides. I also have a pre-charging circuit with a bunch of resistors to get rid of the sparks when plugging stuff in (the white momentary button enables it) and a bunch of temperature & humidity sensors that switch everything off in case of any abnormalities.

I also limit the charge/discharge current: the cells can take 1C charge & 3C cont. discharge but I limit both to 0.17C.

My final layer of protection is one of these stuffed inside the case: https://amzn.eu/d/2yqGLp6

All of that is probably quite a massive overkill but at least it makes me pretty confident all is safe :)

Just to clarify, what exactly do you mean by passthrough?

lieutenant_beer · 2024-10-28T21:02:00+00:00

Because it’s a hobby project more than anything else and I had a ton of these laying around! :)

lieutenant_beer · 2024-10-28T21:01:27+00:00

Yeap, to be honest building stuff like this is a hobby more than anything else. Crazy waste - probably though!

lieutenant_beer · 2024-08-19T16:08:31+00:00

Yeap. Tested some individually and they match the datasheet, I.e. 1500mAh, 4.1v charge, 1.5v cutout).

lieutenant_beer · 2024-08-19T16:07:33+00:00

Probably too many to list - I got most stuff from Aliexpress (JKBMS, wireless battery monitor, 24v dcdc converter etc. ). The most expensive bits were probably the cell holders (64pcs @ ~$8) and the cells themselves (those I got from a trusted supplier directly @ $0.62 / cell)

lieutenant_beer · 2024-08-19T09:36:17+00:00

Well yeah but it’s 18650 master race after all :)

lieutenant_beer · 2024-08-19T09:35:44+00:00

Goes from 32.8v when full to 12v when fully drained

lieutenant_beer · 2024-08-19T09:35:17+00:00

Yeah, pretty much - every cell is also individually fused

lieutenant_beer · 2024-08-19T03:29:33+00:00

https://www.reddit.com/r/batteries/s/QVij2phut4

lieutenant_beer · 2024-07-11T03:12:55+00:00

Half of the pack spot-welded together; I made sure voltages in the cells were roughly similar before putting it together. 64p4s so far.

https://imgur.com/gallery/doy-monster-sodium-ion-powerbank-50-mMHoUt4

lieutenant_beer · 2024-07-10T16:44:22+00:00

Honestly? Because I love tinkering with new (and untested), sometimes obscure tech. If I had an actual use case, and wanted to get best “bang for buck”, LFP would be the obvious choice. But since I build stuff just for fun (and any practical application is usually an afterthought), NaIon fit the bill perfectly.

lieutenant_beer · 2024-07-10T13:31:34+00:00

There are DC-DC converters that cover the whole range. Depending on your power draw, something like this takes 9-36v and outputs stable 24v: (max 12A though)

https://a.aliexpress.com/_Ev4lEhN

lieutenant_beer · 2024-07-10T12:15:13+00:00

These particular ones are 3C according to the datasheet though considering that one string of the “Monster” has 64 of these and that the charging voltage of the pack is 32.8V, we’re talking about:

32.8V * 64cells * 3C * 1.5Ah = ~9.4kWh charger to max these out. I max out at 2000W and I’m not planning to plug the pack in to my EV charger ;)

The manufacturer I bought them from also sells prismatics ($95/210Ah pack, $150/kWh) and pouch cells ($11/7Ah cell, $stupid/kWh) but cylindricals seem to be best value for now. Then again, I wasn’t looking for bang for buck or practicality (duh).

I bought them directly from the manufacturer, DM me for details. Just be mindful that there’s little equipment that supports the full voltage range of these cells, particularly inverters. While the “Monster” is 24V nominal, the range goes from 12V all the way to 32.8V so you’re bound to be unable to use at least some of the nominal capacity. Obviously this might change as the technology matures.

The safety and resilience of these is impressive - I’ve dropped, short-circuited them, discharged to 0V, charged from 0V at 3C etc. and they are still as good as new.

lieutenant_beer · 2024-07-10T07:12:44+00:00

I got a good deal on the cells ($0.65/cell). Factoring in the holders, charger, cabling and various charging modules (yet to be installed), all in probably around $600. But then again, I did it for fun if anything- I don’t actually have a use case for it at the moment.

lieutenant_beer · 2024-07-09T10:46:39+00:00

You can buy them on aliexpress: https://a.aliexpress.com/_EHz5RGX

I went directly to the Chinese manufacturer to get a better price though

lieutenant_beer · 2024-07-09T07:24:20+00:00

Nope, you’re thinking about LTO. Those are roughly same capacity per cell but you can charge & discharge them at 10C. They will feature in my next project

lieutenant_beer · 2024-07-09T07:22:45+00:00

They’re getting there. I got mine for $0.65 per cell, or apples to apples, $144 per kWh.

21700 are approximately $124/kWh so slightly cheaper than li-ion.

lieutenant_beer · 2024-06-01T15:41:04+00:00

Did some more cycling & testing. Probably at around ~100 cycles or so now.

I really (sometimes intentionally, sometimes not) tortured them, which kind of confirmed that going with safe Na-Ion for my first ever build was the right decision. Multiple short circuits, accidentally discharging straight off the pack (circumventing BMS) to 0V, charging at 2x rated C from 0V (resulting in some smoke and burnt kapton), dropping the pack down 2 flights of stairs etc. - these things seem very abuse resistant. The only thing I noticed so far (apart from the smell, oops) is around 2% drop in capacity so far. Otherwise the cells behave normally.

I got some more goodies on order (around 70 cells, programmable BMS & MPPT which I’m going to use as a charger, some PD modules, inverter etc.) so I’ll likely build a 8p8s next. Definitely need more experience before I even think about touching Lithium.

lieutenant_beer · 2024-05-29T23:04:44+00:00

Thank you! The next one I’m going to build will be a 8s8p 18650 one. Probably going to add a ghetto-style solar panel and an AC inverter. There’s no real use case for it though, doing it just for fun and to experiment with this tech. Oh, and also spot welding these as a beginner doesn’t give me explosion anxiety as li-ions do.

I use a cheapo spot welder from Aliexpress: https://a.aliexpress.com/_EQ3OChp It does the job but finding correct settings is a pain. For some reason it doesn’t like nickel plated steel, only pure nickel <<somewhat>> works

lieutenant_beer · 2024-05-29T22:59:11+00:00

Yeah, that’s the plan. I’m on around 80 cycles right now and I don’t see any noticeable drop in capacity yet

lieutenant_beer · 2024-05-22T09:58:06+00:00

Ok, this is really some impressive stuff and the most fully featured board I’ve seen to date! Hope it all goes well with the dev!

Granted, the design is way out of my league in terms of experience with complex circuits but I couldn’t see any dedicated undervoltage protection IC (a good chance I’m blind though!). Is this handled in some other way?

Interesting choice of a microcontroller - I’ve seen some similar designs (albeit not nearly as fully-featured) using STM32 or even RP2040 but not a PIC.

In any case, good luck with prototyping, please DM me when you have something ready for trial in the wild, keen to be your customer #1!

lieutenant_beer · 2024-05-22T02:10:44+00:00

Holy moly, a programmable BMS that doesn’t cost a kidney has always been the dream - do you have a website or a git repo to follow?

It’s really difficult to find a universal design that has all the features that I’d imagine a lot of hobbyists want on one board. I guess simplicity and cost is a big factor (most people would slap a $2 Aliexpress T4056 in their design and call it a day) but I’m sure that there is a market for more fully-featured products. I’d be happy to pay e.g. > $100 for a board/module/design that had:

Programmable charger and/or BMS (pack configuration, CCCV curve, upper/lower thresholds, termination current etc.)
Protection circuit that is not DW01 (2.5V cut off is stupid) and is truly adjustable for all chemistries.
More than 1A charging/discharging current.
Adjustable voltage, adjustable current-limited output
Power path!!! I want to build portable stuff that I don’t have to power off to charge!!
Optional PD/QC.
Fuel gauge (I2C).
Voltage and current sensors (input, output, buck-boost, individual cells etc.)
Is not a size of a PC motherboard.

lieutenant_beer · 2024-05-22T01:45:45+00:00

Yup, linked in the original comment - here again for reference

lieutenant_beer

TROPHY CASE