Reached the Discharge Limit of a Sodium battery? A voltage plateau at 0.3V!
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- čas přidán 14. 03. 2024
- So, it seems, the ZKE Tester can actually discharge to 0V. I have to repeat the test and discharge the sodium cell again, this time letting the tester recording the full voltage curve.
When the voltage dropped to under 1V, everything seemed to be as expected but at 0.3V, something happened which I cannot really explain. It looks like the cell is not able to deliver the 0.5C current any more.
Is there another voltage plateau at 0.3V and the chemistry inside the cell somehow changes/collapses? I'm interested in reading your thoughts about this...
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The 0.35v is limitation of load tester. It has a current shunt resistor to ground with an op amp to drive a MOSFET load device for feedback controlled constant current. The non-inverting input to op amp gets a reference voltage from controller that sets the constant current level through MOSFET. There is limited range on the op amp control and once the battery voltage gets too low the MOSFET Vds minimum voltage is limiting the pull-down voltage to about 0.35vdc.
Yes, I agree. Makes sense... thanks.
You should build a big 17s sodium prismatic battery and test it!! Victron cam use most of its capacity.
A 17s sodium battery will have a voltage range of 25.5V - 67.15V.
Victron can be operated in some of that voltage range, but not most.
So, you will already lose usable capacity with that plus even more due to lower energy density when compared to LFP (+ more space requirement).
So, the price would need to come down a lot. A lot lot... I don't see this happening. LMFP will be the next big thing is my guess.
@@OffGridGarageAustralia63usd per prismatic cell per 210Ah, they are not that expenaive...
Awesome testing. I'm reaching back in my brain to remember the lithium ion curve to compare the density. I had asked a few questions and I already found the answers. According to the graphs of both types of battery for my inverter discharge cut off I would need about 30% more battery of Na+ to maintain the same Wh as lithium. Cut off is at 70% Na+ (Wh/kg lithium 180, Na+ 155.) In warmer areas the charging .5C of Na+ is 113f. Lithium is 150f at 1C. There is a cycle expectancy of Na+ 4000 @.5C and lithium 4000@1C.
Thanks for the work Andy.
Thank you.
Yes, you would need more sodium batteries to compensate for the voltage range, you can actually use plus even more for the lower energy density when compared to LFP.
That was a very interesting series thanks Andy.
Thanks Gary.
With an accurate volt meter and then a small 1W resistor, you could trickle drain the battery and measure the voltage drop to the bottom. Semiconductor based systems and inductive current measurements will have their limitations but directly measuring the voltage across a stable resistor would be very accurate.
Yes, correct...
It looks like the ZKE tester is unable to draw the programmed constant current of 0.65 A below a cell voltage of 0.32 V. Because it cannot reduce its load resistance any further it draws less (you measured it). Consequently the cell voltage decreases much slower from that point on. Later we see a second drawback of the tester. It cannot properly measure currents below 0.1 A and it shows 0 instead. Of course both are excusable failures of the tester because it has to work outside its specification. Usually cells will not be discharged to 0 V and we also cannot blame the ZKE for being unable to measure currents below its minimum discharge current of 0.1 A. But of course it is interesting to go to the limits of both the battery and the tester. Thank you for that.
So no plateau as it seems. You could check it discharging with a 3 Ohms (~1C initially) resistor in monitor mode. But I understand if you want your Na cells to have a rest now and to go on for something less boring than waiting for the cell to reach 0.00 V @3Ohms.
Yeah, good explanation. That makes sense.
Very interesting tests thanks Andy. Where it plateaus off at the end & then immediately starts to rise again to 1.5v or higher, my guess is that in the simplest terms it could be explained as the reverse ‘stadium effect’ you get when charging, so those last few electrons of energy present themselves as a rapid voltage increase when the tester stops it’s discharge cycle.
Interesting. Never heard about this effect before...
@@OffGridGarageAustralia The ‘Stadium Effect’. This term has been used in discussions to describe how a battery (probably more appropriate to lead acid tech) can accept a large current when first initiating charging until it reaches a near full state and then it takes some time to get it to a completely full SOC, say the last 5-10%.
The term reflects the similarities of getting those last few amps of charge in a battery to trying to fill a stadium of 100,000 people and how quickly the first 90% of people can quickly find a seat compared to the last 10% who have to find those last remaining seats.
I’m fairly sure I have heard you use this type of metaphor before to explain how a battery charges & why it takes so long to get those last few amps into it, you may not have coined the term ‘Stadiums Effect’ like others have, but I believe you explained it almost exactly this same way.
So my comment was meant to reflect how although the meter may read 0 volts remaining, there are still those few electrons left the meter doesn’t register while discharging until the load is removed, and this is when & why the voltmeter will show a sudden voltage rise.
The current drop-off at very low voltages is a limitation of the tester. Even when it's discharged transistors are turned fully on, they still have some resistance, this is what is limiting the current.
Also, there is really not much use in discharging a battery all the way. Remember that W=VxA. So just how much power is it putting out 1/2 an amp? Plus, where can you get an inverter that will work perfectly over an 8 to 1 voltage range.
Thank you. We will do an inverter test soon.
It would be interesting to leave them hooked up to your light bulb tester for a few days to see if they still recover.
These batteries would be good for lower power devices that use a buck-boost circuit. Or outdoor solar lighting!
It would need a boost circuit to get any good out of it whatsoever, because the useable voltage range is minimal without it.
Yes, solar lighting is something I have thought about as well. It does not damage the cell. Apparently...
Thanks Andy
Thank you.
Thank you. ☀
Sodium batteries seem to be a good chemistry to have a small battery of this type as part of a larger system, so when using Lifepo4 batteries, if the BMS turns off the Sodium battery would hold the voltage of the inverter at a sensible voltage, no more current spikes when the Lifepo4 BMS turns back on.
Heya, again nice test love to see what you come up next. maybe a 48 volt battery soduim pack ?
I won't build a 48V system. It would not be compatible with anything I already have. I've got something else though 😉
Interesting news!
If you had a circuit with a buck converter limiting voltage to around 1.2v and .05A, and you compared Sodium and Li-ion 18650 batteries, which one do you think would last longer without damaging the battery? That voltage and amperage should be able to keep a memory chip alive. If dropping the sodium battery to close to zero volts doesn't harm them, I can see them being used in devices that have long periods of in activity. Excellent work, as usual 👍
Thanks a lot.
That plateau is the load-meter. The MosFets that do the load fall down to there minimum working point. The gate-voltage has to be be higher than source/drain, and need that minimum - a minumum that you know from Shottky diodes measuring too that is about 0.2 V.
So sometimes its better to then use a real wire resistor (no bulbs, thats to much for such tiny cells and is undefined) - and an ordinary "in-line" Amp meter. That Unitec you use caused so many troubles to me, its bit of trash and just a fast "whats going on here" - meter, but not a precise instrument (and below 1 Amp it really starts to struggle and shows magic numbers).
So if you rerun the test, with a resistor - no constant current - and a voltage monitor, you would be able to see a curve that goes down to 0V - and no magic happens at 0.3V.
But - tbh - that makes no sense, because there is no real life use for that.
Data sheet only says 0V does not damage the cell, like it does on Li-based cells.
Its possible to NiCd and NiMh cells to since ages - with no use.
greetings from Austria (that without kangaroos)
Thanks for the explanation. That makes sense!
But but but, you promised the results from your AI consultation in the last vid. And I had popcorn and everything ready to go....... ☹ 😂👽
I will keep this for the last salty video as the grand finale.
Andy, for a slow burner project, could you get/make yourself a joule thief and run an LED or something off one of the 18650 Sodium Ion cells and really run it flat? Then look at charging it up to check capacity and other tests...
All chemistry needs to be in equalibrium. You can force it to the left or the right of the Gause curve, but it will return into the middle after a while again.
Andy, beautiful weather down here, no clouds, 28 degrees. Battery working well still need to fix solar on shed. But something is coming to fix my problem soon.
Do you have measurements for NiMH done with the same tester ( to compare)?
No, I have not measured NiMH cells ever.
The circuit has minimum resistance value it can't go below. Before that sharp drop off in current, the tester would have been able to keep reducing the circuit's resistance so as to keep current at the set value as voltage dropped. But once it reaches the point of minimum circuit resistance, well the current will also drop.
By Ohm's Law, V = IR, with a fixed minimum resistance then as cell voltage reduces the current must also fall away and it will do so asymptotically.
I think you are on the right track. From my understanding, these types of load testers use large power mosfets to act as variable resistors. As you said, there ends up being a minimum resistance which will end up limiting the current due to insufficient voltage; simple ohms law doing what it does, not the cell having another plateau.
Yes, good explanation. The tester is clearly at its limit here.
I bet that at the end, the electrolyte is gradually consuming some of the electrodes in some chemical reaction rather than releasing energy previously stored when it was charged. It might be functioning more as an alkaline battery at that low voltage, releasing energy from a chemical reaction. I can't believe that discharging this deeply isn't causing some damage or loss of capacity. Could it be that the internal resistance is going so high that a voltage can build up but can't be released as any significant amount of current.
Could be an internal resistance thing. I will confirm that in a later video. Good suggestion.
Hi Andy. Have a nice day
You too, mate.
Oh i don't believe it's age to blame for not realizing settings , it's all those donated beer lol.
Ah, right, hahah, that could be it😆
I can discharge batteries down to 0.1V with light bulbs and FNIRSI FNB58. This tester does measurements down to 0V just fine. Obviously current falls down with low voltages (as load is close to constant resistance at low voltages).
My Ni-Mh cells seem to recover capacity with such a discharge.
Put a strip of copper and a strip of zinc in a glass of salty water, you get a galvanic corrosion cell. That is effectively what a fully discharged rechargeable battery is. As long as they aren't internally shorted, they will always "recover" to this galvanic cell voltage.
Interesting analogy.
@@OffGridGarageAustralia It isn't an analogy, it is basic chemistry. The main difference between a galvanic corrosion cell and a battery is the current path being external with a battery vs internal or otherwise unwanted (ex.: steel fastener into aluminum, copper, brass, etc.) in a typical corrosion cell.
That is why you should avoid letting dissimilar metals touch each other in wet locations as much as possible.
Low voltage is safer for shipping and storage but how about overcharging without creating a fire/explosion?
We don't know...🤷♂️
@@OffGridGarageAustralia I have some marketing for sales of Sodium-ion cells saying that they have been charged to 6V and also baked in an oven without anything bad happening...
maybe sodium batteries have memory effect that is fixed with full discharge to 0 and then full charge again
Maybe! I thought the same...
How many cycles will you get if you keep discharging to .3 V? How will it affect the useful life of the battery?
All good questions but hard to verify and test.
@@OffGridGarageAustralia
We had a test for primary cells in that a load of short duration was applied and the recovery was timed. This indicated the cell cappaciy which was borne-out by long-term testing. Of course, each cell type had its own recovery characteristics, so data tables had to be determined.
I think it is your device, a single schotky PN transition. Check with a capacitor, if you can "discharge" a (non electrolitic) capacitor to 0V
To double-check, connect only a resistor across the battery terminals (like 25 ohm or so) and then measure the voltage across the battery terminals. I = V / R. The current sensors in the testers are going to be way off at such low currents. The multi-meter will also cause some inaccuracies at such low power levels but measuring voltage with a multi-meter across a resistor will be a lot more accurate than the tester's current sensors.
Don't try to use the multi-meter's current measurement... it won't work properly (the discharged battery has too-high an impedance and the multi-meter's internal shunt resistor will mess up the calculation).
I wonder what would happen if you left a resistor connected to the battery for like a week. How long would it take to rehabilitate the battery after doing that 🙂
-Matt
Yes, definitely a limit with the tester...
Awesome my friend....! All of us thank you very much....! I know that I do not want to spend lots of $$$ on Lithium ion phosphate batteries....! With a 12 Volt system, it is not feasible... and have to worry about fire/explosions..? =)
Thank you!
No inverter what can it use.. prismatic cells are the same voltage?
Yes, all sodium cells are the same (some have a higher max charge voltage)
The battery engineer.. 😉
Hahaha, I thought I was the BMS godfather?😄
I think the big question is did you damage the battery. Does it impact life?
We don't know and may never find out. But good question.
I think you found a limitation of the tester. It's internal load is unable to maintain the set current at that low of a voltage. Aka, the load resistance is to high.
A voltage of 0.414V and a current of 650mA suggests that the load is around 0.637 ohms total including leads and circuitry.
Agreed.
The battery seems quite rugged, how has this effected its performance? This sort work is not healthy for Lithium.
Like# 2 - Dropped during Grilled Lamb Chop Lunch!
maybe the chemical basis potential of the ions and their place in the periodic table? Just guessing.🤣
What was the reason you didn't use this in the first video? It wouldn't work to 0 volts? The other discharge failed at 0.5 so I guess this is better at ~0.3
Also where'd that guy asking you to test hemp batteries go.. I wanted to laugh more lol
As I said, I was somehow under the impression, the tester only discharges to 1V and cannot be set lower. I was wrong, hence the new test.
meine Mutter und Großmutter findet dein clasicher deutsche Dialekt so funny.
There is no dialect!🤔
There are better options than a clamp meter to measure mA currents...
🐸🐸🐸
Hello Berlin!
@@OffGridGarageAustralia 🤫 das darf doch keiner wissen, das mit Berlin 🤫
The rather impractical working voltage range of sodium batteries could be moderated by some clever cell wiring. If, for example, you had 12 cells that could be switched between 2S (6+6), 3S (4+4+4) and 4S (3+3+3+3) configurations as the cell voltage dropped then the working battery voltage range narrows significantly. For example, by using 2S for the cell voltage range 3.9V to 2.6V, 3S for 2.6V to 1.95V and 4s for 1.95V to 1.5V then the battery voltage always stays between 5.2V and 7.8V -- not great, but with more cells you could use more configurations to improve things further. However, some ugly things might happen at the moment the configuration switches over -- I guess you'd need some sort of supercapacitor to smooth the output.
very practical idea 😢😊
Yes, I thought about something like this as well, but the wiring effort with cables, contactors and controllers is huge and probably makes this very uneconomical.
I think the load tester is reaching some limit at 0.3V set your power supply to 0.3V attach it and see what current you can draw, then lower the supply voltage seeing how he load tester preforms.
The load tester A/D cannot measure negative current, also the shunt has an offset, so as the current approaches zero theres a dead spot where the indicated current drops off.
Andy very interesting your doing these measurements, but your running into the accuracy and uncertainty of your test equipment, which can be frustrating. Relax and have another SPAT.
I know, the tester is not meant to be used for such testing. I was just curious to see where the limits of the equipment and battery is.
@@OffGridGarageAustralia
Always interesting to find the limits, see what you can squeeze out of the test equipment.
Myself I use my Rigol EL3021 electronic load for battery testing, it has its own quirks.
Interesting and great work you are doing.
This was a tester limitation, Andy. Just the way it works. Also, you can’t measure 20mA using a clamp meter if you DONT zero it at the SAME spot!
Agree. Tester limitation.
Proudly Not First 🙂
Self-recharging cells ? 😂
Put this in a car and it will run forever. Toyota and Nissan may be interested in this😄
Im late
still 🥈
once upon a time i had a tiny rc car.. smaller than my finger.. it had a mini lipo which tried to raise voltage and the tini car never fully stoped working... it was probably killing more cycles of the lipo pouch but in my mind it just worked!!! ,