Every cell is different, which is why i found the generic meters hopeless for 30Q cells. I convert the discharge curve to a series of linear lines to get a very accurate high resolution meter.
https://danielz.uk/making-an-accurate-battery-meter/
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Iām getting slightly lostā¦
Can someone correct my numbers? I can then reverse the calculations to understand better 
12s6p 30q
@danielz this is by far the most correct answer, but I was looking for a less-accurate table of ten voltages.
Though you bring up a good point, we should use the resting voltage, not voltage under load. We want it to be accurate when you stop and wait a few seconds, and not have to be under full power to have an accurate reading. Sag will change it by a lot.
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This site is really good for extracting image data and getting the points you want
https://apps.automeris.io/wpd/
I did for 0.2C since in my experience is what represents better, and using the energy content, not capacity, and also considering 10 Wh in each cell since this is what I usually get out of them
Keep in mind that the actual energy content doesnāt matter if you just want to relate voltage to state of charge, even when the cell degrades the % points stays roughly the same when measuring unloaded
@b254 I did some test when I made my Arduino based capacity indicator, and the 0.2C curve matched better, but you canāt ever take the measurement under load, the way I got around it is talking to the VESC via UART and when it detected any current going in or out of the battery it wouldnāt update the values, if no current is measured it waited a 3 seconds before taking the measurement to allow the voltage to stabilize
For the 30Q@0.2C it looks likes this:
100% - 4.17 V
90% - 4.07 V
80% - 4.04 V
70% - 3.95 V
60% - 3.86 V
50% - 3.79 V
40% - 3.71 V
30% - 3.62 V
20% - 3.5 V
10% - 3.35 V
0% - 3.12 V
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@Pedrodemio that is really awesome; I added it to the first post.
Is there any way to run those same numbers for the A123 ANR26650M1B LiFePO4 cell with a 3.65V charge voltage?
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I can, but for lifepo4 open circuit voltage is a really bad way of determining state of charge, as you can see the discharge curve is almost flat, and any minor deviation on measurement results in a huge state of charge error, best way for them is coloumb counting
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I know, LoL I use them all the time and have noticed how flat it is. I also like how they donāt really feel much sag at all. Or they sag a lot. Either way you look at it, what Iām saying is the sag is nearly constant throughout the entire discharge cycle so it feels like no sag at all.
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Yeah, these are some amazing cells, you can charge them in 20 minutes and still get 2000 cycles out of them
Unfortunately the capacity is way too low to compete with the cells we have today
Or is it? I have long range lithium-ion boards but when I donāt need extreme range, I prefer LiFePO4
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I think for that application the 30T or 40 T is better
The problem that the A123 is also heavy, you can have a 10S1P with both of them that is lighter, or a 10S2P with 18650 cells that is also just a little bit heavier, but both have way more capacity
Unless you need to charge them quickly, but then a charger that can supply 10A to charge them is bulky and heavy to carry
30T and 40T donāt address cold weather operation nor extended lifetime issues, on boards where you donāt need a super long range. Also li-ion tends to sag more. At least, itās more noticeable, even if itās less, it changes more throughout the charge cycle, which makes it really easy to notice and annoying.
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Yeah, thatās something Iāve never experienced, the cold here is the summer of most places
Take a look at this, pretty interesting. Revolectrix spent some effort on these cells
http://www.revolectrix.com/support_docs/item_1229.pdf
And also this, thereās some interesting details. In fact, at a quick glance I realize I had only skimmed it. Thereās gems about vents, monitoring, balancing, SOC, etc.
One thing thatās standout about small packs made with these cells, you can regen a TON of current into them. Standard fast charge is 4C (10A). I believe someone did a long data logged test with 10C charge cycles monitoring temperatures. No problems. Searching for the writeup, no luck so far. 10C is 25A, and if sustained will charge the cell in 6 minutes. (CC/CV means itāll take longer in practice)
Another thing is these cells can take a lot of abuse. The specs have a section on charging how to 4.2v. Thatās +0.6v overcharge endorsed by the manufacturer. I think I remember folk on rcgroups consistently charging them to 4.2v for their lifetime with no explosions. Iāve drained packs to zero and revived them (more than once, but not 100% success rate).
EDIT found the link on abusive tests
https://www.rcgroups.com/forums/showthread.php?732148-A123-cells-on-the-long-term-(brief)
The link to details, the title is " A123 long term: 1st 1,000 CYCLES done, 2nd +800cycles highC done, 3rd to 0V going on" lol
This graph came from a123 apparently. subtext says 20c charge rates are fine. wtfā¦
These are fantastic cells for a first build, as they will let you get away with a lot of mistakes that kill normal $400-600 packs.
Oh yeah, they also will do 70A bursts happily if you donāt let them get too hot.
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wtf from here
OK my original 3S packs has been charged at just over 100 amps. stating current and full charge in just over 4 minutes. It has been charged at 10amps.,ran,charged ,ran,repeat,repeat and has reached 150F. It has been charged at between 15 and 20 amp. avearge( approx. 6 min charges) a bunch of time. it has been discharged to 5 volts (no load) and it still keeps going.
Another 3S has been charged at 10 amps. on a real charger approx. 25 times (first 15 then on rare occasions) . All other charges have been in 8 min. or less,most around 6 min. and recently closer to 5 minutes.Charged to 11.55(3.85 per cell) After 417 flights it still has 89% of itsā original capacity. Highest recorded temp. was just over 140F.
I charged a 4S as a 5S by mistake to 18.25 volts (4.5625 per cell) at flight #44 and now with 217 flights on it all is still well.
100A charge! Thatās over 40C!
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Lithium titanate seems very similar to iron in safety but more life cycles and I think even faster charge ability. Saw some great deals. Takes more room being less energy dense but paired with a high power chargerā¦
reminds me how someone was explaining how everyone wants an electric car with a minimum of like 300 mile range but they almost never need to go 300 miles. With titanate cells and a powerful charger, one day Iāll travel the world charging at coffee shops in less time to drink a coffee
These abuse resistant cells (I think titanate as well) are probably the best beginners cells as said.
Great video on YouTube of the headway cells being over charged and shot w crossbow
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LTO does looks amazing just not for eskate? You can only get 1500w or so out of a wall socket (37A for 10s) The charger will be monstrous.
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Well 37 amps seems good enough! Is that 1500 watts typical for coffee shops too?
Ive looked for the smallest lightest charger a couple times and there are maybe 1000 models out there and havenāt found the dream supply yet. With coffee shops having ice and water be great if that could be utilized too
120v. Most circuit breakers are 15A or 20A. 120v x 15A = 1800w. Leave some power for other customers, dodgy wires, old circuit breakers, call it 1500w.
Ever notice all power tools, hair dryers, space heaters, etc. seem to max out at about 1500w?
PSU will lose some energy in conversion, so a bit less than 37A. Even less if 12s.
Taking an example, if you have a 12Ah pack (4p 30q at 3Ah/cell), 37A will take over 20min to charge to 100% (cc/cv).
You might need to hook up to a EV charger
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If not doing cc/cv or going to full charge jam in more faster.
If u find a supply that can do even ten amps and fit in my pocket thereās a prize.
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