Yes you can take your cells below 3.5v, its just “dangerous” because you risk dropping your cells so low that they wont charge normally anymore and would need to use something like a benchtop power supply to recover the overdischarged cells. Yes this permanently damages your battery but so does using it normally, every time you use your battery you are permanently damaging it, its just a matter of how much.
If you’re at 3.5v you have anywhere from 0%-5% capacity left depending on your manufacturer. You could pull 1A continuous and inch your way home very slowly and cautiously and maybe you wont overdischarge. But if you decide to bomb up hills at full throttle at 3.5v, you’ll probably end up with cells under 3v (assuming no vesc cutoff). Remember the voltage curve isn’t linear, the time it takes to go from 3.5v to 3.0v is a lot faster than say 3.8v to 3.7v.
Like everyone keeps saying, its a tradeoff between lifespan and useable capacity.
In all the research I’ve done, the chemistry and construction of LiPo pouch packs seems to limit them to under 1000 charge cycles, no matter how they’re taken care of. Typically even quality packs are advertised as 300-500 cycles. Meanwhile, the quality li-ion cylinder cells we’re using are quoted at 2000 cycles.
If you’ve got a lipo pouch over 2-3 years old with over 500 cycles I’d love to know the brand.
Additionally, i don’t think the use case for a big enough drone/ rc vehicle that would run a 6s1p 8Ah lipo is that different than esk8 to warrant a significant increase in cycles, but I’d love to learn something new.
considering a cycle of 80% (i.e., 16 Ah, 8 for discharge and 8 for charge) the predicted life results are equal to 10000 cycles that is higher than the data given by manufacturers for this kind of battery.
Reading this paper from 2015, it seems they tested three, single-cell (3.7V) 10Ah lipo laptop-style pouch packs made by General Electronics Battery Co.
under various charge-discharge patterns in order to “investigate the effect of the duty cycle on the batteries lifetime”.
The final paragraph of the conclusion:
The results, obtained from the analysis of the collected data, show that the ageing of the Li-ion battery is correlated with the total electric charge that flows into the battery cells and in particular with the square root of the total moved charge.
Then, it is possible to state that the duty cycle does not practically affect the battery ageing. It is worth to note that the life prediction does not take into account all the reactions that can occur when the voltage is close to the minimum or to the maximum but refers to the best use of the batteries in the linear region.
In addition, a change in degradation of the battery after a high number of cycles can be foreseeable. Therefore, further tests are needed to investigate this issue.
I’m not sure what information you’re trying to draw from this particular paper. What you quoted was a side-note in a paper testing something totally different:
It is worth to note that the life prediction does not take into account all the reactions that can occur when the voltage is close to the minimum or to the maximum but refers to the best use of the batteries in the linear region (i.e., where the voltage is a linear function of the SOC). Anyway, considering a cycle of 80% (i.e., 16 Ah, 8 for discharge and 8 for charge) the predicted life results are equal to 10000 cycles that is higher than the data given by manufacturers for this kind of battery. A change in degradation of the battery after a high number of cycles can be foreseeable. The prosecution of the test campaign will investigate this issue.
(emphasis mine)
If the authors drew a general conclusion on all Lipo pouch packs being widespread underrated by their manufacturers due to a non-ideal charge-discharge factory test pattern, that would be an interesting and more relevant discussion point. Unfortunately they only tested a single battery model. And since the authors nor the spec sheet list a cycle life for this particular battery, we have no reference point for that 10,000 number either.
Does anyone on this forum have 1000 cycles on a lipo?
No, I am saying blanket statements like “Lipos die after 100 cycles” or “Li-ions have higher lifecycle than Lipos” should be dismissed.
if you want more Lipo info, you are better off going to endless-sphere. Lots of Lipo info there and is what eventually convinced me to go 100% Lipo a few years back. I kind of summarised all my knowledge here
Cheap, safe, airline friendly, 10x less work and no li-ion will ever compete with Lipos in terms of performance simply because of the discharge curve.
A perfect example of why the details matter when discussing different chemistries and their advantages/disadvantages. He uses very “shallow” discharge cycles, typically 4.1V to 3.8V, and that can fundamentally affect cycle life.
LiPo’s*** have some distinct disadvantages, like any of the chemistries, but they don’t have to have a short cycle life. Any cell used at its limits (voltage, temp, current, etc.) will have a shorter life.
***trying not to rant here about the commonly purchased LCO chemistry pouch cells not actually being lithium-polymer. “LiPo” as a term for these cells is universally accepted though and I just need to deal with that.
Hey- anyone know a cheapie small soldered pc board with a diode/etc. to keep a 12.8V LiFePO4 6AH battery from dropping to low in case I get distracted? I’m simply using it with a fan in a duct over my wood heating stove to pull up heat along with a DC voltage step down board for a 4V fan that fits my duct perfect. So now, I don’t want to “86” this minor power convenience (re-charge on a Off Grid Trek panel else if lazy the Suaoki Charger (same for my AGM in 4Runner). The main thing is to spend near $0 and insure a bit of safety to the cells or even a reminder would work theoretically if it talks to a phone app or that talking disc some of us have. I’ve been out of the tronics world for a few decades but disability tends to free up some time here in snowy CO. Piece- and thx for any assist. Amazon, Alibaba- whatever would work for a cheap board I can wire in simply like my buck convert. Fly Eagles Fly.
I saw some graph posted elsewhere in the forum stating that cycle life was significantly lower on lipo. Something of the magnitude of 100-400 for lipo, 1000 on other (cylindrical) chemistries. I’d love to believe they are the same because I’d never build another cylindrical pack if that’s the case.
First off: @Battery_Mooch is Mr smarty farts, not me. But I’ll do my best to answer this with the limited info I have,
This is the case, the minimum, maximum, and average cycle life will be longer with li-ion as compared to lipo
Me too sadly though I believe you’re misunderstanding Mooch’s point.
He’s saying here that if you use shallow discharge cycles (in reference to lipo, however the effect would be the same with li-ion) your battery will last longer.
I believe mooch is asserting that you can make lipo’s last substantially longer than average by sacrificing range and using shallow discharge cycles, still however you could use the same method of shallow discharge cycles to prolong the life of a cylindrical lithium ion battery.
It’s all just tradeoffs and deciding which ones you’d like to make.
I’ve spent a decent amount of time attempting the same thing, to save money using lipo without sacrificing cycle life, range, or discharge.
In my experience doing this research will just lead you to the conclusion that P42As are nigh impossible to beat in terms of value.
The prerequisite question to this is: can you even trust the manufacturer’s C-rating without personally testing it yourself? These seem like they could be mostly marketing at this point. Bigger numbers sell more shit.
Not directly, no.
But you might want to adjust the cutoffs based on how hard you are using the cells and what their current rating is.
Cells that will have huge voltage sag for the way you’re using them might benefit from lower cutoffs to allow you to get a bit more range. Their voltage will bounce back a lot (since a lot of sag) so the lower cutoffs won’t result in overdischarge (if being reasonable when setting cutoffs).
It can be and often is. IMO this is due to the crappy quality of the hobby LiPo cells that we all buy. There are good quality ones (much more expensive) that have pretty good cycle life.
As mentioned by @Egtscs, limiting their voltage range can extend their cycle life. Charging to 4.05V or so and stopping at 3.2V or higher can significantly extend the life of a LiPo. But that comes at the expense of range. There’s always a tradeoff with Li-Ion.
sadly though I believe you’re misunderstanding Mooch’s point.