No performance, as in lack of sag
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Oh voltage sag, right you were still kinda talking about the wack 4P 25R packs.
Glad I decided to order more after I got my first 48.
Plz think of me as the guy who took 2 years to build a real board after my Turnigy skateboard conversion kit experience.
Also anyone thinking about using crap lipos please point them to me and Iāll tell them they will die (the cells).
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Iāll hijack this thread, I have a lipo question I canāt seem to get a clear answer on.
What is the minimum safe voltage for longer cycle life on a Lipo, both under load or just sitting? I am thinking equivalent to 3.3v on a liion cell.
My lipo pack sags 0.4v max under full load on deep grass, and 0.1v under most situations otherwiseā¦ Everything I read online is from RC forums of guys pushing small packs, saying under load they shouldnāt go below 3.0, 3.3, or 3.4vā¦ that sounds like liion voltage to me, but then that you shouldnāt go below 3.7v when sitting still. My 3.7V will sag to only 3.69v thoughā¦ so can I realistically go lower and still keep a healthy long lasting pack? Itās just crazy that people say minimum pack voltage should be anywhere from 3.0 all the way up to 3.8 or 3.9v depending on where you read your information and when you measure the voltage. I only charge to maybe 4v per cell max anyways, it just makes absolutely no sense to only discharge from 4.0v to 3.9vā¦ and while 4.0 to 3.7v is quite a bit of capacity, it still doesnāt seem like a lot. Gah. Any perspective would be nice, thanks!
Hi,
I have a 12s 4.6Ah 90c Graphene pack running 80 battery amps, 44V (3.66v/cell) soft cutoff and 42.6V (3.55v/cell) hard cutoff in my esc. I have monitored my cell deviation at lower cell voltages and as long as I stay at these voltages or above my deviation stays within 12mv or 0.012V if I discharge deeper with high amperage the deviation increase quick. My voltage sag at high amp is around 1v according to HUD.
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Donāt discharge your lipo cells below ~3.5 resting. Some people say 3.3, some people say 3.6 or even 3.7. I think most of those people are wrong, but like you mention, you also have to take into consideration what kind of sag youāll see at that low level of capacity.
So youāll probably sag to around 3.0 worst case if you only discharge to 3.5, which isnāt too bad. Any time you use your battery (charge or discharge) youāre damaging it, thatās just how batteries work. If you push them to any extreme, you damage them faster, but you get more out faster too. A trade off. There are efficiency targets to aim for though, taking into consideration usability. The graph looks something like this.
Charging to only 3.9~4.1 significantly increases cycle life as well, at the cost of lost useful capacity in each charge.
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I try to cut off at 3.6V. If I drop lower to come the last meters home I do no hard accelerations or something that does stress the cells. From 3.5V there is not much energy left in the cells and itās easy to fuck the pack up. I had it happen once, that I dropped below that 3.5V and some cells instantly dropped to 2.8V while others stayed at 3V of 3.4V. Took one minute on the charger to get them back to the same voltage which means the cells did not hold much energy below a voltage of 3.5V.
Disclaimer here, there is probably also a bit of a difference which brand and c rating the LiPo has. Some might tolerate a bit lower cut off than others.
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Agreed. My soft cutoff for lipos is set to 3.6, so I donāt sag it too hard beyond that. 3.6 to 3.5 is the emergency reserve tank.
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oof, I said wrong number for sagā¦ I meant 0.04v full load, so at 3.6v Iāll sag to 3.56v under full load.
Great graph btwā¦
with only sagging a bit, Iām curious if itās okay to ride down to 3.5Vā¦ and Iām generally unclear if 3.5v is 0%, 10%ā¦ Right now I consider 3.6v to be 0%, just seems high ish if full load sag at 0% would = 3.56v.
Iām pretty sure my soft cutoff is set to 3.65v and hard cutoff at 3.55v.
Lipos tend to settle from whatever down to 3.9 very quickly, and drop off after 3.5, but itās a pretty steady decline between that. 70mv/10% is what is used by those silly battery meters. Because of the curve I just mentioned, thatās only so useful, but I imagine thatās what was used for the purpose of this graph.
Those cutoff settings are real reasonable. Only charge to 4.0 or even 3.9 for many more cycles if you can sacrifice the single charge capacity.
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