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Old Jun 30, 2015, 08:57 AM
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A few general Lipo charge / discharge / storage questions?

Ok, don't shoot the messenger, just passing on what I was told.
1. If I cycle my batteries to 3.20-3.25v then recharge for storage to 3.80-3.85v, how is this different than having a battery above 3.85v and discharging it to 3.8-3.85 for storage? Reason I ask? The resting voltage is higher on the charged too batteries than the discharged too battery (same batteries different cycles)? Should they be charged or discharged to 3.8 for proper storage?
2. FMA /Cellpro (I have a PL-8) tells me that (for quality batteries) 3.20v won't damage a cell / battery and that the "hard deck for damage is 3.0v". He also stated that the 3.20 is a safety or fudge factor number to keep mfg's warranty claims in check and add a "cushion" and some info about the newer batteries chemistry vs. the old? Any thought /comments?

If this is actual, then why all the banter about running to LVC (assuming you have tested and verified that your esc actually does cut at 3.2? I know some / many will go lower before cutting and I understand that IS bad but in my case I have verified my esc's LVC points and none of them are less than 3.18. So why not get full capacity runs if this is the case. I'ts kinda like having a V-8 and pulling two plug wires or a 20 gallon tank and only filling to 18? Just asking?

Capt. Thomas

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Old Jun 30, 2015, 12:47 PM
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#1 Doesn't make any difference practically speaking. I prefer 3.8V for storage and set the storage charger to that value.

#2 Most(?) battery packs are made from unmatched cells. Cells of different capacity that is.
If you have a 3s2000mah pack that contains cells with capacities of 1900, 2000, and 2100mah, what will happen when the pack is discharged?

The #1 cell will reach 3V or lower while the higher capacity cells are still in the safe range.
That is one reason why it is recommended to not discharge below 3.7V (80% discharged). That keeps the lowest capacity cell from being over discharged.

Now if you have matched cells with essentially the same capacity (quality battery), that is not a concern.
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Old Jul 01, 2015, 01:59 AM
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So as a battery discharges through the main leads (not the balance tap) it does not discharge evenly across the cells and a esc is only seeing the voltage of a single / individual cell to know when to activate LVC? I thought voltage was a function of absolute measure for charge state, not capacity? Is a battery of 2100 mah at 3.2v more powerful than a battery of 1900mah at 3.2v? I see the ability to run longer but not be more power or to be damaged more or less at the same voltage. With regard to balance charging or discharging, yes I see that because the tap allows it. But in this case 3.2v in one cell is the same 3.2v in another cell or in the case of 1s batteries is it not?

Along the same lines, how many batteries are actually the name plate rated Ah/Mah? Since the voltage (either too high or too low) is the measurement of when and if damage occurs, mah
doesn't figure into a over charge / over discharge, mah is just kind of along for the ride as a function of voltage isn't it?

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Old Jul 01, 2015, 03:23 AM
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No unfortunately you have most of that exactly the wrong way round.

1. The ESC LVC isn't measuring the voltage of one cell. It's measuring the overall voltage and hoping that all cells are more or less equal. So when you say 3.2V/cell and use a 3S pack it's stopping at 9.6V and just hoping that isn't made up of 3.4V, 3.4V, 2.8V. Fortunately cells aren't usually that badly out of balance so it is normally o.k.

2. The capacity (mAh) is the capacity. The voltage at any discharge level is just a reasonable guide to the capacity left. And that's another reason why we generally allow a bit of leeway. Because it is overdischarge that actually damages the cell and the cell voltage just gives you an IDEA of whether you're overdischarged.

BTW "more powerful" isn't really very meaningful. A 2300mAh cell at 3.2V probably has more energy left in it than a 1900mAh cell at 3.2V. But power is voltage x current and there's no mention of current here .

Steve
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Old Jul 01, 2015, 06:57 AM
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No I'm not including current for these questions because it is not a measure of reference for the purpose of charge / discharge / safety / maintenance. I'm just trying to wrap my head around all the hub bub of the comments like "well they are your batteries do what you want if you like replacing them every three months" or "your a fool, your model is going to explode if you treat your batteries like that" etc. Common sense must apply as we know that puffed cells and fires do happen and are a direct cause of improper use and handling. But when one of the more / most respected mfg.'s of not only chargers but also batteries tells me that (and again qualified with) with the newer design's and chemistries for quality batteries 3.20v is not a problem and won't damage or degrade the cell / cell's even over time I have to wonder if all these comments are antiquated, at least for quality batteries and those that actually verify there cells and equipment?

Like I said not trying to argue just trying to understand the different schools of thought and the advise / comments being given. If 3.7 volts under load is indeed 80% discharge then I wonder where the 3.2-3.3 figures came from?

I guess the bottom line is I don't mind spending the time and I have the equipment to verify ESC, max loads, LVC etc. and I don't buy cut rate batteries. My hanger uses Revo, Dinogy, Pulse, Glacier etc. and if I do buy a cheap battery it's likely for one of my micros and they $2-$6 each, if it puffs or only lasts a few month's then I really don't care vs. flying for 3 min. and a battery lives for a year or I can fly it for 5-6 min or more and it needs replacement more often? I think some people are WAY over protective and or working off of old info IMO.

I don't abuse, I buy quality and I spend thousands on tools and equipment to be informed of operational conditions. Hell I dyno every model I buy or build both gas and electric before it goes in the air as well as check and tweek everything thing that comes out of the box because I don't really like to have to USE the warranty, I'd rather catch it before we go wheels up. For those that don't and just "plug and play", I understand the mfg. having there safety recommendations and cushions in place.

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Old Jul 01, 2015, 08:00 AM
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Quote:
Like I said not trying to argue just trying to understand the different schools of thought and the advise / comments being given. If 3.7 volts under load is indeed 80% discharge then I wonder where the 3.2-3.3 figures came from?
3.7V/cell is not under load. It is the resting voltage which represents a remaining capacity of about 20%.
The 3.2-3.3V/cell is the under load voltage/cell which is the LVC setting for the ESC.

Roughly speaking, a cell with an underload voltage of 3.2V will measure 3.7V (resting) when the load is removed. The actual amount of rebound will depend on the load as the amount of rebound increases as the load increases.

Quote:
But when one of the more / most respected mfg.'s of not only chargers but also batteries tells me that (and again qualified with) with the newer design's and chemistries for quality batteries 3.20v is not a problem and won't damage or degrade the cell / cell's even over time
3.2V will not damage a cell but under 3V is getting iffy. I guess are attempts to explain why one cell in a pack could go below 3V in a multicell pack as did slipstick, are not working. The ESC is measuring total pack voltage, not individual cells. See page 44 in this article, http://ygdes.com/LiIon/technique/Kokam_LiPo.pdf Look for "Zone of Temptation".
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Old Jul 01, 2015, 09:23 AM
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You need to be clear about the difference between voltage UNDER LOAD, which is what the LVC is measuring and voltage OFF LOAD, which is what you would measure after a flight when the battery voltage has rebounded, as they all do.

The normal recommendations are no lower than around 3.2V (some say 3V etc) UNDER LOAD. That should lead to about 3.7V OFF LOAD, which equates to roughly 20% remaining. It's that 3.7V which is important in capacity terms.

The reason it's difficult to be definite about the voltage UNDER LOAD is because that's quite variable depending on how much load CURRENT you are drawing. At high currents the battery voltage drops more and so 3V may equate to 3.7V OFF LOAD. At very low currents then 3.5V UNDER LOAD may equate to 3.7V OFF LOAD. But again it's the 3.7V you're looking for.

So that's probably confused you more...but the reason why you can't get a simple answer is because the situation is inherently fairly complex.

Steve
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Old Jul 03, 2015, 03:06 AM
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Understood Steve, and I have stated several times above "under load" and mentioned testing ESC's / LVC and dyno'ing power systems, all of which occur under load as well as data logging flight & load conditions. I thought I made that clear. Personally I find "resting voltages" and mention's to them as almost useless in most cases since there are to many conditions and variables involved with seasoned and broken in batteries. I think you nailed it that I'm not going to get a straight answer because there is a lack of current and or definitive actual knowledge. It appears that most of this "information" is dated / antiquated at best and worse too "monthly replacement of batteries and burned up models on a weekly basis". Some of this I hear in the forum's, much of it at the field.

I think I'll go with the mfg's info and as long as my gear is above 3.1-3.2v (too be on the safe side of the 3.0v hard deck) under load...... I'm fine with it and full capacity flight times allowed by real time data.

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