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What's the reasoning behind LV cutoff being so low?

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What's the reasoning behind LV cutoff being so low?

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Old 11-30-2018 | 08:05 AM
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Default What's the reasoning behind LV cutoff being so low?

Let me just start with where I'm coming from. I've been a professional drone racer for about 3 years and it's my current source of income. A typical 4s race drone pulls anywhere from 70 - 130a depending on KV / prop choice. Our lipos are tiny in comparison to surface RC with the average size pack being a 4s 1500. As you can imagine pulling 130a from a 1500 mah battery is really hard on the pack.

That being said the main thing we do for longevity is to make sure to not drain the pack below 3.6v per cell. I'm even more conservative and won't go below 3.8v when I'm practicing. We've learned over the years if you regularly go below 3.6v your $40 lipos are not going to last very long. When I say long my packs usually last over 200 cycles barring any physical damage.

I've recently got back into surface vehicles and with all of them the options for LVC is really low like 3.4 or 3.5v. By default my son's Tenacity T was set to 3.2v I think. Why? If I could I would set it to 3.8v on everything because these packs are really expensive lol.
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Old 11-30-2018 | 10:17 AM
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For an rtr like the tenacity it is likely to increase runtime for the consumer. I work at a hobbyshop on the weekends and one of the top three questions we get is how long does the battery last. For the everyday basher they don't care about IR or longevity of the pack so much as they want to play as long as possible on one pack.
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Old 11-30-2018 | 10:23 AM
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You have this a little backwards. For maximum longevity LiPo's have a "sweet spot" somewhere between 3.6 and 4.0v, holding them at high charge voltages for storage can damage the pack, as can over-discharging the pack. As for the cutoff voltages being set where they are the packs may not have as long of a life being heavily discharged, but it shouldn't cause acute failure and I think it would be a bigger issue for the drone to quit at the end of a race than it would be to have it give what the battery pack has to give.

So don't store batteries charged, store them at about half charge and in the fridge. Heat will degrade lipos, and can make them puff.
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Old 11-30-2018 | 11:23 AM
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As stated earlier, mostly for run times, and to prevent premature cuttoffs. One thing to note, some modern brushless systems have a high amp draw at full throttle. Even good Lipos can/ will have a voltage sag in those conditions. Often times, you can hit LVC of 3.4v, and by the time you pull the battery and check it, it's rested long enough to go back to 3.7 or higher depending on the pack.
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Old 11-30-2018 | 11:30 AM
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a couple of points. A lot of ESC's you can set the LVC so if it comes preset too low for your taste, just increase it. If you have an RTR type ESC that you can't program, you can always add a cheap battery alarm. I got some from Hobbyking and you set a voltage and they start beeping.

Not sure where you set your drone LVCs but the LVC is going to kick in on loaded voltage. So the resting voltage of the battery after LVC will typically be higher than the LVC setpoint. I would think you see that on the drones with your very high C-rates.
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Old 12-01-2018 | 10:48 AM
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Originally Posted by Di_spencer
For an rtr like the tenacity it is likely to increase runtime for the consumer. I work at a hobbyshop on the weekends and one of the top three questions we get is how long does the battery last. For the everyday basher they don't care about IR or longevity of the pack so much as they want to play as long as possible on one pack.
That actually kind of makes sense. In the fpv drone world we require a pretty high level of knowledge to even get started which is probably why interest has been fading since 2016 lol.
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Old 12-01-2018 | 10:50 AM
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Originally Posted by DesertRat
You have this a little backwards. For maximum longevity LiPo's have a "sweet spot" somewhere between 3.6 and 4.0v, holding them at high charge voltages for storage can damage the pack, as can over-discharging the pack. As for the cutoff voltages being set where they are the packs may not have as long of a life being heavily discharged, but it shouldn't cause acute failure and I think it would be a bigger issue for the drone to quit at the end of a race than it would be to have it give what the battery pack has to give.

So don't store batteries charged, store them at about half charge and in the fridge. Heat will degrade lipos, and can make them puff.
I assumed general lipo maintenance was a given. The single biggest killer of lipos is over discharging barring any physical damage. You can literally destroy a brand new lipo running it down to 3v if the cells aren't quality.
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Old 12-01-2018 | 02:55 PM
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Originally Posted by Furadi
I assumed general lipo maintenance was a given. The single biggest killer of lipos is over discharging barring any physical damage. You can literally destroy a brand new lipo running it down to 3v if the cells aren't quality.

I somewhat disagree, in my experience most lipos puff or are rendered unusable instead of failing catastrophically, and I would say most of that is caused by heat or being stored over 60% charge. I've run cells to the cutoff, and they charge up just fine. Obviously this isn't something you want to do consistently but running a LiPo down to 3.0V per cell should not destroy it or hurt it.
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Old 12-02-2018 | 08:46 AM
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Too low of a LVC? If you absolutely want to have a higher LVC suited to one's taste, there are high-end speed controls out there that will allow you such programming.
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Old 12-02-2018 | 09:15 AM
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Originally Posted by rustyus
Too low of a LVC? If you absolutely want to have a higher LVC suited to one's taste, there are high-end speed controls out there that will allow you such programming.
plenty of budget esc also have this. Not all RTR do.
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Old 12-02-2018 | 11:52 AM
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Originally Posted by rustyus
Too low of a LVC? If you absolutely want to have a higher LVC suited to one's taste, there are high-end speed controls out there that will allow you such programming.
Right now I have a Mamba X in my Rock Rey and Dynamites in my Tenacity's. They all have adjustable LVC. My point is they're all low. 3.4 or 3.5v. It should at least go up to 3.6.

What brand ESC goes higher cause I'll keep that in mind for the future...
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