What is available capacity of lipo?

[Jesse J]

My LHS buddy was just telling me that the mah rating on the battery is the amount you can safely take out of it. :confused2: This is very different from what I have believed until now... (not that I believe it yet). He is saying that they actually have more capacity beyond that written, and can take in more that what is written...

So, anybody care to clear this up for me/us?

Now that I think about it; I just charged up a 3S lipo, 4900 mah written capacity, and on my lipo cell meter there was one bar left, meaning that it was above 20% remaining "capacity", barely. I then charged it up and it took 4400 mah...

What is the real truth about this issue?

[Steven Vaccaro]

I've always gone by what people have posted at try not to take more than 80% or so out.

[Ub Hauled]

Go by voltage... set your LVC to 3.4 and go until then or less... every battery is different.
unless you are going for SAW type drain then it would be different,
then go by percentage...

[Jesse J]

I've always gone by what people have posted at try not to take more than 80% or so out.

80% of what? I know, the numbers written on the pack. But are these numbers already 80% of the true capacity?

UB, why do you go by voltage rather than capacity? I have heard others say that once the LVC shuts you off, you are already doing damage.

[sailr]

If you set your cutoff voltage at 3.2V per cell or higher you will never do damage! Fully charged, each cell has around 4.2V. This falls off very quickly to 3.7V per cell and stays there for a period of time before tapering off.
Normally, the mAh rating on the pack is what it is! It is NOT 80% of the capacity. What would be the point? The manufacturer is going to want to label it with it's MAX capacity, not something lower!

[Ub Hauled]

If you set your cutoff voltage at 3.2V per cell or higher you will never do damage! Fully charged, each cell has around 4.2V. This falls off very quickly to 3.7V per cell and stays there for a period of time before tapering off.
Normally, the mAh rating on the pack is what it is! It is NOT 80% of the capacity. What would be the point? The manufacturer is going to want to label it with it's MAX capacity, not something lower!

I think what he meant was use only 20% of the capacity and leave 80% of it there...
also, the voltage that it'll drop to under load is directly related to how hard he's running and also which cells are being used.
.02

[Ub Hauled]

80% of what? I know, the numbers written on the pack. But are these numbers already 80% of the true capacity?

UB, why do you go by voltage rather than capacity? I have heard others say that once the LVC shuts you off, you are already doing damage.

no... if you set the LVC properly there will not be any damage, that's why CC and other strongly suggest that one has to set the LVC properly if using lipos.
I use Voltage because it is the measurable variable in the pack... the voltage in the pack is a direct result of the mAh in the pack

[sailr]

I guess you're right. 3.4V is 80% of 4.2V . Makes sense.


I think what he meant was use only 20% of the capacity and leave 80% of it there...
also, the voltage that it'll drop to under load is directly related to how hard he's running and also which cells are being used.
.02

[Jesse J]

This is starting to make sense. Glad I have my cell meter to do the thinking for me. Reckon I will start using LVC.

[NativePaul]

Your LHS friend is correct, to a point, if we take a 5000mAh pack for example the cell manufacturer will have rated it at 5000mAh down to their predetermined cutoff it is normally a safe one but lower than we would set our LVCs to for a decent battery life, often 3v but sometimes lower I have seen cells quoted down to 2.8v and even 2.6v this figure is often not disclosed leaving it in doubt, but if we take an average example of at 3v you can achive its 5000mAh capacity which is safe and the cells may last a couple of dozen runs, or you can set your LVC to 3.4v and get 4200mAh out but your cells may last a couple of hundred runs but on the other hand you can not set the LVC and drain the cells completely down to 2v which will likely ruin the cells on that one discharge but you may get 5700mah out of them, how much of that extra is useful for our purposes is debatable as the voltage and ability to dish out current are diminished at the end to the point where there is little power there.

[Steven Vaccaro]

I see there is some talk about 3.4 volts for the lvc. I've spoke with the engineers at Dimension Engineering, at 3.4 volts they said some high amp setups could hit that voltage under peak situations. for example, take off or reentry.

[sailr]

I totally agree Steven. I normall set mine at 3.2V or even 3.0V.


I see there is some talk about 3.4 volts for the lvc. I've spoke with the engineers at Dimension Engineering, at 3.4 volts they said some high amp setups could hit that voltage under peak situations. for example, take off or reentry.

[Jesse J]

Sweet, you guys are awesome, I knew a little discussion could go a long way. So a good way to go would be to start at 3.4V and the lower it if needed to keep it from cutting out right when you need to get out of the hole.

OK, so if you are running two packs in parallel, do you think you would have a better chance of staying above 3.4V even on digging out etc.?

[sailr]

Yes. Remember, two in series doubles the volts, while two in parallel doubles the amps. If you have a high amp draw setup, paralleling the batteries will give you more capacity to run longer before the volts drop. This IS, if you are paralleling two batteries the same mAh as the single you would have run otherwise. It doesn't work if you would run two 2500mAh packs in parallel or one 5000mAh. Same-Same. It DOES work if paralleling two 5000mAh packs.

Hope that's clear enough.


Sweet, you guys are awesome, I knew a little discussion could go a long way. So a good way to go would be to start at 3.4V and the lower it if needed to keep it from cutting out right when you need to get out of the hole.

OK, so if you are running two packs in parallel, do you think you would have a better chance of staying above 3.4V even on digging out etc.?

[Jesse J]

yep! makes perfect sense.

[m4a1usr]

OK, so if you are running two packs in parallel, do you think you would have a better chance of staying above 3.4V even on digging out etc.?

Thats what logic would indicate but unless you are monitoring each individual cell you have no clue as to what is happening in each pack. All you are doing when using the LVC on your speedo is taking the packs cell average. Add a pack in parallel and the situation worsens. The voltage sag in any one individual cell may be far lower then the safe cutoff setting. It depends on the quality of your pack and how much useage it has seen. Using a LVC device like one that monitors each cells voltage is the only safe way to ensure the health of a pack if you want to take out as much as possible from your packs. Not my opinion. A fact.

John