Watt hour for lippo and lithium-ion

[bionicon]

Hello I have a question about the wh between a lippo and a lithium-ion.
If i have a 30ah lippo pack and a 30ah lithium-ion pack wil i theoretically can drive the same distance?
I ask this because a full lippo is 4.2 volt and a empty is 3.0 volt but with a lithium-ion battery full is 4.2 and empty is 2.5 volt, so there is a diffrence of 0.5 volt in empty cells will this result in diffrent milage?

 

[flat tire]

Title in watt hours, post in amp hours. And as you'll see the two are not the same.

First and most importantly, you do not ever want to discharge a lipo to 3 volts resting. That will ruin the battery. Better to limit discharge to around 3.6v resting for longevity.

The simple answer is lipo (not fcking lippo, jesus) is 3.7 volts nominal while li-ion tend to be 3.6 so the capacities of the 2 30 amp hour packs are actually different:

lipo: 3.7* 30 = 111Wh
Li-ion: 3.6* 30 108Wh

Multiply this by the series count to get full pack capacity. Anyway as you can see the difference is very small.

 

[bionicon]

sorry for misspelling lipo.
I can calculate wh, but what I actually mean is that if you discharge the same wh battery you can go the lipo (this is purely theoretical) to 3volt and the lithium cell to 2.5volt, and my question is whether this results in longer distance? Because you start with both of a maximum voltage of 4.2 volts.

 

[hemo]

In real world use the lion should edge it due to it's safer lower discharge, lipo will hit the cliff at a bit below 3.6v for ebike use where as lion will be ok down to 3.2 - 3.3v. No one takes lion to 2.5v and again not many would take lipo to 3v let alone much below 3.6v.

 

[amberwolf]

fwiw, the discharge curves are different for the different cells.

so the total wh available in those curves is different, especially under different loadings.

so, when comparing different chemistries (or radically different types of cells within a chemistry), you probably can't just calculate what each one would be to compare them directly.

if you really want to know if the two packs you have are comparable, you'll need to charge each pack to it's full level, then discharge each pack separately under the same conditions, same load, thru a wattmeter, to see how much wh you would actually get out of each one.

they will probably be pretty similar, for most comparisons, but some will be noticeably different because of different cutoff points in bms lvc, or because of cells in one pack that don't provide as much energy under higher loading conditions that the other pack cells do provide under.


if you're not using a bms with appropriate lvc for each cell type, and only manually shutting off based on overall pack voltage, the comparison may be different depending on what you choose to do at shutoff point / when you choose to shutoff.

 

[dogman dan]

Theoretically, an amp hour is an amp hour. But vendors sell based on theoretical capacity, not real world watt meter tested capacity. And alas, sometimes vendors just plain lie, but that is easy to tell just by price. If you are buying a 48v 20 ah battery for 200 bucks, they are lying.

But back to real capacity. you can make a pack using cells that are rated to add up to 48v 20 ah, but the combination of the bms, and the charger supplied, results in a full charge being a bit less than 4.2v, and the bms may cut off before every single cell in the pack is empty. Its supposed to do that, protect from both overcharge and under charge. And the result may mean a few watt hours less.

Then there is lipo. If you mean RC packs, they come with no bms. This means, if you are smart, you stop very conservatively early. And you may choose to slightly undercharge, since there is no bms. The combined result can be that you routinely use only 16 ah, out of a 20 ah potential.

Then there is wear and tear. With very cheap cells of any type, real world capacity can drop quite quickly, in months rather than years. This can happen because each cell is simply being stressed too hard by the discharge rate. The more stressed the pack is by the discharge rate, the lower the real world capacity will be.

BTW, those Ah ratings for each cell, they do those with a test at very low amps. Real world amps are nearly always a lot more than the test. So your rate of discharge can vary a lot depending on the size of the battery, and how its discharged, and can result in big differences in real world capacity. Different types of cell can stand higher rates of discharge. In general, the RC type lipo has much higher ability to discharge at high amps, but also can wear out extremely fast if amps are extreme. Great choice for the drag strip, but maybe not so great choice for the commute.

However, if you size your battery correctly, meaning it is large enough and results in a low rate of discharge, closer to the test rates, then each type should have very similar range per amp hour.

Lastly, when you get down to the last amp hour, a battery that can discharge to a lower voltage will result in lower speed at the end. This is because your speed is determined by voltage, and if volts are lower at the end, you are slower in the last few miles.

 

[bionicon]

I am planning to make a 20S 33ah pack with 11000mah (4s) lipo battery.
I gonna balance them with a ant bms, probably will charge them to 4.15volt and low cut-off wil be 3.5volt.