Sleepless’ post is a really good one Sprung vs unsprung weight is important. Strategic weight reduction that can help everyone regardless of how heavy you are.
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Push every now and then ? 
damn I wish I could push 45km/h without dying
Yo thought about, but never build something with
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I just can here to say the same.
I made a Samsung 40t 12s10p pack for high current use to maybe replace the lipos I use.
It was unreasonably heavy, used it for a week and gave it to someone.
I was under the impression LiPo batteries had a strictly worse Wh/Kg than Li-Ion?
Go Team W/kg!!!
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My use case is for power packs. All the Amps Right damn now for only 5-10 miles. Li-ion sucks for the weight I’m used to and power I like to use.
I too like all the amps right now, but at the same time I like to go for a reasonable distance.
This conversation gas been making me lean more towards LiPo than I ever have before, you think I could get better energy density with them? as in, more longevity at the same amp loads, or more amps with the same longevity for the space available?
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Looking at some specific power/specific energy plots with generalized chemistry’s.
They all trend with lipo characteristics below li-ion.
I’m confused. I should probably do some reading.
Based on what’s available to buy commercially right now, what’s reasonably priced and in stock, 15-10ah packs from reputable lipo brands are light weight and generally meet the watt demands of bigger boards.
I don’t know anymore than that.
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Your post above this one answers your question…
LiPo li-ion cells typically have a lower energy density than “standard” chemistry li-ion cells. This means shorter run times for the same weight.
LiPo can be better for more current for the same space/weight though due to the (typically) lower internal resistance of the cells. All depends on the particular cells chosen though, of course. Only talking generally here.
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So much depends on how old those charts are but…
LiPo li-ion cells can have incredibly low internal resistance vs “standard” li-ion chemistry round cells and that decreases the voltage sag at high power levels
That allows for running the LiPo cells harder, at higher power levels, before the low voltage cutoff is reached. Technically perhaps the power density isn’t as great as we think for LiPo’s but the practical advantage of that lower internal resistance means we can often run good LiPo cells harder.
So many things all at work at once, crazy to all sort out if someone just wants to know what to buy.
I guess, in the end, forget about theoretical density and just look at the specs for the cells you are considering using. Their weight, size, performance, and price will guide you to the that is best for your application.
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Lets do a Cubic Centimeter per Watt hr. Comparison
Lipo Pack.
16ah @ 14.8v (4s) = 236.8Wh
4.4x7.3x17.9cm=574.95ccm (pack area)
Thats .41Wh per ccm
Question is, With the cylindrical cell and the area loss between each cell how much watt hr per ccm is there when you stack a 236.8Wh pack for Wh per ccm area comparison.
1.36kg for the weight comparison
Somebody please do the Cell pack Math so we can compare energy density per real area used.
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8 - 16 km
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i find this super interesting so decided to do the math as i was curious.
Firstly lets swap ccm for L as industry standard for this is Wh/L.
So the li-po pack is 16Ah and 4s giving 236Wh. its total volume is 0.574L so its energy density is 410Wh/L
lets compare this against a similar pack made from P42a.
a P42a is about 4.2Ah or 15.5Wh per cell. A 4s4p config gives 16.4Ah or 248Wh so its not far from your li-po pack.
Assuming you arrange in a grid (worse case with no staggering), the p42a in a grid of 16 cells in 4x4 arrangement would be 8.4x8.4x7 = 0.494L.
For the P42a pack that’s 502Wh/L . Almost 20% more Wh for the same volume.
If you run this math with an energy optimised 5Ah cell that increases further to 600Wh/L.
And neither of these include stagger stacking the cells in larger packs. The volume of a cell above is assumed as a rectangle 21x21x70mm so 0.031L per cell, but if you consider them as hexagons as you would in a brick pack then this volume is reduced to 0.27L making a the same 248Wh fit in just 0.426L.
This give a staggered P42a pack an energy density of 582Wh/L
or a staggered 5Ah cell pack an energy density of 693Wh/L
TLDR:
Bad P42a pack is ~ 25% more Wh/l
Staggered P42a can but up to ~35% more Wh/L
Staggered 5Ah cells may be up to ~55% more Wh/L
EDIT: fixed mistake, factor of 1000 out for Wh/l.
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That definitely puts it into perspective.
Nice work
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Side Note:
The P42a datasheet rates the cell at “615 Wh/l”. I think to get this number they are assuming the cylindrical volume which is not practically achievable in most EV designs. But is only 20% ish out from what we have calculated suggesting its probably fair to use 80% of this number from the datasheet as a good estimate of what might be achievable.
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Fair enough.
All calcs are good calcs, but why do we care about volumetric energy density?
At some point we run out of room of course
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build bigger boards/bigger enclosures.
is nobody looking at Wh/Kg?