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EV newbie here with some questions about LiFePO4.

I'm working on a motorcycle build, and wanted to go with LiFe. The impressive lifespan, low weight, and chemical stability are very appealing, particularly for a platform where crashworthiness is a major concern. A 96v nominal 100Ah system is easily doable for weight distribution and physical spacing.

At 3.2v per cell, am I correct in building a 30-cell pack, or is a 32-cell pack necessary? My charger shopping seems to refer to both setups as 96V.

LiFePO4 has a ridiculously flat voltage profile. Does this make voltage useless for determining SoC? What would make a viable "fuel gauge"?

What would a BMS bring to the table that a charger alone wouldn't handle? It'd be fairly simple to rig a differential voltage indicator to identify any bad cells for a few pennies each. Why is even a cheap BMS several hundred dollars?

My background is in aviation, so I've got a decent handle on electrical basics, but with little experience in anything outside SLA the collective wisdom here is much appreciated!
 

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EV newbie here with some questions about LiFePO4.

I'm working on a motorcycle build, and wanted to go with LiFe. The impressive lifespan, low weight, and chemical stability are very appealing, particularly for a platform where crashworthiness is a major concern. A 96v nominal 100Ah system is easily doable for weight distribution and physical spacing.

At 3.2v per cell, am I correct in building a 30-cell pack, or is a 32-cell pack necessary? My charger shopping seems to refer to both setups as 96V.

LiFePO4 has a ridiculously flat voltage profile. Does this make voltage useless for determining SoC? What would make a viable "fuel gauge"?

What would a BMS bring to the table that a charger alone wouldn't handle? It'd be fairly simple to rig a differential voltage indicator to identify any bad cells for a few pennies each. Why is even a cheap BMS several hundred dollars?

My background is in aviation, so I've got a decent handle on electrical basics, but with little experience in anything outside SLA the collective wisdom here is much appreciated!
Yes, voltage is not a useful SoC gauge for lifepo4 batteries. It's common to use amp-hours.
 

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The energy density of LFP is much lower than using li-ion 3.7Vnominal chemistries.

But cycling lifespan 10x longer

New Grade A cells from a top maker, cared for properly might reach 3-5000 cycles even in a propulsion use case.
 

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My 2cents worth. I have used LiFoPo4 cells now for about 10 years on my Electric KTM (EV Album 3817) They are good, and lasted for 4 to 5 years, My first set of 16S Prismatic 40AH 10C cells (48V nominal). This pack would give me 400A and my motor would handle 400A (ME1004) all matched well. And this pack weighed about 52lbs with BMS. I lost cells due to carelessness, and lots of use (mostly carelessness). This pack is about 1.9KW for 52lbs. Now on a dirt bike weight is critical as well as max current (and or voltage ) for max power. The second set of LiPo's were Headway 15AH 40152 cells, with 15C. I configured these for 48V also and 16S3P. This gave me a potential or 675A, at 48V and about the same weight as before. My motor is rated at 400A, but my controller will allow me to go to 500A, which I am going to try soon. My mistake on my first set of Headways was not putting a BMS on it and monitoring cells occasionally. I lost a bunch of them, and have now just replaced the bad ones and put a BMS on it. I use the BMS only for Charging, since the cost of one for 400-500A output is high, and it is bigger "weight". Note, go with a Smart BMS, You can see so much more about each cell group, I will explain a little later.
Now this battery pack can give me 45AH and is about 2.3KW for about 55lbs. My motor is not rated for 72V but I could reconfigure the pack to give my 72V 30AH 24S2P and 450A peak. (2.2KW pack energy)
When you are choosing a motor, it has to be rated at a certain amount of voltage and current. You can run higher current than the motor is rated at, for a while, but there are consequences. I ran a ME0909 motor at 400A (it is rated at 200A (6 smaller brushes) and it eventually melted the brush block.) The ME1004 am now running is rated at 400A, the brush blocks are huge, and there are 8 of them, no problems there. That is why I will probably bump the current up to 500A, and see how hot she gets.

Now my new bike. A ME1302 PMAC brushless motor. Rated at 120V 660A. I am not running the motor at max Voltage. My new battery pack is Sony VTC6 Li-Ion 420 cells in a 20S21P configuration. It gives me 72V with about 600A. ( I have them in 3 packs of 20S7P for theoretically 72V at 210A each, but I measure about 190A actual out of each pack.) The advantage of these cells and pack size is that its almost twice the stored energy as the LiPo4's. 72V x 63AH, or 4.5KW of pack energy and 57lbs. I also put a Smart BMS (Daly Brand) rated at 50A charge. You can monitor each cell group when they are charged up when they are discharged to see if all 7 cells are working in a group. on my dash I monitor the Voltage for discharge, as well as a watt meter bar gauge.
With the new battery, I get over twice the laps on a motocross track, as I got with my KTM and smaller capacity battery.
Anyway I think that is a little more than 2 cents worth.
Don
 

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My 2cents worth. I have used LiFoPo4 cells now for about 10 years on my Electric KTM (EV Album 3817) They are good, and lasted for 4 to 5 years, My first set of 16S Prismatic 40AH 10C cells (48V nominal). This pack would give me 400A and my motor would handle 400A (ME1004) all matched well. And this pack weighed about 52lbs with BMS. I lost cells due to carelessness, and lots of use (mostly carelessness). This pack is about 1.9KW for 52lbs. Now on a dirt bike weight is critical as well as max current (and or voltage ) for max power. The second set of LiPo's were Headway 15AH 40152 cells, with 15C...

My new battery pack is Sony VTC6 Li-Ion 420 cells in a 20S21P configuration. It gives me 72V with about 600A. ( I have them in 3 packs of 20S7P for theoretically 72V at 210A each, but I measure about 190A actual out of each pack.) The advantage of these cells and pack size is that its almost twice the stored energy as the LiPo4's...
Your terminology is confusing - you seem to be using "LiFoPo4", "LiPo", and "LiPo4'" all to mean the same thing. The electrode chemistry that we're talking about is LiFePO4 (or "LFP"), and that's likely what you mean; "Li-Po" means lithium-ion with polymer electrolyte, which is an unrelated term.
 

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LiFePO4 and LFP

are the canonical terms for that chemistry

In some contexts you see LiFe.

But nothing to do with LiPo, which although it is just a packaging technology, is a term from the RC hobby market

and always used with the higher density but short cycle life 3.6-3.7V chemistries e.g LCO or LMO
 

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Google shows some youtubers and asian marketeers using the string

LiPo4

to mean LFP (LiFePO4)

But IMO that should be shunned as confusing.
 

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To clear this up, I was using LiFePO4 in all the cells in the KTM. They have a nominal cell voltage of 3.2V . Thus a 16S group of these cells will give you nominal 48V pack.
The Sony cells mentioned later are
Sony VTC6 (Murata) 18650 Battery Authentic Flat Top Rechargeable 3.7V Li-ion
There are too many to miss call on all these cells chemistry acronyms.
And my 20S group of these will give you a nominal 72V pack.
 
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