After jumping in a couple of threads today with irrelavancies (wristslap), I was looking at a 12v battery I have that’s lightweight, good energy density & a long lifespan.
So why aren’t they more popular? BMS charge/cutoff problems?
This looks promising, anyone used this company? https://www.ev-power.eu/LiFePO4-small-cells/LiFePO4-High-Power-Cell-3-2V-20Ah-Alu-case-CE.html?cur=1#tab2
LiFePO4 Don’t need a bms there chemical chemistry self balance them self. That battery only has 3c discharge that you listed . I think the major reason we don’t use them or most of us is because there big and bulky compared to 18650 cells.
LiFePO4 usually boasts a higher current draw. But are far from the density of top 18650 models. LiFePO4 might be abit more robust but they do still need balancing.
They were abit pricy for awhile, not sure if they still are.
Dimensions: Length: 178 mm Width: 71 mm Height: 28 mm Volume: 353.86 cc/ml Weight: 650g
Electrical properties: N Voltage: 3.2v Capacity: 20Ah Energy: 64Wh Max Discharge: 200A Power: 640W
Energy Density: 180Wh/L Power Density: 1800W/L Specific Energy: 98Wh/kg Specific Power: 980W/kg
Dimensions: Length: 65mm Width: 18.3mm Height: 18.3mm Volume: 21.76785 cc/ml (assuming it’s a cube) Weight: 47g
Electrical properties: N Voltage: 3.6v Capacity: 3Ah Energy: 10.8Wh Max Discharge: 20A Power: 66W (20A at 3.3V)
Energy Density: 496Wh/L Power Density: 3031W/L Specific Energy: 230Wh/kg Specific Power: 1404W/kg
30Q pack is 2.75 times more energy dense and 1.68 times more power dense. It has 2.38 times higher specific energy and 1.43 times higher specific power.
They are not popular because of this. It would mean for the same battery size and weight, you would have less energy and power and nobody wants that. Except for boosted boards… They’re weird…
E: added A123 cells from post below to keep it all in one post and modified the power data for 30Qs based on discharge curves.
Dimensions: Length: 65.15mm Width: 26.62mm Height: 26.62mm Volume: 46.16688 cc/ml (assuming it’s a cube) Weight: 70g
Electrical properties: N Voltage: 3.3v Capacity: 2.3Ah Energy: 7.59Wh Max Discharge: 70A (No discharge curve provided above 40A) Power: 231W (Extremely inflated as the cell sags 0.6V at 40A) Realistic power: 108W (Based on discharge curve on datasheet, 40A at 2.7V)
Energy Density: 164.4Wh/L Power Density: 5004W/L (3.3v and 70A) Realistic Power Density: 2339W/L (based on 40A discharge curve) Specific Energy: 108.4Wh/kg Specific Power: 3300W/kg Realistic Specific Power: 1543W/kg
The A123 compared to Samsung 30Q: Energy density ratio (30Q/A123): 3.02 Power density ratio (30Q/A123): 0.606 (based on 70A and 3.3V) Realistic power density ratio (30Q/A123): 1.296 based on discharge curves. Specific Energy ratio (30Q/A123): 2.12 Specific Power ratio (30Q/A123): 0.425 (based on 70A) Realistic Specific Power ratio (30Q/A123): 0.91 (based on discharge curves)
They are rated for a LOT of charge/discharge cycles.
I believe Metroboard uses LifePo correct?
A123 cells also have life chemistry if i remember correctly
I use them. A123 26650.They are great but they have their drawbacks also. Lower energy density compared to liion. Very few producers. And pretty high priced.
But man they are rigid. I have tortured them in all possible ways. They are safer. I have discharged them to 0.5V many times. They don’t show any wear. I have used them for spot welding also :). They are pretty much fire safe. They have high discharge current and really flat discharge curve. I like them a lot honestly. I run them without any type of balancing and they are still in 0.05V different.
I hear people call boosted board stupid for using them but I can disagree.
There is a thread here where someone uses these
http://www.evassemble.com/index.php?main_page=product_info&cPath=2&products_id=19
I did the price comparison based on using 12s3p of 30q to 14s1p of these and it was about $70 more and 7 lbs heavier. Maybe the higher Ah cells would be another option but would for sure make a heavy board.
That is the answer that makes sense, thanks you
Their Shortboard uses a 12S 5Ah LiFePO4 battery, yeah. They are also more rugged and last longer and have a smoother power curve; they stay near nominal voltage for longer during their discharge cycle. But yes, of course they are less energy and power dense than most 18650 cells. For a shorter-range board that needs to be RUGGED they can be ideal in certain narrow circumstances. My daily driver is one of these, modified slightly
There’s a big difference between generic lifepo4 and A123’s implementation. I’ve run my 12s2p pack for one year of almost daily commutes. Ridiculous batteries. Saved me from myself many times. Runs ruthlessly in the frozon nyc winters.
Pros:
Cons:
I think a 14s1p of A123 can fully feed just about any motor used for eskate. Nothing can touch it for regen, so amazing for hub motors.
I’ll run the numbers against 30q ala @PXSS if I remember.
I’ve looked, but am generally of the opinion you can forget about non-a123 LiFePO4 cells. The 200a EV cells sound impressive, but for a 12s setup that’s 7.8kg of battery! Admittedly the 20Ah will get you a fair distance, but being able to travel 40km on a single charge hasn’t been too high up on my list of priorities.
Specific power of the a123 26650 cell is listed at 2600 W/kg; that’s a bit higher than quoted for the 30q above (1532W/kg). a123 cells actually have a higher power to weight ratio, so Boosted may not be so weird after all 
Then there’s the nail penetration tests that make an interesting comparison. Not saying this is particularly relevant, but it certainly highlights the difference in stored energy density.
I went looking for the A123 cell datasheet and found it here.
So here’s the same analysis:
Dimensions: Length: 65.15mm Width: 26.62mm Height: 26.62mm Volume: 46.16688 cc/ml (assuming it’s a cube) Weight: 70g
Electrical properties: N Voltage: 3.3v Capacity: 2.3Ah Energy: 7.59Wh Max Discharge: 70A (No discharge curve provided above 40A seems fishy, no temperature profile accompanying the data either) Power: 231W (Extremely inflated as the cell sags 0.7V at 40A) Realistic power: 104W (Based on discharge curve on datasheet)
Energy Density: 164.4Wh/L Power Density: 5004W/L (3.3v and 70A) Realistic Power Density: 2253W/L (based on 40A discharge curve) Specific Energy: 108.4Wh/kg Specific Power: 3300W/kg Realistic Specific Power: 1486W/kg
The A123 compared to Samsung 30Q: Energy density: 30Q is 3.02x higher Power density: 30Q is 0.66x lower based on numbers. Power density: 30Q is 1.47x higher based on discharge curves. Specific Energy: 30Q is 2.12x higher Specific Power: 30Q is 0.464x lower based on numbers Realistic Specific Power: 30Q is 1.03x higher basedon discharge curve.
There is a caveat with the realistic numbers!!!
It is based on the discharge curve of the A123 but not the 30Q. So my 30Q numbers could have also been a little inflated. I must go to work so I will not be able to adjust those numbers until tonight. I don’t expect it to change drastically. Maybe ~8% lower.
30Q avg voltage is 3.3V at 20A, not 3.6. So yes, 8% lower is correct
Data added to post # 4
Maybe a monster Trampa build with 200mm+ tires would make sense. That EV pack comes to 7.8kg as mentioned which is a lot of weight for a pack on top of the rest of the running gear. in general ATB packs tend to be around a 3-4kg, so this is doubling on weight.
Price is very good for the amount of Ahrs you get €258 & assembly and protection woould be a breeze in this form factor
Where you get A123s and their price is another matter
Edit: Ok a123 on our old favourite https://www.nkon.nl/rechargeable/26650/a123-systems-anr26650m1b-a-grade-3-3v-a-grade.html
I’ve decided to pull apart the Veruzend pack and liberate 72 30Q cells based on the above, more 18650 cells down the road
hub motors eh? A123 cells mmmm interesting.
I’ve recently decided to use a123 cells on all my boards cause I don’t trust my kids to not make a mistake when riding and charging when I’m not there. They might smoke for a second but they won’t catch fire. Still wondering how many layers of 10mm x .15 nickle would be needed for the current. Really thinking of soldering gold coated copper battery bars like back in my old rc car days.
If you run different voltages with different chargers & the risk is a random charger plugged into a random board then use different conectors for each board? better than a fire or a smokebomb.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=58541 Nickel strip amperage = SA(mm)x19/4. It’s quite low. Ie 8mm x.15mm nickel = approx 6amps
nice chart here https://endless-sphere.com/forums/viewtopic.php?t=68005
about 10A with 0.15mm X 10mm pure nickel
And a resource on-site here
Good idea. All the kids have 6s packs and they have their own chargers with a serious training lesson. I’m harvesting these cells from electric bus batteries and got the price down to 1.50 per cell.
Are the cells still in good condition with good lifespan though? Read that the electric buses put considerable strain on these batteries, even if they’re highly rated a123 cells