Fsr they want to make the path longer and therefore higher resistance? Taking the “electricity is like water” analogy too far?
On a different note, builders that have a 3d printer with a heated print bed - you can use it to help flatten shrink on the ends super nice by preheating the bed to 95-105c depending on your shrink and setting the to be flattened pack on it. Let the whole pack come up to temp then apply the shrink - works automatically
Say you have a 2.1KW pack that you just got done using. If the temps are around 35c, is it ok to put on the fast charger right away? Or is it best to let it sit for a bit, even if the cells are cool enough to charge?
The closer they are, and stay, to room temp the better. Occasional warm charging won’t do any big damage but regularly doing it will noticeably affect cycle life.
“ The ideal operating temperature range for most lithium-ion batteries is between 20°C and 45°C (68°F to 113°F) . During charging, the temperature may rise slightly but should remain below 50°C (122°F). Exceeding this range can damage the battery and pose safety hazards”
“There’s no guesswork here — the recommended lithium-ion battery operating temperature range is -20°C to 60°C for discharge and 0°C to 45°C for charging, depending on the battery chemistry and quality.“
These are pretty high temps and the two sources conflict.
Agreed, over 45°C is above “warm” and 60°C is getting too hot to hold.
But those temp limits conflict only because they are either discussing different cells and/or have different priorities and thresholds for what is an acceptable rate of aging.
Going over 50°C won’t cause “safety hazards”, even for a 60°C rated cell (typically only ultra-high capacity energy cells) and most are rated 80°C. A few are 70°C though.
The higher you consistently bring a cell though the faster it ages. But as long as you’re staying at under its max temp limit you aren’t creating a safety hazard beyond that which the manufacturer finds acceptable, i.e., it’s very low.
The max temp ratings and the recommended operating conditions for decent cycle life will always be different and different people will have different recommendations.
Those who prioritize cycle life might recommend never exceeding 45°C. Those who want max power with some acceptable level of accelerated aging will say stay under 60°C. Those who value max power at just about any cost will say you can go to the cell’s rated max temp every cycle without greatly increasing the safety risk…and they’re right. But the cycle life for most cells will be pretty short when doing that.
So the bottom line is pretty much “it depends”. But we have a lot of leeway and there are many “correct answers” depending on our priorities.
Any updates on any tabless cells performance/prices? Me and @Pecos aren’t satisfied with P45b performance. Felt like we aren’t getting the miles we’re suppose to get, even when riding conservatively.
The Reliance RS50 should be in stock beginning of next month.for 5.95$
Funny how a little l over a year ago the P45B was the bench mark, and now looking at Mooch’s charts at 40 and 100amps continuous, it sags harder, gets hotter and delivers the least wH before hitting 80c.
One thing that I dont think we talk about enough in the battery builders club is delivered capacity (mAh or Wh) down to our cutoff voltage.
Most cells are rated with a 2.5V cutoff, and all their capacity ratings are based on discharging all the way to that cutoff pretty slowly. But we dont do that. We discharge pretty quickly, and we set our cutoff at 3.0V/cell (or thereabouts, for most people).
So if you want to PROPERLY compare cells, you need to look at actual (measured) delivered energy discharge graphs, at the current levels you expect to use. Look for voltage sag, and the shape of the discharge curve. And most importantly, look for the delivered energy at the cutoff voltage you plan to use.
It doesn’t matter if a cell is rated for 6000mAh, if it sags to shit at the current you plan to use. In the same way, it doesn’t matter if a cell is rated for 6000mAh if it only delivers 4000mAh down to 3.0V cutoff.
This is a lot more common than I think people realize. For example, when comparing the delivered energy of the P42A, P45B, and P50B at 20A discharge…
Look at the blue curve (20A) in all these graphs. And look at where that blue curve crosses the 3.0V line on the graph’s scale. That cross-over point tells you how much capacity that cell will deliver at that discharge current and at that cut-off voltage.
The P42A @ 20A discharge to 3.0V delivers ~3600mAh.
The P45B @ 20A discharge to 3.0V delivers ~3800mAh.
The P50B @ 20A discharge to 3.0V delivers ~4000mAh.
That’s not a big jump between each cell. Definitely less than the ~500mAh jump on those cells datasheets. Part of that is because some of the remaining capacity lives between 3.0V and 2.5V. This is not me advocating for lowering our cutoff voltages. I’m just pointing out that our cutoff voltage affects what we get our of our cells, and so you cant just assume you’re getting the full rated capacity stated on a cell’s datasheet.
Honestly im aware but have grass is greener or green eyes or maybe just eating the hype. My experience with the 50s cells in an 8p pack consistently provided 4000mah usable capacity at 25a a cell vs a p45b in a 6p pack at a marginally higher draw (30a a cell) which i planned to and should be giving up 3400 but is actually doing closer to 2800mah. Sourced the cells from a reputable supplier and confirmed weight matched the specs within my ability to accurately measure.
Whatever the deal is these p45b cells are significantly under performing for me. Measured wh output is 1.1kwh and i tried to build a 1.5kwh pack which 18s6p p45b should have been able to do.
Temps are amazing but i was trying to thread the needle for 35-40miles of range and im consistently rolling in to charge at 30-33 miles at 3.2v or less. If the performance of the tabless cells is an improvement, at a lower price point, and higher safety factor; then im gonna try em.
@Battery_Mooch i actually have some of the p45b cells leftover from this order fresh and unused but just kept at low storage voltage since the build. Would you be interested in testing a couple of them if i sent them to you? I know they are old news and you are plenty busy im sure but they really do seem to be performing under spec OR im doing my math wrong OR my usage telemetry is inaccurate (vesc and megan).
They just don’t seem to be doing what they should be doing. Maybe i got a batch of mistreated or counterfeit cells? Maybe im just a whiny baby who wants too much from the cell idk
What are you charging to and from? That does seem low. I’m pretty sure a full charge on 18s4p p42 is like 900 Wh for me, and if anything, I’m averaging higher draw and actually higher consumption. I average like 45 Wh per mile and get about 20 miles of range if I’m really hitting it.
Maybe my maths is off, im charging to 4.2v but it settles around 4.18v. Then i am also running to 3.16v for the 33miles of range. That’s probably my oversight. Let me put all my math down here for a little community audit:
P45b 18s6p 30a a cell or 180 battery amps max total for 2wd (90a each esc)
At 30a from 4.2 (settles at 4.18v after 20min resting after charging) to 3v a cell cutoff but 3.2v is where i usually stop to charge. Should be something close to 3.6ah a cell but im just gonna call it 3.2ah to compensate for my narrower band of usage
64.8v (nominal) x 19.2ah = 1244.16wh
27wh a mile light usage, 35wh high. Megan measured average of between 31 and 34 wh per mile.
Edit: my average amperage per side over 5 rides is 17a or 34a total or 5.6a per cell. Maximum draw is 180a peak total or 30a a cell for at most .5 to .25 seconds.
This should net me at least 35 safe miles of range ya? I thought this would be 35 miles of range with a buffer but im sneaking into charge at 3.16v at 33 miles taking the first and last miles hella conservatively
Did i miss something here? Maybe im not topping the cell up enough but i figured reducing my estimated cell ah from 3.6 to 3.2ah was going to create a better margin
Maybe i just need to set a lower cutoff end keep the cutoff start to eek out the last little bit of range
I have a lot of shunt based ammeters, and some hall effect too.
All seem to have a range where they are somewhat accurate, and a range where they appear to have been smoking crack for 3 days straight.
Usually at lower currents, they read super low, or even nothing at all when there is still 0.5 to 0.8 amps flowing.
I am not sure how well any Vesc accurately measures Amperage, but I assume measurement error whenever my numbers don’t match expectations and no other variable can account for the difference in expectations and results.
It may have something to do with the way my average draw is calculated vs how much of an effect high draw bursts affect this cell chemistry and how much it reduces its ability to output energy. I just picked the p45b because of its better performance at higher amperage but whatever im doing its really murdering the availability energy per charge. But then there are new better performing cells out now and even better ones on the horizon and this makes me pretty critical of this build’s shortcomings.
