Basically, set it as high as you need to for desired braking performance.
Also, I’d love to hear @Battery_Mooch chime in on this subject. On a 1P P42A, is 20A charge a problem? It wouldn’t last more than maybe 2 or 3 seconds at the most before rapidly falling, unless you’re being pulled by a car or you weigh 800 lbs (360kg)
Nice I’ve also played with this idea on and off over time, very well done. Suggest getting on the tpu for some of these parts or at least for little soft spacers for things. Tpu is small nightmare to get working right but once printed the parts are typically very durable.
^^ those are my doing, the black is tpu on the longboard for the battery/bms. Orange is petg, with the straps eating some of the energy from impacts etc. it works fine but not nearly as pretty as yours 
I am planning on a lightweight board too for commuting in-between buses and subways. I think one motor is plenty for that and will give you like 30-40% more range since you have less drag, only one motor to drag so almost none. I have done test with a 6P lipo and does well. Thanks for posting, I might do a 12s also.
This is false. With light EVs in particular, there’s no where near enough thermal mass to dump all the energy of your momentum into heat. Ever seen a racecar with glowing red-hot brake rotors from hard braking? We don’t have that luxury.
With esk8, when you brake, all the energy from you slowing down goes into the battery (excluding losses of course). That means that if you have no regen, the energy can’t go anywhere, and you have no brakes.
(This is also why if your battery is disconnected when going down a hill, like in the case of a non-bypassed BMS, you will lose 100% of your brakes. And this is why you shouldn’t go down a long steep hill on a full charge.)
More regen = more brakes.
This is especially important at high speeds, where the braking power (and thus the regen power) must be highest. That’s why increasing the regen current improves your brakes at high speed.
Cool build. Love the idea of an electric street deck. 
looks like fun
Is it really an ollie, if it’s off a ramp though…? 
Good lookin’ build.
Is it a problem? Yes.
How much of a problem? I don’t know.
As I understand it, heating will be minimal but pulsed fast charging accelerates aging of the cell and can plate lithium onto various surfaces…that’s bad. The ions literally bunch up and plate out wherever they are since they are unable to get into the nooks and crannies of the anode material quickly enough.
As usual a lot depends on the cell, how much current, the cell voltage (state of charge), how long the high charge current is flowing, temperature, etc. I’ve seen pulsed current fast charge methods but they are set up for one particular type of cell (usually for an EV) and issues are always mentioned. It’s always a tradeoff between the convenience of fast charging vs cell life.
20A charge into a P42A will cause accelerated aging (damage) but I don’t know enough to be able to quantify the damage. You might be able to do that thousands of times before there’s a noticeable performance drop or increase in the risk of using that cell. Or you might start having issues after doing it only a few dozen times.
I’ll ask someone I know who works with Molicel on a lot stuff and see what he says.
Even if I shake it up SUPER well? Jk lol
Very good way to think about battery performance.
Is there really any difference between discharging and charging a cell as far as high Amps damaging the cell?
Yes. There can be different damage mechanisms involved when charging versus discharging and it happens at different current levels.
Most of the stuff that happens, for both charge and discharge, results in loss of capacity and an increase in internal resistance (causing more voltage sag). Specific things though can help metallic dendrites form that can eventually cause an internal short circuit (slow or fast)…charging when too cold, over-charging, and over-discharging are some.
Thanks for clarifying this. I really thought the energy would “turn into” heat hence my conclusion.
I apologize for giving out the wrong info.
Some of it does, but it’s not the majority.
There are losses in the conversion process, in the motors, the ESC , and the battery, and those losses all result in some heat being generated. But it’s probably less than 20% of the overall energy of braking.
Sorry for the late responses. The forum understandably limits the number of times I can reply on my first day after posting.
Is that a harder TPU? I’ve never played around with that material before. Once I found PETG I went PETG-only. That would be a pretty solid replacement for the foam underneath the batteries. What TPU do you recommend?
And yeah that’s like the same exact thing! I like the straps, that looks pretty quick to swap. Plus then you don’t have to worry like I do about the battery completely falling off if the thing decides to break on you.
I highly recommend it! That’d be a perfect use for it. When the weather was less gross where I live I used to take it out on my lunch break to grab some food. It’s perfect for bringing inside restaurants.
I’d say go with the single drive for so many reasons. It’s cheaper, weighs less, and gives you more range. I went with 2WD mainly because I like to ride with loose trucks and with such a short wheelbase I’d definitely notice the board turning on me when I accelerate hard. Plus I’m a fiend for torque. You might want to go with 6S though since you’d have more braking power without hurting your cells. The only big disadvantage of 6S would be less speed, but imo you don’t want to go very fast with a small board like this. That’s just me though.
Haha thanks man. You’ll have to be the judge of that.
Please update us on what he says! I’m going to increase it to 12A regen per cell and I’ll update this post with what the capacity drains down to after a few hundred cycles. Thankfully with the smart BMS I’ll be able to (somewhat) accurately track the number of cycles. I might log the data over time too, we’ll see.
I can compare this to another P42A cell I’ve been cycle-testing in my spare time. It’s only cycled at 0.4A discharge to 3V and 1A charge so the comparison between the 40A discharge to 2.7V and 12A pulsed charge with 4.5A continuous charge on this pack could be interesting. So far I’m 86 cycles into the single cell test with a relative capacity of 94.5%. I’ll update this post with how it performs over the long run alongside the stressed 12S1P pack updates.
Also @Battery_Mooch, if you don’t mind, what is the mechanism behind what sets the lower limit in temperature when charging these cells? I’d assume it’s the density of the electrolyte changing with temperature, causing ions to clump up, but I know little chemistry and I’m talking out of my ass here so I’d love to know what the real reason is. Also is pulsed charging okay in low temperatures? I ask because a buddy I built a pack for is on a mission to ride his board in the winter, and it gets down to -40C (-40F) here. I told him it’s fine to ride (its a 12S6P P42A so the increased sag shouldn’t be an issue), but he’d have to let it come up above zero before he charges it. Could you let me know if I’m letting him destroy his battery?
Ah sorry, I just meant TPU itself not something different was just typing on phone. I used some from hatchbox TPU it’s not super stretchy but definitely flexible enough and if you make the walls 3 thick then it’s pretty rigid but can take some blows and will flex around still with screws a bit instead of cracking (I also tried the battery box in PETG at first but cracked where the bolts/screws hold it into the deck)
IMO, the biggest issue is plating out of the lithium at high charge rates. This could eventually lead to soft or hard internal short circuits…never a good thing.
I agree, slower ion diffusion rates through the electrolyte and anode material at low temperatures is what causes plating out of the lithium. There might be other mechanisms at work though, I don’t remember.
Using cells that are at low temperatures is more of a performance issue than a safety issue IMO but it could depend on the cells and certainly could depend on the actual cell internal temps.
If the board was stored indoors and then used outdoors in cold weather the cells might never have a chance to get cold since using them generates heat and they’re insulated a bit in the pack and pack enclosure.
I recommend letting the cells come up to room temp before charging. That way if things are ever rushed a bit it’s still okay. Does your friend have a way to read the temp of a cell? Thermistor for the ESC which can be read via an app? If not, wait a few hours after bringing it indoors and charge then.
No type of charging at low temps, pulsed or continuous, is okay IMO. Even a 100mS pulse is still straight DC current for that entire time and will do the same thing over that time period as a 100mS portion of a fully continuous charge.
Looking forward to your cycle life comparison!
Sweet thanks, I’ll check that out. Hopefully it prints okay with a bowden extruder…
I had a lot of cracking when I first starting printing enclosures in PETG when I had the layer plane parallel with the deck. After I starting printing them like they are here I haven’t had issues because the walls are able to flex instead of the layers flexing and shearing apart. I also make sure that the bolts hold the enclosure along the length of the deck which also allows the enclosure to flex.
Jeez okay that’s not fun. I’ll keep an eye out on the cells right after charging then to see if they start to lose their charge immediately due to the shorts. If so I’ll live with the poor braking.
Yeah he has the same smart bluetooth BMS from LLT with two thermistors, one on bare metal of a cell in the pack. As far as I know he’s been playing it safe and charging around 10 degrees but I’ll link him to this comment chain so he can read up.
So really he just should never store his cells in low temps for a long period, especially if charging? I’ve talked with him and he was riding while it was below zero out, but the cells were at like 12 degrees, so I guess that’s fully fine. It’s just that once he lets his pack sit in the cold he shouldn’t ride it but if he does he should never brake.
Thanks! Me too haha.
Thanks for your time!
Most li-ion cells are rated for storage at down to -20°C and use at anything above that (but performance is miserable if cold) . Charging must never take place below 0°C though.
Update post almost a year later:
The battery is dead and the board is to be scrapped.
Surprisingly the high charge/discharge rates are not what killed the battery. I left it plugged into the board for one month and the damn Flipshit anti-spark slowly drained the low capacity battery down to 2V/cell… I could recover the pack but I won’t because I rarely used this board anyway. I only cycled it 10 times in one year…
If you’re curious, the parts of the board will all go to good places.
Update on my low-budget, low-stress cycle life testing of Molicel P42A:
Honestly idk why I did this but I find it kind of interesting even though its results don’t really apply to esk8 whatsoever.
Test conditions:
Currently at 275 cycles and just under 90% capacity of initial discharge (initial capacity was 3757 mAh).
It seems like 500 cycles to 80% is likely. I’ll probably stop the test at that point. This is less than Molicel rates it for in the DS (500 cycles to ~85% at 20A discharge to 2.5V and 4.2A charge) and what other have measured (1000 cycles to 75% at 20A discharge to 2.5V and 2A charge).
I think there is accelerated decay of the cell I’ve tested as each time it is cycled I have to manually restart the test. I restart the test each morning, and each discharge/charge cycle takes about 11.5 hours. This means that the cell has sat idle at 4.2V for more than half of its life.
So I guess what you can get from this is that to get more life out of your packs, make sure to only charge them before you use them, and not right after you’re done using them. This limits how long they sit at 100% SOC, where the cell seems to degrade a lot quicker. This isn’t anything new, and I think most people do this already, but its good to see the data to understand why you’re doing it.
