Our motors and ESCs only work so well as space heaters. Increasing the amps going back into the battery will give you better braking at high speeds, where regen IS the bottleneck.
@BrassMittens unfortunately your battery pack is quite small, so you’ll be ruining your cell life with high regen, but it’s your only option. 10-12A is definitely safe, and I would even set it to 20A for emergencies, but keep the limit in mind when braking normally.
Edit: I see your BMS isn’t bypassed, so make sure not to fry it / trigger its cutoff. I don’t know that model’s specs off the top of my head, but usually there’s a limit of 20A, so something like 18A would be safest.
Fair enough. The regen energy has to go somewhere I suppose.
@BrassMittens unfortunately your battery pack is quite small, so you’ll be ruining your cell life with high regen, but it’s your only option. 10-12A is definitely safe, and I would even set it to 20A for emergencies, but keep the limit in mind when braking normally.
I’m already running the cells at 40A discharge so I’m not too worried about the cycle life as it is haha. I’ll bring it up to 12A for emergencies. I rarely go very fast on this board anyway so in an emergency I’d probably just run it off.
I’ve gotten it to cutoff discharge due to undervoltage (I forgot to set the BMS cut-off to 2.7V from 3V) and overvoltage, but never for overcharge or overdischarge. The BMS is rated for 60A in and out though, so I assume it will be fine, but I’ll definitely give that a test.
Man I love this build this idea is insane being able to quickly switch batteries plus you pulled it off really nicely
How long would it take to change batteries and how many spare do you have?
Taking under an hour to charge a pack means you’re decreasing longevity a little bit. For maximum pack lifetime maybe get another charger. Of course, it’s a swappable battery, so… yeah. Might be fine
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.
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.
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.
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.
(my charger/discharger seems to have periods where it’s very accurate)
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.
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.
looks like fun
