I am in the process of making my first DIY electric mountain board. I think I understand most of the build, but am super confused when it comes to what BMS to choose. I plan on running dual 6384 190kv motors, using a Go-FOC DV6s ESC, and am planning on making a 12s7p battery using samsung 18650 30Q cells. How should I go about choosing a BMS, any suggestions would help. also any anti-spark suggestions?
my nominal cell voltage is actually 3.6, not 3.7 sorry for the typo
Basically just crabs in a bucket mentality but applied to cell voltages
2 Likes
This is a nice little smart bms.
I am using a couple.
And I also run some Flipsky anti spark switches like this.
if you can fit 21700’s, you should.
The Samsung 30Q is an old cell of comparatively mediocre performance, and is Not inexpensive either.
In DIY esk8, most everybody uses their BMS as a charge only BMS. This allows a much physically smaller BMS, enough to handle the max expected charge current.
The ESC handles the low voltage disconnect. So basically th main + and - from the battery go directly to the ESC, they don’t go through the BMS.
This is done as the BMS cutting power under acceleration, when one or many cell groups start flirting with 2.5v, can throw the rider who was braced for acceleration, not braking, and if the rider does not get thrown, they then have no brakes.
If you want to use a BMS for discharge it needs to be big enough to handle the maximum current that the ESC can draw, with a healthy overhead, and you need to expect the BMS to potentially cut out under acceleration when the battery is at a low state of charge, or one parallel cell group is way lower than the others/ out of balance and/or capacity compromised.
In general the BMS cutting power might be really good at preventing the battery from going out of its safe voltage range, but it might put the Esk8 rider in the hospital.
A Small BMS wired for charge only is much physically smaller making it easier to do wire management inside the enclosure.
The Antispark switch might not be necessary depending on Which ESC you use, just use a XT90S antispark connector from the battery.
If you are really stuck on 18650’s, and are in the US, right now molicel P28A is priced right and will easily outperform the samsung30q. It will sag less voltage, and stay cooler, and a cool battery lasts longer, and less sag generally means a spicier more responsive throttle.
If money is no Object and 18650s have to be used, then the Eve30PL and Ampace JP30 are the two best 18650 power cells available as of march 2026.
3 Likes
Nominal is just a name, it’s not the actual cell voltage. Things saying “3.6V” or “3.7V” are all 4.2V cells, generally. Both of those work for 30Q cells, which are not the best cells you can get. This is mostly to differentiate them from LiFePO4 cells which might be named “3.2V” but are typically charged to around 3.65V. (not to be confusing or anything)
It also depends on what you want. Do you want to be able to diagnose problems without taking it apart, by seeing battery data on a phone, but also have the power to break it in more novel ways? Then you want a smart BMS. Otherwise, you don’t. Those are also often larger physically and have a larger price tag. Especially with the 30Q cell choice I would highly recommend it, but don’t change settings with it if you don’t know exactly what you are changing, why, and how it can break it.
Not everyone, but there are advantages and disadvantages:
Yes, I would emphasize the word “healthy”, like double it. At least.
So first figure out whether you need discharge or bypass configuration, then figure out whether you need a smart or dumb BMS, and then we can suggest specific models if needed.
1 Like
Thanks! I’ll check both of those out.
Ah ok, I was only going to use the 18650’s because I had seen other people use them. I’ll check out the 21700’s. Also thanks for the explanation about the BMS, I was having a hard time finding anything useful describing how and what I should use. I think I’ll go with the charge only so I don’t break anything.
Awesome, once I figure out what I’m working with I’ll see if yall have any specific models in mind.
Any suggestion on where I can find 21700’s that are legit, and what “type” (50E, 50S or other) I should be looking at?
if you are in the USA 21700 Battery Cells .
Nelvick @DIY500AMP.COM is a member here and has done a lot for the community by getting the latest and greatest cells into the hands of @Battery_Mooch quickly, for professional testing.
Cells largely fall into 2 intended applications, energy cells and power cells
An energy cell usually has a lower 60C max temperature rating and a lower maximum continuous discharge. They have higher resistance and will sag more voltage under load than a power cell.
A power cell usually is rated to 75 or 80C under discharge, has a lot lower resistance, will maintain a higher voltage under load( less sag) and stay a lot cooler.
While energy cells like the samsung50E can be used in less powerful boards when there are many in parallel, very few here would recommend using an energy cell over a power cell.
The Samsung50S was kind of th efirst crossover cell with both high capacity and a pretty good power delivery, but in the power delivery department it will sag far more and get way hotter than the newer generation of power cells, referred to as tabless cells. note that tabless is a widely accepter but inaccurate term. They still have tabs, but the ‘jellyroll’ itself inside has a continuous tab connecting to the current collector plates instead of one single tab.
The Best Tabless 21700 cells available at the moment are the RelianceRS50, TenPower50XG, Eve 50PL, Ampace JP50. The BAK45D is also a very good ‘tabless’ cell.
There are the 4000mah tabless cells like the Ampace JP40, eve40PL, reliance RS40 which are a bit less money, and they sag little and run cool.
Molicel P42A is a well respected cell and so is the P45B and P50B, but none are ‘tabless’ and they will sag more and run a bit warmer. Molicel is a very respected cell manufacturer that someone new to the Li-ion battery world, who only recognizes Samsung or LG as a brand name, might not realize.
if You are intending to build your own battery you must realize it is a lot of work, and the tools and materials and skills required to do it properly, for just one battery build, will cost more than having a custom pack built for you by a professional. There are a few here who will build you a high quality custom battery.
An Esk8 battery needs to be able to handle board flex and vibrations( even on pneumatics) that no other application has to deal with, so there are methods to address this that no Ebike battery builder has had to ever think about.
There is also some opinion and personal philosophy regarding cell choice. I have built several batteries now, and my biggest regrets are not using better cells, trying to save some money or thinking the nominal capacity of the cells actually correlates to actual range in use.
I have had batteries just get too hot for comfort, and a hot battery degrades faster and is a lot less safe if it exceeds it max temperature rating, or approaches that temperature regularly.
I am personally all about getting cool running cells as I am running only 1 or 2P and they have to work pretty hard, even though my power is a fraction of that of the enthusiasts here.
it is hard to not shop for cells based on price, but every time I chose a cell based on price I regret it, and wish I spent more for a better cell. Certainly some cell deals can be had on desirable cells but those rarely apply to the latest and greatest, like the 5.0Ah ‘tabless’ cells I listed above.
if you are deadset on building your own battery, you have a lot of research ahead of you, and skills to build, and tools to acquire, and a cheap soldering iron or Spot welder will come back to bite you in the butt and cost you more in the long run.
3 Likes
This. Building a battery doesn’t save money. It’s not even close.
Building 100 batteries can save money. That is why, unless you want to create them for personal reasons or start a battery business, it’s generally better to buy one from another person.
There are also a ton of things you need to do or need to not do in order to make it safe, and it will take you a very long time reading to know of all these things.
Batteries are also extremely dangerous, akin to bottled lightning, and they have to be built correctly if they’re ever to be stored/charged inside your home.
4 Likes
I would third the advice that building batteries is hard and super time consuming.
You should really consider buying a pre made pack.
5 Likes
Thanks for all that info, and for the links to the people I should talk to about getting the cells I will need. I think I may still try to build my own battery as it is something I’ve been interested in for a while but I will definitely consult these forums before I try. Maybe I’m looking in the wrong spots, but from what I’ve seen buying a battery like a 10S8P can cost upwards of $900. Am I looking in the wrong spots or is that around what I should expect to spend? Also thanks for all the help explaining this.
U can get a cheap spot welder for like 100$ and stack layers of nickel or even copper and stainless steel and building can be much cheaper
Batteryhookup.com is a good resource. For first battery if u want to be safer could do lifepo4 battery chemistry
1 Like
This welder rocks.
1 Like
Suggesting that the first step is buying a welder is bad advice in my opinion.
If ur making a battery u need a welder.
@Pringlesbuilder ive got another welder i dont need I’d sell for 30$ but dont see where ur located
NO body was going to be able to talk me out of it either, as it was something I wanted to do.
I found Shuttershocks’s videos to be a great watch when beginning to confront everything I did not even know that I did not know, about building an esk8 battery.
here is one:
Everytime I do build another battery I rediscover how much work it is, how many different stages ar required, and how far it can be taken to make it perfect and overkill.
You need to know how to solder too. I thought my Soldering skills were OK, far above average, and compared to joe six pack they were, but building an Esk8 battery I learned they were not very good and still are not where I want them to be. Nothing beats experience. Don’t try and learn when needing to soldering live 10awg to an XT90s.
Lots of safety equipment involved too. You don’t want to be breathing fumes from the soldering flux or getting solder all over your fingers and touching your food, or the corner of your eye.
Also get a large metal bucket with some sand and a lid and have a plan to get it out of the workspace ASAP, and be able to ventilate the toxic fumes.
When you short a battery the sparks will require fresh underwear, at best.
2 Likes
I’ll check this welder out!