How do you use a jk bms in a 10s4p build?

[vanillafish]

This is my first time putting together a pack, I have a JK_B2A24S15P that I got from AliExpress and I’m trying to use it with a Hobbywing ESC that is already built into an old skateboard I have. The battery pack configuration is 10s4p of samsung 30qs.

My confusion largely stems from the fact this bms has 2 wires labeled P- and 2 wires labeled B-

The B- as I understand should be soldered to the negative end of the battery pack. But there are 2 wires, do I solder both? Additionally I recall reading on this forum it’s common practice to bypass the bms discharge functionality and let the esc handle it. What does that actually mean - is the positive wire from the battery pack supposed to be connected directly to the esc?

Likewise a source of confusion is the esc has a wire with an XT60H-M connector that I know should be attached to the battery pack. I understand I have to make a wire and connector that pairs with it - and attach that somewere to the bms

Could really use some help here don’t want to burn anything down!

[SternWake]

Stating the model or posting a link of JK BMS would help us help you.

But,

That BMS looks capable of 32S. Using it on a 10 S battery is overkill.

A lot of higher amp rated BMS use two inputs, and outputs, as soldering 4awg to the PCB is difficult at best and damaging at worst.

In esk8, the BMS is often only hooked to the charge port. This is done as if it wete between ESC and battery, and if the BMS cuts power, it will likely do so under high throttle when one is braced for acceleration. Streetface possible.

If this does not cause a fall, one then has No Brakes. Dangerous.

A BMS of high enough amp rating to handle the discharge of a powerful esk8, takes up a lot of room inside an already tight enclosure, where most would rather have more battery cells instead.

Samsung 30q cells are still sold, but old.
They have a max charge rate of 4 amps, so a 4p configuration would be 16 amps max charge.

Old batteries will heat up far faster, and should likely not be charged at or perhaps even near their max rate.

Basically you can get a 20$ dumb Daly BMS, wired to charge port only, and let the Hobbywing ESC handle the low volage cutoff.

If a smart BMS is desired JBD seems to be the preferred brand, and i think these are also sold as LLT.

@Pecos will have better info on this

If you are replacing the BMS only, as the old one seemed faulty, consider the strong possibility it was not faulty. Consider the fact it might have saved the battery.
Old 30q cells have known issues with high self discharge. When any one.of the 10 P groups falls below 2.5v, the BMS prevents charging. This is its job, one.of them.

Trying to put new oversized BMS on this old 30q battery might be a giant waste of time. Measure the P grouo voltages.
If any or all are below 2.5v, the battery should be recycled.

There are Far Far better 18650 cells than 30Q. It had brief period when its 3000mah rating made the numbers look good, but it is only rated for 15 amps continuous, when new and healthy, and even then, only deliver 3000mah at a very low discharge rate.

Today the Ampace JP30 can deliver 3000mah at 28 amps continuous.

The molicel p26, p28, p30 can easily outperform the Samsung 30q.

I’d consider your old 10s4p samsung 30q as a waste of space. Trying to put a new BMS on it is likely a giant waste of time, for multiple reasons.

[Pecos]

Jbd smart bms are cheap and good

https://www.aliexpress.us/item/3256806831782876.html?

This one is my go to for low p count packs and i have one on one of my 10s6p packs and its doing great. The 40a version is the same form factor as the 20a version but has huge wires and some slightly different pcb population. I like smart bms so i can monitor the battery health and these are easy to configure. Everything @SternWake has suggested for cells is good advice - if you dont have free 30q cells or haven’t already purchased them the newer power cells will give you more bang for the buck and a better riding experience for likely cheaper or only very marginally more expensive

If you can make them fit 21700 cells have much better performance per kilogram ratios and higher performance cells are cheaper than the 30Q which is close to $4 a cell

The bak 45d is on sale right now for 3.25 a cell

18650 store 45d

Even if you plan on using only a small portion of the cells maximum continuous amperage, it is better to get higher output cells as they will be able to deliver more wattage at lower temps getting you closer to the maximum output capacity of the cell. In the same way as staying out of the throttle can get you more range - you just build that aspect into the specs and will constantly get more range.

Bypassing the bms and adding a loop key are standard practice nowadays on low voltage packs (16s and over the loop keys don’t work without special modifications)

[Pecos]

The battery builders club

For starters, post some pics of your battery build for some feedback as this seems to be your first attempt. Re BMS wiring, typically the below diagram will work for most BMS’s with common port but it could be different based on what brand you’re using. This is wire for “charge only” where you have bypassed the BMS for discharge and is, generally speaking, the preferred method for Esk8 batteries. There is also a loopkey wired in here in place of anti-spark which will serve much the same purpose…

Also check out @Common_good ’s post about bypass wiring, @b264 had a really good diagram somewhere too or maybe it’s the same idk

[b264]

@b264

BMS bypassed with loopkey and discharging with lights/accessories circuit

If your BMS doesn’t have C- or CH-, then connect that wire to P-

[b264]

Discharge via BMS or Bypass BMS? [SRO]

Let’s hear the pros and cons to both. If you know specific models of BMS and whether they cut brakes on overcharge or not, please list the model numbers.

[vanillafish]

Thanks for everyone’s comments - as an update to the thread I was able to wire everything up and ride my board for an hour last night! Here is some more context to the story since I didn’t provide that much info in the OP

My board is a Verreal RS from 2020 and the issue with it beforehand was whenever it experienced any amount of load the board would shutdown. On the bench I could throttle things upto 55km/h no issues for an hour straight. My initial belief was there is some cell within the pack that is dead and I simply have to identify and replace the culprit.

I took the pack apart and used an Opus charger to test resistance and capacity of all 40 cells which took about 2 weeks. None of the cells had a capacity under 2750 or an internal resistance reading above 80 so I’m assuming they are all healthy.

I had initially HOPED that the problem would be a dead cell, but since that is not the case my next bet was a faulty BMS so I ordered the overkill jkbms you see in original photos. The specific model of the one I have is JK_B2A24S15P. It’s rated to go upto 24s15p so I can use it in other projects, but for the purposes of using it in a longboard the biggest issue is all the extra wires I’m forced to keep bundled up in the pack. The back of the connectors is filled with silicon so I can’t really remove the excess without first trying to remove said silicon/glue.

In terms of wires there are 2 bundles of them and both must be included. The first bundle is from balance wires b0 to b14, where b0 get’s connected to the pack’s negative with the rest of the balance wires going to the pack groups in order. For the second bundle, the only wire that I had to use was the very last b+ wire. This one goes to the pack positive. So in total I have 12 balance wires going to my 10s4p pack, and in addition the fat B- wire also goes to pack negative. The P- wire I attached to the charging cable’s negative.

To connect to the bms I downloaded the Android app because the iOS version wouldn’t let me type into it - bug infested garbage. The Android version has it’s screen cutoff so it’s a farcry from being perfect, but it’s usable. On connecting I changed things in the settings to match my pack specs (default it assumes is 24 series so I had to adjust down to 10). It beeps everytime you navigate the app or change settings, which is a nice feature to know you are infact affecting the bms. I set it to automatically start balancing when voltage difference across cells is over 0.05

I tried riding the board last night because I wanted to confirm if everything works, I only took the board upto 25km/h top speed, originally pack started at 40.7V and after an hour it was down to 40.3 with no balancing required according to the app. So I’m going to assume the batteries are fine at this point. I do have a plethora of other issues that I didn’t think off originally

There are currently 3 inserts missing from the board, and in general I was only able to get 2 screws in. The enclosure is mostly being held in place right now because of scotch tape

And while I am thinking of upgrading to duct tape I feel the smarter approach is to fix the missing inserts - I got M5 13mm threaded inserts from Amazon but I’m not sure if it’s the correct thing to use

If those are in fact good to use what is the best way to put them in place?

From the photos you may have also noticed I’m using weatherstrips to raise the enclosure by ~26mm. There are 2 thick 10mm strips and then a thinner 6mm strips for the 3rd layer. This is because the bms is sitting on top of the cells and is 23mm thick - so that’s about by how much I need to raise the enclosure.

Does anyone have any better ideas in terms of how to raise the enclosure? Or perhaps somewhere I can buy a readymade one that will fit the deck I have and is deep enough to house everything?

There are two other issues that are pretty critical and I’m wondering if they’re related. The board has alot of trouble starting from rest because the belt skips teeth with the pulley system on the wheels. They are cloudwheel rover 165r that I got specifically because I knew I had to raise the board off the ground to have space for a deeper enclosure. The pulley and wheel do not fully fit to begin with in the sense that they cut into the protective aluminum cover that should sit over the belt. As a result I removed that cover. There is also some slack on the belt itself which is probably what is causing the belt/pulley teeth skipping issue (at higher speeds this issue does not exist it’s going from 0-7km/h that’s unnerving).

In that photo you can see the black aluminum piece that sits over the backside of the belt. This piece grinds into the wheel, so I had to remove it

And this leads to my the most pressing issue, the remote disconnects during riding. I have a video recording but not sure if I can upload here, essentially what happens is the remote screen shows it’s disconnected but I am still able to throttle.

When the remote reconnects it shows the speed is 0 for a couple of seconds until it updates to become the correct speed. Could the “teeth skipping” issue I described earlier cause the motors to have some type of reset that in turn causes the remote to reset? Thanks for reading

[b264]

@vanillafish

threaded inserts

Bolts through the deck with nylon locking nuts on the other side are superior to these.

[b264]

@vanillafish

These are bad solder joints.

[Belgarion]

how did you manage that?

[itsrow]

Don’t know how no one else commented on this, these should be reflowed, theyre all cold and potentially brittle/not mechanically safe.

[glyphiks]

reasons could include

• Iron not hot enough
• Tip not big enough/not enough thermal mass to heat the whole joint
• Poor quality solder

i remember getting joints like this when i first started soldering and after going through several different soldering irons and tips, progressively losing my mind getting the same results, i changed my actual solder and all my issues disappeared

[JustNeL]

What tips are you using now? Have a new iron sitting in my cart waiting for me to decide on what tips to get.

[glyphiks]

Please excuse the horrendous condition of my tip, it is due to be changed

This is my workhorse, dirt cheap 80w iron with a fat chisel tip. I use this for 99% of soldering that I do. I have a smaller adjustable temperature soldering station that I use for very small stuff like splicing balance/sensor wires.

expensive soldering irons are a joke. I think this one costs about 30aud and replacement tips are less than 10aud. These irons last me a few years before they crap out.

[b264]

@glyphiks

i remember getting joints like this when i first started soldering and after going through several different soldering irons and tips, progressively losing my mind getting the same results, i changed my actual solder and all my issues disappeared

Buy 63/37 leaded. Or at least 60/40 leaded. Nothing else.