BMS for @Winfly compression battery

I assembled a 12S6P battery pack from the @Winfly compression holders and need to figure out my BMS and ancillary items for spacing / enclosures. Rather than 3D printing them , I milled the battery holders from Delrin on my CNC and threaded a set screw above the terminals on both ends to secure the braided wire up against the batteries. Otherwise it’s the same design as @Winfly. Since milling them, I have bought a 3D printer so I’m looking to print an enclosure for the Flipsky 6.6 VESC I bought. Found something close on Thingverse - the power connectors on my Flipsky are out the side compared to the motor connections on Thingverse. So that’s a good starting point.

I’m not sure what BMS to use or how to connect the BMS wires to my cell holders. I’ve read quite a bit about various BMS options on this site. The braided wire is slightly exposed where it exits each holder - then it’s protected by heat shrink up to the XT90 connectors. I probably should have used XT60, but went conservative with the larger connectors.

Now that I have the pack assembled, I plan to CNC or print something to hold them together and provide enough separation at needed points.

If I do solder the BMS wire to the braided wire I’m not sure if I solder it on the side leaving the holder or the side entering the holder? I’m guessing it would be on the side existing the holder but I’m not sure exactly how a BMS does what it’s supposed to accomplish.

This VESC has a power button adapter and I’d like to fuse the connection from the charger. Reading about that - aside from space issues - any reason not to use a DC Circuit breaker rated accordingly? Seems easier to flip a switch than replace an epoxied fuse… But that’s also why I want to lay things out, to see if space will be an issue. The deck is fairly big - 670 mm (26.3 in) length - for supporting the underlying electronics so I think I have a decent amount of space to work with…

Any thoughts are appreciated.



@thisguyhere @MrDrunkenMobster

What thingiverse file are you using? As for the bms, you need to look at the pcb on the bms or the bms schematics and determine your balance connector type. Most bms’s have an extra balance lead that always hooks up to the main negative terminal then the remaining balance leads go to each and every positive side of each series. For example a 10s bms with 11 balance leads will need the very first lead to be connected to the main negative terminal and the remaining 10 leads will connect to all positive terminals. The 11th wire will connect to you main positive terminal. As for curcuitbreakets you need to determine the latching and unlatching limits, I’ve seen them fail because they couldn’t unlatch fast enough and the connectors inside arced enough to fuse.

Thanks. If I’m understanding correctly, Pack 1 has the negative lead and Pack 12 has the positive, so the extra balance lead hooks up to the negative of Pack 1, and then the first line solders to the positive of Pack 1, with the 12th soldering to Pack 12. Assuming the BMS works in ascending order - I’ve seen some that work in descending order.

Forgot to mention I’m using Panasonic NCR18650BD batteries which are rated for 10 Amps continuous. When connected, my volt meter was reading 49.2 Volts. I used the LiitoKala Lii-500 Battery charger to Vol Test and charge all the batteries since they are salvaged.

1 Like

This is the Thingverse files I downloaded…

Yep, just make sure to compare this general rule with the bms schematics.

Not sure where so many web sites got that 10A number. The datasheet does not list a current rating, which means it is low…very low. The discharge graph in the datasheet shows a lot of voltage sag starting at around 6A, the highest discharge shown.

For decent performance and cycle life I wouldn’t use them beyond 5A/cell or so.

Is that something I would control in the VESC Tool?

1 Like

Yes, it would be “Battery Current Max”

For a 6p it would be 30A, which you would split to 15A for each VESC if it is a dual.

1 Like

Mooch - is this based upon your review from 2016? JoeyZ5 - thanks for that info, it will be a dual set up. I bought the Flipsky BH 6374 190KV 3500W motors.

Panasonic NCR18650BD 3200mAh 10A cell's capacity test. This is a separate testing review FYI. Seems to imply 10A continuous is reasonable. But other reviews indicate maybe 7A continuous…

So if I set “Battery Current Max” in the VESC Tool to 10A per cell, so 60A total and 30A per motor, does that pose a safety issue? Or just a shorter battery life or other issues?

Thanks for your input.

That is my test report from 4-1/2 years ago but the standards I use for my advice regarding safety, good performance, and cycle life changed a couple of years ago. This was due to all the additional testing I have done since 2016, showing me what happens to cells when operated near or above their continuous current rating.

If I retested the BD cell now it would get about a 6A rating.

Any battery can be rated at just about any current level. It all depends on the degree of safety, performance, and cycle life you are looking for. Sure, you can use the BD at 10A. But the risks go up, life expectancy goes down, and performance is worse versus using it at 5A.

You can run them at any level you want, it’s your call. :slightly_smiling_face: My recommendation is to run at 6A or under.

1 Like

Thanks! I’ll start at 5 Amps and see how it performs. Board is for my 14 year old son so hopefully he’s not trying to break any speed records early on :grinning_face_with_smiling_eyes: