Li-Ion battery pack without bms!?

Hello, I found this Video on youtube and I think its pretty good, what do you think about it?


If you don’t use a BMS and don’t balance your cells, chances are something is going to go wrong after 10+ cycles. :popcorn:

EDIT: This is completely incorrect.

Good quality cells actually seem to stay in balance pretty well from the few instances I’ve seen.

I’ve also personally never charged my board above 90% (so the BMS balancing function has probably never kicked in) and I would’ve done somewhere between 500 - 1000km on it so far. The cells were all still within 0.01V of each other last time I checked. I also never let my battery go below 25% either though so keeping the battery mostly in the 30% - 80% range the majority of the time probably helps with this, and it certainly increases your cycle life as well.

In saying all that, its still better to have a BMS, particularly if you’re not the kind of person who’s willing to check their cell voltages every so often


It can be done, and he makes some good points. BUUUUUT, many of those points depend on the user being attentive and careful all the time. I dunno about you, but I have my bad days, and I can’t be arsed to care about my battery sometimes. With a BMS, that doesn’t matter, since it keeps track of it for you.

Yes, a BMS can become defective. You should always check your stuff once in a while, even if nothing is wrong. It’s called preventative maintenance.

Yes, most BMSs only balance at a few tens or hundreds of milliamps. BUT, our batteries are quite a bit smaller than most ebike packs, or powerwall setups, so the actual fraction is larger.

TL;DR yes, you can build a BMSless pack, but it’s a more involved process and requires more commitment from the user. A BMS is a labor saving device. What are esk8ers but people who love labor saving devices?


You need to double check your answers/advices before you post them :point_up_2:


Dude, you gotta stop.

Its a proven fact that you can discharge a pack to 3.4v, charge to 4.1 and it will self-balance. The problem exist when you discharge too much or fully charge. I have a 10s3p 30q pack I’ve been running for months this way, it hasn’t been balanced since it was first built and the cells are always within .1v of each other.


I mean I guess if you keep a strict cycle. I was just trying to lean him towards getting one. Chances are, he doesn’t have a power supply to charge his pack. The lipo that I haven’t balanced for 20 cycles already has a max delta of more than 0.1v, that I use a power supply though. :no_mouth: @rok You’re right brotha :full_moon_with_face:

Steering someone one direction is fine, but if you do it without telling them its manipulation and that ain’t cool. Just give the info and let them decide…or better yet, let them ask for opinions.

This is a subject that has been given lots of screen time and many people have argued over it for months. I went so far as to have a 30q pack made so I could prove it one way or another. It turns out that if you dont fully charge or discharge the cells will self-balance sans BMS.


also, going back to the original video, instead of a bms he’s using a balance charger. so…it’s still being balanced.

it’s that specific video that led me to use a balance charger on my first build using that exact same charger (1010b+).

i don’t know about you, but plugging in a charge cable and balance leads to my board every time to charge got to be a PIA.

wait, not sure if that’s true. a parallel pack will self balance, so the cells within a P pack will balance out. but voltage drift across S packs will not self-balance, right?

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That’s what I’ve heard, but in practice, on my pack specifically built for this test, I have had no drift over .1v across P groups. I have literally never balanced this pack, for the sole purpose of finding out what happens when not balancing and only charging to 90%, discharging 90% of its capacity. I have well over 1000 miles on this pack, no issues to date.


right, new high quality cells from the same production batch should have nearly identical properties, ie internal resistance, and would / should charge and discharge at nearly identical rates.

now…my 12s3p pack of 25r cells, despite being brand new when it was built, does drift a bit when fully discharged down to 3v per cell, so a balance is needed when charging.

moral of the story is, you may NOT need to balance, but balance to be safe and ensure longevity.

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@whitepony runs all his builds with no BMS last I checked… and he hasn’t had any problems yet…though I think he occasionally will check to see their voltages as a precaution.

A BMS is an simple, one-plug-to-charge solution. There are alternatives, like using hobby chargers, modified VGA ports, ebike ports, etc. Lots of stuff to try, if one is willing to experiment.

Absolutely, balancing in NEVER bad. I just wanted to know for sure if you could run a battery pack for a long time without balancing if you did not completely charge and discharge. I’m satisfied that you can. I actually have a BMS for this pack, just haven’t had a need to put it on it yet :).

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What If I install a bms on my battery pack but just for charging. For discharge I simply plug in the plus and minus of the battery. Does this work?

I have several 10s 4p boards that do not have BMS’s. They each have about 300 miles on them. I got tired of the BMS’s killing cells. With that said, it is always a good idea to have a QUALITY BMS in the mix.

Damn! I should probably check the cells. I haven’t in a couple months. :smile:


@mccloed And how do you charge and discharge safelly?

Laptop style charger and voltage cutoff settings in the VESC’s. Might not be the safest, but that’s what I do.

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What vesc do you use?

Both Focboxes and Torqueboards VESC’s.

How did you made the vesc to cut off at a specific voltage?