no bms ok for 10s1p minimalist build?

hi all,
Just getting ready to make a couple 1p Micro packs with Samsung 40t 21700 For a stealth build that I would typically use RC battery packs for. as I am trying to keep the form factor as small as possible I was looking to run these with no BMS. In my mind, it's OK, I'm not doing it for a customer or anything it's for personal use and they will be properly cared for and looked after. Any negative repercussions in doing this? Just wanted to check Since most of you have more experience than I do.

Thanks in advance

With alarms ? I only run a 18ah pack no BMS and get 16.5ah. Now playing with 8ah no BMS and get 7ah. At what amps draw.

Sounds like I'm good to go, thank you
would consider alarm but at the most i will be pulling 15 amps and have Lvc on the controller set around 31v and volts showing on the display at all times. I feel like there's minimal chance of a set up like this going out of balance being used the way it will be. For the application, it's either this or Lipo, and this will do what I want while fitting better

You shouldn't do it but you know that. I don't think it's fine but it Will probably not burn.

If it does, then you will feel guilty.

Manbeer said:

Just getting ready to make a couple 1p Micro packs with Samsung 40t 21700 For a stealth build that I would typically use RC battery packs for. as I am trying to keep the form factor as small as possible I was looking to run these with no BMS. In my mind, it's OK, I'm not doing it for a customer or anything it's for personal use and they will be properly cared for and looked after. Any negative repercussions in doing this?

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The harder you push cells the more you need a BMS. Will you be gentle with these? (i.e. 1-2C discharge, slow charge rates, balancing charger) Or will you be pulling lots of power and using a dumb charger?

I ran no BMS for most of my years of riding. The more you closely match the cell's capacity and IR in the pack, the more the pack will inherently stay in balance.

An iCharger 1010b+ is capable of balancing and checking the balance of the pack in full. So when you design it, absolutely include a pair of 5S leads so you can check things later on. It will eventually fall out of balance.

I do recommend setting the LVC and full charge voltage to be conservative. Differences in cell voltages change rapidly at the low and high end of the charge.

See my sticky post about this in the battery technology section. I'm talking about RC lipo, but that applies here too.

Good answers, thank you. Looks like balancing leads will be a necessity which isn't a huge deal. For this application I can potentially go to 12s, So perhaps I can even do 2s balance lead set up To keep things a bit more precise. Not going to be hammering the cells too hard, I think they are rated for 35 amp continuous discharge, ill be pulling 15 peak. slow charging as well. They will have an easy life, main thing is that I want to have multiple tiny packs, the smaller the better, So if I'm making four or five of these Not only can I make them smaller but I can save a couple hundred bucks this way

A battery is only as good as its weakest cell.

i just realized i was doing voice to text before and i have no clue what i was trying to say

Going bareback while in use is crazy dangerous

for those who do **not** have the know-how and "substitute gear" to test / monitor / balance the cells well enough to compensate for the lack of "a BMS".

Which is 99% of the eBike owners out there, but the members here mostly are more clueful.

A pack-level LVC (or obvious alarms) really is all you "need" in use discharging, especially if the pack is kept well bottom-balanced.

Then cell-level HVC is only needed while charging.

Re-balancing would only be done as an occasional maintenance procedure, many ways to skin that cat better than all but the priciest "all in one" BMSs, which generally only do top balancing anyway.

Finally OCP / short protection can just be fuses.

In reality cheap BMSs should not be relied upon as much as noobs do, without understanding how to test / monitor them as the (usually) weakest link in pack safety, often causing more problems than they prevent

and sometimes earning the "Battery Murdering System" nickname.

I can absolutely believe that, This would be for my own bike so I'm not too worried and can usually spot the telltale signs of the pack going out of balance Just based on the performance/longevity characteristics So more than likely I'll catch it before anything becomes too serious, As for the cheap BMS's, Of all the bikes belong to other people that I've worked on, aside from the ones with literal bottom of the bucket Chinese talcum powder cells, Every battery failure encountered was either due to a bad BMS or the BMS itself completely failing. Because of the results, that is one of the reasons that I don't want to add bms to all these packs. It will either be expensive for decent ones, Or a false sense of security going cheap