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Why not build a no-frills bulletproof BMS?

Agreed…good point.
If this scenario is a concern for the pack then a smart BMS with a fast update rate would be best. I feel that this would be only for a small number of packs though.

Thank you for your thoughts!


It’s not like spot welds can’t come loose as well.


But not as likely. No one here is speaking in absolutes

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Charge termination current is the one I always change of the top of my head this even changes depending on the charger on the same pack

I feel though that any setup where something like this intermittent loss of contact is happening more than once in the lifetime of the pack it doesn’t warrant the use of a smart BMS. It warrants the changing of how the pack is built…whether NESE or welded….so it never happens again. Why accept it?

Not passing judgement, just wondering why we accept certain situations.



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All I’m saying is that it’s something that can happen and I have personally experienced it (though not to the degree that would actually cause damage). And if it happens it’s good to be aware. With a smart BMS, the chance of finding out is much higher than with a dumb BMS.

Plus, this is just one example of why having a smart BMS is better. There may be other battery pack issues one can discover by monitoring the cell voltage. Also, being able to see that all is nicely balanced is good for the peace of mind.

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If that possible few mAh difference is important then a smart BMS is the better choice. There’s very little practical difference though between the run time for the different charge termination current values typically used. It wouldn’t need to be a setting for the majority of people IMO.

We like being able to choose lots of settings but very few have a practical effect on the pack unless we are overriding the charger. For example, stopping as soon as 4.15V is reached to extend cell life. As you alluded to, the charge termination current is typically set (or is fixed) at the charger.

I think this idea is pretty sweet, and i do love the idea of a single LED that can be mounted through the enclosure to communicate.

You bring up some interesting points Mooch, why do we want to worry about our cell voltages? :sweat_smile: i love smart bms and the ability to see and control everything from the comfort of my phone… but i don’t know why :sweat_smile: maybe i’m addicted to the control aspect? Or the anxiety aspect?

Fuck this is getting deep… make the damn bms already.


I am definitely not saying you are wrong or that your preference is bad.
For many problems a smart BMS is most definitely better for diagnosing the issue. A dumb BMS is not always the better choice. It can be a great choice for many though.

A smart BMS is not always better for everyone though, for the reasons I mention in my first post and others. You feel strongly that it is though and it is definitely the best choice for you.

A dumb BMS will never be able to replace the peace of mind one can get by monitoring cell voltages if you are worried about your BMS or cells. Though you don’t have that cell monitoring for any other device and still don’t worry a lot about them. :slightly_smiling_face:

A good, reliable BMS creates some of its own peace of mind though. A lot of our worry comes from us not trusting the BMS to protect the pack IMO.

I accept that you are firmly in the smart BMS camp though. Looking forward to your feedback on my (eventual) post about that!

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I will definitely agree that different people have different preferences. A good dumb BMS will be a good enough solution for many users. Some people just want something that works without them having to worry. Some wouldn’t even know what to make of the cell voltage readings.


This is all I’ve ever wanted! I think a lot of others would want it as well, especially folks building and selling battery packs to the DIY community… their customers want something custom but are not likely to care (or know how to) explore P-group voltage in a meaningful way. If you make this, I think there are a lot of potential applications in esk8. It won’t be right for everyone, but that shouldn’t deter you…


Im sold. Put me down for 4!!

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Do eet

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I’ve always been a big fan of status LEDs and sometimes a beeper. But I’ve been thinking…is an LED/speaker actually needed? Does the normal functioning of the BMS provide enough information without a dedicated status indicator?

This is a no-frills concept, and I need to be brutal to keep feature-creep away, so I want to keep out any feature that doesn’t add real value (without crippling the usefulness of the BMS).

Here are a few thoughts…

  • An external LED adds parts cost, wiring, increases development and testing time, and will inevitably be done wrong by several users. This affects the reputation of the BMS (“the LED doesn’t work!”), and increases support costs/time. Not by any huge amounts but little things like this all start to add up and suddenly there is a much more expensive, larger, harder to develop BMS that has drifted from its no-frills roots.
  • A charge-only BMS would need to alert the user if there was an issue during charging. But if there was an issue then the BMS would shut off current flow from the charger and you would know something was wrong. IMO an LED wouldn’t add any functionality for this scenario. The LED couldn’t tell you what was wrong so it wouldn’t tell you more than a charger that wasn’t charging would.
  • The BMS would ideally protect the pack from discharging too far and over- and under-temperature and overcurrent situations when you are riding. But a charge-only BMS can’t do that. It can only shut off power to the accessories when there is a discharge-related issue during a ride. An LED wouldn’t help us here since we’d know there was a problem because the accessories died.
  • If you had no accessories then we’re using the ESC’s pack voltage readout to monitor the pack. Since a charge-only BMS can’t protect the pack during a ride we must use other methods to monitor the pack and an LED wouldn’t tell us much.
  • If you were not monitoring pack voltage in some way then an LED would be useful for knowing if the BMS has cut power to its accessories port because of some issue. The LED would need a momentary- contact button though so it was not drawing power constantly. Now we have the additional parts costs and we need to cut a hole in the enclosure for the LED illuminated status button. Worth it?
  • If the BMS was made smarter you could have two or three multi-color LEDs to create a status display for indicating over- and under-temperature, overcurrent, over- and under-voltage, etc. But then we have a “slightly smarter” BMS with its higher cost, longer development time, LED installation issues, etc.

I agree that status displays and indicators are great but does a “slightly smarter” BMS add enough usefulness? Is that worth the higher BMS cost, larger size, added development and support time, etc? Would LEDs or a beeper/speaker be a must have for you?



I think beeps are good bc it can give you warning from something gradual. This is good for anything sitting idle

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We’d need to have a smart BMS though, some sort of interface/telemetry to point out the specific issue and definitely a way to turn off the beeper entirely or at least shut it off for the existing issue.

I like beepers for getting my attention but I go crazy if it beeps more than a couple of times and/or if I cannot enable/disable the beeper when I want to. :grin:

Thanks for your thoughts!

Mooch, if you come out with a BMS, you can count me in for at least ten.


So much this :joy:

Ok, so you got ne out of status LEDs.
What about charge only instead of charge and discharge?
You say size matters and I think discharge does add quite a bit of size to the bms.
Sure there is no discharge protection, but I think most of us do think like:
Better fuck the battery, than get fucked by the battery because the bms cut out while braking.

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