I see your culometers … I would personally advice against using china stuff, but if there is nothing else available or price difference is of an order of magnitude … than I understand the motive.
Also, percentage is not always enough… I hate to do the calculation in my mind each time, knowing that 10% maybe corresponds to 2.7km for example. (if max range is 27km)
Plus, voltage drifts, so for precise reading you always need to let the voltage to rest a bit to return to steady state.
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With ‘‘coulometer’’ - Wh / Ah shown, I know that my battery is 400wh total, for example, then I see 50wh consumed and I know I still got 350wh to go…
With percentage there is no way to accurately measure this as the energy use might change.
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Basically, with smart enough bms / coulometer, a ‘‘precise’’ tool for range estimation could be created…
If riding at steady speed consumes 300w, then it would calculate the max range based on capacity left in the battery… now tell me, how can i achieve the same with percentage display?
Well actually if you have a BMS with a precise measurement and true energy calculation you don’t have to wait for voltage to settle … problems you describe are from devices that are crap (or have a crap firmware).
As a comparison, some folks produced a pretty awesome calibration for us and over a long drive test when we used a range extender and consumed total of 350KWh, SOC reading was off by less than a 0.7kW (tested by charging pack to max and balancing it).
So if firmware is done properly and none of measuring devices are bad - a SOC reading should be more than enough.
ahhhhh the old “range” question … well your range depends on how you drive, drag, how fat you are, incline, driving style … so it’s never the same … but I can precisely tell you how much real energy you’ve got in a pack … over time you will automatically know - 10% get’s me that far …
still voltages, watages etc are redundant in my opinion.
Ok, this would be an overkill but there is a way of doing range based on “last X miles driven” so what you do is look at how much power you used per mile (km) in last 1000 miles (km) and you build a profile out of that … considering how much energy you’ve got left in pack it becomes academic … but you need to know wheel size, rpm etc.
Right, but I mean, make one at home, I couldn’t do it without contacting a factory of pcbs! And I (and a lot of people) don’t have that programming skills, I just know Arduino Code!
Let me get this straight - those bms come not populated ?
Also why you worry ? once somebody writes a code you can replicate it without a hassle Also if you use arduino studio you already write code in C … that’s a lot more than some of self proclaiming software engineers that I’ve seen in my time
Populated you mean assembled? If yes, the answer is no, it will come assembled. But I think they don’t have producing date
Yeah, Is easy copy the code, but both projects don’t shows the code, so we’re blind
I would love to make my owm Bms (Also because mine don’t arrived, Brazil isn’t a good place to buy things on Ebay) but there are somethings that is better buy manufactured, like the lipo packs, it is cheaper to make one with 18650 cells but it is harder! I will buy a Imax b6 this week, but want to buy other Bms on the future, because my power supply arrived (Man, really, don’t mind living in Brazil and building e-boards)
Well @Stef I did take on board your input about overtly complex designs in eskate world, and it there are things that can be done with that to make end user life easier … also it’s not my “project” it’s a general thread on what’s there and how stuff can be done / improved … might be a need to design something / implement it …
Wow, Ok … look at least you know that they will emerge at some point … also you choose a right attitude - don’t complain where you live just get on with it ! Keep it up !
Eeek so much arrogance it hurts…
A little piece of advice, humbleness takes you a long way in life and with people.
Then you’re using it wrong. I get SOC within 3% by simply using coulometer data in real world scenarios.
Wrong, the difference is in packaging not chemistry, and it is spelled Cobalt.
Reputable Lipo makers do take this into account. A Lipo is not meant to ever be under 3V. I have run several LiPos at full 60C and they never dropped below 3.2V/cell although they do not discharge 100% capacity, they normally do 85-90% which is expected, given losses due to heat etc.
If your Lipo internal resistance is that high then you should replace it.
And the same thing doesn’t happen with LiPos… right.
If you discharge a cell from full to empty at 50A, and then charge that same cell from empty to full at 50A you will get mighty close results… The difference is that the reaction is slightly endothermic during discharge and exothermic during charge. The voltage sag/rise almost cancel each other out.
So when your mate asks me “Do you know how a CAN bus works ?” and then replies with “Your type of arrogance makes me feel sick, goodbye” you don’t call him hypocritical for being arrogant and then calling somebody else being arrogant.
Can you provide data for that ? because we tested in real world environment and spend ~20k on this test just to eliminate bms that use pure culomb counters out of equation …
I could change cobalt to kobalt but it nicelly highlights the spelling guild here. And no, you’re wrong - 18650 use different substrate to be able to roll those without cracking, calendar cells don’t have that requirement so use different substrate to give more power density. Those are part of battery chemistry unfortunately.
Let me put it this way:
Please tell me which 60C max rated cell when discharged at 60C is giving you 3.2V … I’ll plug it into our digatron, I’ll even compress it so there is no substrate de-lamination, I’ll even drop it to climatic chamber to keep it at perfect temperature (that I’ll let YOU chose) and I’ll provide you with discharge graph at full 60C and corresponding voltage. Hey I’m dumb and all people that I work with are dumb and we would love to see that battery in action.
And did I say anywhere in that post that I’m talking about lipo ?
So you are telling me that you’ve done accelerated life cycle test of a 18650 and lipo over a 5000 cycles and you found different data than a whole industry dealing with batteries and spending billions on it - is just wrong ???
endothermic batteries ? you want to tell me that you’ve got battery that converts (any significant) heat energy into electricity ? that actually cools down while discharging ???
soooooo this 2 packs of 18650 that we’ve killed for reference data with that test are imaginary ?
So far I’m trying to provide data to users that was achieved through lots of resources and time put into testing - not a hobby equipment with multimeter, if you don’t find it useful that you get this without signing NDA - maybe this thread is not for you. Also if you don’t have anything to bring into this thread in terms of answering my bms questions - thanks for participating and don’t point into arrogance if you intend to be arrogant your self.
And don’t throw users under the bus with statements that stressing batteries under a certain voltage does not decrease their life span - it’s plain malice.
Also if you use arduino studio you already write code in C … that’s a lot more than some of self proclaiming software engineers that I’ve seen in my time 
