eMark
100 kW
eMark said:
Lithium battery question
- Thread starter twilloug
- Start date
I do not understand your question about that specific BMS.
Its functionality will be normal, similar to all the thousands of other cheap ones.
Obtain it and test, or at least get the detailed spec sheet and we will know more.
Of course build quality, quality of components used, reliability accuracy and longevity will be a roll of the device
unless someone happens to have already bought and used that specific one.
Its functionality will be normal, similar to all the thousands of other cheap ones.
Obtain it and test, or at least get the detailed spec sheet and we will know more.
Of course build quality, quality of components used, reliability accuracy and longevity will be a roll of the device
unless someone happens to have already bought and used that specific one.
eMark
100 kW
It's not a difficult question. If it applies to a $15 BMS then it possibly applies to most all BMSs unless one is defective from factory.
Is the following claim bogus or true? If it's even partially true please explain ...
Not a difficult question. Do you know of any inexpensive BMSs like this $15 BMS capable of such a bold claim as underlined?
Is the following claim bogus or true? If it's even partially true please explain ...
Is this individual cell balancing claim completely bogus or partially true? If somewhat true--how does it work and to what extent?eMark said:
Not a difficult question. Do you know of any inexpensive BMSs like this $15 BMS capable of such a bold claim as underlined?
eMark
100 kW
You're not the only one. It invariably happens to all of us, even an ES expert. Some may even go so far as to call out someone for being "Dead wrong!" then later learn they were a little too hasty. FWIW, some ES experts frown upon Mooch youtubes as if he isn't scientific enough to be a reliable source ... and so the world keeps turning.HK12K said:
john61ct doesn't know how to answer my previous posted question ... care to give it a try :thumb:
john61ct said:
Mostly that IMR, INR and ICR are essentially just general descriptions of the cell as a whole and not necessarily representative of the specific chemistry inside. Also that the terms have been so grossly misused over the years that they are effectively meaningless when researching batteries.
Also that NMC and NCA are closer cousins to what would be described as ICR than I had really been aware of, less volatile than lico/lipo but more volatile than I had given them credit for.
In a nutshell I had been led to believe that ICR cells were less safe because they tended to ignite their electrolyte solution and explode with fire and shrapnel when shorted or otherwise driven to thermal runaway and that NMC and NCA were markedly less violent under the same circumstances. Turns out that's not necessarily the case.
Now if the can is marked lico on the other hand, I might still treat B+ like a mortar and point towards enemy. Or at least away from my crotch.
Emark- Honestly I don't even want to venture a guess about the BMS, lest I prove myself wrong twice in the same thread. I'm not familiar enough with the things to say, aside from the Adaptto unit which I have a bit of experience with.
*(Though if I had to take a WAG I'd say, assuming it does have a balancing function to begin with, as soon as the first parallel group hit the set max voltage it would cut the connection to the charger completely and begin bleeding down towards whatever they set for the balance voltage. As that group bleeds down below the max set voltage the bms reconnects the charge circuit until a group hits max again... rinse, repeat, until all the groups are equal at max. At that point it'll bleed them all down to the set balance voltage.
As for the charger itself and how it would behave during all of this I'd expect it would depend on the charger. If it's fanless and only has the green light to indicate full charge it may never appear to do anything if it's max voltage is higher than whatever the bms' max is set to because the pack may never be allowed to get that high. Or, if they're set the same, it may go green once it's fully balanced or a few cv on/off cycles before as things get close to the top end. On the other hand if the charger gave some indication of when it was actually charging, like fans or other lights, it might cycle on and off every few minutes after that first group hits max until it's done. Could take minutes, could take days, depending on the pack.
Again though, that's not an educated guess. It's just a guess. I honestly have no idea but am interested to hear what the room has to say, just to see how far off I might or might not be.
Assuming I'm close though I'd want to know where they set all of the voltage thresholds, at the very least.)
I do not see anything underlined.eMark said:
Yes it is not a straightforward issue, only an "easy question" if you have all the required data, which requires more knowledge about how balancing works than it appears you possess. Without those data, the question is not just hard, but impossible to give a simple answer, much less in the binary Y/N you seem to expect.
**Any** balancing BMS can balance a pack **eventually**, if the Ah capacity per group (or cell) is not "too great" and the V delta is not "too high".
Its balancing-related **specs** are what determines the level of effectiveness **for a given context**, assuming they are accurate. Which is why I asked you, please give us the specs of the BMS you are curious about.
A balancing current rate of 2A (or even higher!) will be quicker, or handle a bigger delta and/or be suited for a higher capacity bank
better than the usual sub-amp rate.
One that has (or lets you adjust to) a lower start-balance V setpoint, say 3.9 for li-ion cells,
will have longer to get the job done **within** your usual desired charge profile.
While one with **both** a low Bcurrent **and** a late (say 4.15V) start-balance point, requires a too-harmful AHT, maybe even days, and certainly should not be selected for a large pack, nor one where the V delta gets too high.
Some BMS can be balancing all the time, which I think would be silly,
but that also means they can balance **at any voltage/SoC**, so such a BMS could even be used for middle- or bottom-balancing if that is your preference,
if using "active" capacitance or shunt-method balancing rather than bleeding-resistance method, does not need to be while charging,
just turn the balancing on when at rest at your desired balancing-point SoC, and let it complete however long that takes.
____
As for "green lights" the meaning of that would vary by charger, there are dozens of possibilities for how a charger determines "battery Full", and really that should also be adjustable.
The "how long" question has the same answer as "is a piece of string", depends on the four variables discussed above.
Note also that the "finish balance" Vdelta setpoint can be a high vs low delta, and that would have a big impact, and should (of course) be adjustable as well.
Yes well known I thought.HK12K said:
Think of them as just model# "product line" indicators within a given maker's offerings.
> less volatile than lico/lipo but more volatile than I had given them credit for.
Note LiPo also has even less relation to a specific chemistry.
If you mean risk of thermal runaway, that really depends more on how they're treated, all but LFP and LTO (I think) are pretty dangerous, say for charging unattended inside a human living space.
The exploding shrapnel thing happens even with lead but again not so much with knowledgeable diligent cautious owners.
Your description is basically generic for all resistance/bleeding balancing, including when it's a charger doing it.
The specifications discussed just above is what distinguishes between those that do it better/faster than others.
Personally I would not select a cheap BMS for its balancing performance anyway, the protective functions and general build quality, reliability, longevity are more important, you can always buy additional dedicated balancing gear anyway later on when (if) needed, or just do it periodically manually.
> it may go green once it's fully balanced
Most chargers work off pack-level voltage only, have no awareness of cell/group imbalances.
Which is why adjustability becomes important especially for normal-usage fast-charging sessions without balancing.
> it might cycle on and off every few minutes after that first group hits max until it's done. Could take minutes, could take days, depending on the pack
Again, most rigs the charger is not controlled (per se) by the gadget doing balancing.
> Assuming I'm close though I'd want to know where they set all of the voltage thresholds, at the very least.)
Who they?
john61ct said:
Apparently I hadn't been paying close enough attention in the past, but am now aware.
Volatile in the sense of fizzling hot liquid vs blowing it's endcap and launching it's contents like a shotgun shell. If we're talking thermal runaway risk it should be minimal for any of them if they're never mistreated and are quality pieces to begin with. It's the concern of what happens when they're not for one reason or another that becomes the worry. To the casual observer though it appears that the more cobalt involved in the mix the more it's volatility becomes an issue, regardless of which way you look at it. Though as you noted, even a sla can happily explode when shorted.
Good, then I do have my head wrapped around it. Seemed as if he was asking if it actually balanced and if so how, unless I misunderstood, which is always a possibility with a 2.5 year old nearby constantly stealing focus. Glad I was able to offer a cohesive if basic description.
People often refer to them as battery murdering systems for a reason I'd imagine.
I misspoke. It'll go green when the pack is full, which may or may not be the bms max voltage setppoint. Then it will probably do whatever it does when the battery is unplugged as it bleeds down.
Meh, hard to believe no negligence requiredHK12K said:
> Though as you noted, even a sla can happily explode when shorted.
Not just shorted externally, just the clueless owner continuing to use them **way** past the 80% SoH EoL point. FLA as well.
> People often refer to them as battery murdering systems for a reason I'd imagine.
Yes their lifespan is often (usually?) **much** shorter than the cells they're supposed to be protecting.
And cheap ones haven't had sophisticated design work to ensure graceful handling of the various failure modes.
And "optimistic" ratings, counterfeit / shoddy component selection, sloppy QA controls are all the norm at the low end.
Always confuses me how people can spend thousands on quality cells then begrudge a couple hundred on their infrastructure.
> I misspoke. It'll go green when the pack is full, which may or may not be the bms max voltage setppoint.
green when the charger's algorithm says Full
Definition of "working" Full is actually arbitrary should be up to the owner. Vendor spec is harmful.
The charge termination in normal use should be way below the BMS "never used last ditch" HVC.
Usually the owner needs to test/calibrate everything to ensure the BMS is done balancing before the charger shuts off.
> Then it will probably do whatever it does when the battery is unplugged as it bleeds down
Dunno what that means.
>> Again, most rigs the charger is not controlled (per se) by the gadget doing balancing.
> Not controlled, but influenced by. If the bms cuts the connection the charger is likely to do whatever it does when the battery is disconnected because that's what's effectively happening.
Nope. If the BMS cuts the connection between the charger and the pack, the systems design is faulty. Should only happen if (when) the charger's broken. See above
> So if the charger whizzes and buzzes and lights up when charging but sits there quietly otherwise you might notice it switching between those two states is what I was suggesting.
Dunno what that means.
> The purveyors of cheap bms' with presumably static settings.
Plenty of cheap BMS are fully adjustable, see the bluetooth threads.
The non-adjustable ones just hard code the values in the hardware, or its firmware.
Is that what you were asking?
-Meh, hard to believe no negligence required
Life moves pretty fast. If you don't stop and look around once in a while, you could miss it.
-green when the charger's algorithm says Full
Definition of "working" Full is actually arbitrary should be up to the owner. Vendor spec is harmful.
The charge termination in normal use should be way below the BMS "never used last ditch" HVC.
Usually the owner needs to test/calibrate everything to ensure the BMS is done balancing before the charger shuts off.
Afaik the specifics of the charger were never discussed. If they had been changed from the expected norm for the nominal pack voltage (a good idea) it would seem to stand to reason that a programmable bms would be a bit of a prerequisite if it were intended to do the balancing whilst connected to the charger. The bms linked above made no reference to it's ability to be programmed, had no obvious io comm ports that I noticed, no mention of bluetooth, and yet claimed to balance charge. So if it's hardcoded it would be nice to know where they set the variables, since we're fiddling with the chargers termination voltage and all. Otherwise calibrating it all might become problematic.
-Dunno what that means.
Nope....
Dunno what that means.
If you're pack is that far out of balance it would not be unusual for the weakest group to hit top soc while the strongest lagged far behind. The charger is ignorant of individual group voltage and cares only about total pack voltage. It's reasonable to believe that if there were a severe imbalance in cell health within the pack that the weakest group could be severely overcharged before the strongest group has moved past nominal without the charger being any the wiser. Without a bms to step in under such a situation that is.
Looking at the above linked bms there is a jst xh connector, a solder pad for B- and a solder pad for P-. If this thing is going to top balance a pack while simultaneously connected to a charger I can't see how it would do so if not by using the jst to monitor groups, and interrupting b- and p- everytime the weakest group whacked 4.1 or 4.2, or wherever it happens to be programmed.
-Plenty of cheap BMS are fully adjustable, see the bluetooth threads.
The non-adjustable ones just hard code the values in the hardware, or its firmware.
See above.
-Is that what you were asking?
Possibly?
Life moves pretty fast. If you don't stop and look around once in a while, you could miss it.
-green when the charger's algorithm says Full
Definition of "working" Full is actually arbitrary should be up to the owner. Vendor spec is harmful.
The charge termination in normal use should be way below the BMS "never used last ditch" HVC.
Usually the owner needs to test/calibrate everything to ensure the BMS is done balancing before the charger shuts off.
Afaik the specifics of the charger were never discussed. If they had been changed from the expected norm for the nominal pack voltage (a good idea) it would seem to stand to reason that a programmable bms would be a bit of a prerequisite if it were intended to do the balancing whilst connected to the charger. The bms linked above made no reference to it's ability to be programmed, had no obvious io comm ports that I noticed, no mention of bluetooth, and yet claimed to balance charge. So if it's hardcoded it would be nice to know where they set the variables, since we're fiddling with the chargers termination voltage and all. Otherwise calibrating it all might become problematic.
-Dunno what that means.
Nope....
Dunno what that means.
If you're pack is that far out of balance it would not be unusual for the weakest group to hit top soc while the strongest lagged far behind. The charger is ignorant of individual group voltage and cares only about total pack voltage. It's reasonable to believe that if there were a severe imbalance in cell health within the pack that the weakest group could be severely overcharged before the strongest group has moved past nominal without the charger being any the wiser. Without a bms to step in under such a situation that is.
Looking at the above linked bms there is a jst xh connector, a solder pad for B- and a solder pad for P-. If this thing is going to top balance a pack while simultaneously connected to a charger I can't see how it would do so if not by using the jst to monitor groups, and interrupting b- and p- everytime the weakest group whacked 4.1 or 4.2, or wherever it happens to be programmed.
-Plenty of cheap BMS are fully adjustable, see the bluetooth threads.
The non-adjustable ones just hard code the values in the hardware, or its firmware.
See above.
-Is that what you were asking?
Possibly?
ExactlyHK12K said:
Nor the BMS specs relevant to balancing.
Nor the group Ah capacity, nor the average V delta at balancing time, nor the desired finish point, etc etc. . .
Which is why the Q is a "how long is a piece of string?" question.
> The bms linked above made no reference to it's ability to be programmed, had no obvious io comm ports that I noticed, no mention of bluetooth, and yet claimed to balance charge.
None of those things are in theory related to the ability to balance effectively in a given context.
Only to the owner's ability to vary the effectiveness for a wider context range, and for her to verify how well it's doing its job,
in order to adjust the charger or BMS or frequency of balancing sessions, etc
> So if it's hardcoded it would be nice to know where they set the variables
I still do not understand those words. Where? as in the designer/builder's latlong location? Or inside which chip? or using what device?
Maybe give an example answer so I can understand what the question is supposed to be. . .
> If your pack is that far out of balance it would not be unusual for the weakest group to hit top soc while the strongest lagged far behind.
Yes, ideally you use a sophisticated setup where the BMS is controlling the charger, say via CAN messaging. As long as the BMS HVC is separate, to protect against a rogue failed charger. And a failsafe design so when there is no BMS signal received for say 15sec, the charger stops.
That is not how the cheap stuff works though. A good systems designer / MCU programmer may be able to try to emulate such with cheap components, but then you're looking at a mostly DIY setup rather than just buying "a BMS".
And that's just charger control, nothing to do with the balancing functionality.
> Looking at the above linked bms there is a jst xh connector, a solder pad for B- and a solder pad for P-. If this thing is going to top balance a pack while simultaneously connected to a charger I can't see how it would do so if not by using the jst to monitor groups, and interrupting b- and p- everytime the weakest group whacked 4.1 or 4.2, or wherever it happens to be programmed.
Yes exactly. That does not mean that design is a good one though.
eMark
100 kW
If we could get back to twilloug's thread it would be helpful if one of you vouch/confirm his understanding ("should be fine right") that his 7S4P 24V pack is capable of a max continuous discharge current of 30.6 amps ("max of 30.6") being that each EVE cell has a max continuous discharge current of 7.650 amps. Assuming that's the correct interruption.twilloug said:
Maybe, it's about time to distinguish the difference between what is a max continuous discharge EVE cell rating of 7.650A and max continuous discharge rating of 30.6A for 7S4P battery. How do you figure the Wh rating for this EVE cell ?
Let's use the Samsung 26 F 2550mAh cell specs for comparison. Its max discharge rating is 5.2A. Its max power energy is 9.62Wh with its max discharge rating of 19.24Wh (4 cells in parallel).
My biggest folly was not realizing that I was stepping into a preexisting pissing match while looking for a bit of thoughtful discussion. It's an ES thread that made it's way past the first page... I should have known better.
I hope that the OP is able to find the information he is seeking.
I hope that the OP is able to find the information he is seeking.
eMark
100 kW
It's not the first time and probably not the last that he uses misdirection. My previous post was an attempt to get us back on track. Assuming twilloug is correct when he says his EVE 7S4P battery is rated at a max continuous discharge current of 30.6 amps. Being it's a used older battery probably closer to 85% or 26 amps.HK12K said:
My previous post was relevant so will rephrase [hopefully] for clarification ...
eMark
100 kW
twilloug said:Just to clarify ... if my battery is rated for 30.6 amps continuous draw, am i ok with 7s4p battery or do i need to go with different battery If so what size? Everything else is new why not another battery.
john61ct said:
Doesn't running two similar 7S4P batteries in parallel theoretically equate to doubling the continuous draw from 30.6 amps to 61.2 amps? Even if realistically closer to 50 amps what is gained with two paralleled 7S4P batteries for a "huge boost to power" with his 30A controller? Wouldn't he need to get at least a 40A controller to take advantage of a "huge boost to power" with his upgrade from a 250W motor to his 500W motor ??
No, draw is determined by the load, i.e. slope weight speed, controller + throttle etc.eMark said:
Having a bigger Ah bank just makes more capacity - both amps (C-rate cut in half) and Ah (range) - **available**
at double the weight/space and cost of course.
If the battery is not a limiting factor then of course there is no benefit
eMark
100 kW
As it is now his 7S4P 30.6A EVE ebay battery will be too stressed with the 30A controller especially at full throttle. Besides the actual max discharge current of his Chinese ebay battery may be closer to 26A.
There is no "huge boost in power" as you contend with his 30A controller and 500W motor. The real advantage of paralleling to another 7S4P (if room) would be less battery stress, increased mileage and battery longevity (7S4P to 7S8P = 30.6A to 61.2A max continuous discharge rating).
So, YES there's and advantage paralleling with another 7S4P to make a 7S8P. But not for a "huge boost in power" with his 30A controller. The advantage is less stress by paralleling to another compatible 7S4P battery to make up a 7S8P battery. Then rated closer to 52A-61.2A max continuous discharge so less stress on the battery and greater mileage.
There is no "huge boost in power" as you contend with his 30A controller and 500W motor. The real advantage of paralleling to another 7S4P (if room) would be less battery stress, increased mileage and battery longevity (7S4P to 7S8P = 30.6A to 61.2A max continuous discharge rating).
So, YES there's and advantage paralleling with another 7S4P to make a 7S8P. But not for a "huge boost in power" with his 30A controller. The advantage is less stress by paralleling to another compatible 7S4P battery to make up a 7S8P battery. Then rated closer to 52A-61.2A max continuous discharge so less stress on the battery and greater mileage.
Feels like you're constructing some straw man to argue against.
Could you cite a post#? I do not recall discussing anything about OP's specific components.
As I stated there will not be any power increase at all from improving a battery unless that is a limiting factor.
Could you cite a post#? I do not recall discussing anything about OP's specific components.
As I stated there will not be any power increase at all from improving a battery unless that is a limiting factor.
eMark
100 kW
twilloug said:
Realistically that Chinese EVE max discharge rating is probably closer to 26 amps. Even if it were 30 amps that battery is going to be stressed out at full throttle with your 30A controller, not to mention the 500W motor.twilloug said:Based on my last post, if my battery is rated for 30.6 amps continuous draw, am i ok with 7s4p battery or do i need to go with different battery. If so what size? Everything else is new why not another battery.
Modifying your scooter for paralleling another EVE 7S4P ("huge boost in both power and range") may not be possible or just too much expense and bother ... unless you could have it safely housed/protected atop at lower vertical column. So, ideally you need a different battery with cells rated at max discharge of 10-15A (4P=40-60A) for your 30A controller for battery health and longevity.
Doubt you can find a scooter elongated battery shape with max discharge rating of at least 40 amps which is what you need for your 30A controller to satisfy your zest for speed (max continuous discharge). You may want to consider getting a 20A controller as its top speed (12-15mph?) may have to do ... plus it's safer.
Also, if you parallel another 7s4p EVE battery may want to upgrade to 750W motor from your 500W motor rated at 28 amps. How fast is fast enough not only for your scooter (with two batteries), but also your safety ??
Thanks again for all the responses. I don't need to go fast just want scooter to work. It sounds like i need a better battery rated for higher amps. Again i dont need to go full throttle all these time i just want it to work. Where is the best place to get such a battery?
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