Electric Unicycle's BMS problem and solution

[Lorents]

With current EUC battery packs you should not worry (to much) about electrocuting. You are right about the current, who is the one who could kill you - but you need a voltage high enough to make the current flow through a given resistence. So up to 120V DC it is considered save for healthy adults, up to 60V DC for healthy kids and livestock ( i love these formulations ) under normal circumstances according to IEC.

I guess "western riders" are good for 500V or more

[esaj]

 

With current EUC battery packs you should not worry (to much) about electrocuting. You are right about the current, who is the one who could kill you - but you need a voltage high enough to make the current flow through a given resistence. So up to 120V DC it is considered save for healthy adults, up to 60V DC for healthy kids and livestock ( i love these formulations ) under normal circumstances according to IEC.

Right, forgot totally that human bodies have internal resistance, and more voltage is required for strike-through... 

 

Qualitywise is should be very hard to make it worse than what you can see on the pics of the !original! ?Firewheel? BMS vee posted some time ago. That kind of production quality gives a much higher risk for a burning euc than shunting it properly.

Yup, that's the exact same wheel I now have     Luckily vee fixed the bad BMS solders and shunted it before selling it to me. Usual Firewheel "quality", I guess, I wonder if their QC personnel are either blind or nonexistent...

 

Maybe (one of) the "misunderstanding" between eryk and hobby derives from different point of views - "we europeans" tend to think, that if we give ideas/instructions its up to the reader and his responsibility that he implements it properly! If someone is unsure, he has to ask or leave it. If one does not know what, why or however can happen he should not do it -that's common sense. He can ask a friend that knows what to do or whatever - it is HIS responsibilty and there is no reason to warn everyone about everything that eventually could happen.

In other cultures it is impolite, if one does not warn you that it is dangerous to short the battery pack...

Anyhow - its a pity that no detailed technical discussion occured...

However, the best solution is a good and sane design directly from the manufacturer anyhow. If i had a Firewheel or similar i would eagerly shunt it before risking a faceplant.

​Yeah, common sense takes a long way, but still I'd prefer to warn of any possible problems/dangers beforehand, if at all possible and known... there are people to whom electricity is just something that comes out the wall socket and "makes things work". Then they wonder why the fuses blow or the wires melt when they put extension cord with multiple sockets after extension cord with multiple sockets and put something on each socket... to me, it's just common sense, I know enough to not do that, and if I have doubts, I at least research or ask other people who know better before doing something I'm not that sure of.

Naturally I don't expect anyone else to take any responsibility but the person doing the mod him/herself. Or in my case, since the shunt wasn't done by me, but I am aware that it is there and now know about the new possible dangers related to it, I'm personally responsible if something happens. I have the choice to open up the wheel and remove the shunting, if I'm worried about it, or leave it there and take the risk that "something" happens. Other people have the choice to shunt or not to shunt their own wheels, but it's their own choice and responsibility.

And yeah, I would have liked it if eryk and hobby had come together, discuss the possible problems more rationally and come up with a possible better mod that's safer, if needed. But, at least we know now a little bit more of possible problems that the shunt may cause...

[Chriull]

 

...

The fusing is probably a good idea, but also probably it would be most useful to show people schematic and pictures of the fuse in place, so it goes in the correct place, should they choose to mod .

 

This usage of such a BMS in a EUC is just a very bad design choice. Hobby's shunting is a nice compromise to make riding safer. Of course things like charging it overnight without "supervision" is not recommendable. But this was not recommendable with the original , too . Regarding this soldering no one should store this kind of EUCs unattend at any "burnable" place...

I am not sure if a fuse will really improve safety for the "mass" - if one does it properly it should be done and is a great idea! But if not one produces new points of risk: if the new connections break mechanicly you faceplant again and additionally the broken connections can cause a short of the battery pack....

Edit: After reading the following post i revoke to my above statement regarding the fuse. If its choosen with the wrong type and/or strength it just gives you a chance for a faceplant again... 

 

 

[hobby16]

Problem is that lithium metal is very flammable  - there are several battery chemistry and their stability varies on composition safest would be Lifepo4 (solo wheel cells) on the other spectrum you have the LCO and LMO chemistries that are more volatile.

​No sh.t Sherlock, lithium is very flammable, and water is wet and fire burns. But Captain Obvious, where is your evidence that shunting the BMS will increase the HYPOTHETICAL risk up until the point to negate the benefits of shunting to avoid being faceplanted by a sudden cutoff and having the cells damaged by violent shocks because of the sudden cutoff ?
Where is your evidence that Ninebot would have an undervoltage cutoff in its BMS ?
What will happen to that "secured" undervoltage cutoff with one of more defect cells with aging.
Where is your evidence that a BMS can "ramp out" the power ?
Where is your evidence that Ninebot is immune from a thermal runaway and lithium fire with its supposedly well designed BMS
Where is your evidence that a undervoltage cutoff or a short-circuit protection with current threshold over 60A (that's what are implemented on the BMS, which is totally useless anyway) will prevent a lithium thermal runaway ?
etc, etc...

Until you have responded to the many many inconvenient questions instead of blathering the obvious to evade them, I conclude in interim that you are a water muddying troll. Because what you are trying to say is it'd better not to shunt to have a CERTAIN faceplant than to have a hypothetical and NEVER realised risk of lithium fire attributed by some mysterious and magical links to the shunt. More farcical, you are also implying it's better to risk a faceplant than to risk misunderstanding the mod's instructions and soldering a bad wire. Hard to find more nonsensical logic !
I hope that as a wheel vendor, with such a bad faith, irresponsible and ignorant attitude, you are grilled. Now, that's karma for a guy crying fire in the crowd.

Ah I forgot, please, stop quoting Wiki or showing a video of fire without knowing if it was by LiPo or LiIon and how it happened, as if it could be evidence of anything whatsoever. Because if the name of the game was throwing around information and bringing in no understanding or critical thinking, I can quote a much more reliable source than yours : http://batteryuniversity.com/learn/article/lithium_ion_safety_concerns

Let me assure the reader that lithium-ion batteries are safe and heat related failures are rare. The battery manufacturers achieve this high reliability by adding three layers of protection. They are: [1] limiting the amount of active material to achieve a workable equilibrium of energy density and safety; [2] inclusion of various safety mechanisms within the cell; and [3] the addition of an electronic protection circuit in the battery pack.
These protection devices work in the following ways: The PTC device built into the cell acts as a protection to inhibit high current surges; the circuit interrupt device (CID) opens the electrical path if an excessively high charge voltage raises the internal cell pressure to 10 Bar (150 psi); and the safety vent allows a controlled release of gas in the event of a rapid increase in cell pressure. In addition to the mechanical safeguards, the electronic protection circuit external to the cells opens a solid-state switch if the charge voltage of any cell reaches 4.30V. A fuse cuts the current flow if the skin temperature of the cell approaches 90°C (194°F). To prevent the battery from over-discharging, the control circuit cuts off the current path at about 2.50V/cell. In some applications, the higher inherent safety of the spinel system permits the exclusion of the electric circuit. In such a case, the battery relies wholly on the protection devices that are built into the cell.

We need to keep in mind that these safety precautions are only effective if the mode of operation comes from the outside, such as with an electrical short or a faulty charger. Under normal circumstances, a lithium-ion battery will simply power down when a short circuit occurs. If, however, a defect is inherent to the electrochemical cell, such as in contamination caused by microscopic metal particles, this anomaly will go undetected. Nor can the safety circuit stop the disintegration once the cell is in thermal runaway mode. Nothing can stop it once triggered.

[esaj]

@hobby16: While I do not agree with the tone of your message, you still make good points... Like I've already stated numerous times in this thread, I do not know enough to say whether the shunting can or cannot cause any extra danger on top of the (very rarely occurring) possible problems/dangers Li-Ion already have, with or without the shunt mod in the BMS.

While you two seem to hate each others guts , at least I'd like to see eryk88 answering these questions. Anyone else who knows their way around electronics and/or lithium chemistry? I'd like to see this matter torn apart and inspected at very close level.

[hobby16]

@hobby16: While I do not agree with the tone of your message, you still make good points... Like I've already stated numerous times in this thread, I do not know enough to say whether the shunting can or cannot cause any extra danger on top of the (very rarely occurring) possible problems/dangers Li-Ion already have, with or without the shunt mod in the BMS.

While you two seem to hate each others guts , at least I'd like to see eryk88 answering these questions. Anyone else who knows their way around electronics and/or lithium chemistry? I'd like to see this matter torn apart and inspected at very close level.

Hi esaj,

I am really sorry to annoy you with my tone, sincerely.  My position is that concerning security, one cannot take a casual attitude and made wild claims without solid evidence to back them up, because words here involve bodily harm.

But don't take it as "hate", really, just cultural difference. I see no problem throwing mud to each others and shouting "f.ck you" over the table in a heated debate, then joking afterwards and going out drinking with each others. Well maybe, I should not take it so personal and let other "cruisaders" like KaleOsaurusRex chime in. If there is blood with our resident troll, that would be your fault

 

[Fahrtwind]

I use these kind of LiPo Batteries (same Anode/kathode Material like LiIon but different electrolyte) for years in my Rc Helicopters, up to 12s (44.4V). I learned a lot about the best handling of these to get a high amount of cycles and how to reduce aging and the risks of a fire.

No Lipo Battery for RC Flying has got a BMS, so you have to keep an eye on the Batterie by yourself. The most dangerous condition for these is the situation when it is completely charged. Usually, you should charge them just before go flying. The risk for a autocatalytical thermal runaway is high. The best possibility to get a fire is overcharging the battery! It will ignit! So we use expensive Chargers with monitoring for each cell when charging.

You usually store the Batteries with 20-30% charged condition to keep the aging low and: cool! Kepp themm in the cellar or maybe fridge. But never <0°C.

 

On the other way, the lower the energy in the battery, the lower the risk of a thermal runaway. I never heard about a battery fire by overdischarging it. This is a typical process if you give away old lipo batteries. Discharge them completely, yes, overdischarge with a halogen light e.g.

What I do want to say: I don´t see a risk for a fire, caused by an overdischarged Battery caused by missing overdischarge protection.

But: even if your EUC is let´s say half full (on a small 132 Wh Battery) and you have peaks of high current, you´ll have cell voltage drops that may harm the battery and you will loose capacity. On Lipo when flying helicopters, I have Peaks of 120A @44.4V (up to 5,5 kW), the cell voltage drop must not exceed 3,4V before you damage your battery. I do fly with a telemetry sensor that counts the real used mAh when flying. I never fly beneath 20% remaining capacity.

Normaly these batteries do age by time, not by use. My first prioritiy for the helicopter: keep it flying even on low battery. The priority on EUC should be: keep the driver upright till the last mAh was squeezed out of the pack!

 

So, here is the way I´ll handle my generic shunted Wheel to keep the battery and myself in a healthfull condition:

If I know I don´t ride for a long time, I don´t recharge it after last ride, (25-50% Charged maybe) an store it at a cool place.

I never ever leave it in the car on hot days! It is the dead for a charged battery and there is the risk of a fire!

I won´t drain the battery to a minimum. When the battery is low, prevent high loads such as mountain climbing....

Don't forget to switch it off without a BMS! You will kill the battery (nothing more)

 

However, the Battery is an article of daily use and is the part with the highest wear in the EUC I guess...

 

I don´t like the sound of some of the posts here. Keep cool even if the weather is hot...;-)

 

Manu

[Eryk88]

I would like to address this modification.

I am sure that the engineer/author of this mod has done DFMEA of the whole unicycle system.

He would noticed that there are several modes of failure and each of them has a risk and consequences.
- The uni cutting out has a high probability and high severity - no one argues that this needs to be addressed but this has to be done in a correct way.
- The batteries failing in a safe mode have low probability but very high/catastrophic rating - meaning that this point has to be addressed also, ideally with a system which mitigates both failure modes at the same time.

Simple question to the author (I am not an expert on risk of Li-ion, we (P42) use Intertek as they have access to those) - Does the pack with you mod violate UN38.3 guidelines? - 'YES' it does therefore its UNSAFE! With this mod the pack violates T5.

No one cares if the authors house will catch fire, but we at P42 we are liable as a business for customers and we do alot of internal product testing, including factory visits of the manufacturer that we represent and their suppliers. If you would. We do not represent companies that do not comply with EU safety regulations and produce unsafe systems. We do internal and external engineering assessments of the products, their batteries etc. Unfortunately some of those test are confidential to us, and I am not going to reveal which manufacturers undergo wchi tests. But as a treat we have recently conducted a short circuit testing of some LiFepo4 cells which led to a failed test - resulting the battery insulation catching fire as there was no over current protection - attach a thermal snapshot of the test - one important job of the BMS that this mod bypasses!

From my perspective the problem is as such there is no under voltage protection (Some unis use a very primitive potential diver going to the MCU as monitoring SoC, measuring voltage as SoC is not the best practice for Li-ion batteries due to their discharge voltage profile relatively flat all they way wilt a sharp drop off but that is besides the point). The main board doesn't provide enough protection for the battery pack in many cases (not all but most). 

The issue is once you have discharged batteries over the critical voltage their internals get damaged, like siad before this will have impact on their paramters such as internal resistance which could lead to potential risk of fire when the charging process goes wrong (the passive balancing of most of the shelf BMS is very small <50mA according so several battery suppliers).

As a conclusion this mod will address one problem but creates another, secondly its easy to short out the wrong mosfet and disable overcharging protection if some one doesn't have enough knowledge/understanding of the risks to do this mode.  1st for the author as he likes automotive examples: its like removing ABS/DSC from your car - it will be fine in normal use 95% of time but this once when you do something wrong, too much throttle in a sharp bend you will pay the consequences!

My advice - buy a safe product in the first place! Remember you get for what you pay for!

2nd for the author as he likes automotive examples:

I have met with this types of 'home made advisors' in my previous job, where clever people were advising to bypass the car seatbelt alert with a plugin a fake buckle to the harness. Modern cars do a lot of calculations (weight of the driver, speeds accelerations, temperatures and if the seatbelt is fasten) prior the crash to adapt the seatbelt pretension and inflation pressure of airbag, by providing misleading information to the vehicle is possible to cause more bodily harm when the speed of deployment of the airbag is set for a person wearing a seatbelt. Its all because some smart person think they have an in-depth knowledge of a system when they clearly do not.

ST-SG-AC10-11-Rev5-Amend1e.pdf

[hobby16]

 

-  The uni cutting out has a high probability and high severity - no one argues that this needs to be addressed but this has to be done in a correct way.
- The batteries failing in a safe mode have low probability but very high/catastrophic rating - meaning that this point has to be addressed also, ideally with a system which mitigates both failure modes at the same time.

Simple question to the author (I am not an expert on risk of Li-ion, we (P42) use Intertek as they have access to those) - Does the pack with you mod violate UN38.3 guidelines? - 'YES' it does therefore its UNSAFE! With this mod the pack violates T5.

You have not assessed at all how much a shunt would add to the probability of catastrophic failure, you just make claim. If the probability is increased from 0.001% to 0.002%, your theory falls apart. Moreover, you inflate your perceived risk by throwing out that an external short would lead necessarily to "very high/catastrophic danger" with such laughable claims like "a lithium battery fire can not be extinguished" (of course utterly false like any hobbyist worth his salt knows well, see e.g. my above link to battery-university), which is again mere claim based on claim.

While we are making claim, I can also claim that my mod doesn't violate any guideline whatsoever because the 18650 LiIon cells all have internal protection, vents, PTC, permanent fuses etc and simply shutdown in case of external short. But contrary to you, I have credible claims and hold them as claims, not as absolute truth.

Besides, citing some battery general guidelines as if they were guarantee of anything (if so, then why are there so many cases of electric cars or computers catching fire ???) and ignoring the whole system and especially the specificity of a monowheel, where low voltage protection or even battery thermal runaway rmust be at the lowest of lowest priorty compared to power continuity (hence NO CUT OFF, even in case of low voltage or thermal runaway) is evidence of a particular lack of critical thinking. You can't see the forest for the trees and you are making definitive security recommendations to people who have been seriously harmed by a cutoff ? Pleeease !

 

No one cares if the authors house will catch fire, but we at P42 we are liable as a business for customers and we do alot of internal product testing, including factory visits of the manufacturer that we represent and their suppliers. If you would. We do not represent companies that do not comply with EU safety regulations and produce unsafe systems. We do internal and external engineering assessments of the products, their batteries etc. Unfortunately some of those test are confidential to us, and I am not going to reveal which manufacturers undergo wchi tests.

Argument-from-authority rhetorics based on vague claims, sorry I'm not impressed.

You haven't even addressed what would happen if a single cell is defective and triggers the undervoltage cutoff on a "compliant" BMS (according to your "confidential" tests, of course, how convenient).

Until then, let me believe that your safety regulation compliance or whatever, if real, is mere bureaucratic window dressing for suckers. It doesn't improve security  in any way since it only tries to comply to general regulations disconnected from the reality of monowheels, that is NO POWER CUTOFF ! Ninebot monowheels are compliant with every imaginable regulations or guidelines, having every certificates they can get, costing them inumerable money and time. It does not prevent them from faceplanting many experienced riders, right ? (don't believe me ? go there : http://trottinetteselectriques.heberg-forum.fr/forum52_ninebot-one.html).

Imagine a prospective buyers reading you here, do you really believe he'd be impressed by your evading attitude ? When in the hole, stop digging.

 

From my perspective the problem is as such there is no under voltage protection (Some unis use a very primitive potential diver going to the MCU as monitoring SoC, measuring voltage as SoC is not the best practice for Li-ion batteries due to their discharge voltage profile relatively flat all they way wilt a sharp drop off but that is besides the point). The main board doesn't provide enough protection for the battery pack in many cases (not all but most). 

The issue is once you have discharged batteries over the critical voltage their internals get damaged, like siad before this will have impact on their paramters such as internal resistance which could lead to potential risk of fire when the charging process goes wrong (the passive balancing of most of the shelf BMS is very small <50mA according so several battery suppliers).

Why do you keep repeating that a shunted battery has no undervoltage protection on monowheels ? That simply false. The mainboard always protects the battery from undervoltage, period. You couldn't cite a single mainboard that doesn't. And when the mainboard is switched off, there is nearly no iddle current (some mA, by the power stage stray current). Implying that, because of the shunt and no more undervoltage protection, it could drain the battery voltage down to dangerous and worse, fire prone levels is nonsense.

And no, deeply discharging LiIons pose no measurable additionnal risk of thermal runaway, overdischarge do, I'm not the only one trying to tell you that so please, listen ! On the contrary, deeply discharged LiIons tend to wear prematurely and hold less charge, thus REDUCING thermal runaway. No link whatsoever to a BMS shunt anyway.

 

 Its all because

some smart person

think they have an in-depth knowledge of a system when they clearly do not.

​Wise remark, perfectly suited to you, since I'm not smart

BTW, what about my questions please ? I expect claims and more claims...

[hobby16]

 I never heard about a battery fire by overdischarging it.

​Eryk88 has read it on wiki and seen a wheel on fire, so it must be true

BTW, you made good battery use guidelines. As hobbyists, we take them for granted, but laymen are not necessarily aware of them.

I think we should write down a post to sum up the most sensible and usefull steps to take care of our wheels' battery.

[Chriull]

Hopefully it's not that the first riders have to die from a bms induced faceplant until the situation really changes ;( 

Hopefully your (not always patient  ) hard work of enlightment to this topic and the growing number of local european/american/etc resellers (where you can refund for faulty products and have great chances to win law suits for negligent/reckless consumer endangerment) helps to eridacate this idiotic design choices!

 hobby16 said: (sorry dividing the quote didn't work as excpected... ;( )

"While we are making claim, I can also claim that my mod doesn't violate any guideline whatsoever because the 18650 LiIon cells all have internal protection, vents, PTC, permanent fuses etc and simply shutdown in case of external short. But contrary to you, I have credible claims and hold them as claims, not as absolute truth.

Besides, citing some battery general guidelines as if they were guarantee of anything..."

The UN38.3 guideline is imho only/mainly for transportation. So the EUCS with the battery pack can be shipped (see the thread from ^tom^ regarding his planned journey - if he has the certificate he can put his euc in the luggage...). Thats imho the main reason why the bms got into eucs... ;( Like others stated that for ?modellmaking? (cars, helicopters, etc...) its very common to use this packs without a bms - all these local shops sell the battery packs without bms, you have to optionally order it. Just because they need no shipment...

Reading, understanding and thinking about all this as any local reseller should create nightmares and bring them to stop business immediatly - praying that no accidents happen with the already sold eucs.

 hobby16 said: 

"Ninebot monowheels are compliant with every imaginable regulations or guidelines, having every certificates they can get, costing them inumerable money and time. It does not prevent them from faceplanting many experienced riders, right ? (don't believe me ? go there :http://trottinetteselectriques.heberg-forum.fr/forum52_ninebot-one.html)."

sh..t - mine will arrive shorty  Let's see if i void the guarantee, put in another battery back with an bms without overcurrent protection...

fortunately my french is not good enough to dig into this forum ...

 

[hobby16]

 hobby16 said: 

"Ninebot monowheels are compliant with every imaginable regulations or guidelines, having every certificates they can get, costing them inumerable money and time. It does not prevent them from faceplanting many experienced riders, right ? (don't believe me ? go there :http://trottinetteselectriques.heberg-forum.fr/forum52_ninebot-one.html)."

sh..t - mine will arrive shorty  Let's see if i void the guarantee, put in another battery back with an bms without overcurrent protection...

fortunately my french is not good enough to dig into this forum ...

 

​Maybe I was not clear and misled you. The Ninebot has faceplanted users but because of software glitches, not because of the BMS. So don't change any hardware, just enquire about the firmware versions' problems (you can use google translate to read a French forum).

What I meant is that complying with regulations which Eryk is obsessed with doesn't mean anything concerning us users' security.

[Chriull]

​Maybe I was not clear and misled you. The Ninebot has faceplanted users but because of software glitches, not because of the BMS. So don't change any hardware, just enquire about the firmware versions' problems (you can use google translate to read a French forum).

What I meant is that complying with regulations which Eryk is obsessed with doesn't mean anything concerning us users' security.

​Ah good to know! .. Or not? A faceplant is still a faceplant... But at least i do not have to spend any work on the wheel

Maybe i try to polish my french again a little bit - don't know if i can stand google translate 

[Eryk88]

@hobby16 I am sure you have the certificates to prove your claims.

About probabilities I am also sure that you deal 100's of unis and know all the common problem that regular customers have with them... So sorry your are right your assessment is much better then mine.

Lastly how the main PCB works I am also sure that you have 100% understanding of the system and also how software works... Tested and measured how efficient the voltage regulators are - if you take a thermal camera to any PCB

you will notice that they super inefficient taking about 50~100mA this is when the inverters are not working, this means that if you have a battery 10% charge left you will over discharge over night* (assume a 130Wh and 50mA current it will be flat within appox 5hours). 

There is nothing to stop that happening as most of the cheap wheel use a latching switch which goes to the enable pin to the buck! exception to this is ninebot and inmotiov which have auto shutdown when their on idle - again proving my point that well design system is a way to go! Not a bypassed safety feature...

While you read about thin on the internet i deal with unis as my job, all makes powers etc... so I don't think you have any grounds to challenge me about the workings of the unicycles.

As for your answers I will give you them when the time is right, so be patient....

 

ST-SG-AC10-11-Rev5-Amend1e.pdf

[SirGeraint]

I had an idea but I think I'd better ask a question first.  It's not my intention to take sides in the argument so I will try to word this carefully.

On the EU's that @hobby16 believes should be shunted, do they give an audible warning at the time that they shutoff (I am meaning simultaneously so I realize there would be no time for the rider to react but just wondering if they make a sound)?  Or I guess put another way do the shunted EU's make a sound at the time they would have cutoff?

Thanks...

[hobby16]

@hobby16 I am sure you have the certificates to prove your claims.

About probabilities I am also sure that you deal 100's of unis and know all the common problem that regular customers have with them... So sorry your are right your assessment is much better then mine.

​If you are so sure, then it must be true...

 

Lastly how the main PCB works I am also sure that you have 100% understanding of the system and also how software works... Tested and measured how efficient the voltage regulators are - if you take a thermal camera to any PCB

you will notice that they super inefficient taking about 50~100mA this is when the inverters are not working, this means that if you have a battery 10% charge left you will over discharge over night* (assume a 130Wh and 50mA current it will be flat within appox 5hours). 

There is nothing to stop that happening as most of the cheap wheel use a latching switch which goes to the enable pin to the buck! exception to this is ninebot and inmotiov which have auto shutdown when their on idle - again proving my point that well design system is a way to go! Not a bypassed safety feature...

​I don't know which board you are talking about and in what usage conditions. If you are saying a step down converter is not efficient and has iddle current, it's nothing new. If you are saying letting the wheel powered on permanently will drain the battery, it is nothing new, it's laughably obvious, why not saying "throwing the wheel by the window is dangerous" ? If you are saying a powered off wheel drains about 50 ~ 100 mA, it's utterly false.

Maybe you are not capable to formulate a cogent demonstration, maybe you are making diversion with irrelevant babling in order not to reply to inconvenient questions, maybe whatever, but I can't get what you mean. Can you please elaborate ?

 

While you read about thin on the internet i deal with unis as my job, all makes powers etc... so I don't think you have any grounds to challenge me about the workings of the unicycles.

As for your answers I will give you them when the time is right, so be patient....

​You may be a Nobel prize winner or an astronaut, no offense but I don't care. In science and technology, argument from authority or claim of expertise don't count.

What counts is the logic, facts and absence of BS. And you fail so far.

And yes, I have all the time to wait for your answers, but not much hope.

 

 

[hobby16]

I had an idea but I think I'd better ask a question first.  It's not my intention to take sides in the argument so I will try to word this carefully.

On the EU's that @hobby16 believes should be shunted, do they give an audible warning at the time that they shutoff (I am meaning simultaneously so I realize there would be no time for the rider to react but just wondering if they make a sound)?  Or I guess put another way do the shunted EU's make a sound at the time they would have cutoff?

Thanks...

​No, definitively NO. The BMS (battery management system) can't make any sound and doesn't have any communication means whatsoever with the mainboard ! It could have been added a loud buzzer, like on any $2 lipo checker, but isn't. It simply shuts down, the mainboard has no more power, the motor stops and you fall.

Yeah it's as incredibly crazy as that !

[SirGeraint]

​No, definitively NO. The BMS can't make any sound and doesn't have any communication means whatsoever with the mainboard ! It could have been added a loud buzzer, like on any $2 lipo checker, but isn't. It simply shuts down.

Yeah it's as incredibly crazy as that !

​That's what I was going to recommend.  Adding another FET and connecting its Gate to the Gate of the BMS MOSFET gate and then connecting 12V to the Source and then connect the Drain to a piezo-speaker.  Then if you have the shunt you would have a warning of when you are using too much current.  Have you already done that?  I think I would do it if I had one of the EU's that had this problem.

What do you think?

[hobby16]

What do you think?

I think it doesn't prevent a faceplant.

But it's definitvely a good mod to have a faceplant AND a lot of noise.

[esaj]

But it's definitvely a good mod to have a faceplant AND a lot of noise.

Humiliation-factor would go through the roof...

​

[SirGeraint]

I think it doesn't prevent a faceplant.

But it's definitvely a good mod to have a faceplant AND a lot of noise.

I was thinking more like with a shunt in place it would warn the rider that they were doing something that would have caused a shutdown. 

Something must have been lost in the translation when I said "Then if you have the shunt you would have a warning of when you are using too much current.".

[hobby16]

I was thinking more like with a shunt in place it would warn the rider that they were doing something that would have caused a shutdown. 

Something must have been lost in the translation when I said "Then if you have the shunt you would have a warning of when you are using too much current.".

​Sure, a BMS manufacturer could have added a loud beeper warning before any shutdown (timing is important). It could have added a signal wire for the BMS  to warn the mainboard of imminent shutdown so the mainboard can warn the rider to climb down. It could, no, it must have desactivated the redundant low-voltage protection (the mainboard has it already) and kept only the short-circuit protection. It could have recalled all the faulty BMS. It could have fired the bloody guys who have designed and permitted the use of such utterly dangerous BMS...

A lot of things could have been done, but not a by a simple buzzer driver on an existing BMS.

We're talking about a mod to mitigate an catastrophic situation, not about the design of a perfect BMS (if it ever exists).

[Tilmann]

I am afraid, the impressive level of adrenalin in this discussion may just drown @SirGeraint's interesting idea.

If I may interpret his thoughts (@SirGeraint, please correct me, if I'm  wrong): Instead of only shunting (i.e. disabling) the BMS, how about still disabling it, but turning it into a warning device at the same time?

In other words: keep the monitoring function of the BMS working, but make it honk INSTEAD of cutting the power and send me flying.

To me (anything but an expert on the subject), that sounds like a very reasonable idea. And, yes, I totally agree, this could be a poor replacement of a properly designed BMS at best. But: those TG T3-style generics are out in the wild by the thousands. And I bet, most of them have been bought without the faintest knowledge about either the risk of unpredictable power cut off or awareness of the fire risks with larger Li-something batteries (jepp, I'm one of those idiots...).

Only shunting the BMS would bear the risk of me happily abusing my wheel's battery without ever knowing before they are ruined - if only by forgetting to switch off the wheel after riding. Having an audible alarm that my battery might not be happy with what I'm doing would be a plus. It should be distinguishable from the regular speed alert and such after market mods should only be done by folks, who precisely know what they're doing (I'm out).

And, guys, kindly try to keep your calm. I really appreciate all the thoughts that went into keeping us as safe as possible, but the yelling at each other spoils the fun for me a bit.

[hobby16]

@Tilmann, @SirGeraint

It quite possible to shunt AND to add a buzzer directly between the 16V and the cufoff mosfets' gate.

In case of cutoff, the gate will fall to zero volt, activating the buzzer while not shutting down power thanks to the shunt.

Since the cutoff is latching, the buzzer will beep until you are home connecting the charger. Unless you add an on/off switch to the buzzer. And not forget to switch it on.

Not exactly my philosophy of KISS (keep it simple stupid), but why not.

[Tilmann]

@hobby16: thanks much! Considering your advice, I should probably spend the extra buck for a melody buzzer to cheer me up on the way home when the BMS wanted to fire ... :-)