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hobby16

Electric Unicycle's BMS problem and solution

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Thank you, hobby16! :)  As this issue has come up a lot, I'll pin this topic in this subforum, so it's easier for people to find.

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Hi,

thanks so much for the help, I shunted my generic Wheel as suggested in the pic above:

BMS.thumb.jpg.3baed8931521a7271436a20093

I already charged the Battery without smoke :)

Quite easy to do. Especially in winter a plus for safety! Thanks again!

Manu

 

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Hobby16, Thanks for the pictures. If it's so simple with a blob of soldering, why aren't manufactures doing it? Are they that dumb?

I have a TGF3. In your pictures, you have it all 3 shunted.

image1.png

But earlier you said don't do the "... Warning, avoid shunting Q2 Mosfet." Am I missing something? Thanks a bunch anyway.

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I'm going to make it my business to pressure every manufacturer that posts here to address this problem. It would be lovely to have everyone else join in.

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Hobby16, Thanks for the pictures. If it's so simple with a blob of soldering, why aren't manufactures doing it? Are they that dumb?

I have a TGF3. In your pictures, you have it all 3 shunted.

But earlier you said don't do the "... Warning, avoid shunting Q2 Mosfet." Am I missing something? Thanks a bunch anyway.

Hi PP,

Q2 does not mean the middle mosfet. Q2 like Q1 may be made of several mosfets in parallel, see the schematics and the markings on the picture of "Aliexpress generic battery BMS". Once you know where Q1 is (are) and sure it's NOT Q2, you just need to shunt one of its mosfets, or two, or all (2 or three in the pictures of the TGF3).

As to reason why manufacturers don't do that, I can only guess. I suspect they derive a schematics from of-the-shelf bike batteries and implement that without addressing the specificity of unicycles. The first culprit being Airwheel since others have copied on it. Another guess about how this blunder can continue for so long is that in Southern China, it's not cold enough for the BMS to cut off so often so they think they can let this spurious problem go away.

And yes indeed, it's unbelievably dumb.

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Guys please do not do this if you value your house - this modification has a big potential to cause the battery pack to catch fire!

The BMS is there to protect the cells - Under voltage, over voltage and short circuit! If you do this mod then you are bypassing this protection, although it might seem to work fine for now on a ocasion that you decide to go down a steep hill you migh find this happens!

Discharging Li-Ion batteries over the nominal voltage 2V damages the chemistry - so if you accidentally leave the wheel on you will damage the cells, again damaged Chinese li-ion cells are likely to catch fire!

Please do not do this unless you want this in your house:

https://www.youtube.com/watch?v=f4vhV97vVgw&feature=youtu.be

Li-ion fire is not fun as you cant put it out

 

   

Edited by Eryk88
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Guys please do not do this if you value your house - this modification has a big potential to cause the battery pack to catch fire!

The BMS is there to protect the cells - Under voltage, over voltage and short circuit! If you do this mod then you are bypassing this protection, although it might seem to work fine for now on a ocasion that you decide to go down a steep hill you migh find this happens!

From what I've understood, this only bypasses the overdischarge protection (undervoltage), all the other protections in the BMS are left in place? Can a too low voltage actually ignite the battery? I do know it can damage the cells permanently, but at least MOST wheels seem to have undervoltage protection on the mainboard? From what I've heard, Ninebot has already removed the overdischarge protection entirely from their BMS (if there ever even was one), as did Gotway on more recent models... Solowheel never had it? InMotion doesn't have it?

 

Discharging Li-Ion batteries over the nominal voltage 2V damages the chemistry - so if you accidentally leave the wheel on you will damage the cells, again damaged Chinese li-ion cells are likely to catch fire!

I thought it was 2.5V for most cell chemistries, could be wrong though. And from what I've understood, it might become "dead" (and can sometimes be revived by more advanced chargers, but probably not something everyone should try, and requires special charging equipment). At least Firewheel uses Sony US18650V3 -cells, which should be fairly high quality Japanese cells, I'd expect most bigger brands to use high quality cells? Firewheel's mainboard also induces the "Power is low" -warning and prevents you from riding (well, you can try if you insist, but you'll probably faceplant), I recall that hobby said this happens around 56V (so with 16 cells in series, that's 3.5V per cell, way above the 2.5V minimal voltage described in Sony US18650V3 datasheets)... the nominal voltage is 3.7V, so it's not even much under that, the max after full charge is 4.2V.

I'm not saying any of this wouldn't be possible, and if it is, please share more details how this can occur with undervoltage? Does bypassing the mosfets shown in pictures/schematic also bypass something ELSE than the overdischarge protection?  I do understand that if someone goes and causes a short circuit while modding the bms, the whole thing could ignite or explode, but can UNDERvoltage actually cause a fire? From what I can tell from the schematic in @hobby16's post, charger-side overvoltage-protection and voltage inversion protection -diode are left untouched by the modification, but I'm not an electronics engineer...

PS. As you're clearly a reseller (project42 -email), would you mind disclosing yourself as one?

Edited by esaj

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Eryk88 doesn't know the difference between overdischarge protection and overcharge protection, so he is essentially trolling.

If he does not substantiate his claims, and I am pretty sure he can't, he is just poisonning the well and his posts can be safely deleted.

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@esaj Thanks for your message.

I can see you have done a fair amount of research on this topics. You asked so many questions let me answer some of them:

1. Your are right it bypasses low side FET's only which means that you will have no over discharge and short circuit protection.
2. The only uni that doesnt have it it Solowheel true, Inmotion and Ninebot both have this protection but their system is well designed so cut out do not occur, this protection is needed for UN38.3 and MSDS certificates.
3. 2.5V or 2V it doesn't matter what matters is that below certain voltage the cathode of the battery gets damaged and this presents a risk when you next charge cells as you affect cells parameters like internal resistance which makes it harder to charge evenly in such a large serial packs [14s~16s].
4. BMS should also protect the cells thermal and over current (Critical for most chemistries apart from LiFePo4 mainly over current), this mod removes this protection.
5. Well designed BMS doesnt cut out but slowly ramps out.

Any further questions please ask

I have added a footnote to my profile about P42

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Eryk88 doesn't know the difference between overdischarge protection and overcharge protection, so he is essentially trolling.

If he does not substantiate his claims, and I am pretty sure he can't, he is just poisonning the well and his posts can be safely deleted.

​Now, let's all calm down, no need to be hostile (I hope I didn't come off as hostile in my own post), this could be an honest mistake... Let's wait what @Eryk88 has to say about this.

As for the reseller-status, we do welcome resellers here, and they are a valuable source of information, because they usually have ridden more wheels than most people, and can tell the good and bad sides of them. Also they might have some useful "inside" information, and can help with more unusual/rarer things happening with the wheels, as they might have seen those before, at least more probably than someone who owns just one wheel. For example, Jason McNeil has been a very valuable member to this forum, and he's a reseller.

Edited by esaj

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Eryk88 doesn't know the difference between overdischarge protection and overcharge protection, so he is essentially trolling.

If he does not substantiate his claims, and I am pretty sure he can't, he is just poisonning the well and his posts can be safely deleted.

​Sure thing boss - sound like you know it all good luck with your fire wheel :)

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@esaj Thanks for your message.

I can see you have done a fair amount of research on this topics. You asked so many questions let me answer some of them:

1. Your are right it bypasses low side FET's only which means that you will have no over discharge and short circuit protection.
2. The only uni that doesnt have it it Solowheel true, Inmotion and Ninebot both have this protection but their system is well designed so cut out do not occur, this protection is needed for UN38.3 and MSDS certificates.
3. 2.5V or 2V it doesn't matter what matters is that below certain voltage the cathode of the battery gets damaged and this presents a risk when you next charge cells as you affect cells parameters like internal resistance which makes it harder to charge evenly in such a large serial packs [14s~16s].
4. BMS should also protect the cells thermal and over current (Critical for most chemistries apart from LiFePo4 mainly over current), this mod removes this protection.
5. Well designed BMS doesnt cut out but slowly ramps out.

Any further questions please ask

I have added a footnote to my profile about P42

Thanks for answering so quickly! :)

1. I didn't know that it also bypasses short circuit protection, is there a way to make the mod either so that the short circuit protection isn't bypassed, or so that the undervoltage protection wouldn't be so sensitive? From what I've gathered, this has caused some serious injuries to people due to cutouts.

2. Ok, good to know, I've been under the impression that the circuitry wasn't even there

3. Yes, I was under this impression, overdischarging the cells can and probably will damage the cells (permanently), however, I've understood that the mainboard low voltage protection (ie. warnings on the wheel) should warn the user much before this happens?

4. I think I understand enough (probably not ;)) to see how it could also be triggered by overcurrent, but I don't understand how the mosfets could sense overheating, but that's probably besides the point. And that's just my lack of understanding electronics. I did do some classes on electronics a long, long time ago, but have happily forgotten even the little I knew about circuit design back then... :rolleyes:

5. Yes, this would be ideal, all the protection in place, but they wouldn't cause any unnecessary cut outs, even ramping down power would be much better.

Edit: Oh, and like I mentioned above, resellers are most welcome here, but we'd like them to disclose that they are in fact such, so that people can use their own judgement when/if they make any comments about different brands (ie. some reseller could just say that all the brands he doesn't sell are just sh*t, and those he sells are the best wheels ever, but at least people can then filter such comments themselves, knowing that they're resellers ;))

Edited by esaj

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​Sure thing boss - sound like you know it all good luck with your fire wheel :)

Sound like you like to make claims. ​I'm not a know-all guy, and always happy to learn.

But take no offense, you haven't learn me anything yet and I'm pretty sure there are things you are telling that are BS.

For example, you said a BMS can "ramp down the power", but how the hell it can do it with an on/off switch ? Another example, you post a wheel on fire then imply the shunting would be the cause of the fire, it's pure nonsense, period. If there was some logic, it would be the wheel is on fire precisely because it has NOT been shunted, right ?

Then you give no evidence Ninebot or Inmotion's BMS have the undervoltage cutoff and you sweep under the carpet the fact recent Gotway's BMS has no undervoltage cutoff, you just make claims. Sorry for not being impressed, it's not what I would qualify as "subtantiate",.

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1. I didn't know that it also bypasses short circuit protection, is there a way to make the mod either so that the short circuit protection isn't bypassed, or so that the undervoltage protection wouldn't be so sensitive? From what I've gathered, this has caused some serious injuries to people due to cutouts.

This is becuase alot of makes do not do the necessary testing, yes you just have to fiddle with the BMS design but I would not recommend this to anyone as a mod. I see your point about distributors, I am only going to say there are companies like in-motion and ninebot which have over 100+ engineers working and testing the products and you have gotway which is run by two guys from a garage (I have been to several uniwheel factories around china). 

3. Yes, I was under this impression, overdischarging the cells can and probably will damage the cells (permanently), however, I've understood that the mainboard low voltage protection (ie. warnings on the wheel) should warn the user much before this happens?

Because most uniwheels have a physical laching switch (Unlike ninebot or in-motion) of someone can leave it peramaneltly on, leading to complete discharge of the cell pack there are 100's of solowheels with this issue because of lack of undervoltage protection. If a product is not well design you have to put up with compromises. its very easy to do if some wheels dont restart after the battery warning so its and easy mistake to make.

4. I think I understand enough (probably not ;)) to see how it could also be triggered by overcurrent, but I don't understand how the mosfets could sense overheating, but that's probably besides the point. And that's just my lack of understanding electronics. I did do some classes on electronics a long, long time ago, but have happily forgotten even the little I knew about circuit design back then... :rolleyes:

 You are right transistors dont sens temperature they act as a switch only, its up to controll logic to decide if they are open or not - 80~90% if BMS design will have at least one thermistor either on the BMS or inbetween batteries for more accurate temperature sensing of the actual cells
 

 

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Sound like you like to make claims. ​I'm not a know-all guy, and always happy to learn.

But take no offense, you haven't learn me anything yet and I'm pretty sure there are things you are telling that are BS.

For example, you said a BMS can "ramp down the power", but how the hell it can do it with an on/off switch ? Another example, you post a wheel on fire then imply the shunting would be the cause of the fire, it's pure nonsense, period. If there was some logic, it would be the wheel is on fire precisely because it has NOT been shunted, right ?

Then you give no evidence Ninebot or Inmotion's BMS have the undervoltage cutoff and you sweep under the carpet the fact recent Gotway's BMS has no undervoltage cutoff, you just make claims. Sorry for not being impressed, it's not what I would qualify as "subtantiate",.

​Boss read a book about transistors and do some electronic online courses before you start accusing me of stuff

FET's are not ON/OFF devices by varying the voltage on the Gate you change the resistance between the Source and Drain, if you are worried about heat dissipation of a partially turned on FET you can always use PWM.... please spend some time on WIKIPEDIA

Regarding ninebot and inmotion -> please go buy one and take it apart I will not reveal their proprietary information on a public forum 
 

 

 

Edited by Eryk88
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Please don't either of you start a flamewar, I don't really know even remotely enough to say who's right and who's not about any of these things, but I think we can discuss this politely without insulting each other, pretty please? ;)   Hobby16 has been a respected member here and has made very good points about a lot of things, while Eryk88 also seems to know a lot about what he's talking about, but I can't really tell whether his points really hold water or not... We're all adults, let's act like such, ok?

As for the shunt, the lack of at least short circuit protection is worrying, but could maybe be handled by a large enough fuse in the BMS (in the middle of the shunt-wire)? Personally, I'm going to leave the shunt in place, knowing the track record of Firewheel's cutouts and the injuries caused by it, but that's on me, if my house burns down, it's no-one elses fault. That being said, I think I'm going to keep the wheel in the separate garage building from now on, even though the short circuit shouldn't happen easily (unless some wires come off or such...)

Edited by esaj

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​Boss read a book about transistors and do some electronic online courses before you start accusing me of stuff

FET's are not ON/OFF devices by varying the voltage on the Gate you change the resistance between the Source and Drain, if you are worried about heat desippation of a partially turned on FET you can always use PWM.... please spend some time on WIKIPEDIA

Regarding ninebot and inmotion -> please go buy one and take it apart I will not reveal their proprietary information on a public forum 
 

​So bad for you I'm an electronic engineer. Now please, explain how a BMS can ramp out power with a PWM by mosfets on the low side and having no inductance, inquiring minds would like to know. Just sketch a schematics, it would be really an interesting design to learn, if it ever exists. Oh let me guess, it does NOT.

And taking the pictures of the BMS is not revealing to the public the manufacturers' proprietary information. So please do it, instead of making claims.

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As for the shunt, the lack of at least short circuit protection is worrying, but could maybe be handled by a large enough fuse in the BMS (in the middle of the shunt-wire)? Personally, I'm going to leave the shunt in place, knowing the track record of Firewheel's cutouts and the injuries caused by it, but that's on me, if my house burns down, it's no-one elses fault. That being said, I think I'm going to keep the wheel in the separate garage building from now on, even though the short circuit shouldn't happen easily (unless some wires come off or such...)

​There is no short circuit protection for any and every car batteries either, esaj. And there are billions of them, running over a much longer period than monowheels. So what ?

It's always a matter of compromise. Arguing for an unsafe BMS with tremendous risk of bodily harm with many many serious occurences because of a highly hypothetical fire risk with ZERO proven case is plainly stupide, and it really piss me off.

You can remark Eryk88 does not mention what would happen with a  "well designed BMS with undervoltage cutoff protection" (whatever it means)  when one or more cells become defective with age. Expect this unconvenient fact would be swept under the carpet, like many others.

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​I'm an electronic engineer. 

​I think not for long if your employer would find out that you are posting in public such an irresponsible and dangerous mod... As an engineer you should know that 

FYI Cars have lead acid batteries, you just proven your credibility to me as an engineer with this statement - comparing Li-ion to lead acid ...

Edited by Eryk88
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​I think not for long if your employer would find out that you are posting in public such an irresponsible and dangerous mod...

FYI Cars have lead acid batteries, you just proven your credibility to me as an engineer with this statement - comparing Li-ion to lead acid ...

​Who cares what you "think" about my employer woud think and about your claim the mod is irresponsable and dangerous ??? Please, give evidence, instead of claims. Because while we are making claims, me too, I can think your claim that it would better to be harmed by a not-shunted BMS is irresponsible and stupid, but who cares. Oh wait, a lot of people who are happy with the mod do.

Car lead batteries have caused many fires by short circuit. And they don't have a short circuit protection. That's simple logic, try to grasp and think about it.

So, my questions, please ?

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I try to remain impartial, and think that this discussion is important, so people know both the GOOD and the (possible) BAD sides of doing such mods, and then make the choice themselves, but let's not throw dirt on and piss off each other, but instead try to get conclusions...

-Non-shunted too sensitive overdischarge protection (or whatever it is called, if it also acts as short circuit and/or temperature protection?) can lead to serious bodily harm

-Shunted circuitry removes also the short circuit protection and/or temperature protection and/or overcurrent (discharge side?) protection of the battery, and has a (low?) chance of causing a fire and/or battery explosion (I believe this could happen also without the shunt, if the battery overheats due to being left in the sun or near a heat source or such, but is a bit more possible to happen with shunted circuitry?)

-Shunting or even cutting open the battery shrink wrap WILL void the warranty on the battery

Now, is there any way to alter this mod to possibly lower the risk should a (likely improbable?) short circuit occur? Very large fuses (way above the normal peak current)? Different wiring, other components in-between? What about discharging overcurrent, that should also be possible to handle with fuse(s) similarly to short circuit? Possible temperature problems, can we make the cooling better, add thermal resistors or something? Of course these would likely also cause a cutout, if a fuse blows or such, but if they were fitted with "high enough" ratings, that shouldn't happen until the battery is nearing a critical state any way?

Edited by esaj
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Hi There,

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.

Please read this extract from Wikipedia "

If overheated or overcharged, Li-ion batteries may suffer thermal runaway and cell rupture.[110][111] In extreme cases this can lead to combustion. To reduce these risks, lithium-ion battery packs contain fail-safe circuitry that disconnects the battery when its voltage is outside the safe range of 3–4.2 V per cell.[50][98]Lithium-ion cells are very susceptible to damage outside the allowed voltage range that is typically within (2.5 to 3.65) V for most LFP cells. Exceeding this voltage range results in premature ageing of the cells and, furthermore, results in safety risks due to the reactive components in the cells"

Essentially what this post encourages you to do is to remove the protective circuit for the cells. 

BMS design and optimisation is a costly and challenging task that's why most of manufacturers use off the shelf BMS which is not suitable for unicycles application due to its very peaky current profiles during normal use (eg hitting a bump) if the BMS is fast acting it will cut out to protect the cells from high current to prevent the thermal runaway.

The problem is that the battery in fact in 95% of the cases can deal with this short peaks leads but the BMS is not designed for this applications so it cuts out. There are uni's there which have a bespoke BMS design which is optimise for this scenario and works very well ( I have to say the only wheel I trusted was the Ninebot as I have done just under 1600 km on it and it never cut out) I believe that in life you get what you pay for so if you choose a BYD over a BMW i3 you will be stuck with many problems.

Dont get me wrong - I fell off many times and hurt myself badly and now there are uni wheels that I stay clear from. My advice is that you that you are fully aware of the dangers that this solution can pose. Especially if you confuse the Fets and bypass the wrong ones!

If any one is considering this mod please install an 20-30A automotive fuse at least. They are relatively slow acting so they will permit the short peaks and should protect large contiounus currents

lastly for the gentlemen - you are not making much sense as shorting a lead acid the current it produces is your enemy and it will cause fire - in lithium battery is the combustible metal (lithium) is the biggest problem, the current is a second problem

 

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Hi There,

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.

True, I've written a little bit about the chemistries here: http://forum.electricunicycle.org/topic/475-higher-capacity-battery-tech/?do=findComment&comment=4857  (mostly just linked to battery university, as it has far more information, I don't claim to really understand the chemistries). LiFePo4 seems the safest option from the common chemistries, and at least Ninebot and Firewheel use LiNiMnCoO2 (NMC), but at least the tables in Battery University didn't rate it any higher in safety than LMO (but higher than the most volatile LCO). Lithium-titanate seems safe also, but suffers from low(est?) energy density.

Thermal runaway is always possible with lithium, the most safest, at least in this sense, seem to be the undisclosed chemisty "lithium-metal oxide" (especially the military-version) from Tadiran and their Lithium-Thionyl-Chloride -batteries they manufacture (the "Extended temperature" -version seems to have usable temperature range between -55 and +125 Celsius). Probably cost a ton in comparison to more common chemistries, don't ever expect to see these in the wheels, unless you buy the cells and build the battery yourself or have someone do it for you... And I don't know if the other features of the chemistries "play nice" with the kind of use the wheels do anyway.

 

BMS design and optimisation is a costly and challenging task that's why most of manufacturers use off the shelf BMS which is not suitable for unicycles application due to its very peaky current profiles during normal use (eg hitting a bump) if the BMS is fast acting it will cut out to protect the cells from high current to prevent the thermal runaway. The problem is that the battery in fact in 95% of the cases can deal with this short peaks leads but the BMS is not designed for this applications so it cuts out. 

Yes, this is exactly the problem, cutting costs at the expense of safety. While I leave the choice to people themselves whether to shunt or not (and want to offer as much information about the shunting as possible, including any and all bad sides and unwanted side-effects!), I will personally keep my Firewheel shunted. ;)

There are uni's there which have a bespoke BMS design which is optimise for this scenario and works very well ( I have to say the only wheel I trusted was the Ninebot as I have done just under 1600 km on it and it never cut out) I believe that in life you get what you pay for so if you choose a BYD over a BMW i3 you will be stuck with many problems.

​Yes, I nearly became a Ninebot owner, but due to delayed shipment, I ended up buying the used Firewheel, and then little later cancelled the order (I didn't see the need for another 16" wheel with similar range and lower top speed). But I don't doubt that Ninebots are high quality wheels, if they produce a 30+km/h version with battery capacities in the 500+Wh range, I'm all in  ;)  Right now I'm looking to buy larger batteries to the Firewheel, either 2*264Wh originals in parallel, instead of one 528Wh, to have redundandy in case another one fails, or I have also asked for quotes from Finnish companies that sell 18650 and other cells, if they could build & test the batteries themselves for custom built sets. Now that I know more about the shunt, if I get good quotes, I might instruct them to find a BMS that isn't too sensitive instead of shunting it.

Dont get me wrong - I fell off many times and hurt myself badly and now there are uni wheels that I stay clear from. My advice is that you that you are fully aware of the dangers that this solution can pose. Especially if you confuse the Fets and bypass the wrong ones!

If any one is considering this mod please install an 20-30A automotive fuse at least. They are relatively slow acting so they will permit the short peaks and should protect large contiounus currents

Exactly, people should always be very, very careful if they choose to start messing around with large batteries, as the energy they contain (even less charged) is huge, when talking about hundreds of Watthours. You don't want to electrocute yourself (remember, it's not the voltage but current that kills you! Something like 100mA = 0,1A through the heart is enough to stop it) or puncture or short circuit the battery, especially a lithium battery. That stuff is like thermite, burns hot and nearly impossible to put out, I've understood that it can't be/is very difficult to extinguish with water and keeps burning because the oxygen is being released from the oxide-metal(?). Probably best idea is to dump it into metal bucket filled with sand or such, if possible, and maybe do any mods outside/somewhere where the fire can't spread, should it happen. And know all the bad sides the mods could have, even when done right. 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 ;).

Edited by esaj

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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.

​Imho the biggest risk with this modification is, that people mess it up - i assume its not the best experience shorting a x00 Wh battery pack ;(.

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.

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.

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