Electric Unicycle's BMS problem and solution

[hobby16]

Did I do it wrong?

(see picture) 

Or do you guys think it's a different problem?

Yes, what you did is totally, horribly wrong.

Do like below : 1) green lines or 2) white line. Chose  green or white, not both.

[noisycarlos]

Oh boy. So I shunted the overcharge one? 

Crap. I'll fix that immediately, thanks a lot!

 

Just a quick question, so I can learn a bit. I shunted Q1A because I saw in the original post that Q1=T1.  How do you know which is which? Is it because the Q2 has three mosfets (Q2A, Q2B, Q2C) ?

 

Thanks again. I really appreciate it.

[noisycarlos]

 

Do like below : 1) green lines or 2) white line. Chose  green or white, not both.

UPDATE: It's fixed! Thanks!

I unshunted the mosfet in red and ended with connecting the terminals marked with the white line.

Shunting the mosfets marked in green did not work, I tried that first but when I turned the wheel on it just beeped and immediately shut off. So I undid that and did the white line, which, like I said earlier, worked.

Thanks again!

 

I included a picture of the solution, in case you want to add it to the post.

[hobby16]

Just a quick question, so I can learn a bit. I shunted Q1A because I saw in the original post that Q1=T1.  How do you know which is which? Is it because the Q2 has three mosfets (Q2

Very good question.
The markings on your BMS is faulty. If I have not missed anything according to what I see on the copper routing, Q1A should be Q2. Added to the fact that Q1 & Q2 are inverted compared to my tutorial, it's quite misleading indeed, I will update this caveat in my BMS article.

To know what to shunt for sure, the rule is to look at the most paralleled mostfets and where it's connected to P- (power -) going to the mainboard : it's where most current flows. The mosfet NOT the shunt (usually alone) is the mosfet going to C- (charge -), less current flows there since it's connected to the charger delivering only 2A.

Also, don't forget that you must not shunt pin 1 of the mosfets, only pins 2 and 3.
I suspect the cutoff is originally caused by a defective cell (lower voltage than all others, a check with voltmeter on each cell should tell). If you can ride without cutoff but the range is much reduced, that's it ! Same problem as @cg, look up the post where he solved it.

Do you have a picture and name of your wheel so I can document it if added to the list ? Is the battery accessible from outside or you must open the two half of the housing ?

[John Eucist]

Does anyone know where King Song stands in terms of this BMS issue?

[KaleOsaurusRex]

@John Eucist

I want to know exactly what the answer is, so let's get the brains on this one if we can. Here's a link to a comparison between King Song and Gotway electronics, done by @hobby16 Not sure if this helps with this particular question.

http://hobby16.neowp.fr/2015/07/29/king-song-gotway-comparison/

[AURITA]

No, those wheels are X3 clones,  they all use the same battery with 16 cells in series so, mainboard, battery, all are interchangeable.

If you buy up to 170Wh capacity (should cost about $100), there won't be any space problem since they use 18650 cylindrical cells.

With higher capacities, like 340Wh, you'll have 32 cells instead of 16 and the pack won't fit in your Weerda, forget it.

Up to 170 Wh.

If you love your lady, shunt the BMS. Don't shunt if you want her to go away.

omg I forgot to shunt the new weerda as it was not cutting off yet.. But last night :-/ it did it.. I felt on the floor like a stupid..  Turned on whe wheel and all the sudden it cutted off just after 1 minute of use..!! @hobby16

[AURITA]

Here I am again with the shunt situation.. 

As I have posted above,  my new wheel cutted off yesterday..  So I'm going to shunt the BMS..  But now this one have a different battery.. 

So what mosfets do need to shunt?  The 2 in the middle right?    @vee73 @hobby16 

[EUC Extreme]

I'm sorry but I will not part with certainty for you to answer. Have to wait Hobby response.

[hobby16]

Aurita's mod is like many generic : http://hobby16.neowp.fr/2015/07/24/bms-shunt-various-wheels/#generic

What is head scratching is noisycarlos' BMS above. The copper routing is totally incoherent, as an electronician, I still can't make sense of it.

[Jacky Heshi]

How would I shunt a TG-T3? Is it just the first image on the thread? 

Also how would I know when the battery is too close to being low then?

[hackerse7en]

Hi, before all, let me congratulate you all for the amazing job, i already fell 2 or 3 times of my unicycle, at this moment i prefer ride on him catching fire than having him throw me away like a stone, -.-, i was almost  breaking my unicycle with a hammer when i saw this post, i´m not sure if its the same problem because, once it happens it doesnt turn on anymore, only when i get home and charge it, and since i have some daughts regarding this i decided to post them here,  hoping you guys can help me.
1- what is my model -.-'? Pictures Here
2- Is the shunt in my picture correct, or should i shunt the 3rd one?

3-I noticed over the mosfets it says "M19", instead of "Q1" or "T1", like i saw on some pictures, is that a problem?

Thanks a lot for the help, and have a safe ride
 

[noisycarlos]

Very good question.
The markings on your BMS is faulty. If I have not missed anything according to what I see on the copper routing, Q1A should be Q2. Added to the fact that Q1 & Q2 are inverted compared to my tutorial, it's quite misleading indeed, I will update this caveat in my BMS article.

To know what to shunt for sure, the rule is to look at the most paralleled mostfets and where it's connected to P- (power -) going to the mainboard : it's where most current flows. The mosfet NOT the shunt (usually alone) is the mosfet going to C- (charge -), less current flows there since it's connected to the charger delivering only 2A.

Also, don't forget that you must not shunt pin 1 of the mosfets, only pins 2 and 3.
I suspect the cutoff is originally caused by a defective cell (lower voltage than all others, a check with voltmeter on each cell should tell). If you can ride without cutoff but the range is much reduced, that's it ! Same problem as @cg, look up the post where he solved it.

Do you have a picture and name of your wheel so I can document it if added to the list ? Is the battery accessible from outside or you must open the two half of the housing ?

Merci beaucoup monsieur :-)

I finally got around to taking pictures of my wheel and the battery for the archives. I hope they're useful. 

In the end, the shunt worked. But alas, I started getting the low battery signal after traveling just a mile or so I think you're right about some cells being bad.

I ended up ordering a NB One, and I'm trying to get a refund for this wheel (though the chances of that are slim). Plan B is to get a new battery and keep it as a trainer for friends and tricks. I'm not confident enough to change individual cells, so if anybody knows of a good place in the US to get battery packs I'm all ears.

Thanks again for the help :-)

[Rash]

Disabling BMS on NB1

[Chriull]

Hi Rash - thanks for sharing this video!

Since i have a ninebot e+ myself, do you know which ninebot this is?

In the slow motion it seems, like the driver gave the ninebot an initial acceleration (bending his knee forward) before the ninebot stopped keeping the pedals straight. So could it be, that he overleaned the ninebot or was this just his last attempt to balance out the shut off of the ninebot?

In some other thread quite some time ago in this forum one posted a link to a BMS he ordered to build a custom battery pack. There in the specification was the shut off current for the BMS specified to be between 30A and 60A. If for the ninebot there is also this wide spread it could be that the one with the 30A (~60V*30A=1800W) could shut off and a shunt sounds feasable and the ones with 60A (~60V*60A=3600W) are safe?!

[Tishawn Fahie]

Thanks for sharing that Ninebot One video - That's exactly what happen to me the other day. The thing just kicked me right off. I don't think I over accelerated....

[Rash]

This problem arises at many owners of NB1

[EUC Extreme]

I went from one cheapo EUC from the battery broken.

http://www.banggood.com/132W-Electric-Unicycle-Battery-18650-22PM-lithium-Ion-Battery-60V-p-977887.html

I bought such a place.
@hobby16  could you tell which parts of the soldered

[dpong]

 

In the slow motion it seems, like the driver gave the ninebot an initial acceleration (bending his knee forward) before the ninebot stopped keeping the pedals straight. So could it be, that he overleaned the ninebot ........?

I think you might be right. 

[Then again, it may just be wishful thinking.]

[Edit again:  It looks like cutoff to me now.  I really can't tell which, would like to hear others' opinion.]

[hackerse7en]

Hi, before all, let me congratulate you all for the amazing job, i already fell 2 or 3 times of my unicycle, at this moment i prefer ride on him catching fire than having him throw me away like a stone, -.-, i was almost  breaking my unicycle with a hammer when i saw this post, i´m not sure if its the same problem because, once it happens it doesnt turn on anymore, only when i get home and charge it, and since i have some daughts regarding this i decided to post them here,  hoping you guys can help me.
1- what is my model -.-'? Pictures Here
2- Is the shunt in my picture correct, or should i shunt the 3rd one?

3-I noticed over the mosfets it says "M19", instead of "Q1" or "T1", like i saw on some pictures, is that a problem?

Thanks a lot for the help, and have a safe ride
 

no one ?
I have my unit oppened awaiting for this answer, please someone  ..............

[esaj]

no one ?I have my unit oppened awaiting for this answer, please someone  ..............

I'm not really qualified to answer, and it looks like hobby16's gone underground for the past couple of weeks (maybe working on the telemetry-project, or just otherwise busy), but you could try either locating the P- and B-  -points, and join them with a thick wire, or measure the voltages to locate the correct mosfets:

T1 and X1 are detected by measuring the mosfet' gate voltage (pin 1) : paralled mosfets have the same gate voltage..

The first post has more details with pictures, although if you're unsure, I'd wait for hobby16 or someone else with more knowledge of electronics to answer.

[EUC Extreme]

All right. I need to put the battery into place without any changes.
Since this ring is to be sent to a friend.

[Chriull]

I went from one cheapo EUC from the battery broken.

http://www.banggood.com/132W-Electric-Unicycle-Battery-18650-22PM-lithium-Ion-Battery-60V-p-977887.html

I bought such a place.
@hobby16  could you tell which parts of the soldered

 

 

Seems like Q4B, Q4A and Q4 are the ones to be shunted (shortcut between middle and right leg)

[EUC Extreme]

Okay. This is not me anymore

[robca]

A word of caution for people considering this modification: there's more to what the BMS does than protecting the battery from over discharge.

Let me say upfront that if the EUC motor is not too big, and if the battery pack is big enough, I believe this modification to be safe.

If, on the other hand, the motor is much more powerful and the battery pack of small capacity, there is a risk in making this mod.

See this post for background info: http://forum.electricunicycle.org/topic/969-sample-rates-ewheel-performance-monitoring/. Please note that in that post I use the specs for a A-rated Panasonic battery, most of the cheap no-name cells used in cheap EUCs will not meet those high specs (neither real nominal capacity nor ability to handle high C discharges)

An EUC can draw pretty big currents, and the Li Ion batteries used cannot provide a lot of current. If operating within specs, each additional amount of current required by the motor results in a normal voltage sag, that has no impact on the battery. So a Li Ion battery with enough residual capacity operating at 3C for a peak of short duration (still within specs), will experience a normal voltage sag that a BMS might interpret as an over discharge and shut down the pack, with bad consequences. In this case the mod is safe, and the under-voltage protection at the EUC level can handle the case where the pack is really too low.

But if the motor is big and the battery pack small, you can easily get into a situation where the controller now requests a very high current from the pack, to the point where the batteries are operating outside of the safe envelope, and voltage sags is magnified. In that case, voltage sags because the chemistry of the battery is being damaged. Not cutting the voltage to that cell is now bad, and can result in a cell fire. The worst part is that not all cells in a pack are identical, there always be one where the internal resistance is marginally higher. That call will experience the highest voltage sag of the pack, and at high currents be damaged marginally more, in turn increasing resistance and decreasing ability to safely provide current. Repeat a few times, and you now have a battery in the pack that will sag much more than all others, and operate more and more frequently outside of the safe envelope. Bad things will happen

Unless the main board knows how to limit the current draw for the whole pack, the individual mosfets for each battery are the only protection against over-current discharge. If the manufacturer relies on the BMS for over-current, you have a problem when shunting it

Based on Jason's empirical data, a good rule of thumb would be: if your battery Wh is at least half as your motor W, you should be safe making this change. If your motor W rating is higher than twice your battery Wh, you should think twice before doing it. If you have Jason's logger, you can instrument your specific EUC/battery pack and decide with 100% confidence if the shunting is safe or not