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Electric Unicycle's BMS problem and solution


hobby16

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I am not an expert so don't take my advise as final. The Three mosfets named QDA1, QDA2 and QDA3 are the ones that seems to be grouped together. You will find that the right leg of these 3 mosfets are connected to each other. and mosfet QCA1 is separated and named differently. Please confirm either with Chriull or Hobby16 to make sure.

This is what I did with my generic as advised by them and I'm happy to say that I got no BMS shutdowns until now. I just don't let my battery level go down too much.

One more thing. Shunting the BMS will not prevent shutdowns due to overspeeding on generic EUC's.

swznds.jpg

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I am not an expert so don't take my advise as final. The Three mosfets named QDA1, QDA2 and QDA3 are the ones that seems to be grouped together. You will find that the right leg of these 3 mosfets are connected to each other. and mosfet QCA1 is separated and named differently. Please confirm either with Chriull or Hobby16 to make sure.

This is what I did with my generic as advised by them and I'm happy to say that I got no BMS shutdowns until now. I just don't let my battery level go down too much.

One more thing. Shunting the BMS will not prevent shutdowns due to overspeeding on generic EUC's.

swznds.jpg

Thanks for the help, I think you're right but I'll wait until @Chriull or @Hobby16 or someone else can double validate before I go exploding my battery.

Also, by overspeeding do you mean just going too fast regardless of battery level, or going too fast on a low battery?

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It's regardless of battery level. But I might be wrong and some generic brands might have some sort of tiltback safety measure. The thing is you won't know unless you try. So better be safe and run within the limits.

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My TG T3 will shut down if I quickly accelerate past its speed capacity. It is more likely to happen when going downhill (but now that I know it happens I don't "floor it" to maximum quickly.) If I accelerate sanely, it will give ample warning in increasing frequency beeps and increasing tiltback of pedals (which is strong enough that it is hard to accelerate past the speed limit.)

You can simulate this speed related shutdown by lifting the EU off the ground and letting it accelerate unchecked until it surpasses the max and shuts off the motor.

Beyond this, I think there may still be a more sinister unpredictable shutdown possible.

I have not shunted, but I don't ride down below 2/4 battery level indicators and have not had a BMS low battery shutdown. As the temperature is dropping I will be curious to see if I encounter a shutdown in the winter with the cold-temperature behavior of the 132 Wh battery.

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My TG T3 will shut down if I quickly accelerate past its speed capacity. It is more likely to happen when going downhill (but now that I know it happens I don't "floor it" to maximum quickly.) If I accelerate sanely, it will give ample warning in increasing frequency beeps and increasing tiltback of pedals (which is strong enough that it is hard to accelerate past the speed limit.)

You can simulate this speed related shutdown by lifting the EU off the ground and letting it accelerate unchecked until it surpasses the max and shuts off the motor.

Beyond this, I think there may still be a more sinister unpredictable shutdown possible.

I have not shunted, but I don't ride down below 2/4 battery level indicators and have not had a BMS low battery shutdown. As the temperature is dropping I will be curious to see if I encounter a shutdown in the winter with the cold-temperature behavior of the 132 Wh battery.

I think a spill I had on my TG T3 must have been down to accelerating hard going downhill.

Have you had any shutdowns going up hills?  Mine failed on a very steep hill last weekend.  And when hitting a bump on a slightly less steep part.  Both at 4 lights battery power.

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No, I have not experienced a shutoff going up hill. But as the saying goes "Once bitten, twice shy" I don't think I have pushed it uphill to the danger zone. 

However once uphill it balanced at an inaccurate balance point that had the pedals tipped about 30 deg forward. I was going particularly fast. I ejected uninjured. There was however no shutdown/loss of power. After turning off/on it balanced fine.

I have started wearing wrist guards: an elastic sleeve that has a strip of abs plastic from the palm to the forearm. I'm so impressed and cringe at all the videos of EU riders without a helmet; I'm just not that confident! I have however gotten good at my "run really fast" method for when I dismount unexpectedly. 

This may be a motorized activity, but at my skill level there is still a lot of use of muscles!

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Multiquote still does not like me ;(
 
@Tom  Post from Oct 5:
 
As already written you still have a chance for overspeed shut-down,additionally ther could be thermal protection shutdown and under voltage shutdown.

Imho the best chance for a damaged cell to catch fire should be while charging. But that is not changed by shunting.

Shunting should not really stress or "misuse" your batteries much more than it is already done by normal (unshunted) operation. (As long as you have no shurt-circuit ;) )

 

@Tom  Post from Oct 5:

You could look at hobby16's blog - there he collected quite some EUC shunting instructions: http://hobby16.neowp.fr/category/battery-management-system/ 

QDA1,QDA2,QDA3 seem like the canditates for shunting. To get 100% safe you could also shunt from B- to P- or open more of the cover and compare the pcb with the schematics.

If you can read french you could also look to http://trottinetteselectriques.heberg-forum.fr/ - maybe there are experienced people following the BMS "development/usage" in different EUCs. The start of the BMS shunting thread here in the forum is already from June - i don't have any ideas if anything changed with the BMS or they still use the same systems...

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  • 1 month later...

Hi guys,

I've finally shunt my TG F3 after experiencing my share of BMS cutoff. Thanks @hobby16 and everyone for sharing knowledge on how to overcome this flaw.

My TG F3 BMS seems like the generic one as hobby16 described. I've shunt by connecting B- to P- as in this picture. Could someone tell me if i've overlooked anything?

WP_20151205_01_15_53_Pro edit.jpg

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30 minutes ago, stillet said:

Hi guys,

I've finally shunt my TG F3 after experiencing my share of BMS cutoff. Thanks @hobby16 and everyone for sharing knowledge on how to overcome this flaw.

My TG F3 BMS seems like the generic one as hobby16 described. I've shunt by connecting B- to P- as in this picture. Could someone tell me if i've overlooked anything?

WP_20151205_01_15_53_Pro edit.jpg

I'm not certain, and could easily be wrong (I'm an amateur with electronics and can't tell from the picture how the BMS connections between components go), but if you look at the original picture from Hobby16's post:

bms_generic.jpg

The B- is wired to the metal plate of the leftmost Q1 (no transistor there in this picture), the metallic body of the transistor itself is connected to one of the pins. The actual output P- pad is seen to the far left with the "outgoing" wire soldered there.

Here's what I think:

F3PgHNI.png

The simple schematic on the left (with mosfets M1-M3) shows how I understand the shunting works: the shunt-wire bypasses the transistors that handle the protections by turning the transistor to non-conducting state when voltage goes too low / current goes too high / whatever the third one is for (short circuit protection maybe). On the right is what I think you did (mosfets M4-M6 in the schematic). The shunting only bypasses the first transistor on the right. But like said, I could be wrong, hopefully some of our forum electronics experts can confirm that either I'm wrong or if the shunt needs to be redone.

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5 minutes ago, stillet said:

thanks esaj for checking. I picked that connection point above the rightmost mosfet as shortest to B-, my simplistic assumption that the point directly connects to P-, yea maybe i'm wrong here. Will wait if @hobby16 could comment.

He does not visit the forum anymore. You can get his answer by sending him an email on his web store.

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&esaj : Are you sure you drawing is correct ? Hobby16 says Mosfets are mounted in parallel and this seems normal to divide huge intensities. So Stillet could be right in assuming his point has a strong link to H16 recommanded point. Probably can be tested with a simple meter, but I'm not a specialist...

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9 minutes ago, Maxime said:

&esaj : Are you sure you drawing is correct ? Hobby16 says Mosfets are mounted in parallel and this seems normal to divide huge intensities. So Stillet could be right in assuming his point has a strong link to H16 recommanded point. Probably can be tested with a simple meter, but I'm not a specialist...

hi Maxime,

I did check. The point that hobby16 suggested (at Q1) is connected to P- and all other connection pads along that horizontal track (as P-) at least at top layer. Not sure if theres lower layer connections that could affect connection to P-, my electronics is 50% guesswork :)

 

 

bms_generic.jpg

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35 minutes ago, Maxime said:

&esaj : Are you sure you drawing is correct ? Hobby16 says Mosfets are mounted in parallel and this seems normal to divide huge intensities. So Stillet could be right in assuming his point has a strong link to H16 recommanded point. Probably can be tested with a simple meter, but I'm not a specialist...

No, I'm not sure :P  Like said, I'm an amateur, and could very well be wrong. If the orange area in the PCB is conductive, it would seem they could very well be in parallel, as all the mosfet drains (the metallic backplates) would then be connected together, and all the sources go to the same tracks (with some capacitors/resistors in between Q1's and the single Q2 sources, assuming those are mosfets with "normal" leg order)... It also seems that the gates also get their signal from a single conductor. How it all works, beats me ;)  But if those are the connections, then it shouldn't matter and the shunt should work just fine.

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20 hours ago, SlowMo said:

He does not visit the forum anymore. You can get his answer by sending him an email on his web store.

I asked hobby16 on web store (thanks SlowMo for his contact), he confirmed that my TG F3 shunt is OK :)

TG F3 BMS - I shunt by connecting B- and P- (black wire on the right)

WP_20151205_01_15_53_Pro edit.jpg

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Had an accident with a NoName (VEVOR X3) because of BMS shut down causing a severe accident. See "Warning to use Chinese NoName Units."

I have no clue if the Gotway MSuper has the same stupid BMS behavior. Someone has experiance with the Gotway MSuper BMS?

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@hobby16 My generic [Dragonmen Hotwheel] after 6 weeks faceplanted me 3 times - the factory has been anything but helpful to remedy my EUC. I am now too afraid to ride it without fixing the problem.

Consequently, I am trying to decide from the many BMS systems you have shown in your post of June 16 where I have to place the shunt.

Can you please advise where I shunt from my photo? 

5667927d90cee_BMS2.thumb.jpeg.06a80e7b2d

 

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1 hour ago, AlanR said:

@hobby16 My generic [Dragonmen Hotwheel] after 6 weeks faceplanted me 3 times - the factory has been anything but helpful to remedy my EUC. I am now too afraid to ride it without fixing the problem.

Consequently, I am trying to decide from the many BMS systems you have shown in your post of June 16 where I have to place the shunt.

Can you please advise where I shunt from my photo? 

@AlanR please send him a message directly to his email:

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2 hours ago, stillet said:

Want to share my shunt with Airwheel X8, this is what I did.

So far I tested the charging OK, charger light ended in green (from red), so i think I didn't wrongly shunt the 'overcharge' MOSFET.

Looks fine - seem to be the right Mosfets you shunted. Maybe just the right solder blob could be "cold" ( https://learn.adafruit.com/adafruit-guide-excellent-soldering/common-problems )?

If one shunts the overcharge Mosfet one would not see any difference while normal charging - just once the charger is faulty and outputs too much voltage the overcharge protection Mosfet would become active.

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7 hours ago, Chriull said:

Looks fine - seem to be the right Mosfets you shunted. Maybe just the right solder blob could be "cold" ( https://learn.adafruit.com/adafruit-guide-excellent-soldering/common-problems )?

If one shunts the overcharge Mosfet one would not see any difference while normal charging - just once the charger is faulty and outputs too much voltage the overcharge protection Mosfet would become active.

Thanks Chriull for the soldering tips, cant say I'm proud of that solder finishing B). Hope it holds good until I open the casing to put snow tire (my next plan).

Next question is how to test if the shunt is really doing its job. I've shunt both my TG F3 and the X8 but after the BMS cutoff experience, I'm scared to try riding them out to low enough battery to reach the low battery alarm. Anyone has better way to test?

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47 minutes ago, stillet said:

Thanks Chriull for the soldering tips, cant say I'm proud of that solder finishing B). Hope it holds good until I open the casing to put snow tire (my next plan).

Next question is how to test if the shunt is really doing its job. I've shunt both my TG F3 and the X8 but after the BMS cutoff experience, I'm scared to try riding them out to low enough battery to reach the low battery alarm. Anyone has better way to test?

Short circuit the battery and see if it blows... ;) Just kidding, never do that on a shunted battery, even if you suspect the shunt might not work (actually, never short circuit a battery, period). Other (real) suggestions I can think of is trying to ride it slowly uphill on a near empty battery, although that's going to strain it a lot... if you know the cut-off voltage, you could discharge the battery below that and see if still gives out voltage, or maybe cutting the gate-trace going to the mosfets and seeing if it still gives out voltage (if those are n-channel mosfets, when there's not enough voltage at the gates, the mosfets should not conduct)? Again, better maybe ask someone who knows better first... :D

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15 hours ago, stillet said:

Thanks Chriull for the soldering tips, cant say I'm proud of that solder finishing B). Hope it holds good until I open the casing to put snow tire (my next plan).

Next question is how to test if the shunt is really doing its job. I've shunt both my TG F3 and the X8 but after the BMS cutoff experience, I'm scared to try riding them out to low enough battery to reach the low battery alarm. Anyone has better way to test?

After shunting his TG3 Jez_vila had the first time a kick-back warning while riding, which never happened to him before the shunting. (http://forum.electricunicycle.org/topic/1892-tg-t3-advice-wanted/)

Maybe this could be a clue?

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