To shunt or not to shunt

[techflyjy]

Hi

Newbie here, just got a TG-f3 2 weeks ago. After past couple of weekends agonizing learning process finally got hang of it,  I can do mount on wheel and back and forth straight line. (My tailbone still hurts when I sneeze since last fall L )

After you body learned how to twist left and right to balance the wheel, then without the notice my speed pick it up… didn’t even realize till EU start beeping.  I look through the forum seems like TF brand do has BMS unexpected shutdowns problem,  I see people here suggest shunt the battery MOSFET (side effect might damage the battery in long run?) , should I do it ASAP or if I keep low speed shouldn’t be that big of deal? Or even buy a BMS broad from Alibaba replace the broad?

Any TG-F3 owner here shunt their board? is dramatic improved riding experience ?

[esaj]

From what I've understood, most wheels (don't know about TG) have the voltage protection (at least in the form of warning the user) in their mainboard (whether it is in firmware logics or as a separate circuit, I don't know). Shunting or otherwise modifying the BMS circuit board (or even cutting the battery open) will void your warranty (at least on the battery, if not the entire wheel). Also you should be very careful not to electrocute yourself, or go short circuiting the battery if/when modifying it, as both can and probably will have disastrous consequences.

I don't know if there's any "dramatic improvement", it seems it's mostly a safety issue, but at least on my Firewheel, the previous owner said it would shutdown a couple of seconds after the last warning (around 28km/h), if you didn't slow down. He then shunted the battery before selling it to me, and didn't test the max speed. I've ridden it at 31.5km/h at max, and have ridden it with the last warning playing continuously all the time, and never had a cutout. So I don't know if the shunting did something to that also, or not. Our weight difference isn't much (I'm 57kg, he's 65kg, if I remember correctly), so I doubt it could only be from that. I don't know if the FW could be ridden even faster without any cutout, haven't dared to try and not planning to, at least in the near future. MAYBE once I get bigger batteries on it, as it should then be able to handle larger loads with less voltage drop.

That being said, a new member called @Eryk88, did this post on the BMS-shunting thread:

I don't know if this is true or not, if you have not had any problems with the BMS causing a cut out, I'd maybe wait until he gets back and answer some of my questions, so we can get some clarity on this. Probably hobby16 can also chime in once he's online.

[techflyjy]

Thank you for the reply.

I think for now I will just leave it be, since my riding skill is poor better take it easy keep it low speed anyway.

[Fred]

Hi techflyiy,

i'm also new on electric unicycles.

Recently I bought a TG-F3 from Banggood and I'm still waiting it to be delivered.

Are you happy with your unicycle?

I hope to learn it in a couple of weeks and use it for arround 6 months until buying a better model.

[techflyjy]

I got it from banggood too..
So far it holds up fine.. fall down on my back, wheels spinning on the ground couple of times. Build Quality its OK seems has a strong shell Case. My peddle already scratched up pretty bad but its functional. I can do back and forth on playground about 2 hours in low speed, so I guess that's the standard for 260wh battery.

​I do got beep alert couple of times and peddle rise up, its not pleasant feeling since you are just in learning mode. So far haven't experience the shut off power yet ... knock on wood.

Since i don't have any experience with skateboard or roller skate, Leaning curve is higher then I expected, used training wheel for about 1 hour that is easier way out, but u can not learn balance and can not make good turn so I took it off , 1st day its really frustrating, legs and back really hurts. That night I almost consider get a 2 wheel version instead. 
Don't learn how to mount it 1st.. just find a post or wall on your both side move back and forth eventually you will get it. Right now i think is about 20 hours in..I can do straight line and mount , my turns still shaky.  I cant say i'm enjoying the experience yet,  hopefully its temporary. Once up my skill, get on road I think i will enjoy a smooth ride.
Good luck learning, be safe.

[hobby16]

Hi guys,

TG is reputed to cut off easily, it's the wheel where I have witnessed the most modders.

Mine is really cutoff prone since I have a very small battery. But this guy has a big battery (360Wh) and still needs to shunt too : http://trottinetteselectriques.heberg-forum.fr/sutra14027_solution-probleme-bms.html#14027

For the moment, with hot weather and low speed, the cutoff problem is not accute. But be prudent, wear protections and DON'T LET DOWN guard (you feel confident, you forget protection gears, and Murphy law occurs).

Try also to trigger the cutoff on purpose, by rapid accelerations forward and in reverse, holding yourself to a support and with the wheel battery nearly empty, you'll realise how frightening it could be when the cutoff occurs !

Otherwise, enjoy, it's an decent and solid wheel.

Another thing, TG & Bangood may sometimes cheat on battery capacity. Mine is 130 Wh nameplate, but in reality, I only have 90Wh. You can check it easily with my "charge doctor", and eventually ask for a rebate from the seller. No mistake, I like Banggood very much otherwise.

I decidedly have bad chance, my recent GW14 is affected by cheating too, I bought a GW 340Wh but got only 280 Wh, 15% less battery capacity, and hence, range !

[Eryk88]

Do not shunt! Its dangerous - better buy a safer product 

[dmethvin]

If you're worried about the shunt causing issues on a malfunction, just use something like a 30A automotive inline fuse instead of a length of wire. That is actually how my 14-inch wheel is protected rather than a BMS cutout, you can see the fuse here. For a larger wheel I'd probably go with 40A but even so they can take sub-second surges larger than their rating so they're unlikely to blow accidentally.

I'd think that by far the most common reasons for battery fires are physical damage or manufacturing defects, and neither would be affected by adding this shunt. I can tell you that when I had a dead short in my Firewheel's control board the BMS did kick in, but when I later reconnected the battery it simply melted the connector before the BMS could respond. So electricity finds a way with or without a BMS. 

[hobby16]

Most monowheels' BMS short "protection" are rated for 60A or above. What's a joke ! On monowheels, the wires are mostly surrrounded by plastic, so the probability of short is among the lowest. And in case of short, it means a power of 65Vx60A= 3.9 kW would flow ! A lot of things has burned long ago (wires, especially the motor's wire which are quite thin, pcb copper traces, mosfets pins, and in your case the connector contacts...) , acting as fuses, before the BMS is triggered.

People who believe a compliance to some regulation imposing an active short-circuit protection would mean more secure wheels have clearly not thougt out the problem, they merely follow the herd, led by some regulation writing bureaucrats.

[Eryk88]

@hobby69 - well done you can multiply some numbers u must be really on top of your electronics... 

Even if the current limit is set to 60A before you come to your convulsions about what would or wouldn't melt you need to look in much more depth, than quoting ohms laws and power equations. You haven't looked in the data sheet to for the BMS about the time of the reaction to over current event. But I am not here to teach you things as you already know everything  

[hobby16]

stop trolling Eryk88 !

[Fred]

Hi guys,

I bought a TG-F3 to start learning, but I haven´t received yet.

Meanwhile, I decided to read more about all issues that envolves EUC's and finally found out what the term "shunt" mean.

To be honest, based on all that was discussed about this topic, I'm really unsure about what to do.

I'm also pretty scarried with the consequences of both situations (accidents x risk of fire).

Anyway, I would like to ask you guys some questions about the behaviour of the TG-F3 to have a better understanding about the risks and how to deal with them.

Maybe this can help other users in the same situation.

As I could understand, most of EUC's suffer from the BMS problem, that cuts the energy to the engine, causing the EUC unballancing and also an accident.

My first question is about this problem in TG-F3 that I know that suffers from this issue.

I know that this EUC sounds beeps when you try to accelerate beyond the 12Km/h and in some moment it tilts its pedals.

If I keep the speed this slow or at least very close to this limit, will I be reducing the risk of engine shutdown due to the BMS trigger?

I mean, if I stay slow, will I be safer?

I'm buying it to commute low distances and I really don't need to move fast.

I also know that the problem happens when you force the engine with sudden accelerations or high hills.

If I keep riding it on flat surfaces, that is 90% of the city I live, and keep accelerations smooth and progressive, will I be reducing the risk of engine shutdown due to the BMS trigger?

I'm planning to implement a mod using a key switch such as the image attached to this message.

I would use it to interrupt the push button that turns the EUC on, so that it would be necessary to have a metal key to turn it on.

Do you believe that this can cause any kind of problem in the operation of the device?

Thank you very much!

Fred

[esaj]

If I keep the speed this slow or at least very close to this limit, will I be reducing the risk of engine shutdown due to the BMS trigger?

I mean, if I stay slow, will I be safer?

If I keep riding it on flat surfaces, that is 90% of the city I live, and keep accelerations smooth and progressive, will I be reducing the risk of engine shutdown due to the BMS trigger?

From what I know, yes, the risk of cutout is lower if you don't demand as much power spikes from the battery. But still, especially during cold weather, it can occur. Also remember that more power is needed for a very short while when going over a smaller bump too, as the wheel tends to tilt forwards a bit, and the mainboard thinks you want to accelerate. And when the BMS cuts the power, it's not just the motor that shuts down, but the entire wheel, and it won't turn back on until you've plugged the charger into it for at least a few seconds (and of course the charger must be attached to an outlet). I don't know if there's any other way to reset it (if it's the latching type, some BMSs might have protections that trigger, but then automatically reset themselves after some seconds, if the voltages etc. are back to normal?).

 

I'm planning to implement a mod using a key switch such as the image attached to this message.

I would use it to interrupt the push button that turns the EUC on, so that it would be necessary to have a metal key to turn it on.

Do you believe that this can cause any kind of problem in the operation of the device?

Again, I'm no electronics or battery expert, but I'd suspect probably no problems, if it just sits between the wire from power button to mainboard, at least as long as it doesn't have high resistance (but probably ignition locks should have very, very low resistance). Since it's metallic, just make sure it's placed so that it can not cause a short anywhere and that it cannot "lock" by accident during riding, ie. it would shut down the power (if the power button is the latching type)...

[Chriull]

 

 

Again, I'm no electronics or battery expert, but I'd suspect probably no problems, if it just sits between the wire from power button to mainboard, at least as long as it doesn't have high resistance (but probably ignition locks should have very, very low resistance). Since it's metallic, just make sure it's placed so that it can not cause a short anywhere and that it cannot "lock" by accident during riding, ie. it would shut down the power (if the power button is the latching type)...

I assume that the "power button" is just processed by the logic of the mainboard. So the resistance of a switch should not matter.

If the power button is a real button (not latching and has no latching logic included), you cannot turn your euc off if you lock the switch by accident. The switch and the button are in series.

So your procedure would be: Unlock the key switch, press the power button to start - drive. Then be sure the key switch is unlocked, press the power button to turn of the euc and lock the key switch.

You also should check that you can remove the key from the switch whilst it is unlocked - or you have a broken key in the lock if the euc falls... Or you unlock, press the button, lock - everytime you want to start/stop the euc, which will become quite unhandy especially in the beginning when you have to restart the euc quite often!

[esaj]

I assume that the "power button" is just processed by the logic of the mainboard. So the resistance of a switch should not matter.

If the power button is a real button (not latching) or has some latching logic included, you cannot turn your euc off if you lock the switch by accident. The switch and the button are in series.

Thanks for correcting, I meant exactly that, if the button logics is handled by the mainboard, ie. it just gets shorted between two pins when the power button is pressed and the mainboard then "remembers" its state (stays on/off), even after the button circuit opens again, like ATX-PSUs/motherboards, then it won't matter even if the lock wasn't closed during riding, but if it's a "real" button (ie. it opens/closes the circuit and keeps it that way until pushed again), then locking while the wheel is on would cut the power... don't know what kind of switch it is in the TG.

 

[hobby16]

I assume that the "power button" is just processed by the logic of the mainboard. So the resistance of a switch should not matter.

If the power button is a real button (not latching and has no latching logic included), you cannot turn your euc off if you lock the switch by accident. The switch and the button are in series.

The power button is indeed just feeding the mainboard logic. The power stage (mosfets & driver) is constantly connected to the battery powered but is designed to consumes very little iddle power when the mainboard is off.

The power button is always latching on the TG (and Firewheel, Airwheel...). Only wheels that have the possibility to auto powerdown like the Ninebot may have a momentarily button.

 

@Fred

 no problem to serial connect to the power button an additional key switch with metallic key, apart from it's not rain impervious. You can even replace the button by the key switch, which is a reversible mod, more visually appealing but probably not very practical in everyday use.

Remember that the BMS cutoff can happen at any moment at any speed. The only thing you gain with reduced speeds is being able to run instead of falling WHEN the cutoff happens. I have had a shutdown even after one meter. You didn't say the battery you chose for your TG, but even with a beefy battery (say 260Wh), it happens.

Don't wait for a faceplant to shunt, do it ASAP. The reasonning against the shunt because of a hypothetical fire risk is totally nuts when you weight it against the REAL risk of being badly hurt, I'm getting sick and tired of repeating it because a troll has made an exagerated and unfounded scare story. Hey hobbyist by the millions use billions of Lithium batteries without an undervoltage and short protection (that is "shunted" packs), and most of times without BMS and they even have some battery fires. So what ?!?

If you are (rightly) scared of fire, buy a fire detector and an extinguisher, never leave the charging sesssion unattended, buy a charge monitor to detect suspicious parameter changes, never become complacent, that's the things to do.