How do brake interrupt sensors work? (aka brake cutoff sensors)

[maarten_almighty]

Hi all,

When pressing the brake lever on my ebike the controller 'cuts power' to the motor until the brake lever is released again/sensor is deactivated. I would love to know how that works/what happens.

I am wondering what causes the power to be 'cut off' when the sensor is triggered by pressing the brake lever.
My theory is that the power (5v +) to the throttle and pedal assist sensor are cut off when one of the brake sensors is activated, this in turn causes the user to be unable to 'apply throttle' .

Perhaps my theory is way off, do any of you know how this works? Does it differ per case/controller ? Or is the method (of cutting off the power when one of the brake sensors is activated) quite universal ?

I am trying to troubleshoot my ebike which does nothing when twisting the throttle..
PS: The bike also does nothing when connecting the 'self learning wires' together, which is strange, since I believe that should cause the motor to start rotating when the controller is turned on regardless of if there is a throttle installed/if the brake sensor is activated or not (not entirely sure about that last part about the brake sensor...).
The battery is directly connected to the controller (bms has been bypassed) so the bms is not the issue, battery is properly charged and also with the charger connected directly to the controller the bike appears to do nothing (no throttle response), so battery is not the issue. Power lock wire (wire that I connect to the positive side of the battery appears to be in good condition.
I measured the voltage on the red/black ('power') wires going to the throttle and there is no voltage across them, which (assuming the controller is indeed turned on) makes me think the brake sensor wires may have a short circuit somewhere, which would cause the controller to 'think' the brake levers are being pushed which might be the cause of my issues.

The bike has been acting up for a few weeks now, normally when i flip the switch the bike works immediately (as soon as the switch is on there is throttle response). Lately there have been a few times where the bike took some time to 'start up' (I had to wait 3-5 seconds after flipping the switch before the bike started doing something (aka before there was throttle response). And now it has stopped working completely.

What might be the issue? What checks could I perform to narrow it down?

I am using:
- BMS: 20s 10parallel li-ion battery (cells in good condition). No bms atm for testing (as previously mentioned).
- this controller: https://a.aliexpress.com/e1R175D8X
- generic BLDC motor

Thank you very much for any input! It is greatly appreciated :wink:

 

[amberwolf]

When pressing the brake lever on my ebike the controller 'cuts power' to the motor until the brake lever is released again/sensor is deactivated. I would love to know how that works/what happens.

not sure how much detailyou want, but basically that depends on the controller. i'll give you as much detail as i can quckly explan, not getting into software, and you tell us if it's enough.

there are other versions of this, but for most of them, the ebrake is just a normally closed switch, held open by the pressure of the brake lever and cable pulling on it.

when you pull the lever you release the switch so it closes, shorting its' contacts.

thos contacts run from the ebrake signal line from the controller to the ground from the controller.

the controller has a resistor inside it called pullup from the signal to 5v, holding the brake signal to around 5v, untll the lever is pulled and the switch is closed.

when the contacts in teh switch close, it shorts the siganl to ground.

the controller mcu (microcontroller unit, it's brain chip) reads that signal every so many software cycles, and when it detects it's grounded (on) then it stops sending control signals to the gate drivers that control the fets for teh mtoro phases.

the motor then just spins along doing "nothing".

if the controller also has regen braking, then it starts sending a different pattern of control signals to the gate drivers, so that they run the fets in a way that *takes* power out of the motor, slowing it down.

when you release the lever, the reverse of these things happen, and the motor begins providing power again based on your throttle or pas input.

I am wondering what causes the power to be 'cut off' when the sensor is triggered by pressing the brake lever.
My theory is that the power (5v +) to the throttle and pedal assist sensor are cut off when one of the brake sensors is activated, this in turn causes the user to be unable to 'apply throttle' .

while that is not how the ocntroller itself does this, it *is* possible to create an ebrake signal this way. for instance, if your ocntrller has regen braking that cannot be changed or disabled, but you don't wnat to use it, you just want the motor to stop spinning whenever you pull the brakes, you could wire the 5v for throttle/pas in series with teh ebrake switch, instead of wiring the ebrake switch like it normally would be.

since the siwtch normally only connects whenever the lever is pulled, you owuld either have to change the switch out to one thtat normally conencts when the lever is *not* pulled, or wire up a relay to do this instead, which gets progressively more complicated so we won't cover that here.

so...while it doesn't work this way, you can make it do so.

I am trying to troubleshoot my ebike which does nothing when twisting the throttle..
<snip>
I measured the voltage on the red/black ('power') wires going to the throttle and there is no voltage across them,

if this is also true with only battery and "lock" connected, then the controller is not putting out 5v anymore. assuming you don't have any lcd display or other switches anywhere that might not be working to turn it on.

if you've not already made sure your switch is working, short across it with a wire. if it is a tiny little switch, little wires work. fi t's a big fat switch you'll need thick wires like the ones going to it.

if the switch is working, then it could be a failed 5v regulator, or the whole low voltage power supply in the controller could be failed.

the most common thing is just replace the controller, but osmetimes you can fix it. we'll get to that if you need to.

there are lots of possible problems to test first though.

first, disconnect throttle and ebrake and pas sensor and the motor connecotrs, so you only ahve batery power and the lock wire connected to the controller.

if 5v starts working something is probably wrong with the throtlte pas, or ebrake or motor halls or the wiring for them.

if it doesn't, the controller has failed and you'd have to open it up to start testing insides if you want to fix it, or else just replace it.

conect only the ebrake and retest 5v.

if it still works it's not that.

if it doesn't disconnect it and connect only the throttle, the ebrake might be shorted internally, keeping the brakes on.

connect the throttlle and if it still works then thats not it.

if it doesnt' still work then disconnect it. somthing may be damaged in the thtrotle itself, shorting the 5v. we'll cover finding that if necessary.

connect the pas sensor and retest.

if it still works it's not that.

if it doesn't, same applies as the throttle.

connect only the motor wires and retest

if 5v works it's not that

and so on.

 

[maarten_almighty]

Wow, thank you for the very detailed reply! Very interesting info indeed.

As you suggested I have shorted the 'power on' switch, with no result unfortunately.
I also replaced the original 'power on' switch (before testing using the shorting method), and tested the new switch with a multimeter (it appeared to be working just fine, the switch).

I read online that if a controller has blown FETS the motor should have more resistance than usual, I checked this and there is no more resistance than before (the issue ocurred), so the FETS are probably fine.

I have connected a 4v li-ion battery to the signal/ground wire of the throttle in order to simulate a 'throttle signal' , I thought this might help to solve the issue (since the throttle is not receiving any voltage over its 'power leads' with the bike turned on). Result: bike still does nothing. Is there a better way for me to test if the 5v/low voltage regulator is working (if I have to open up the controller that's no problem for me)? I will try to get a wiring diagram for my specific controller (I've asked the seller on aliexpress).

I will check the controller for blown caps/mosfets/other components (see if anything looks damaged/burnt), but I don't suspect blown caps/fets could cause an issue such as this (I could be wrong).

I will perform the tests you suggested (disconnect all but the bare minimum of wires -battery, power lock-, see if 5v is working, and then connect all the rest to see which causes the issue).

Thanks once again, I'll post an update as soon as I've performed some tests.

 

[dogman dan]

Typically, a problem like yours is very simple, but hard sometimes to identify which wire lost connection.

Start at the battery, make sure the controller has power, then start looking real hard at all other connectors in the system, and for flaws in wiring.

Its not always a wiring issue, just 90% of the time or so.