WOT fear for the brushed setup

[alex77roma]

Hi everybody ,
I have about a month from an Quantya used motorbike .
I like this bike for commuting in Rome , where is nimble in traffic and Has very good suspensions .
In the past I always used brushless system for my homemade electric bicycle with cromotor at 120 volts, and I never used brushed setup before this motorbike .
Reading all around in the web I learned that unlike brushless setup , if the brushed controller (Quantya has an Alltrax 4844) defeat I get WOT with my bike and I read that someone has got this bad problem.
I am very worried about it, I'm thinking to sell my bike or putting in a brushless system but in this case the problem is that it will be very expencive since I have to change motor, controller and battery also.
Am I exaggerated to worry so much?
All the peaple have brushed setup are quiet on this eventuality?

 

[amberwolf]

Unfortunately I have no idea what problem you are asking about; it didn't come thru your translation.

What specific problem at WOT are you referring to?

 

[bowlofsalad]

I think what he is saying is if the brush on his brushed motor fails, the motor fails into wide open throttle(although I don't understand how or why that would be). In otherwords, he is afraid of not being able to stop the motor.

Ebrake levers are, in my opinion, essential. Ebrakes are bicycle brake levers that have a switch that, when activated, tells the controller to cut power to the motor. If that isn't good enough for you, there are ways to have it so you can yank a power cable so a pair of connectors come apart which will remove the battery power from the controller all together. This yank method is probably the most safe technique.

http://em3ev.com/store/index.php?route=product/product&path=41&product_id=102

http://em3ev.com/store/index.php?route=product/product&path=41&product_id=176 These are two versions of ebrake setups, different configurations of the same idea.

 

[amberwolf]

I think what he is saying is if the brush on his brushed motor fails, the motor fails into wide open throttle(although I don't understand how or why that would be). In otherwords, he is afraid of not being able to stop the motor.

Well, if hte brush itself fails, it will either not conduct any power anymore and the motor will spin down, or it will weld itself to the commutator and the motor will stop instantly and further damage or even destroy the brush and commutator segments involved.


As for ebrake levers, all they will do is tell the controller to turn off. On a brushless controller that will work fine, as there is no normal failure mode of a brushless controller that could cause the motor to continue to run, and a kill switch that turns off MCU power will take care of any of the other modes.


But a brushed controller can fail in a way that causes full battery voltage across the motor, and no ebrake lever will stop that, unless the lever controls a contactor that actually cuts battery power completely off from the controller.

 

[gogo]

You can always attach one side of a forklift-type connector to some type of lever that is quickly accessible. Some thing that can be kicked with a foot might be a good idea since you may be holding onto the handlebars for dear life.

 

[amberwolf]

Another option is a fuse sized for the worst normal load the system should see.

Then simply pull the mechanical brakes hard, and the overload on the motor will blow the fuse, stopping the runaway.

 

[alex77roma]

Thank you for your suggestions.
Yes, wot is wide open throttle, differently from a brushless setup, when in a brushed setsetup the controller faiLs (as in the case of a MOSFET breakage) the battery goes in short circuit directly with the motor and this is very dangerous if youyou don't have any security systems.
Usually the people link the conctactor to the throttle switch, so every time you release the trhottle , the conctactor open the circuit and if the controller fails there is no WOT risk.
The only problem is that I unlike to ear the conctactor noise everytime I turn the throttle.
The only two solutions I think to have is linking the throttle switch to contactor, or buying a better brushed controller that has a logic to control the circuit.
First solution in noisy but unexpensive, second one is better but expensive.

 

[John in CR]

Brushed motors require a proper way to be able to cut power from the battery under load, which means a properly sized DC contactor. This is necessary because the motor doesn't require the controller brain to operate, so controller or other failures can result in a WOT condition that can't be stopped except by interrupting the battery mains. While the risk of failure could be remote, a runaway condition is too serious to ignore. Your only options would be to ride it out until the battery dies, jump off the bike and it continue to accelerate until it crashed, or stay aboard while it crashes. None of those are acceptable, so buy a proper relay and install the low power switch to operate it where it can be easily accessed in an emergency.