stuck full throttle

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neogeo   10 µW

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stuck full throttle

Post by neogeo » Mar 25 2011 12:15pm

hello all,

I have been fixing up a chinese e-scooter and got new batteries for it and the first time I try to use it, its stuck on full throttle as soon as I turn it on wether or not the throttle is plugged in. does anyone know what could be wrong? is the controller fried?

itchynackers   100 kW

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Re: stuck full throttle

Post by itchynackers » Mar 25 2011 12:19pm

Sounds like one of the throttle wires is cut. I'd try a different throttle first, as it may be the cheapest solution.
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Rassy   10 MW

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Re: stuck full throttle

Post by Rassy » Mar 25 2011 12:29pm

I don't think it is your throttle if the problem still happens when you unplug the throttle. It is probably a short in either the wire from the controller to the throttle plug in point, the throttle plug in socket itself, or within the controller where the throttle wires are attached. Worse case there is something blown inside the controller. Good luck. Let us know what you find.
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neogeo   10 µW

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Re: stuck full throttle

Post by neogeo » Mar 25 2011 1:18pm

well I found part of the board was disconnected...I soldered it and I still have the problem... I tried removing the throttle plug on the controller side and same problem. I tested resistance between all throttle wires on controller side and all showed some resistance.. so I think the controller is fubar. I ordered a new one

neogeo   10 µW

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Re: stuck full throttle

Post by neogeo » Mar 25 2011 3:51pm

and unfortunnately I realised that connecting the wires for the brake lever it still doesnt stop the motor

dnmun   100 GW

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Re: stuck full throttle

Post by dnmun » Mar 25 2011 3:54pm

maybe the magnet is jammed next to the hall sensor. you can test by using a small battery 1.2-3V should show a response from the controller. not sure which color is which on yours but usually it is the green wire and black is ground, but open the old throttle and see where the magnet is positioned, you may be able to glue it back into the correct spot, they seem to break a lot. also remove the spring if you want to have no resistance in the throttle, but put a small rubber band on the outside to return it and keep the throttle off when not in use.

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amberwolf   100 GW

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Re: stuck full throttle

Post by amberwolf » Mar 25 2011 4:11pm

If this is a typical brushed motor and controller, then the likelihood of the controller being blown inside (shorted MOSFETs) is high. It's a common failure mode of them and why killswitches on the handlebars (or otherwise within easy instant reach) that actually cut power are a Really Good Idea for brushed motors. (much less important on brushless)

neogeo   10 µW

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Re: stuck full throttle

Post by neogeo » Mar 25 2011 4:22pm

dnmum- I don't think its the throttle because it does the same thing with the throttle disconnected

amberwolf- I think you are right because I tested resistance between battery and motor wires and positive is obviously 0 ohms and negative ones are about 212 ohms with nothing connected so its obviously messed

neogeo   10 µW

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Re: stuck full throttle

Post by neogeo » Mar 25 2011 4:24pm

also the part on the board that was mesed up was a pos+ to a mosfet

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vanilla ice   100 MW

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Re: stuck full throttle

Post by vanilla ice » Mar 25 2011 4:34pm

I have a couple that died this way. Stuck WOT. New controller is probably easier than trying to repair. How powerful is the scooter? Brushed controllers are fairly inexpensive.

torqueon   1 kW

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Re: stuck full throttle

Post by torqueon » Mar 25 2011 6:47pm

amberwolf wrote:If this is a typical brushed motor and controller, then the likelihood of the controller being blown inside (shorted MOSFETs) is high. It's a common failure mode of them and why killswitches on the handlebars (or otherwise within easy instant reach) that actually cut power are a Really Good Idea for brushed motors. (much less important on brushless)
I have heard about this happening if a pot wire breaks, However a mosfet shorted after touching the controll broad. Static ?
What do you think fries these mosfet ? More incentive to install a kill button

neogeo   10 µW

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Re: stuck full throttle

Post by neogeo » Mar 25 2011 10:07pm

well I'm not the one that fried it, and it was250watt so I bought a new one........... 500watt this time :twisted:

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amberwolf   100 GW

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Re: stuck full throttle

Post by amberwolf » Mar 25 2011 11:27pm

torqueon wrote: I have heard about this happening if a pot wire breaks, However a mosfet shorted after touching the controll broad. Static ?
What do you think fries these mosfet ? More incentive to install a kill button
Same thing that fries any of them: overcurrent, overheating, or overvoltage. ;) Most commonly the overvoltage would happen from the RF spikes induced into the wiring from the brushes/commutator on these motors. There can be quite a lot of RF noise from those, and there is never enough capacitance of the right types to filter it out. Some of the spikes could by random chance be high enough voltage to induce the FET to conduct, too, so when it's supposed to be off it might engage, and if that happens when the bottom FET in a bridge is conducting, you just shorted the battery thru them, and it'll probably blow up the FETs from overcurrent.

Most small simple controllers don't have a bridge setup, so tend not to be vulnerable to pass-thru events like that, but they can still die from RF noise, heat, overcurrent (when the motor is under too much load). I don't see shunts to monitor current in most of these brushed controllers, so the FET is usually used as the shunt, which is not very accurate if it's resistance changes with heat are not compensated for in the current limiting circuits. So you might easily overcurrent them under the right conditions.


I blew up lots of FETs learning about brushed controllers the hard way, trying to rebuild a ScootNGo unit, and then later trying to design my own. :lol:


As for repairing them, it is pretty easy to do if all that fries is the FETs. fairly often the little transistors used to drive the gates blow up too, so I would tend to just replace those along with the FETs, and verify the gate resistors are still good (they get cooked by overcurrent sometimes, and change resistance or burn open). Lots easier to troubleshoot than a brushless, too. :lol:

crank2giri   100 µW

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Re: stuck full throttle

Post by crank2giri » Apr 27 2016 9:36am

I am the latest victim.
I have a Sabvoton 72V 100A Controller the new gen. :
Was out testing the setup was working all good then it just died all the regular troubleshooting steps failed and when i finally hooked up the computer to the controller the throttle is full 4.96V. I even tried swapping the throttle the same problem. Then measured the throttle on the bench with a multi meter, it works fine. Any suggestions would be appreciated. Getting a new controller is not a options.. :( . Too expensive.

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LEVer   10 kW

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Re: stuck full throttle

Post by LEVer » Apr 27 2016 2:00pm

Ahh...my brushed motors days. Good times. :D

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