velowatt
1 W
- Joined
- Apr 6, 2009
- Messages
- 60
I have technical question for the ES brain trust!
Been using an older bike for a short hilly commute to work. Throttle has an indicator with an on-off switch for the controller, and a 3-LED light system to indicate battery level (high, med, low). The brake levels have reed switches that cut the motor when applied as a safety measure.
After traveling about 1-1.5 miles (about 5 min or so), the bike suddenly goes into WOT mode (on the flat without pedaling, this is only about 18 mph). Throttle does not respond, and swithching "power off" does not stop the bike. Forcibly applying brakes can stop the bike and eventually the system shuts off (dead, all lights off, unresponsive). After sitting a few hours, all its well, normal function. Bikes works great- for about 5-10 minutes and then the WOT fail happens again. The second time was in 6" of snow, and a thrilling ride it was! Of course, the battery cut off switch is inside the fairing where it can't be reached easy while riding. I never worried about an emergency cut off, since I have never needed it on this little bike.
Details of the bike: It is a Mini- ebike (made around 2005 by the company that Lee Iaccoca founded and and then went broke). This is old tech: a Heinzmann 24V brushed DC motor over voluted at 36V. The motor controller is a circuit board mounted inside the faired main triangle. The batteries were 7Ah NiMH 36V which died long ago, and I have been using a 12S Headway 10Ah LiFePO4 pack I built up a couple of years ago. The throttle is based on a 5k pot.
I understand that the switching transistors (MOSFETs) rend to fail in "full on" state. I have inspected the circuit board and can't find any damaged components, tracings or shorts. All wiring and connections are good. Put it together and fail continues after a while, only to normalize after sitting overnight.
My theory: one or more FETs is failing, heats up after 5 min or so and fails wide open, then 'resets' when it cools down. Does this sound reasonable? I have blown a FET or two over the years,but I have never had one fail intermittently like this. I plan to either replace the controller with another generic brushed controller, or try replacing the FETs on the existing board (I can post pix & numbers later, right now the board is inside the bike). By the way, this controller is drawing peak watts of about 1200 (according to watts up meter) when starting from a stop on steep hills, so I estimate it is designed for 25-30 amp or so). There are only 3 big semiconductors on the output end, looks like 2 switching FET and one that controls the gates.
Does this seem like a reasonable explanation for the behavior? Otherwise, I am stumped!
Thanks!
Been using an older bike for a short hilly commute to work. Throttle has an indicator with an on-off switch for the controller, and a 3-LED light system to indicate battery level (high, med, low). The brake levels have reed switches that cut the motor when applied as a safety measure.
After traveling about 1-1.5 miles (about 5 min or so), the bike suddenly goes into WOT mode (on the flat without pedaling, this is only about 18 mph). Throttle does not respond, and swithching "power off" does not stop the bike. Forcibly applying brakes can stop the bike and eventually the system shuts off (dead, all lights off, unresponsive). After sitting a few hours, all its well, normal function. Bikes works great- for about 5-10 minutes and then the WOT fail happens again. The second time was in 6" of snow, and a thrilling ride it was! Of course, the battery cut off switch is inside the fairing where it can't be reached easy while riding. I never worried about an emergency cut off, since I have never needed it on this little bike.
Details of the bike: It is a Mini- ebike (made around 2005 by the company that Lee Iaccoca founded and and then went broke). This is old tech: a Heinzmann 24V brushed DC motor over voluted at 36V. The motor controller is a circuit board mounted inside the faired main triangle. The batteries were 7Ah NiMH 36V which died long ago, and I have been using a 12S Headway 10Ah LiFePO4 pack I built up a couple of years ago. The throttle is based on a 5k pot.
I understand that the switching transistors (MOSFETs) rend to fail in "full on" state. I have inspected the circuit board and can't find any damaged components, tracings or shorts. All wiring and connections are good. Put it together and fail continues after a while, only to normalize after sitting overnight.
My theory: one or more FETs is failing, heats up after 5 min or so and fails wide open, then 'resets' when it cools down. Does this sound reasonable? I have blown a FET or two over the years,but I have never had one fail intermittently like this. I plan to either replace the controller with another generic brushed controller, or try replacing the FETs on the existing board (I can post pix & numbers later, right now the board is inside the bike). By the way, this controller is drawing peak watts of about 1200 (according to watts up meter) when starting from a stop on steep hills, so I estimate it is designed for 25-30 amp or so). There are only 3 big semiconductors on the output end, looks like 2 switching FET and one that controls the gates.
Does this seem like a reasonable explanation for the behavior? Otherwise, I am stumped!
Thanks!
