Hello
I'm hoping some kind soul will give me some help.
I'm building an electric go-kart for my four year old. It's not a high budget project. All the welding is done and Dan can steer himself round the garden if I push him. Now I need to sort out propulsion.
I've cannibalised a kid's stand up scooter off ebay for motor and battery (among other things). For reasons I won't bore you with I can't use the switch etc from the scooter. I need a proper speed controller.
That's no problem. For 15 quid I can get a PWM controller intended for an electric scooter. Wiring the controller itself seems straightforward enough.
The problem is these cheap PWM controllers have no reverse function.
The motor is just an ordinary DC motor that I can drive backwards by reversing the polarity. But the currents involved are quite hefty. 250 watt motor at 24V means DC currents of the order of 10A, I think. If I were to just wire a switch to reverse polarity and if the driver switches it over when the motor is at full throttle I imagine nasty stuff could happen.
What I'm thinking is this. I need a reversing arrangement that can only switch polarity when current through the switch is low (or maybe it's easier to do it only when voltage across the motor is low). Maybe the user's switch could just toggle between forward and reverse, subject to switch current/motor voltage being low enough.
Does that sound daft?
I keep trying to doodle arrangements of multiple relays but I'm obviously reinventing the wheel.
What's the right answer please? Any help hugely appreciated.
As someone who's perpetually trying to make something he barely understands, it never ceases to amaze me how generous people are on these forums with their time and expertise.
I'm hoping some kind soul will give me some help.
I'm building an electric go-kart for my four year old. It's not a high budget project. All the welding is done and Dan can steer himself round the garden if I push him. Now I need to sort out propulsion.
I've cannibalised a kid's stand up scooter off ebay for motor and battery (among other things). For reasons I won't bore you with I can't use the switch etc from the scooter. I need a proper speed controller.
That's no problem. For 15 quid I can get a PWM controller intended for an electric scooter. Wiring the controller itself seems straightforward enough.
The problem is these cheap PWM controllers have no reverse function.
The motor is just an ordinary DC motor that I can drive backwards by reversing the polarity. But the currents involved are quite hefty. 250 watt motor at 24V means DC currents of the order of 10A, I think. If I were to just wire a switch to reverse polarity and if the driver switches it over when the motor is at full throttle I imagine nasty stuff could happen.
What I'm thinking is this. I need a reversing arrangement that can only switch polarity when current through the switch is low (or maybe it's easier to do it only when voltage across the motor is low). Maybe the user's switch could just toggle between forward and reverse, subject to switch current/motor voltage being low enough.
Does that sound daft?
I keep trying to doodle arrangements of multiple relays but I'm obviously reinventing the wheel.
What's the right answer please? Any help hugely appreciated.
As someone who's perpetually trying to make something he barely understands, it never ceases to amaze me how generous people are on these forums with their time and expertise.