DC rated switches.
Posted: Sat Apr 05, 2008 12:19 pm
Hi folks.
The City El's brake switch and accelerator switch seem to be an Achilles heel. I've replaced so many switches in the past two years that I've lost track, but it seems to be that the switches just can't take the DC Voltage they need to.
Obviously, AC rated switches can't cope with anywhere near the voltage or current that a DC EV needs them to, and both the throttle switch (which switches the +43V low current to the controller) and the brake switch (which handles the +12V for the brake circuit) seem to fail with depressing regularity.
I could do several things here:
1) remove the throttle switch. It's only really a safety to make sure the contractors aren't engaged when the car is stationary but in gear. As long as the throttle pot doesn't jam or fail it should be okay. However, it's a bit risky not having one and perhaps a bit questionable on safety grounds. (Shorting out the switch on the way home to get you home doesn't count as it's an emergency fix).
2) Place a relay in the circuit for the accelerator and actually use a DC rated 12V switch to switch the relay to switch the larger 43V to the controller. But that adds another failure point....
3) Do something involving a solid state circuit. Much more robust, and perhaps more suited to life in an EV with very little suspension!
The only problem I have is that I must still have something which will turn the second heater coil on and off as I drive. In City Els the second stage of the heater turns off when you apply the throttle to prevent excess current drain on the batteries. With Lead Acid this is really important as the car only ever develops 120A, but I think the lithium with their increased range and ability to provide larger currents may negate this...
Help?
Nikki.
The City El's brake switch and accelerator switch seem to be an Achilles heel. I've replaced so many switches in the past two years that I've lost track, but it seems to be that the switches just can't take the DC Voltage they need to.
Obviously, AC rated switches can't cope with anywhere near the voltage or current that a DC EV needs them to, and both the throttle switch (which switches the +43V low current to the controller) and the brake switch (which handles the +12V for the brake circuit) seem to fail with depressing regularity.
I could do several things here:
1) remove the throttle switch. It's only really a safety to make sure the contractors aren't engaged when the car is stationary but in gear. As long as the throttle pot doesn't jam or fail it should be okay. However, it's a bit risky not having one and perhaps a bit questionable on safety grounds. (Shorting out the switch on the way home to get you home doesn't count as it's an emergency fix).
2) Place a relay in the circuit for the accelerator and actually use a DC rated 12V switch to switch the relay to switch the larger 43V to the controller. But that adds another failure point....
3) Do something involving a solid state circuit. Much more robust, and perhaps more suited to life in an EV with very little suspension!
The only problem I have is that I must still have something which will turn the second heater coil on and off as I drive. In City Els the second stage of the heater turns off when you apply the throttle to prevent excess current drain on the batteries. With Lead Acid this is really important as the car only ever develops 120A, but I think the lithium with their increased range and ability to provide larger currents may negate this...
Help?
Nikki.