Yes, I can start and stop the motor and run it with the slider bar in the control panel. Each time before I connect the battery I measure the voltage and make sure it is not over 28 volts. And to you question about the motor controller’s Tx connections, no I never did connect them together. Second smc’s tx line to first smc txin. First smc’s tx line to Arduino Rx(pin 7). I was VERY careful with wiring the serial connection. And likewise I made sure that the Tx (pin 8) from the Arduino was wired to the Rx on the smc. The power source is about 1.5 feet from the smc. The wires that I am using for the power are 8 awg silver lined wire (50 amp) and I do have the stock cap installed.
Unfortunately, measuring the voltage before connecting power is not a sufficient way to limit your peak voltage. Noise on your power line while the motors are running can be higher than the voltage you measured prior to making your connection, and even the simple act of connecting power to your board can cause destructive LC voltage spikes that are much higher than the voltage you measured. I strongly advise against using this version of the Simple Motor Controller with a 24 V battery unless you add additional circuitry to prevent voltage spikes from ever exceeding 30 V. If you want to use a 24 V battery, I recommend using an SMC 24v12 or SMC 24v23.
I think at this point the best thing would be for you to send the malfunctioning board back to us to take a look at. Please contact me directly by sending an email (with your original order number, if you have that handy) to ben at pololu dot com and I will give you an RMA number and return instructions.
Okay, I’ll send the board back. Would you guys be able to send me a 24v23 if Paid the difference?
We can discuss the details of the return via email.
Just to provide some resolution to this thread, I was unable to find anything wrong with the TTL serial interface of the returned controller. I do not know why you were having trouble communicating with it, though from the condition of the board I suspect there might not have been a good electrical connection to the board’s RX pin.