- Re-drilled circuit board and added "jumpers" ... so that ground is switched for all components.
- Tested, and there is NIL leakage when circuit is "off". In other words, total and complete isolation (which was the idea !).
- This was a LEARNING EXPERIENCE.
- I hadn't thought about "reverse" leakage through components such as a capacitor, 555, and transistor.
- I could have tested for this on the breadboard, before committing to the circuit diagram.
- Learning lesson is:
- Write down clear objectives (ie no leakage ... no possible wrong connection ... voltage and current levels ... different input voltage ranges).
- Include "heat dissipation" in the testing criteria.
- Make a "testing checklist" ... to test circuit before committing to final build.
- Then do final build, and once more test against the checklist.
- More examination of the circuit, and I realised that the "Seat Switch" part of the circuit didn't work.
- This was because there was a logical error in the zener regulator circuit for the 555 and relay part.
- This error of logic actually leaves the relay and 555 operated simply through voltage dividers. As luck would have it, the voltage dividers work just fine.
Worked out how I could salvage the PCB (cutting links, and adding dividers) so the Zener would work. - However ... trying to calculate values so the Zener would provide a stable 12 Volts ... gives very high wattage through resistors, and high wattage through the Zener.
- Ultimate decsion ... is to leave the voltage divider circuit in place. If it doesn't provide enough current for the relay at low voltage ... then simply remove one of the four 150 ohm resistors. See excel spreadsheet of values here:
- The other problem, is that the Zener after the Contactor gets very, very hot.
- This is unexpected. The Contactor draws 207mA at 27 volts. This means the Zener drops 12V at 207mA, which is 2.4W. This is probably why it is hot ! It is a 5W Zener, so it won't break down, but dissipating the 2.4W is a problem.
- I've move the circuit items, so the Zener rests against the Cement 5W resistor ... the idea being that the heat will dissipate here.
- I've used heat transfer silicon paste all over the 5W resistor and the side of the cement resistor. This could be a problem, as the stuff doesn't seem to have set. If it drips onto the board, it might short something. Yuk !
Battery Balancing
- Assume: Battery internal resistance = 0.006 ohms, and battery difference (voltage potential) = 0.070 V.
- If hook batteries together with "perfect" wire ... then power is 0.07/0.006 = 11A !!
- With 1 ohm resistor between them, power is 0.07/1 = 70mA
- Discoved standard "hook up" wire has resistance of 0.117 ohms / metre. See here.
- Therefore, if balance taps are standard hookup wire, and are 10cm each ... then between each cell is resistance of 0.2 * 0.117 = 0.023 ohms.
- Directly hooking balance taps could produce 0.07/0.023 = 3A !!
- Adding another 30cm of hookup wire between each balance tap, means 0.07/0.0581 = 1.2A !!
- Hookup wire will take this much power (but not happily). Max is 1.5A.
- Calculated that 6 core alarm cable has resisance of 0.078 ohms / metre (ie better).
Driving
- Hooked it up for the boys to drive in the afternoon.
- When Tommy was driving, the accelerator jammed fully open !
- Brakes weren't strong enough to hold the Kart.
- He went crashing through the front gate, down the driveway, and across the road (out of control !).
- This was a LEARNING EXPERIENCE:
- I should have refused to allow them to drive it, until I had installed all safety features.
- I should have installed brake microswitch to controller "stop".
- I should have installed Kart control, including start and emergency stop switch.
- I should have insisted that all safety features were installed before the boys drove the Kart.
- I should have listed all safety features, and made a checklist ... and thoroughly worked through the checklist before letting anyone drive the Kart.
See Safety Feature Checklist
Kart Progress
- Connected brake lever (switch) to controller. Works well !
- Moved accelerator to other side handle (to prevent locking).
- Took seat off, and mounted controller onto frame (beautiful !)
- Did wire soldering controller to motor (beautiful !)
- Taped up wires, to make them look better (excellent !)
