Sport E Sprinting - Dyno time
Entry posted by johnev
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Finally, I have my Sport E repaired and working again - just in time to miss the season!
It's been a long haul - over 2 years actually. Last month I completed the wiring and so took the car over to Potenza Technology for electrical testing (my sponsor). Here is a picture of the car in the workshop alongside the original Westfield iRacer. The iRacer had been recently recommissioned (and painted) for a trade show. This is a quick car. About the same power and weight as today's Formula E cars. A car before its time I think.
Initially my car was checked over for electrical safety and to ensure all the original safety features were still in place and working. Tick.
After a nut and bolt check I we tried to drive it. First problem, the motor rotated backwards! I'd forgotten that the motor/diff had been reversed. Digging around in the Potenza document archive, we found the original instructions and passwords to reconfigure the power controller. The direction was changed and we tried again - it went forwards this time but cut out at 10 mph - not a great start. This fault was eventually traced to an interference issue caused by a missing ground strap on the power controller.
The second test drive was much more successful with the car pulling away strongly. After a few tentative runs, I did a full power, zero to 'sorry officer' run. It cut out again this time under full power. After some head scratching and several more runs the problem seemed to go away. Anyway, I booked the car into Northampton Motorsport for a geometry check and dyno test.
At Northampton, the high power cutout problem reappeared but only for the first few runs. It became clear that the battery voltage was sagging badly under heavy load causing the power controller to stop working. After a few runs the battery warmed up, the voltage drop was less and so the power controller continued to work. I'll have to add a power limit to the control software at low battery temperatures to stop it from tripping.
Back in 2014, I had the original car dyno tested. The graph below shows the 2014 graph (red) alongside the new graph (blue).
More power - yay, but the new power curve is now a different and odd shape. One factor is the gearing. This year the car is fitted with 15 inch wheels instead of the original 17 inch so the gearing is lower. This could account for the steeper initial slope. Also the original Sport E limited power to about 120 BHP at the wheels. I removed this limit (it's a race car after all) and now the controller gives maximum torque at all motor speeds but power now appears to be limited by the lower battery voltage at high speed.
Overall a good result - especially considering the car is also 200Kg lighter than the 2014 car - it's still 660Kg plus me though.
Now if I can just up-rate the battery before next season ........
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