This blog documents the restoration, and conversion, of a 1965 Humber (Singer) Vogue to a fully electric vehicle. The Vogue will be powered by an 11kW(modified), 3 phase industrial AC motor, controlled by an industry standard Variable Speed Drive (VSD) or Inverter. To be able to produce the 400 volts phase to phase the VSD will need about 600 VDC of batteries. A big thanks to the contributors on the AEVA forum:

Wednesday, September 12, 2012

Speedo Inaccuracy Explained (mostly)

The tyres I plan on using are 185/65R13. With the Vogue's 3.89:1 differential ratio, that works out to be 41.48km/h at 1500 RPM. In the speedo software I divide motor RPM by 36 (41.67 from 1500 RPM) and round up to the nearest integer so it should show 42km/h.
I placed the Vogue on axle stands last light and locked the controller's maximum motor speed to 1500 RPM.

I set the PC to monitor various controller variables including actual motor RPM.
Flooring the accelerator gave me 1499.9 RPM on the PC monitor and 42km/h on the speedo in the car.

So all the calibration and calculations are actually correct - so why does it show 67km/h when we are doing 60km/h?

About the only thing left is the diff ratio - but that can't be wrong - can it?
Historically, the Mk3 Vogue sedan was shipped with a 3.89:1 diff. The earlier Mk2 has a 4.22:1 then later in the run changed to 3.89:1 - or so the rumors say.

The 3.89 to 4.22 would make about an 8% difference to speedo ready. My 67 to 60 is around 10 to 11% - but it's close. The current tyres on the car are 175/70R13 which are ever-so-slightly larger than the ones I calibrated for but it's not much (this should slightly counter the different diff.).

Back to diff. ratio. When I bought the Vogue it had been built from three donor cars. We know one of them was a Vogue Sports because I have the boot lid and badge, BUT, the Humber Vogue Sports never shipped as a Mk3 in Australia, so the boot lid is from a Mk2 - might the diff. be as well?
(The Sports did not sell as a Humber in Australia because all Mk3 Humber Vogues were upgraded to the Sports Alloy Head Rapier spec. motor - no need for a Sports.)

I'm very happy with a 4.22:1 final drive ratio - I had even considered chasing one up so that's good.
So a speedo software change is in the works.

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