REVA G-Wiz Research



Reva G-Wiz Owner's Manual | Energy economy analysis | Development and Launch

Interesting Factoids...

Economy

The battery is 48v by 200Ah, so that's 9.6kWh.

Electric price in the US is around 10c per kWh.
Electric price in the UK is around 10p per kWh.

So the Reva Gwiz would costs 96c or 96p to charge.
Practically speaking it would go about 40 miles from full to flat.
So this is 96/40miles or 2.4 cents/pence per mile.

Realistically, you wouldn't drive the car to completely flat just like you wouldn't drive until the tank is empty,
so most of the time it would be a partial recharge -like topping up the tank- costing less than 96 cents/pence.

...in the US

Fuel (gasoline) price is about $3 per gallon
On $3 (cost of a gallon of gas) the car would go 125 miles so this is equivalent to 125 mpg.

...in the UK

Fuel (petrol) price in the UK is about £1.15 per litre
1 gallon is 4.55 litres so UK is £5.23 per gallon
In the UK on £5.23 (cost of a gallon of petrol) the car would go 218 miles so this is equivalent to 218 mpg.

So here in the UK I get about 220 mpg out of my Reva Gwiz!
And this is at full speed of 50mph.

Most piston engined cars have a peak efficiency around 30-40 mph, below which you actually waste more fuel driving slowly.
Electric motors have very high efficiency right down to 0mph, so the slower you drive the less charge per mile.

If you are going through towns (slow traffic) the fuel efficiency goes to 1,000mpg equivalent and some.
Now it starts to make sense.

Direct Energy Conversion

Working it out in terms of energy density alone:

Lead-acid battery
Specific Energy (by mass) = 0.17 MJ/kg = 47.2 Wh/kg
Energy Density (by volume) = 0.56 MJ/L = 156 Wh/L = 0.156 Wh/m3

Petrol (gasoline)
Specific Energy = 44.4 MJ/kg = 12.33 kWh/kg
Energy Density = 32.4 MJ/L = 9.5 kWh/L = 43.19 kWh/gallon(UK)

1 gallon of petrol is 43.19 units(kWh) of electricity.
The G-Wiz goes 40 miles on 9.6 units so 4.17 miles per unit.
Conversion from electricity to petrol is 43.19 units per gallon(UK)

...so this would be 180.09 miles per gallon(UK)
and if the G-Wiz could extract all the energy from petrol (e.g. using fuel cell) it would go 1,800 miles on a 10 gallon tank!

So ... what is your engine doing with all that fuel?
Easy: it's a big heater which produces a bit of motion as a by-product of the heating!

Reva G-Wiz Hybrid (just for a laugh)




This generator (Powerstorm 6500) has a 15 litre tank and uses 1 litre/hour for full output 2.5kW
So about 2.5 kW for 15 hours is 37.5kWh for a tank, costing £17.25 or 46p per kWh.

Also at 40miles for 9.6kWh it's 156 miles per tank, which can obviously be refilled at a fuel station.

If this was used for powering/charging the car then £17.25 goes 156 miles, so 11p per mile.
On £5.23 of fuel it would go 48 miles so 48 mpg, using the generator.

So in theory it can power the car for 15 hours, but this would be at a low average speed (probably about 20mph) and you would get 48 mpg not 220 mpg

This is an interesting comparison as it demonstrates the real world efficiency of the petrol engine to be roughly 22%.

Getting inside the Reva G-Wiz





Reviving the Dead Reva G-Wiz Battery





Reva G-Wiz Battery Replacement

Reva G-Wiz battery layout including monitor harness and software mapping order:

Original Gimp Image


Range after replacement

Tested about a month after replacement and daily use.
This was a real journey of about 14 miles (so 28 miles total).

Probably averaged around 40mph on open roads, speed was up to 55mph and then the restrictor kicked in ('B' mode).
The journey involved a couple of steep gradients (A417, Shortlands Hill: 12%) and on boost mode dipped to about 28mph as it approached the top of the hill.

Arrived back in Reading the charge indicator was just entering the yellow (about 1/3rd remaining).
So would not be unrealistic to continue driving for a further 10 miles giving a projected 40 mile range.

Also on the daily commute (about 7 miles one way) the battery did not get charged one night by accident.

The car was fine on the second day and was still in the green (about 50% on the gauge) for the approx 30 miles total for the two days in town traffic.

Interfacing with the Reva G-Wiz:

You can download the EMS Analyser software here, also there are instructions for install and use here.

Serial port is set to 2400 baud 8-N-1
REVA ELECTRIC CAR COMPANY
Trojan Battery EMS Version-V1.15 AC Drive
Copyright RECC
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c1:100:420:0:-406:646:649:652:640:654:646:652:650:5189:389:412:78:3:583:0:709:4000:5989:0:0:0:112:0:0:0:0:
c1:102:420:0:-406:646:650:652:640:655:645:653:649:5190:389:415:80:4:583:0:709:4000:5990:0:0:0:115:0:0:0:0:

These are the fields:
State:Time:Cycle::Ibatt:BV1:BV2:BV3:BV4:BV5:BV6:BV7:BV8:Vpack:Tbat:Tchg:Ahr:Kwhr:SOC::Fault:Iprog:VProg::::Fan TTL/Speed kph:::Throttle:MotorKw:


rc-autopilot.de: REVA Inside | Electric_Vehicle



The Electric Engine

Brushed DC 48v/400amp

So the motor has 2 pairs of inputs and they are of different ratings,
which means this is not just a standard series wound motor.



But, I doubt it would be just a standard parallel wound either,
so we need the wiring if this.

For that we need to see the connections on the controller:



From the 1274 Wiring Diagram we see the field coil has a competely seperate connection:


Further research shows there is no voodoo magic, it's just similar to shunt or series:
MOTOR CONTROLLERS - FAQS
"Can Series motors be converted to SepEx motors?
Yes, generally but require lots of time and effort.
The large gauge wire, low turns field winding can be replaced by a small gauge wire, high turns field winding.
When doing so, the field must be designed to draw the required current but not higher than the controller's maximum field current at low battery, when the motor is hot.
"

Also someoe who appears to know says it's just a shunt with 30% voltage on the field winding
Discussion: Sepex vs Shunt
A Sepex motor has *one-third* the field voltage rating of a shunt field motor.
So regen works down to 1/3rd the full speed RPM's.
On the Bombardier and GEM as example (I worked at GE-EV) when you put a silly scope on the field you can see that at full speed the field on the SepEx motor is a 30% duty cycle since it's rated about 23 volts.


So here is a basic test: