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From the Kantanka EV I could see 2 lead-acid batteries with a space for a third, so I'll assume straight up it had 3 batteries. I looked up standard manufacturer sizes for lead-acid batteries and I saw the biggest being a 100Ah battery with dimensions 343 x 172 x 213mm
Assuming the batteries were connected in parallel that results in about 300Ah. Each outputs 12V so we get 3.6kWh of battery capacity approx.. that add an extra 99kg of weight as each battery weighs 33kg. Assuming a weight of about 650kg (I used the weight of a daewoo matiz for
comparison) without the power unit, the lead-acid batteries would an provide energy-to-weight ratio of 36.4Wh/kg. Now with the motors, let's assume a 3-phase 4 pole induction motor, and let's give a 95% inverter efficiency. If we consider a discharge rate of 1C that translates
to a 100A discharge rate and that will be 3.6kW which will be about 4.8hp - max.
if we factor in inverter losses that will be 4.56hp. If we consider the motor losses (at 95% efficiency), that would be 4.3hp. Here, I've only done for 3 batteries connected in parallel (meaning you're going for max range on 3 batteries)
for max power, we are looking at 4.3 * 3
for max power, we are looking at 4.3 * 3
which is approx 13hp and you only get 1.2kWh of range... ok now let's start to design for Max power versus efficiency
First, a few assumptions:
1. tyre is 165/55R14. Radius = 0.4531m
2. Rolling resistance = 0.015
3. 70% Depth of discharge
4. Constant velocity of 60km/h
Power = weight * angular speed * rolling resistance
P = W*(60/3.6)(0.4531)(0.015) =W*0.113275
Equation (1)
1. tyre is 165/55R14. Radius = 0.4531m
2. Rolling resistance = 0.015
3. 70% Depth of discharge
4. Constant velocity of 60km/h
Power = weight * angular speed * rolling resistance
P = W*(60/3.6)(0.4531)(0.015) =W*0.113275
Equation (1)
Energy consumed per km (kWh/km) = Power/(Velocity * Time)
E = P*0.0599t^(-1)
Equation (2)
Range = (1/E) * Battery capacity * 0.7
Equation (3)
Remember we have an energy density (by weight) of 3.6 Wh/kg
E = P*0.0599t^(-1)
Equation (2)
Range = (1/E) * Battery capacity * 0.7
Equation (3)
Remember we have an energy density (by weight) of 3.6 Wh/kg
I mean 36.4 Wh/kg***
Further assumptions: aerodynamic drag coefficient is 0.344 (same as daewoo matiz)
Frontal area: 1.5m2 (guesstimate)
and not to forget the 95% efficiency both for inverter and motor and then another 95% for transmission
Frontal area: 1.5m2 (guesstimate)
and not to forget the 95% efficiency both for inverter and motor and then another 95% for transmission
Put it all up in an excel sheet... and I must say the sweet spot looks like 9 batteries to me. That would make it 100kg heavier than the daewoo matiz but that will get you 139km of range (with no one sitting in it, that is)
if you add two adults = 160kg, your power increases to about 3.593kW and then you get about 120km of range.
Charging might be a challenge here depending on your charger setup. The charge rate is about 17A per battery from 0 - 80% and about 5A from 80 to 100%. if you have 3, it will take about 26.1 hours if the charger charges only one at a time. a setup that charges 3 batteries
at a time will take 8.7 hours. That's enough for about 40km for 2 adults.
Disclaimer - I haven't factored in things like the volume of the batteries which will affect how many will actually enter the car, and the economic cost to adding extra batteries. Kantanka would optimize for that and that might translate to most likely lower range values.
For more clarification: https://twitter.com/RobertBoatengD1/status/1293098290637045760?s=19
