Using MightyBoyEV - Real Test Drive Data....

Note the following tests are being performed using a 3 day permit from the Department Motor Transport

Vehicle will be fully registered on new plates soon.....

First test drive data on performance

Distance travel = 27 km

MaxSpeed = 66.6 km/h (limited by road speed limits in my area of 50 or 60 km/h)

AvgSpeed = 40.2 km/h

Gear Used = 4th only

Trip duration = 29.8 mins

MaxAmps = 290.5 amps

VMin = 60.8 volts (as occurred when 290.5 Amps pulled,,,)

Watt-Hours per Km = 103.3 w-h/km

Watt Hours used from pack = 2756.9 watt-hrs

Motor Temp = 40 degrees C (max)

Controller Temp = 26 degrees C (max)

Air Temp = 17 degrees C

Starting pack voltage was 79.3 volts (fully charged) and after the 27 km trip, the pack voltage dropped to 74.8 volts with a recovery to 75.7 volts after 2 hours

Using the Power-Sonic supplied Open-Circuit Voltage Characteristics Graph  - a start voltage of 79.3 div 6 or 13.22 volts and 74.8 div 6 or 12.47 volts for the end voltage, the Residual Capacity of the battery pack would be just over 60%.

(Reference for full details)

See the next section for more on this.....

How much can I safely take from the battery back?

Power-sonic actual quote 111Ah for these batteries (see Power Sonic PG-12V103 AGM SLA batteries)….. So for my battery pack (6 batteries) this works out to be 72 volts x 111 Ah = 7992 Watt-hours (but this is at 20 Hour rate and not really useful for EV calculations)

De-rating the battery pack to the quoted 1 hour rating (which is only about 62 Ah) gives me about 4464 Watt-hours. This is a first approximation and does not take into account all the various effects or voltage droop that occurs when pulling high currents.

Being extremely conservative, and looking at a worst case scenario, I intend to not to take more than 3600 Watt-hours (this equals an approximate 80% D.O.D. of the heavily de-rated 4464 Watt-hours) from the pack. Using the limited results so far, this gives me a safe range of 35 km. With more conservative driving habits, limiting my start-up currents via programming the controller and cycling the batteries over the next few months, this all should improve. It is my aim to get the watt-hours/km below 100, after all this car only weights about 560kg (plus 190kg of batteries and the weight of the driver….. and maybe a passenger). In addition, the work in reducing all the factors that effect rolling resistance and drag should now pay off....

As mentioned previously on this site, for my use a range of 20 to 25 km is more then required....

How much does it cost to charge the battery pack?

I am legally charging on the “Off Peak” night rate available in South Australia which is currently about 7 cents per kilowatt hour. So for this run of about 27 km using approximately 2800 watt hours and assuming maybe 80% charging efficiency the cost would be ((2.8 div by .8 X 7 cents) div by 27 km) = about 1 cent per km.

The down side…..

Amortising the cost to the batteries (maybe a 3 years life if treated correctly with a well designed charger) – it’s costing $1600 div by 50 km (the total distance driven so far) or only $30 per km so far!!

For most EV drivers the charging costs are fairly irrelevant compared to recouping the battery pack costs, this is especially true when expensive Li-Ion cells are used .

After some controller adjustments (trying to the limit start-up current slightly) here are some more results....

Test trip involved driving into the Adelaide CBD area and North Adelaide

Distance travel = 17 km

MaxSpeed = 65.6 km/h (limited by road speed limits in my area of 50 or 60 km/h)

AvgSpeed = 44.3 km/h

Gear Used = 4th only

Trip duration = 22.5 mins

MaxAmps = 250 amps

VMin = 61 volts (as occurred when 250 Amps pulled,,,)

Watt-Hours per Km = 87.1 w-h/km

Watt Hours used from pack = 1426.9 watt-hrs

Starting pack voltage was 78.8 volts and after the 17 km trip, the pack voltage dropped to 75.5 volts

Other notable things.... with the start current reduced slightly the 4th gear wheel spin now far less when you really hit the pedal


on the road 60 km/h = 2,800 rpm at the motor

So I think that is about the best I am going to achieve from this combination - but very happy with a 87 Watt-Hour / Km result.

Third Test Drive (to get the vehicle registered)

Test trip involved driving to Vehicle Inspection Centre

Distance travel = 34 km

MaxSpeed = 83 km/h

AvgSpeed = 43.4 km/h

Gear Used = 4th only

Trip duration = 47 mins

MaxAmps = 289 amps

VMin = 60.3 volts (as occurred when 289 Amps pulled,,,)

Watt-Hours per Km = 87 w-h/km

Watt Hours used from pack = 2950 watt-hrs

Starting pack voltage was 78.9 volts and after the 34 km trip, the pack voltage dropped to 72.8 volts

(DOD would be roughly 60 to 65 % for this run)

Other notable things.... driving in an 80 km/h zone on the way home presented no problem with 80 km/h corresponding to a motor speed of 3,900 rpm and drawing 160 Amp.

So still not sure of the vehicles top speed but achieving 85 km/h would most definitely not present any issues. But driving at 80 km/h would certainly reduce the useable range!

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