249kWh/km

I traveled 33.3km last night and averaged 249kWh/km. This is based on voltage measurement. This means to 80% discharge I can travel 38.5km.

WAHOO. Just past engineering signatory inspection.

The Engineer was dissapointed he couldnt make any suggestions or reccomendations. :)

I pick up the paperwork on Friday and then go for a blue slip and finally rego.

First real drive

After a trip to the local weighbridge, I now have the EV Grin! 

... and in the excitement I forgot to take a photo or video. arrgh!

The total weight is as expected.

Front: 628kg - 41%

Rear: 916kg - 59%

===========

Total 1544kg.

The original dry curb weight was 1265. 58%F 42%R

279kg heavier

First run efficiency is 2.4kwh / 7.2km = 333kwh/km.

The silly thing with the Danfoss is that I think that the 2.4kwh includes driving and regen.

Points to note:

This is not counting regeneration.

I was driving quite aggressively, but not fast. Max speed was about 60kph.

I live at the top of a 100m hill.

The motor and controller were only warm to touch, even after a 100m climb in less than 1km.

Regen was set at 20% (3kw)/. I should be able to increase this to 66% (10kw) to have the diesel braking effect.

I have the tachometer reading kW but unfortunately it peaks at the motor maximum (15kw) so is not very useful. I will switch tacho back to RPM.

Cyclic test result for 20Ah Greensavers

I have cycle tested the Greensavers and plotted the capacity. The results were disappointing HOWEVER please see the explanation from Greensaver. It seems I over discharged them. I probably incorrectly assumed the 100% discharge point was indicated by the "Discharge Characteristic Curve" in the data sheet. (see previous post for data sheet)

Director of R&D, Greensaver: "Two comments on the cycle life test result: (a) The cutoff voltage was too low. Overdischarge will cause low cycle life. It is suggested that the depth of discharge is limited to 80%, and the cutoff voltage is set at 11.4 ~ 11.5V.

(b) The average discharge currents were relatively high. In this case, the recharge current is suggested to choose the same rate of high current to improve the cycle life of batteries."

Point 2 would be difficult to implement due to the cost, size and primary current of chargers.


The capacity is normalised to 1Ah discharge as varying discharge currents were used. This eliminates the effect of the Peukert factor at different discharge rates. The 'waves' are caused by slightly different end point volatages at different currents.

Greensaver battery inter cell balance - After Discharge

To satisfy Tuarns (and my) curiosity, I discharged the battery to 11.5v at 20A, let the battery rest, then measured the individual cell voltages. Following are the results.

+
2.0919
2.0966
2.0994
2.0985
2.1004
2.0957
-

Average = 2.097083
Standard Deviation = 0.003079
Range is from 2.0919 to 2.1004 difference = .0085 volts (0.406%)

Again the battery seems to be well balanced.

Greensaver inter cell balance

Greensaver have been very helpful in providing technical details regarding their batteries.
They provided the following diagram of the top of the cell including the interconnecting links.



I drilled 5 holes in the top of the battery according to their diagram and measured the voltage of the 6 individual cells. The battery is measured at full charge. This battery has been (unfortunately) over discharged about 35 times and is only about 1/2 new capacity. A battery that has been cycled like this should exhibit significant imbalance between cells if the cells are not almost identical.



The results below are measured with a meter (not pictured) with 4 decimal places:

Cell : Voltage

+
1: 2.2402v
2: 2.2456v
3: 2.2452v
4: 2.2541v
5: 2.2490v
6: 2.2458v
-

Average cell voltage is 2.2466 volts. This is 100% charged including some surface change.

The standard deviation is .004616

The range is from 2.2402 to 2.2541. A difference of 0.0139v (13.9mv) or 0.6205%

I am not an expert in battery chemistry but this seems to be quite good.

Comments welcome.